kernel/cgroup/cgroup.c

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This source file includes following definitions.
cgroup_ssid_enabled
cgroup_on_dfl
cgroup_idr_alloc
cgroup_idr_replace
cgroup_idr_remove
cgroup_has_tasks
cgroup_is_threaded
cgroup_is_mixable
cgroup_can_be_thread_root
cgroup_is_thread_root
cgroup_is_valid_domain
cgroup_control
cgroup_ss_mask
cgroup_css
cgroup_tryget_css
cgroup_e_css_by_mask
cgroup_e_css
cgroup_get_e_css
cgroup_get_live
__cgroup_task_count
cgroup_task_count
of_css
css_set_threaded
css_set_populated
cgroup_update_populated
css_set_update_populated
css_set_skip_task_iters
css_set_move_task
css_set_hash
put_css_set_locked
compare_css_sets
find_existing_css_set
free_cgrp_cset_links
allocate_cgrp_cset_links
link_css_set
find_css_set
cgroup_root_from_kf
cgroup_init_root_id
cgroup_exit_root_id
cgroup_free_root
cgroup_destroy_root
current_cgns_cgroup_from_root
cset_cgroup_from_root
task_cgroup_from_root
cgroup_file_name
cgroup_file_mode
cgroup_calc_subtree_ss_mask
cgroup_kn_unlock
cgroup_kn_lock_live
cgroup_rm_file
css_clear_dir
css_populate_dir
rebind_subsystems
cgroup_show_path
cgroup2_parse_param
apply_cgroup_root_flags
cgroup_show_options
cgroup_reconfigure
cgroup_enable_task_cg_lists
init_cgroup_housekeeping
init_cgroup_root
cgroup_setup_root
cgroup_do_get_tree
cgroup_fs_context_free
cgroup_get_tree
cgroup_init_fs_context
cgroup_kill_sb
cpuset_init_fs_context
cgroup_path_ns_locked
cgroup_path_ns
task_cgroup_path
cgroup_migrate_add_task
cgroup_taskset_first
cgroup_taskset_next
cgroup_migrate_execute
cgroup_migrate_vet_dst
cgroup_migrate_finish
cgroup_migrate_add_src
cgroup_migrate_prepare_dst
cgroup_migrate
cgroup_attach_task
cgroup_procs_write_start
cgroup_procs_write_finish
cgroup_print_ss_mask
cgroup_controllers_show
cgroup_subtree_control_show
cgroup_update_dfl_csses
cgroup_lock_and_drain_offline
cgroup_save_control
cgroup_propagate_control
cgroup_restore_control
css_visible
cgroup_apply_control_enable
cgroup_apply_control_disable
cgroup_apply_control
cgroup_finalize_control
cgroup_vet_subtree_control_enable
cgroup_subtree_control_write
cgroup_enable_threaded
cgroup_type_show
cgroup_type_write
cgroup_max_descendants_show
cgroup_max_descendants_write
cgroup_max_depth_show
cgroup_max_depth_write
cgroup_events_show
cgroup_stat_show
cgroup_extra_stat_show
cpu_stat_show
cgroup_io_pressure_show
cgroup_memory_pressure_show
cgroup_cpu_pressure_show
cgroup_pressure_write
cgroup_io_pressure_write
cgroup_memory_pressure_write
cgroup_cpu_pressure_write
cgroup_pressure_poll
cgroup_pressure_release
cgroup_freeze_show
cgroup_freeze_write
cgroup_file_open
cgroup_file_release
cgroup_file_write
cgroup_file_poll
cgroup_seqfile_start
cgroup_seqfile_next
cgroup_seqfile_stop
cgroup_seqfile_show
cgroup_kn_set_ugid
cgroup_file_notify_timer
cgroup_add_file
cgroup_addrm_files
cgroup_apply_cftypes
cgroup_exit_cftypes
cgroup_init_cftypes
cgroup_rm_cftypes_locked
cgroup_rm_cftypes
cgroup_add_cftypes
cgroup_add_dfl_cftypes
cgroup_add_legacy_cftypes
cgroup_file_notify
css_next_child
css_next_descendant_pre
css_rightmost_descendant
css_leftmost_descendant
css_next_descendant_post
css_has_online_children
css_task_iter_next_css_set
css_task_iter_advance_css_set
css_task_iter_skip
css_task_iter_advance
css_task_iter_start
css_task_iter_next
css_task_iter_end
cgroup_procs_release
cgroup_procs_next
__cgroup_procs_start
cgroup_procs_start
cgroup_procs_show
cgroup_procs_write_permission
cgroup_procs_write
cgroup_threads_start
cgroup_threads_write
css_free_rwork_fn
css_release_work_fn
css_release
init_and_link_css
online_css
offline_css
css_create
cgroup_create
cgroup_check_hierarchy_limits
cgroup_mkdir
css_killed_work_fn
css_killed_ref_fn
kill_css
cgroup_destroy_locked
cgroup_rmdir
cgroup_init_subsys
cgroup_init_early
cgroup_init
cgroup_wq_init
cgroup_path_from_kernfs_id
proc_cgroup_show
cgroup_fork
cgroup_can_fork
cgroup_cancel_fork
cgroup_post_fork
cgroup_exit
cgroup_release
cgroup_free
cgroup_disable
enable_debug_cgroup
enable_cgroup_debug
css_tryget_online_from_dir
css_from_id
cgroup_get_from_path
cgroup_get_from_fd
power_of_ten
cgroup_parse_float
cgroup_sk_alloc_disable
cgroup_sk_alloc
cgroup_sk_free
cgroup_bpf_attach
cgroup_bpf_detach
cgroup_bpf_query
show_delegatable_files
delegate_show
features_show
cgroup_sysfs_init
   1 /*
   2  *  Generic process-grouping system.
   3  *
   4  *  Based originally on the cpuset system, extracted by Paul Menage
   5  *  Copyright (C) 2006 Google, Inc
   6  *
   7  *  Notifications support
   8  *  Copyright (C) 2009 Nokia Corporation
   9  *  Author: Kirill A. Shutemov
  10  *
  11  *  Copyright notices from the original cpuset code:
  12  *  --------------------------------------------------
  13  *  Copyright (C) 2003 BULL SA.
  14  *  Copyright (C) 2004-2006 Silicon Graphics, Inc.
  15  *
  16  *  Portions derived from Patrick Mochel's sysfs code.
  17  *  sysfs is Copyright (c) 2001-3 Patrick Mochel
  18  *
  19  *  2003-10-10 Written by Simon Derr.
  20  *  2003-10-22 Updates by Stephen Hemminger.
  21  *  2004 May-July Rework by Paul Jackson.
  22  *  ---------------------------------------------------
  23  *
  24  *  This file is subject to the terms and conditions of the GNU General Public
  25  *  License.  See the file COPYING in the main directory of the Linux
  26  *  distribution for more details.
  27  */
  28 
  29 #define pr_fmt(fmt) KBUILD_MODNAME ": " fmt
  30 
  31 #include "cgroup-internal.h"
  32 
  33 #include <linux/cred.h>
  34 #include <linux/errno.h>
  35 #include <linux/init_task.h>
  36 #include <linux/kernel.h>
  37 #include <linux/magic.h>
  38 #include <linux/mutex.h>
  39 #include <linux/mount.h>
  40 #include <linux/pagemap.h>
  41 #include <linux/proc_fs.h>
  42 #include <linux/rcupdate.h>
  43 #include <linux/sched.h>
  44 #include <linux/sched/task.h>
  45 #include <linux/slab.h>
  46 #include <linux/spinlock.h>
  47 #include <linux/percpu-rwsem.h>
  48 #include <linux/string.h>
  49 #include <linux/hashtable.h>
  50 #include <linux/idr.h>
  51 #include <linux/kthread.h>
  52 #include <linux/atomic.h>
  53 #include <linux/cpuset.h>
  54 #include <linux/proc_ns.h>
  55 #include <linux/nsproxy.h>
  56 #include <linux/file.h>
  57 #include <linux/fs_parser.h>
  58 #include <linux/sched/cputime.h>
  59 #include <linux/psi.h>
  60 #include <net/sock.h>
  61 
  62 #define CREATE_TRACE_POINTS
  63 #include <trace/events/cgroup.h>
  64 
  65 #define CGROUP_FILE_NAME_MAX            (MAX_CGROUP_TYPE_NAMELEN +      \
  66                                          MAX_CFTYPE_NAME + 2)
  67 /* let's not notify more than 100 times per second */
  68 #define CGROUP_FILE_NOTIFY_MIN_INTV     DIV_ROUND_UP(HZ, 100)
  69 
  70 /*
  71  * cgroup_mutex is the master lock.  Any modification to cgroup or its
  72  * hierarchy must be performed while holding it.
  73  *
  74  * css_set_lock protects task->cgroups pointer, the list of css_set
  75  * objects, and the chain of tasks off each css_set.
  76  *
  77  * These locks are exported if CONFIG_PROVE_RCU so that accessors in
  78  * cgroup.h can use them for lockdep annotations.
  79  */
  80 DEFINE_MUTEX(cgroup_mutex);
  81 DEFINE_SPINLOCK(css_set_lock);
  82 
  83 #ifdef CONFIG_PROVE_RCU
  84 EXPORT_SYMBOL_GPL(cgroup_mutex);
  85 EXPORT_SYMBOL_GPL(css_set_lock);
  86 #endif
  87 
  88 DEFINE_SPINLOCK(trace_cgroup_path_lock);
  89 char trace_cgroup_path[TRACE_CGROUP_PATH_LEN];
  90 bool cgroup_debug __read_mostly;
  91 
  92 /*
  93  * Protects cgroup_idr and css_idr so that IDs can be released without
  94  * grabbing cgroup_mutex.
  95  */
  96 static DEFINE_SPINLOCK(cgroup_idr_lock);
  97 
  98 /*
  99  * Protects cgroup_file->kn for !self csses.  It synchronizes notifications
 100  * against file removal/re-creation across css hiding.
 101  */
 102 static DEFINE_SPINLOCK(cgroup_file_kn_lock);
 103 
 104 DEFINE_PERCPU_RWSEM(cgroup_threadgroup_rwsem);
 105 
 106 #define cgroup_assert_mutex_or_rcu_locked()                             \
 107         RCU_LOCKDEP_WARN(!rcu_read_lock_held() &&                       \
 108                            !lockdep_is_held(&cgroup_mutex),             \
 109                            "cgroup_mutex or RCU read lock required");
 110 
 111 /*
 112  * cgroup destruction makes heavy use of work items and there can be a lot
 113  * of concurrent destructions.  Use a separate workqueue so that cgroup
 114  * destruction work items don't end up filling up max_active of system_wq
 115  * which may lead to deadlock.
 116  */
 117 static struct workqueue_struct *cgroup_destroy_wq;
 118 
 119 /* generate an array of cgroup subsystem pointers */
 120 #define SUBSYS(_x) [_x ## _cgrp_id] = &_x ## _cgrp_subsys,
 121 struct cgroup_subsys *cgroup_subsys[] = {
 122 #include <linux/cgroup_subsys.h>
 123 };
 124 #undef SUBSYS
 125 
 126 /* array of cgroup subsystem names */
 127 #define SUBSYS(_x) [_x ## _cgrp_id] = #_x,
 128 static const char *cgroup_subsys_name[] = {
 129 #include <linux/cgroup_subsys.h>
 130 };
 131 #undef SUBSYS
 132 
 133 /* array of static_keys for cgroup_subsys_enabled() and cgroup_subsys_on_dfl() */
 134 #define SUBSYS(_x)                                                              \
 135         DEFINE_STATIC_KEY_TRUE(_x ## _cgrp_subsys_enabled_key);                 \
 136         DEFINE_STATIC_KEY_TRUE(_x ## _cgrp_subsys_on_dfl_key);                  \
 137         EXPORT_SYMBOL_GPL(_x ## _cgrp_subsys_enabled_key);                      \
 138         EXPORT_SYMBOL_GPL(_x ## _cgrp_subsys_on_dfl_key);
 139 #include <linux/cgroup_subsys.h>
 140 #undef SUBSYS
 141 
 142 #define SUBSYS(_x) [_x ## _cgrp_id] = &_x ## _cgrp_subsys_enabled_key,
 143 static struct static_key_true *cgroup_subsys_enabled_key[] = {
 144 #include <linux/cgroup_subsys.h>
 145 };
 146 #undef SUBSYS
 147 
 148 #define SUBSYS(_x) [_x ## _cgrp_id] = &_x ## _cgrp_subsys_on_dfl_key,
 149 static struct static_key_true *cgroup_subsys_on_dfl_key[] = {
 150 #include <linux/cgroup_subsys.h>
 151 };
 152 #undef SUBSYS
 153 
 154 static DEFINE_PER_CPU(struct cgroup_rstat_cpu, cgrp_dfl_root_rstat_cpu);
 155 
 156 /*
 157  * The default hierarchy, reserved for the subsystems that are otherwise
 158  * unattached - it never has more than a single cgroup, and all tasks are
 159  * part of that cgroup.
 160  */
 161 struct cgroup_root cgrp_dfl_root = { .cgrp.rstat_cpu = &cgrp_dfl_root_rstat_cpu };
 162 EXPORT_SYMBOL_GPL(cgrp_dfl_root);
 163 
 164 /*
 165  * The default hierarchy always exists but is hidden until mounted for the
 166  * first time.  This is for backward compatibility.
 167  */
 168 static bool cgrp_dfl_visible;
 169 
 170 /* some controllers are not supported in the default hierarchy */
 171 static u16 cgrp_dfl_inhibit_ss_mask;
 172 
 173 /* some controllers are implicitly enabled on the default hierarchy */
 174 static u16 cgrp_dfl_implicit_ss_mask;
 175 
 176 /* some controllers can be threaded on the default hierarchy */
 177 static u16 cgrp_dfl_threaded_ss_mask;
 178 
 179 /* The list of hierarchy roots */
 180 LIST_HEAD(cgroup_roots);
 181 static int cgroup_root_count;
 182 
 183 /* hierarchy ID allocation and mapping, protected by cgroup_mutex */
 184 static DEFINE_IDR(cgroup_hierarchy_idr);
 185 
 186 /*
 187  * Assign a monotonically increasing serial number to csses.  It guarantees
 188  * cgroups with bigger numbers are newer than those with smaller numbers.
 189  * Also, as csses are always appended to the parent's ->children list, it
 190  * guarantees that sibling csses are always sorted in the ascending serial
 191  * number order on the list.  Protected by cgroup_mutex.
 192  */
 193 static u64 css_serial_nr_next = 1;
 194 
 195 /*
 196  * These bitmasks identify subsystems with specific features to avoid
 197  * having to do iterative checks repeatedly.
 198  */
 199 static u16 have_fork_callback __read_mostly;
 200 static u16 have_exit_callback __read_mostly;
 201 static u16 have_release_callback __read_mostly;
 202 static u16 have_canfork_callback __read_mostly;
 203 
 204 /* cgroup namespace for init task */
 205 struct cgroup_namespace init_cgroup_ns = {
 206         .count          = REFCOUNT_INIT(2),
 207         .user_ns        = &init_user_ns,
 208         .ns.ops         = &cgroupns_operations,
 209         .ns.inum        = PROC_CGROUP_INIT_INO,
 210         .root_cset      = &init_css_set,
 211 };
 212 
 213 static struct file_system_type cgroup2_fs_type;
 214 static struct cftype cgroup_base_files[];
 215 
 216 static int cgroup_apply_control(struct cgroup *cgrp);
 217 static void cgroup_finalize_control(struct cgroup *cgrp, int ret);
 218 static void css_task_iter_skip(struct css_task_iter *it,
 219                                struct task_struct *task);
 220 static int cgroup_destroy_locked(struct cgroup *cgrp);
 221 static struct cgroup_subsys_state *css_create(struct cgroup *cgrp,
 222                                               struct cgroup_subsys *ss);
 223 static void css_release(struct percpu_ref *ref);
 224 static void kill_css(struct cgroup_subsys_state *css);
 225 static int cgroup_addrm_files(struct cgroup_subsys_state *css,
 226                               struct cgroup *cgrp, struct cftype cfts[],
 227                               bool is_add);
 228 
 229 /**
 230  * cgroup_ssid_enabled - cgroup subsys enabled test by subsys ID
 231  * @ssid: subsys ID of interest
 232  *
 233  * cgroup_subsys_enabled() can only be used with literal subsys names which
 234  * is fine for individual subsystems but unsuitable for cgroup core.  This
 235  * is slower static_key_enabled() based test indexed by @ssid.
 236  */
 237 bool cgroup_ssid_enabled(int ssid)
 238 {
 239         if (CGROUP_SUBSYS_COUNT == 0)
 240                 return false;
 241 
 242         return static_key_enabled(cgroup_subsys_enabled_key[ssid]);
 243 }
 244 
 245 /**
 246  * cgroup_on_dfl - test whether a cgroup is on the default hierarchy
 247  * @cgrp: the cgroup of interest
 248  *
 249  * The default hierarchy is the v2 interface of cgroup and this function
 250  * can be used to test whether a cgroup is on the default hierarchy for
 251  * cases where a subsystem should behave differnetly depending on the
 252  * interface version.
 253  *
 254  * The set of behaviors which change on the default hierarchy are still
 255  * being determined and the mount option is prefixed with __DEVEL__.
 256  *
 257  * List of changed behaviors:
 258  *
 259  * - Mount options "noprefix", "xattr", "clone_children", "release_agent"
 260  *   and "name" are disallowed.
 261  *
 262  * - When mounting an existing superblock, mount options should match.
 263  *
 264  * - Remount is disallowed.
 265  *
 266  * - rename(2) is disallowed.
 267  *
 268  * - "tasks" is removed.  Everything should be at process granularity.  Use
 269  *   "cgroup.procs" instead.
 270  *
 271  * - "cgroup.procs" is not sorted.  pids will be unique unless they got
 272  *   recycled inbetween reads.
 273  *
 274  * - "release_agent" and "notify_on_release" are removed.  Replacement
 275  *   notification mechanism will be implemented.
 276  *
 277  * - "cgroup.clone_children" is removed.
 278  *
 279  * - "cgroup.subtree_populated" is available.  Its value is 0 if the cgroup
 280  *   and its descendants contain no task; otherwise, 1.  The file also
 281  *   generates kernfs notification which can be monitored through poll and
 282  *   [di]notify when the value of the file changes.
 283  *
 284  * - cpuset: tasks will be kept in empty cpusets when hotplug happens and
 285  *   take masks of ancestors with non-empty cpus/mems, instead of being
 286  *   moved to an ancestor.
 287  *
 288  * - cpuset: a task can be moved into an empty cpuset, and again it takes
 289  *   masks of ancestors.
 290  *
 291  * - memcg: use_hierarchy is on by default and the cgroup file for the flag
 292  *   is not created.
 293  *
 294  * - blkcg: blk-throttle becomes properly hierarchical.
 295  *
 296  * - debug: disallowed on the default hierarchy.
 297  */
 298 bool cgroup_on_dfl(const struct cgroup *cgrp)
 299 {
 300         return cgrp->root == &cgrp_dfl_root;
 301 }
 302 
 303 /* IDR wrappers which synchronize using cgroup_idr_lock */
 304 static int cgroup_idr_alloc(struct idr *idr, void *ptr, int start, int end,
 305                             gfp_t gfp_mask)
 306 {
 307         int ret;
 308 
 309         idr_preload(gfp_mask);
 310         spin_lock_bh(&cgroup_idr_lock);
 311         ret = idr_alloc(idr, ptr, start, end, gfp_mask & ~__GFP_DIRECT_RECLAIM);
 312         spin_unlock_bh(&cgroup_idr_lock);
 313         idr_preload_end();
 314         return ret;
 315 }
 316 
 317 static void *cgroup_idr_replace(struct idr *idr, void *ptr, int id)
 318 {
 319         void *ret;
 320 
 321         spin_lock_bh(&cgroup_idr_lock);
 322         ret = idr_replace(idr, ptr, id);
 323         spin_unlock_bh(&cgroup_idr_lock);
 324         return ret;
 325 }
 326 
 327 static void cgroup_idr_remove(struct idr *idr, int id)
 328 {
 329         spin_lock_bh(&cgroup_idr_lock);
 330         idr_remove(idr, id);
 331         spin_unlock_bh(&cgroup_idr_lock);
 332 }
 333 
 334 static bool cgroup_has_tasks(struct cgroup *cgrp)
 335 {
 336         return cgrp->nr_populated_csets;
 337 }
 338 
 339 bool cgroup_is_threaded(struct cgroup *cgrp)
 340 {
 341         return cgrp->dom_cgrp != cgrp;
 342 }
 343 
 344 /* can @cgrp host both domain and threaded children? */
 345 static bool cgroup_is_mixable(struct cgroup *cgrp)
 346 {
 347         /*
 348          * Root isn't under domain level resource control exempting it from
 349          * the no-internal-process constraint, so it can serve as a thread
 350          * root and a parent of resource domains at the same time.
 351          */
 352         return !cgroup_parent(cgrp);
 353 }
 354 
 355 /* can @cgrp become a thread root? should always be true for a thread root */
 356 static bool cgroup_can_be_thread_root(struct cgroup *cgrp)
 357 {
 358         /* mixables don't care */
 359         if (cgroup_is_mixable(cgrp))
 360                 return true;
 361 
 362         /* domain roots can't be nested under threaded */
 363         if (cgroup_is_threaded(cgrp))
 364                 return false;
 365 
 366         /* can only have either domain or threaded children */
 367         if (cgrp->nr_populated_domain_children)
 368                 return false;
 369 
 370         /* and no domain controllers can be enabled */
 371         if (cgrp->subtree_control & ~cgrp_dfl_threaded_ss_mask)
 372                 return false;
 373 
 374         return true;
 375 }
 376 
 377 /* is @cgrp root of a threaded subtree? */
 378 bool cgroup_is_thread_root(struct cgroup *cgrp)
 379 {
 380         /* thread root should be a domain */
 381         if (cgroup_is_threaded(cgrp))
 382                 return false;
 383 
 384         /* a domain w/ threaded children is a thread root */
 385         if (cgrp->nr_threaded_children)
 386                 return true;
 387 
 388         /*
 389          * A domain which has tasks and explicit threaded controllers
 390          * enabled is a thread root.
 391          */
 392         if (cgroup_has_tasks(cgrp) &&
 393             (cgrp->subtree_control & cgrp_dfl_threaded_ss_mask))
 394                 return true;
 395 
 396         return false;
 397 }
 398 
 399 /* a domain which isn't connected to the root w/o brekage can't be used */
 400 static bool cgroup_is_valid_domain(struct cgroup *cgrp)
 401 {
 402         /* the cgroup itself can be a thread root */
 403         if (cgroup_is_threaded(cgrp))
 404                 return false;
 405 
 406         /* but the ancestors can't be unless mixable */
 407         while ((cgrp = cgroup_parent(cgrp))) {
 408                 if (!cgroup_is_mixable(cgrp) && cgroup_is_thread_root(cgrp))
 409                         return false;
 410                 if (cgroup_is_threaded(cgrp))
 411                         return false;
 412         }
 413 
 414         return true;
 415 }
 416 
 417 /* subsystems visibly enabled on a cgroup */
 418 static u16 cgroup_control(struct cgroup *cgrp)
 419 {
 420         struct cgroup *parent = cgroup_parent(cgrp);
 421         u16 root_ss_mask = cgrp->root->subsys_mask;
 422 
 423         if (parent) {
 424                 u16 ss_mask = parent->subtree_control;
 425 
 426                 /* threaded cgroups can only have threaded controllers */
 427                 if (cgroup_is_threaded(cgrp))
 428                         ss_mask &= cgrp_dfl_threaded_ss_mask;
 429                 return ss_mask;
 430         }
 431 
 432         if (cgroup_on_dfl(cgrp))
 433                 root_ss_mask &= ~(cgrp_dfl_inhibit_ss_mask |
 434                                   cgrp_dfl_implicit_ss_mask);
 435         return root_ss_mask;
 436 }
 437 
 438 /* subsystems enabled on a cgroup */
 439 static u16 cgroup_ss_mask(struct cgroup *cgrp)
 440 {
 441         struct cgroup *parent = cgroup_parent(cgrp);
 442 
 443         if (parent) {
 444                 u16 ss_mask = parent->subtree_ss_mask;
 445 
 446                 /* threaded cgroups can only have threaded controllers */
 447                 if (cgroup_is_threaded(cgrp))
 448                         ss_mask &= cgrp_dfl_threaded_ss_mask;
 449                 return ss_mask;
 450         }
 451 
 452         return cgrp->root->subsys_mask;
 453 }
 454 
 455 /**
 456  * cgroup_css - obtain a cgroup's css for the specified subsystem
 457  * @cgrp: the cgroup of interest
 458  * @ss: the subsystem of interest (%NULL returns @cgrp->self)
 459  *
 460  * Return @cgrp's css (cgroup_subsys_state) associated with @ss.  This
 461  * function must be called either under cgroup_mutex or rcu_read_lock() and
 462  * the caller is responsible for pinning the returned css if it wants to
 463  * keep accessing it outside the said locks.  This function may return
 464  * %NULL if @cgrp doesn't have @subsys_id enabled.
 465  */
 466 static struct cgroup_subsys_state *cgroup_css(struct cgroup *cgrp,
 467                                               struct cgroup_subsys *ss)
 468 {
 469         if (ss)
 470                 return rcu_dereference_check(cgrp->subsys[ss->id],
 471                                         lockdep_is_held(&cgroup_mutex));
 472         else
 473                 return &cgrp->self;
 474 }
 475 
 476 /**
 477  * cgroup_tryget_css - try to get a cgroup's css for the specified subsystem
 478  * @cgrp: the cgroup of interest
 479  * @ss: the subsystem of interest
 480  *
 481  * Find and get @cgrp's css assocaited with @ss.  If the css doesn't exist
 482  * or is offline, %NULL is returned.
 483  */
 484 static struct cgroup_subsys_state *cgroup_tryget_css(struct cgroup *cgrp,
 485                                                      struct cgroup_subsys *ss)
 486 {
 487         struct cgroup_subsys_state *css;
 488 
 489         rcu_read_lock();
 490         css = cgroup_css(cgrp, ss);
 491         if (css && !css_tryget_online(css))
 492                 css = NULL;
 493         rcu_read_unlock();
 494 
 495         return css;
 496 }
 497 
 498 /**
 499  * cgroup_e_css_by_mask - obtain a cgroup's effective css for the specified ss
 500  * @cgrp: the cgroup of interest
 501  * @ss: the subsystem of interest (%NULL returns @cgrp->self)
 502  *
 503  * Similar to cgroup_css() but returns the effective css, which is defined
 504  * as the matching css of the nearest ancestor including self which has @ss
 505  * enabled.  If @ss is associated with the hierarchy @cgrp is on, this
 506  * function is guaranteed to return non-NULL css.
 507  */
 508 static struct cgroup_subsys_state *cgroup_e_css_by_mask(struct cgroup *cgrp,
 509                                                         struct cgroup_subsys *ss)
 510 {
 511         lockdep_assert_held(&cgroup_mutex);
 512 
 513         if (!ss)
 514                 return &cgrp->self;
 515 
 516         /*
 517          * This function is used while updating css associations and thus
 518          * can't test the csses directly.  Test ss_mask.
 519          */
 520         while (!(cgroup_ss_mask(cgrp) & (1 << ss->id))) {
 521                 cgrp = cgroup_parent(cgrp);
 522                 if (!cgrp)
 523                         return NULL;
 524         }
 525 
 526         return cgroup_css(cgrp, ss);
 527 }
 528 
 529 /**
 530  * cgroup_e_css - obtain a cgroup's effective css for the specified subsystem
 531  * @cgrp: the cgroup of interest
 532  * @ss: the subsystem of interest
 533  *
 534  * Find and get the effective css of @cgrp for @ss.  The effective css is
 535  * defined as the matching css of the nearest ancestor including self which
 536  * has @ss enabled.  If @ss is not mounted on the hierarchy @cgrp is on,
 537  * the root css is returned, so this function always returns a valid css.
 538  *
 539  * The returned css is not guaranteed to be online, and therefore it is the
 540  * callers responsiblity to tryget a reference for it.
 541  */
 542 struct cgroup_subsys_state *cgroup_e_css(struct cgroup *cgrp,
 543                                          struct cgroup_subsys *ss)
 544 {
 545         struct cgroup_subsys_state *css;
 546 
 547         do {
 548                 css = cgroup_css(cgrp, ss);
 549 
 550                 if (css)
 551                         return css;
 552                 cgrp = cgroup_parent(cgrp);
 553         } while (cgrp);
 554 
 555         return init_css_set.subsys[ss->id];
 556 }
 557 
 558 /**
 559  * cgroup_get_e_css - get a cgroup's effective css for the specified subsystem
 560  * @cgrp: the cgroup of interest
 561  * @ss: the subsystem of interest
 562  *
 563  * Find and get the effective css of @cgrp for @ss.  The effective css is
 564  * defined as the matching css of the nearest ancestor including self which
 565  * has @ss enabled.  If @ss is not mounted on the hierarchy @cgrp is on,
 566  * the root css is returned, so this function always returns a valid css.
 567  * The returned css must be put using css_put().
 568  */
 569 struct cgroup_subsys_state *cgroup_get_e_css(struct cgroup *cgrp,
 570                                              struct cgroup_subsys *ss)
 571 {
 572         struct cgroup_subsys_state *css;
 573 
 574         rcu_read_lock();
 575 
 576         do {
 577                 css = cgroup_css(cgrp, ss);
 578 
 579                 if (css && css_tryget_online(css))
 580                         goto out_unlock;
 581                 cgrp = cgroup_parent(cgrp);
 582         } while (cgrp);
 583 
 584         css = init_css_set.subsys[ss->id];
 585         css_get(css);
 586 out_unlock:
 587         rcu_read_unlock();
 588         return css;
 589 }
 590 
 591 static void cgroup_get_live(struct cgroup *cgrp)
 592 {
 593         WARN_ON_ONCE(cgroup_is_dead(cgrp));
 594         css_get(&cgrp->self);
 595 }
 596 
 597 /**
 598  * __cgroup_task_count - count the number of tasks in a cgroup. The caller
 599  * is responsible for taking the css_set_lock.
 600  * @cgrp: the cgroup in question
 601  */
 602 int __cgroup_task_count(const struct cgroup *cgrp)
 603 {
 604         int count = 0;
 605         struct cgrp_cset_link *link;
 606 
 607         lockdep_assert_held(&css_set_lock);
 608 
 609         list_for_each_entry(link, &cgrp->cset_links, cset_link)
 610                 count += link->cset->nr_tasks;
 611 
 612         return count;
 613 }
 614 
 615 /**
 616  * cgroup_task_count - count the number of tasks in a cgroup.
 617  * @cgrp: the cgroup in question
 618  */
 619 int cgroup_task_count(const struct cgroup *cgrp)
 620 {
 621         int count;
 622 
 623         spin_lock_irq(&css_set_lock);
 624         count = __cgroup_task_count(cgrp);
 625         spin_unlock_irq(&css_set_lock);
 626 
 627         return count;
 628 }
 629 
 630 struct cgroup_subsys_state *of_css(struct kernfs_open_file *of)
 631 {
 632         struct cgroup *cgrp = of->kn->parent->priv;
 633         struct cftype *cft = of_cft(of);
 634 
 635         /*
 636          * This is open and unprotected implementation of cgroup_css().
 637          * seq_css() is only called from a kernfs file operation which has
 638          * an active reference on the file.  Because all the subsystem
 639          * files are drained before a css is disassociated with a cgroup,
 640          * the matching css from the cgroup's subsys table is guaranteed to
 641          * be and stay valid until the enclosing operation is complete.
 642          */
 643         if (cft->ss)
 644                 return rcu_dereference_raw(cgrp->subsys[cft->ss->id]);
 645         else
 646                 return &cgrp->self;
 647 }
 648 EXPORT_SYMBOL_GPL(of_css);
 649 
 650 /**
 651  * for_each_css - iterate all css's of a cgroup
 652  * @css: the iteration cursor
 653  * @ssid: the index of the subsystem, CGROUP_SUBSYS_COUNT after reaching the end
 654  * @cgrp: the target cgroup to iterate css's of
 655  *
 656  * Should be called under cgroup_[tree_]mutex.
 657  */
 658 #define for_each_css(css, ssid, cgrp)                                   \
 659         for ((ssid) = 0; (ssid) < CGROUP_SUBSYS_COUNT; (ssid)++)        \
 660                 if (!((css) = rcu_dereference_check(                    \
 661                                 (cgrp)->subsys[(ssid)],                 \
 662                                 lockdep_is_held(&cgroup_mutex)))) { }   \
 663                 else
 664 
 665 /**
 666  * for_each_e_css - iterate all effective css's of a cgroup
 667  * @css: the iteration cursor
 668  * @ssid: the index of the subsystem, CGROUP_SUBSYS_COUNT after reaching the end
 669  * @cgrp: the target cgroup to iterate css's of
 670  *
 671  * Should be called under cgroup_[tree_]mutex.
 672  */
 673 #define for_each_e_css(css, ssid, cgrp)                                     \
 674         for ((ssid) = 0; (ssid) < CGROUP_SUBSYS_COUNT; (ssid)++)            \
 675                 if (!((css) = cgroup_e_css_by_mask(cgrp,                    \
 676                                                    cgroup_subsys[(ssid)]))) \
 677                         ;                                                   \
 678                 else
 679 
 680 /**
 681  * do_each_subsys_mask - filter for_each_subsys with a bitmask
 682  * @ss: the iteration cursor
 683  * @ssid: the index of @ss, CGROUP_SUBSYS_COUNT after reaching the end
 684  * @ss_mask: the bitmask
 685  *
 686  * The block will only run for cases where the ssid-th bit (1 << ssid) of
 687  * @ss_mask is set.
 688  */
 689 #define do_each_subsys_mask(ss, ssid, ss_mask) do {                     \
 690         unsigned long __ss_mask = (ss_mask);                            \
 691         if (!CGROUP_SUBSYS_COUNT) { /* to avoid spurious gcc warning */ \
 692                 (ssid) = 0;                                             \
 693                 break;                                                  \
 694         }                                                               \
 695         for_each_set_bit(ssid, &__ss_mask, CGROUP_SUBSYS_COUNT) {       \
 696                 (ss) = cgroup_subsys[ssid];                             \
 697                 {
 698 
 699 #define while_each_subsys_mask()                                        \
 700                 }                                                       \
 701         }                                                               \
 702 } while (false)
 703 
 704 /* iterate over child cgrps, lock should be held throughout iteration */
 705 #define cgroup_for_each_live_child(child, cgrp)                         \
 706         list_for_each_entry((child), &(cgrp)->self.children, self.sibling) \
 707                 if (({ lockdep_assert_held(&cgroup_mutex);              \
 708                        cgroup_is_dead(child); }))                       \
 709                         ;                                               \
 710                 else
 711 
 712 /* walk live descendants in preorder */
 713 #define cgroup_for_each_live_descendant_pre(dsct, d_css, cgrp)          \
 714         css_for_each_descendant_pre((d_css), cgroup_css((cgrp), NULL))  \
 715                 if (({ lockdep_assert_held(&cgroup_mutex);              \
 716                        (dsct) = (d_css)->cgroup;                        \
 717                        cgroup_is_dead(dsct); }))                        \
 718                         ;                                               \
 719                 else
 720 
 721 /* walk live descendants in postorder */
 722 #define cgroup_for_each_live_descendant_post(dsct, d_css, cgrp)         \
 723         css_for_each_descendant_post((d_css), cgroup_css((cgrp), NULL)) \
 724                 if (({ lockdep_assert_held(&cgroup_mutex);              \
 725                        (dsct) = (d_css)->cgroup;                        \
 726                        cgroup_is_dead(dsct); }))                        \
 727                         ;                                               \
 728                 else
 729 
 730 /*
 731  * The default css_set - used by init and its children prior to any
 732  * hierarchies being mounted. It contains a pointer to the root state
 733  * for each subsystem. Also used to anchor the list of css_sets. Not
 734  * reference-counted, to improve performance when child cgroups
 735  * haven't been created.
 736  */
 737 struct css_set init_css_set = {
 738         .refcount               = REFCOUNT_INIT(1),
 739         .dom_cset               = &init_css_set,
 740         .tasks                  = LIST_HEAD_INIT(init_css_set.tasks),
 741         .mg_tasks               = LIST_HEAD_INIT(init_css_set.mg_tasks),
 742         .dying_tasks            = LIST_HEAD_INIT(init_css_set.dying_tasks),
 743         .task_iters             = LIST_HEAD_INIT(init_css_set.task_iters),
 744         .threaded_csets         = LIST_HEAD_INIT(init_css_set.threaded_csets),
 745         .cgrp_links             = LIST_HEAD_INIT(init_css_set.cgrp_links),
 746         .mg_preload_node        = LIST_HEAD_INIT(init_css_set.mg_preload_node),
 747         .mg_node                = LIST_HEAD_INIT(init_css_set.mg_node),
 748 
 749         /*
 750          * The following field is re-initialized when this cset gets linked
 751          * in cgroup_init().  However, let's initialize the field
 752          * statically too so that the default cgroup can be accessed safely
 753          * early during boot.
 754          */
 755         .dfl_cgrp               = &cgrp_dfl_root.cgrp,
 756 };
 757 
 758 static int css_set_count        = 1;    /* 1 for init_css_set */
 759 
 760 static bool css_set_threaded(struct css_set *cset)
 761 {
 762         return cset->dom_cset != cset;
 763 }
 764 
 765 /**
 766  * css_set_populated - does a css_set contain any tasks?
 767  * @cset: target css_set
 768  *
 769  * css_set_populated() should be the same as !!cset->nr_tasks at steady
 770  * state. However, css_set_populated() can be called while a task is being
 771  * added to or removed from the linked list before the nr_tasks is
 772  * properly updated. Hence, we can't just look at ->nr_tasks here.
 773  */
 774 static bool css_set_populated(struct css_set *cset)
 775 {
 776         lockdep_assert_held(&css_set_lock);
 777 
 778         return !list_empty(&cset->tasks) || !list_empty(&cset->mg_tasks);
 779 }
 780 
 781 /**
 782  * cgroup_update_populated - update the populated count of a cgroup
 783  * @cgrp: the target cgroup
 784  * @populated: inc or dec populated count
 785  *
 786  * One of the css_sets associated with @cgrp is either getting its first
 787  * task or losing the last.  Update @cgrp->nr_populated_* accordingly.  The
 788  * count is propagated towards root so that a given cgroup's
 789  * nr_populated_children is zero iff none of its descendants contain any
 790  * tasks.
 791  *
 792  * @cgrp's interface file "cgroup.populated" is zero if both
 793  * @cgrp->nr_populated_csets and @cgrp->nr_populated_children are zero and
 794  * 1 otherwise.  When the sum changes from or to zero, userland is notified
 795  * that the content of the interface file has changed.  This can be used to
 796  * detect when @cgrp and its descendants become populated or empty.
 797  */
 798 static void cgroup_update_populated(struct cgroup *cgrp, bool populated)
 799 {
 800         struct cgroup *child = NULL;
 801         int adj = populated ? 1 : -1;
 802 
 803         lockdep_assert_held(&css_set_lock);
 804 
 805         do {
 806                 bool was_populated = cgroup_is_populated(cgrp);
 807 
 808                 if (!child) {
 809                         cgrp->nr_populated_csets += adj;
 810                 } else {
 811                         if (cgroup_is_threaded(child))
 812                                 cgrp->nr_populated_threaded_children += adj;
 813                         else
 814                                 cgrp->nr_populated_domain_children += adj;
 815                 }
 816 
 817                 if (was_populated == cgroup_is_populated(cgrp))
 818                         break;
 819 
 820                 cgroup1_check_for_release(cgrp);
 821                 TRACE_CGROUP_PATH(notify_populated, cgrp,
 822                                   cgroup_is_populated(cgrp));
 823                 cgroup_file_notify(&cgrp->events_file);
 824 
 825                 child = cgrp;
 826                 cgrp = cgroup_parent(cgrp);
 827         } while (cgrp);
 828 }
 829 
 830 /**
 831  * css_set_update_populated - update populated state of a css_set
 832  * @cset: target css_set
 833  * @populated: whether @cset is populated or depopulated
 834  *
 835  * @cset is either getting the first task or losing the last.  Update the
 836  * populated counters of all associated cgroups accordingly.
 837  */
 838 static void css_set_update_populated(struct css_set *cset, bool populated)
 839 {
 840         struct cgrp_cset_link *link;
 841 
 842         lockdep_assert_held(&css_set_lock);
 843 
 844         list_for_each_entry(link, &cset->cgrp_links, cgrp_link)
 845                 cgroup_update_populated(link->cgrp, populated);
 846 }
 847 
 848 /*
 849  * @task is leaving, advance task iterators which are pointing to it so
 850  * that they can resume at the next position.  Advancing an iterator might
 851  * remove it from the list, use safe walk.  See css_task_iter_skip() for
 852  * details.
 853  */
 854 static void css_set_skip_task_iters(struct css_set *cset,
 855                                     struct task_struct *task)
 856 {
 857         struct css_task_iter *it, *pos;
 858 
 859         list_for_each_entry_safe(it, pos, &cset->task_iters, iters_node)
 860                 css_task_iter_skip(it, task);
 861 }
 862 
 863 /**
 864  * css_set_move_task - move a task from one css_set to another
 865  * @task: task being moved
 866  * @from_cset: css_set @task currently belongs to (may be NULL)
 867  * @to_cset: new css_set @task is being moved to (may be NULL)
 868  * @use_mg_tasks: move to @to_cset->mg_tasks instead of ->tasks
 869  *
 870  * Move @task from @from_cset to @to_cset.  If @task didn't belong to any
 871  * css_set, @from_cset can be NULL.  If @task is being disassociated
 872  * instead of moved, @to_cset can be NULL.
 873  *
 874  * This function automatically handles populated counter updates and
 875  * css_task_iter adjustments but the caller is responsible for managing
 876  * @from_cset and @to_cset's reference counts.
 877  */
 878 static void css_set_move_task(struct task_struct *task,
 879                               struct css_set *from_cset, struct css_set *to_cset,
 880                               bool use_mg_tasks)
 881 {
 882         lockdep_assert_held(&css_set_lock);
 883 
 884         if (to_cset && !css_set_populated(to_cset))
 885                 css_set_update_populated(to_cset, true);
 886 
 887         if (from_cset) {
 888                 WARN_ON_ONCE(list_empty(&task->cg_list));
 889 
 890                 css_set_skip_task_iters(from_cset, task);
 891                 list_del_init(&task->cg_list);
 892                 if (!css_set_populated(from_cset))
 893                         css_set_update_populated(from_cset, false);
 894         } else {
 895                 WARN_ON_ONCE(!list_empty(&task->cg_list));
 896         }
 897 
 898         if (to_cset) {
 899                 /*
 900                  * We are synchronized through cgroup_threadgroup_rwsem
 901                  * against PF_EXITING setting such that we can't race
 902                  * against cgroup_exit() changing the css_set to
 903                  * init_css_set and dropping the old one.
 904                  */
 905                 WARN_ON_ONCE(task->flags & PF_EXITING);
 906 
 907                 cgroup_move_task(task, to_cset);
 908                 list_add_tail(&task->cg_list, use_mg_tasks ? &to_cset->mg_tasks :
 909                                                              &to_cset->tasks);
 910         }
 911 }
 912 
 913 /*
 914  * hash table for cgroup groups. This improves the performance to find
 915  * an existing css_set. This hash doesn't (currently) take into
 916  * account cgroups in empty hierarchies.
 917  */
 918 #define CSS_SET_HASH_BITS       7
 919 static DEFINE_HASHTABLE(css_set_table, CSS_SET_HASH_BITS);
 920 
 921 static unsigned long css_set_hash(struct cgroup_subsys_state *css[])
 922 {
 923         unsigned long key = 0UL;
 924         struct cgroup_subsys *ss;
 925         int i;
 926 
 927         for_each_subsys(ss, i)
 928                 key += (unsigned long)css[i];
 929         key = (key >> 16) ^ key;
 930 
 931         return key;
 932 }
 933 
 934 void put_css_set_locked(struct css_set *cset)
 935 {
 936         struct cgrp_cset_link *link, *tmp_link;
 937         struct cgroup_subsys *ss;
 938         int ssid;
 939 
 940         lockdep_assert_held(&css_set_lock);
 941 
 942         if (!refcount_dec_and_test(&cset->refcount))
 943                 return;
 944 
 945         WARN_ON_ONCE(!list_empty(&cset->threaded_csets));
 946 
 947         /* This css_set is dead. unlink it and release cgroup and css refs */
 948         for_each_subsys(ss, ssid) {
 949                 list_del(&cset->e_cset_node[ssid]);
 950                 css_put(cset->subsys[ssid]);
 951         }
 952         hash_del(&cset->hlist);
 953         css_set_count--;
 954 
 955         list_for_each_entry_safe(link, tmp_link, &cset->cgrp_links, cgrp_link) {
 956                 list_del(&link->cset_link);
 957                 list_del(&link->cgrp_link);
 958                 if (cgroup_parent(link->cgrp))
 959                         cgroup_put(link->cgrp);
 960                 kfree(link);
 961         }
 962 
 963         if (css_set_threaded(cset)) {
 964                 list_del(&cset->threaded_csets_node);
 965                 put_css_set_locked(cset->dom_cset);
 966         }
 967 
 968         kfree_rcu(cset, rcu_head);
 969 }
 970 
 971 /**
 972  * compare_css_sets - helper function for find_existing_css_set().
 973  * @cset: candidate css_set being tested
 974  * @old_cset: existing css_set for a task
 975  * @new_cgrp: cgroup that's being entered by the task
 976  * @template: desired set of css pointers in css_set (pre-calculated)
 977  *
 978  * Returns true if "cset" matches "old_cset" except for the hierarchy
 979  * which "new_cgrp" belongs to, for which it should match "new_cgrp".
 980  */
 981 static bool compare_css_sets(struct css_set *cset,
 982                              struct css_set *old_cset,
 983                              struct cgroup *new_cgrp,
 984                              struct cgroup_subsys_state *template[])
 985 {
 986         struct cgroup *new_dfl_cgrp;
 987         struct list_head *l1, *l2;
 988 
 989         /*
 990          * On the default hierarchy, there can be csets which are
 991          * associated with the same set of cgroups but different csses.
 992          * Let's first ensure that csses match.
 993          */
 994         if (memcmp(template, cset->subsys, sizeof(cset->subsys)))
 995                 return false;
 996 
 997 
 998         /* @cset's domain should match the default cgroup's */
 999         if (cgroup_on_dfl(new_cgrp))
1000                 new_dfl_cgrp = new_cgrp;
1001         else
1002                 new_dfl_cgrp = old_cset->dfl_cgrp;
1003 
1004         if (new_dfl_cgrp->dom_cgrp != cset->dom_cset->dfl_cgrp)
1005                 return false;
1006 
1007         /*
1008          * Compare cgroup pointers in order to distinguish between
1009          * different cgroups in hierarchies.  As different cgroups may
1010          * share the same effective css, this comparison is always
1011          * necessary.
1012          */
1013         l1 = &cset->cgrp_links;
1014         l2 = &old_cset->cgrp_links;
1015         while (1) {
1016                 struct cgrp_cset_link *link1, *link2;
1017                 struct cgroup *cgrp1, *cgrp2;
1018 
1019                 l1 = l1->next;
1020                 l2 = l2->next;
1021                 /* See if we reached the end - both lists are equal length. */
1022                 if (l1 == &cset->cgrp_links) {
1023                         BUG_ON(l2 != &old_cset->cgrp_links);
1024                         break;
1025                 } else {
1026                         BUG_ON(l2 == &old_cset->cgrp_links);
1027                 }
1028                 /* Locate the cgroups associated with these links. */
1029                 link1 = list_entry(l1, struct cgrp_cset_link, cgrp_link);
1030                 link2 = list_entry(l2, struct cgrp_cset_link, cgrp_link);
1031                 cgrp1 = link1->cgrp;
1032                 cgrp2 = link2->cgrp;
1033                 /* Hierarchies should be linked in the same order. */
1034                 BUG_ON(cgrp1->root != cgrp2->root);
1035 
1036                 /*
1037                  * If this hierarchy is the hierarchy of the cgroup
1038                  * that's changing, then we need to check that this
1039                  * css_set points to the new cgroup; if it's any other
1040                  * hierarchy, then this css_set should point to the
1041                  * same cgroup as the old css_set.
1042                  */
1043                 if (cgrp1->root == new_cgrp->root) {
1044                         if (cgrp1 != new_cgrp)
1045                                 return false;
1046                 } else {
1047                         if (cgrp1 != cgrp2)
1048                                 return false;
1049                 }
1050         }
1051         return true;
1052 }
1053 
1054 /**
1055  * find_existing_css_set - init css array and find the matching css_set
1056  * @old_cset: the css_set that we're using before the cgroup transition
1057  * @cgrp: the cgroup that we're moving into
1058  * @template: out param for the new set of csses, should be clear on entry
1059  */
1060 static struct css_set *find_existing_css_set(struct css_set *old_cset,
1061                                         struct cgroup *cgrp,
1062                                         struct cgroup_subsys_state *template[])
1063 {
1064         struct cgroup_root *root = cgrp->root;
1065         struct cgroup_subsys *ss;
1066         struct css_set *cset;
1067         unsigned long key;
1068         int i;
1069 
1070         /*
1071          * Build the set of subsystem state objects that we want to see in the
1072          * new css_set. while subsystems can change globally, the entries here
1073          * won't change, so no need for locking.
1074          */
1075         for_each_subsys(ss, i) {
1076                 if (root->subsys_mask & (1UL << i)) {
1077                         /*
1078                          * @ss is in this hierarchy, so we want the
1079                          * effective css from @cgrp.
1080                          */
1081                         template[i] = cgroup_e_css_by_mask(cgrp, ss);
1082                 } else {
1083                         /*
1084                          * @ss is not in this hierarchy, so we don't want
1085                          * to change the css.
1086                          */
1087                         template[i] = old_cset->subsys[i];
1088                 }
1089         }
1090 
1091         key = css_set_hash(template);
1092         hash_for_each_possible(css_set_table, cset, hlist, key) {
1093                 if (!compare_css_sets(cset, old_cset, cgrp, template))
1094                         continue;
1095 
1096                 /* This css_set matches what we need */
1097                 return cset;
1098         }
1099 
1100         /* No existing cgroup group matched */
1101         return NULL;
1102 }
1103 
1104 static void free_cgrp_cset_links(struct list_head *links_to_free)
1105 {
1106         struct cgrp_cset_link *link, *tmp_link;
1107 
1108         list_for_each_entry_safe(link, tmp_link, links_to_free, cset_link) {
1109                 list_del(&link->cset_link);
1110                 kfree(link);
1111         }
1112 }
1113 
1114 /**
1115  * allocate_cgrp_cset_links - allocate cgrp_cset_links
1116  * @count: the number of links to allocate
1117  * @tmp_links: list_head the allocated links are put on
1118  *
1119  * Allocate @count cgrp_cset_link structures and chain them on @tmp_links
1120  * through ->cset_link.  Returns 0 on success or -errno.
1121  */
1122 static int allocate_cgrp_cset_links(int count, struct list_head *tmp_links)
1123 {
1124         struct cgrp_cset_link *link;
1125         int i;
1126 
1127         INIT_LIST_HEAD(tmp_links);
1128 
1129         for (i = 0; i < count; i++) {
1130                 link = kzalloc(sizeof(*link), GFP_KERNEL);
1131                 if (!link) {
1132                         free_cgrp_cset_links(tmp_links);
1133                         return -ENOMEM;
1134                 }
1135                 list_add(&link->cset_link, tmp_links);
1136         }
1137         return 0;
1138 }
1139 
1140 /**
1141  * link_css_set - a helper function to link a css_set to a cgroup
1142  * @tmp_links: cgrp_cset_link objects allocated by allocate_cgrp_cset_links()
1143  * @cset: the css_set to be linked
1144  * @cgrp: the destination cgroup
1145  */
1146 static void link_css_set(struct list_head *tmp_links, struct css_set *cset,
1147                          struct cgroup *cgrp)
1148 {
1149         struct cgrp_cset_link *link;
1150 
1151         BUG_ON(list_empty(tmp_links));
1152 
1153         if (cgroup_on_dfl(cgrp))
1154                 cset->dfl_cgrp = cgrp;
1155 
1156         link = list_first_entry(tmp_links, struct cgrp_cset_link, cset_link);
1157         link->cset = cset;
1158         link->cgrp = cgrp;
1159 
1160         /*
1161          * Always add links to the tail of the lists so that the lists are
1162          * in choronological order.
1163          */
1164         list_move_tail(&link->cset_link, &cgrp->cset_links);
1165         list_add_tail(&link->cgrp_link, &cset->cgrp_links);
1166 
1167         if (cgroup_parent(cgrp))
1168                 cgroup_get_live(cgrp);
1169 }
1170 
1171 /**
1172  * find_css_set - return a new css_set with one cgroup updated
1173  * @old_cset: the baseline css_set
1174  * @cgrp: the cgroup to be updated
1175  *
1176  * Return a new css_set that's equivalent to @old_cset, but with @cgrp
1177  * substituted into the appropriate hierarchy.
1178  */
1179 static struct css_set *find_css_set(struct css_set *old_cset,
1180                                     struct cgroup *cgrp)
1181 {
1182         struct cgroup_subsys_state *template[CGROUP_SUBSYS_COUNT] = { };
1183         struct css_set *cset;
1184         struct list_head tmp_links;
1185         struct cgrp_cset_link *link;
1186         struct cgroup_subsys *ss;
1187         unsigned long key;
1188         int ssid;
1189 
1190         lockdep_assert_held(&cgroup_mutex);
1191 
1192         /* First see if we already have a cgroup group that matches
1193          * the desired set */
1194         spin_lock_irq(&css_set_lock);
1195         cset = find_existing_css_set(old_cset, cgrp, template);
1196         if (cset)
1197                 get_css_set(cset);
1198         spin_unlock_irq(&css_set_lock);
1199 
1200         if (cset)
1201                 return cset;
1202 
1203         cset = kzalloc(sizeof(*cset), GFP_KERNEL);
1204         if (!cset)
1205                 return NULL;
1206 
1207         /* Allocate all the cgrp_cset_link objects that we'll need */
1208         if (allocate_cgrp_cset_links(cgroup_root_count, &tmp_links) < 0) {
1209                 kfree(cset);
1210                 return NULL;
1211         }
1212 
1213         refcount_set(&cset->refcount, 1);
1214         cset->dom_cset = cset;
1215         INIT_LIST_HEAD(&cset->tasks);
1216         INIT_LIST_HEAD(&cset->mg_tasks);
1217         INIT_LIST_HEAD(&cset->dying_tasks);
1218         INIT_LIST_HEAD(&cset->task_iters);
1219         INIT_LIST_HEAD(&cset->threaded_csets);
1220         INIT_HLIST_NODE(&cset->hlist);
1221         INIT_LIST_HEAD(&cset->cgrp_links);
1222         INIT_LIST_HEAD(&cset->mg_preload_node);
1223         INIT_LIST_HEAD(&cset->mg_node);
1224 
1225         /* Copy the set of subsystem state objects generated in
1226          * find_existing_css_set() */
1227         memcpy(cset->subsys, template, sizeof(cset->subsys));
1228 
1229         spin_lock_irq(&css_set_lock);
1230         /* Add reference counts and links from the new css_set. */
1231         list_for_each_entry(link, &old_cset->cgrp_links, cgrp_link) {
1232                 struct cgroup *c = link->cgrp;
1233 
1234                 if (c->root == cgrp->root)
1235                         c = cgrp;
1236                 link_css_set(&tmp_links, cset, c);
1237         }
1238 
1239         BUG_ON(!list_empty(&tmp_links));
1240 
1241         css_set_count++;
1242 
1243         /* Add @cset to the hash table */
1244         key = css_set_hash(cset->subsys);
1245         hash_add(css_set_table, &cset->hlist, key);
1246 
1247         for_each_subsys(ss, ssid) {
1248                 struct cgroup_subsys_state *css = cset->subsys[ssid];
1249 
1250                 list_add_tail(&cset->e_cset_node[ssid],
1251                               &css->cgroup->e_csets[ssid]);
1252                 css_get(css);
1253         }
1254 
1255         spin_unlock_irq(&css_set_lock);
1256 
1257         /*
1258          * If @cset should be threaded, look up the matching dom_cset and
1259          * link them up.  We first fully initialize @cset then look for the
1260          * dom_cset.  It's simpler this way and safe as @cset is guaranteed
1261          * to stay empty until we return.
1262          */
1263         if (cgroup_is_threaded(cset->dfl_cgrp)) {
1264                 struct css_set *dcset;
1265 
1266                 dcset = find_css_set(cset, cset->dfl_cgrp->dom_cgrp);
1267                 if (!dcset) {
1268                         put_css_set(cset);
1269                         return NULL;
1270                 }
1271 
1272                 spin_lock_irq(&css_set_lock);
1273                 cset->dom_cset = dcset;
1274                 list_add_tail(&cset->threaded_csets_node,
1275                               &dcset->threaded_csets);
1276                 spin_unlock_irq(&css_set_lock);
1277         }
1278 
1279         return cset;
1280 }
1281 
1282 struct cgroup_root *cgroup_root_from_kf(struct kernfs_root *kf_root)
1283 {
1284         struct cgroup *root_cgrp = kf_root->kn->priv;
1285 
1286         return root_cgrp->root;
1287 }
1288 
1289 static int cgroup_init_root_id(struct cgroup_root *root)
1290 {
1291         int id;
1292 
1293         lockdep_assert_held(&cgroup_mutex);
1294 
1295         id = idr_alloc_cyclic(&cgroup_hierarchy_idr, root, 0, 0, GFP_KERNEL);
1296         if (id < 0)
1297                 return id;
1298 
1299         root->hierarchy_id = id;
1300         return 0;
1301 }
1302 
1303 static void cgroup_exit_root_id(struct cgroup_root *root)
1304 {
1305         lockdep_assert_held(&cgroup_mutex);
1306 
1307         idr_remove(&cgroup_hierarchy_idr, root->hierarchy_id);
1308 }
1309 
1310 void cgroup_free_root(struct cgroup_root *root)
1311 {
1312         if (root) {
1313                 idr_destroy(&root->cgroup_idr);
1314                 kfree(root);
1315         }
1316 }
1317 
1318 static void cgroup_destroy_root(struct cgroup_root *root)
1319 {
1320         struct cgroup *cgrp = &root->cgrp;
1321         struct cgrp_cset_link *link, *tmp_link;
1322 
1323         trace_cgroup_destroy_root(root);
1324 
1325         cgroup_lock_and_drain_offline(&cgrp_dfl_root.cgrp);
1326 
1327         BUG_ON(atomic_read(&root->nr_cgrps));
1328         BUG_ON(!list_empty(&cgrp->self.children));
1329 
1330         /* Rebind all subsystems back to the default hierarchy */
1331         WARN_ON(rebind_subsystems(&cgrp_dfl_root, root->subsys_mask));
1332 
1333         /*
1334          * Release all the links from cset_links to this hierarchy's
1335          * root cgroup
1336          */
1337         spin_lock_irq(&css_set_lock);
1338 
1339         list_for_each_entry_safe(link, tmp_link, &cgrp->cset_links, cset_link) {
1340                 list_del(&link->cset_link);
1341                 list_del(&link->cgrp_link);
1342                 kfree(link);
1343         }
1344 
1345         spin_unlock_irq(&css_set_lock);
1346 
1347         if (!list_empty(&root->root_list)) {
1348                 list_del(&root->root_list);
1349                 cgroup_root_count--;
1350         }
1351 
1352         cgroup_exit_root_id(root);
1353 
1354         mutex_unlock(&cgroup_mutex);
1355 
1356         kernfs_destroy_root(root->kf_root);
1357         cgroup_free_root(root);
1358 }
1359 
1360 /*
1361  * look up cgroup associated with current task's cgroup namespace on the
1362  * specified hierarchy
1363  */
1364 static struct cgroup *
1365 current_cgns_cgroup_from_root(struct cgroup_root *root)
1366 {
1367         struct cgroup *res = NULL;
1368         struct css_set *cset;
1369 
1370         lockdep_assert_held(&css_set_lock);
1371 
1372         rcu_read_lock();
1373 
1374         cset = current->nsproxy->cgroup_ns->root_cset;
1375         if (cset == &init_css_set) {
1376                 res = &root->cgrp;
1377         } else {
1378                 struct cgrp_cset_link *link;
1379 
1380                 list_for_each_entry(link, &cset->cgrp_links, cgrp_link) {
1381                         struct cgroup *c = link->cgrp;
1382 
1383                         if (c->root == root) {
1384                                 res = c;
1385                                 break;
1386                         }
1387                 }
1388         }
1389         rcu_read_unlock();
1390 
1391         BUG_ON(!res);
1392         return res;
1393 }
1394 
1395 /* look up cgroup associated with given css_set on the specified hierarchy */
1396 static struct cgroup *cset_cgroup_from_root(struct css_set *cset,
1397                                             struct cgroup_root *root)
1398 {
1399         struct cgroup *res = NULL;
1400 
1401         lockdep_assert_held(&cgroup_mutex);
1402         lockdep_assert_held(&css_set_lock);
1403 
1404         if (cset == &init_css_set) {
1405                 res = &root->cgrp;
1406         } else if (root == &cgrp_dfl_root) {
1407                 res = cset->dfl_cgrp;
1408         } else {
1409                 struct cgrp_cset_link *link;
1410 
1411                 list_for_each_entry(link, &cset->cgrp_links, cgrp_link) {
1412                         struct cgroup *c = link->cgrp;
1413 
1414                         if (c->root == root) {
1415                                 res = c;
1416                                 break;
1417                         }
1418                 }
1419         }
1420 
1421         BUG_ON(!res);
1422         return res;
1423 }
1424 
1425 /*
1426  * Return the cgroup for "task" from the given hierarchy. Must be
1427  * called with cgroup_mutex and css_set_lock held.
1428  */
1429 struct cgroup *task_cgroup_from_root(struct task_struct *task,
1430                                      struct cgroup_root *root)
1431 {
1432         /*
1433          * No need to lock the task - since we hold cgroup_mutex the
1434          * task can't change groups, so the only thing that can happen
1435          * is that it exits and its css is set back to init_css_set.
1436          */
1437         return cset_cgroup_from_root(task_css_set(task), root);
1438 }
1439 
1440 /*
1441  * A task must hold cgroup_mutex to modify cgroups.
1442  *
1443  * Any task can increment and decrement the count field without lock.
1444  * So in general, code holding cgroup_mutex can't rely on the count
1445  * field not changing.  However, if the count goes to zero, then only
1446  * cgroup_attach_task() can increment it again.  Because a count of zero
1447  * means that no tasks are currently attached, therefore there is no
1448  * way a task attached to that cgroup can fork (the other way to
1449  * increment the count).  So code holding cgroup_mutex can safely
1450  * assume that if the count is zero, it will stay zero. Similarly, if
1451  * a task holds cgroup_mutex on a cgroup with zero count, it
1452  * knows that the cgroup won't be removed, as cgroup_rmdir()
1453  * needs that mutex.
1454  *
1455  * A cgroup can only be deleted if both its 'count' of using tasks
1456  * is zero, and its list of 'children' cgroups is empty.  Since all
1457  * tasks in the system use _some_ cgroup, and since there is always at
1458  * least one task in the system (init, pid == 1), therefore, root cgroup
1459  * always has either children cgroups and/or using tasks.  So we don't
1460  * need a special hack to ensure that root cgroup cannot be deleted.
1461  *
1462  * P.S.  One more locking exception.  RCU is used to guard the
1463  * update of a tasks cgroup pointer by cgroup_attach_task()
1464  */
1465 
1466 static struct kernfs_syscall_ops cgroup_kf_syscall_ops;
1467 
1468 static char *cgroup_file_name(struct cgroup *cgrp, const struct cftype *cft,
1469                               char *buf)
1470 {
1471         struct cgroup_subsys *ss = cft->ss;
1472 
1473         if (cft->ss && !(cft->flags & CFTYPE_NO_PREFIX) &&
1474             !(cgrp->root->flags & CGRP_ROOT_NOPREFIX)) {
1475                 const char *dbg = (cft->flags & CFTYPE_DEBUG) ? ".__DEBUG__." : "";
1476 
1477                 snprintf(buf, CGROUP_FILE_NAME_MAX, "%s%s.%s",
1478                          dbg, cgroup_on_dfl(cgrp) ? ss->name : ss->legacy_name,
1479                          cft->name);
1480         } else {
1481                 strscpy(buf, cft->name, CGROUP_FILE_NAME_MAX);
1482         }
1483         return buf;
1484 }
1485 
1486 /**
1487  * cgroup_file_mode - deduce file mode of a control file
1488  * @cft: the control file in question
1489  *
1490  * S_IRUGO for read, S_IWUSR for write.
1491  */
1492 static umode_t cgroup_file_mode(const struct cftype *cft)
1493 {
1494         umode_t mode = 0;
1495 
1496         if (cft->read_u64 || cft->read_s64 || cft->seq_show)
1497                 mode |= S_IRUGO;
1498 
1499         if (cft->write_u64 || cft->write_s64 || cft->write) {
1500                 if (cft->flags & CFTYPE_WORLD_WRITABLE)
1501                         mode |= S_IWUGO;
1502                 else
1503                         mode |= S_IWUSR;
1504         }
1505 
1506         return mode;
1507 }
1508 
1509 /**
1510  * cgroup_calc_subtree_ss_mask - calculate subtree_ss_mask
1511  * @subtree_control: the new subtree_control mask to consider
1512  * @this_ss_mask: available subsystems
1513  *
1514  * On the default hierarchy, a subsystem may request other subsystems to be
1515  * enabled together through its ->depends_on mask.  In such cases, more
1516  * subsystems than specified in "cgroup.subtree_control" may be enabled.
1517  *
1518  * This function calculates which subsystems need to be enabled if
1519  * @subtree_control is to be applied while restricted to @this_ss_mask.
1520  */
1521 static u16 cgroup_calc_subtree_ss_mask(u16 subtree_control, u16 this_ss_mask)
1522 {
1523         u16 cur_ss_mask = subtree_control;
1524         struct cgroup_subsys *ss;
1525         int ssid;
1526 
1527         lockdep_assert_held(&cgroup_mutex);
1528 
1529         cur_ss_mask |= cgrp_dfl_implicit_ss_mask;
1530 
1531         while (true) {
1532                 u16 new_ss_mask = cur_ss_mask;
1533 
1534                 do_each_subsys_mask(ss, ssid, cur_ss_mask) {
1535                         new_ss_mask |= ss->depends_on;
1536                 } while_each_subsys_mask();
1537 
1538                 /*
1539                  * Mask out subsystems which aren't available.  This can
1540                  * happen only if some depended-upon subsystems were bound
1541                  * to non-default hierarchies.
1542                  */
1543                 new_ss_mask &= this_ss_mask;
1544 
1545                 if (new_ss_mask == cur_ss_mask)
1546                         break;
1547                 cur_ss_mask = new_ss_mask;
1548         }
1549 
1550         return cur_ss_mask;
1551 }
1552 
1553 /**
1554  * cgroup_kn_unlock - unlocking helper for cgroup kernfs methods
1555  * @kn: the kernfs_node being serviced
1556  *
1557  * This helper undoes cgroup_kn_lock_live() and should be invoked before
1558  * the method finishes if locking succeeded.  Note that once this function
1559  * returns the cgroup returned by cgroup_kn_lock_live() may become
1560  * inaccessible any time.  If the caller intends to continue to access the
1561  * cgroup, it should pin it before invoking this function.
1562  */
1563 void cgroup_kn_unlock(struct kernfs_node *kn)
1564 {
1565         struct cgroup *cgrp;
1566 
1567         if (kernfs_type(kn) == KERNFS_DIR)
1568                 cgrp = kn->priv;
1569         else
1570                 cgrp = kn->parent->priv;
1571 
1572         mutex_unlock(&cgroup_mutex);
1573 
1574         kernfs_unbreak_active_protection(kn);
1575         cgroup_put(cgrp);
1576 }
1577 
1578 /**
1579  * cgroup_kn_lock_live - locking helper for cgroup kernfs methods
1580  * @kn: the kernfs_node being serviced
1581  * @drain_offline: perform offline draining on the cgroup
1582  *
1583  * This helper is to be used by a cgroup kernfs method currently servicing
1584  * @kn.  It breaks the active protection, performs cgroup locking and
1585  * verifies that the associated cgroup is alive.  Returns the cgroup if
1586  * alive; otherwise, %NULL.  A successful return should be undone by a
1587  * matching cgroup_kn_unlock() invocation.  If @drain_offline is %true, the
1588  * cgroup is drained of offlining csses before return.
1589  *
1590  * Any cgroup kernfs method implementation which requires locking the
1591  * associated cgroup should use this helper.  It avoids nesting cgroup
1592  * locking under kernfs active protection and allows all kernfs operations
1593  * including self-removal.
1594  */
1595 struct cgroup *cgroup_kn_lock_live(struct kernfs_node *kn, bool drain_offline)
1596 {
1597         struct cgroup *cgrp;
1598 
1599         if (kernfs_type(kn) == KERNFS_DIR)
1600                 cgrp = kn->priv;
1601         else
1602                 cgrp = kn->parent->priv;
1603 
1604         /*
1605          * We're gonna grab cgroup_mutex which nests outside kernfs
1606          * active_ref.  cgroup liveliness check alone provides enough
1607          * protection against removal.  Ensure @cgrp stays accessible and
1608          * break the active_ref protection.
1609          */
1610         if (!cgroup_tryget(cgrp))
1611                 return NULL;
1612         kernfs_break_active_protection(kn);
1613 
1614         if (drain_offline)
1615                 cgroup_lock_and_drain_offline(cgrp);
1616         else
1617                 mutex_lock(&cgroup_mutex);
1618 
1619         if (!cgroup_is_dead(cgrp))
1620                 return cgrp;
1621 
1622         cgroup_kn_unlock(kn);
1623         return NULL;
1624 }
1625 
1626 static void cgroup_rm_file(struct cgroup *cgrp, const struct cftype *cft)
1627 {
1628         char name[CGROUP_FILE_NAME_MAX];
1629 
1630         lockdep_assert_held(&cgroup_mutex);
1631 
1632         if (cft->file_offset) {
1633                 struct cgroup_subsys_state *css = cgroup_css(cgrp, cft->ss);
1634                 struct cgroup_file *cfile = (void *)css + cft->file_offset;
1635 
1636                 spin_lock_irq(&cgroup_file_kn_lock);
1637                 cfile->kn = NULL;
1638                 spin_unlock_irq(&cgroup_file_kn_lock);
1639 
1640                 del_timer_sync(&cfile->notify_timer);
1641         }
1642 
1643         kernfs_remove_by_name(cgrp->kn, cgroup_file_name(cgrp, cft, name));
1644 }
1645 
1646 /**
1647  * css_clear_dir - remove subsys files in a cgroup directory
1648  * @css: taget css
1649  */
1650 static void css_clear_dir(struct cgroup_subsys_state *css)
1651 {
1652         struct cgroup *cgrp = css->cgroup;
1653         struct cftype *cfts;
1654 
1655         if (!(css->flags & CSS_VISIBLE))
1656                 return;
1657 
1658         css->flags &= ~CSS_VISIBLE;
1659 
1660         if (!css->ss) {
1661                 if (cgroup_on_dfl(cgrp))
1662                         cfts = cgroup_base_files;
1663                 else
1664                         cfts = cgroup1_base_files;
1665 
1666                 cgroup_addrm_files(css, cgrp, cfts, false);
1667         } else {
1668                 list_for_each_entry(cfts, &css->ss->cfts, node)
1669                         cgroup_addrm_files(css, cgrp, cfts, false);
1670         }
1671 }
1672 
1673 /**
1674  * css_populate_dir - create subsys files in a cgroup directory
1675  * @css: target css
1676  *
1677  * On failure, no file is added.
1678  */
1679 static int css_populate_dir(struct cgroup_subsys_state *css)
1680 {
1681         struct cgroup *cgrp = css->cgroup;
1682         struct cftype *cfts, *failed_cfts;
1683         int ret;
1684 
1685         if ((css->flags & CSS_VISIBLE) || !cgrp->kn)
1686                 return 0;
1687 
1688         if (!css->ss) {
1689                 if (cgroup_on_dfl(cgrp))
1690                         cfts = cgroup_base_files;
1691                 else
1692                         cfts = cgroup1_base_files;
1693 
1694                 ret = cgroup_addrm_files(&cgrp->self, cgrp, cfts, true);
1695                 if (ret < 0)
1696                         return ret;
1697         } else {
1698                 list_for_each_entry(cfts, &css->ss->cfts, node) {
1699                         ret = cgroup_addrm_files(css, cgrp, cfts, true);
1700                         if (ret < 0) {
1701                                 failed_cfts = cfts;
1702                                 goto err;
1703                         }
1704                 }
1705         }
1706 
1707         css->flags |= CSS_VISIBLE;
1708 
1709         return 0;
1710 err:
1711         list_for_each_entry(cfts, &css->ss->cfts, node) {
1712                 if (cfts == failed_cfts)
1713                         break;
1714                 cgroup_addrm_files(css, cgrp, cfts, false);
1715         }
1716         return ret;
1717 }
1718 
1719 int rebind_subsystems(struct cgroup_root *dst_root, u16 ss_mask)
1720 {
1721         struct cgroup *dcgrp = &dst_root->cgrp;
1722         struct cgroup_subsys *ss;
1723         int ssid, i, ret;
1724 
1725         lockdep_assert_held(&cgroup_mutex);
1726 
1727         do_each_subsys_mask(ss, ssid, ss_mask) {
1728                 /*
1729                  * If @ss has non-root csses attached to it, can't move.
1730                  * If @ss is an implicit controller, it is exempt from this
1731                  * rule and can be stolen.
1732                  */
1733                 if (css_next_child(NULL, cgroup_css(&ss->root->cgrp, ss)) &&
1734                     !ss->implicit_on_dfl)
1735                         return -EBUSY;
1736 
1737                 /* can't move between two non-dummy roots either */
1738                 if (ss->root != &cgrp_dfl_root && dst_root != &cgrp_dfl_root)
1739                         return -EBUSY;
1740         } while_each_subsys_mask();
1741 
1742         do_each_subsys_mask(ss, ssid, ss_mask) {
1743                 struct cgroup_root *src_root = ss->root;
1744                 struct cgroup *scgrp = &src_root->cgrp;
1745                 struct cgroup_subsys_state *css = cgroup_css(scgrp, ss);
1746                 struct css_set *cset;
1747 
1748                 WARN_ON(!css || cgroup_css(dcgrp, ss));
1749 
1750                 /* disable from the source */
1751                 src_root->subsys_mask &= ~(1 << ssid);
1752                 WARN_ON(cgroup_apply_control(scgrp));
1753                 cgroup_finalize_control(scgrp, 0);
1754 
1755                 /* rebind */
1756                 RCU_INIT_POINTER(scgrp->subsys[ssid], NULL);
1757                 rcu_assign_pointer(dcgrp->subsys[ssid], css);
1758                 ss->root = dst_root;
1759                 css->cgroup = dcgrp;
1760 
1761                 spin_lock_irq(&css_set_lock);
1762                 hash_for_each(css_set_table, i, cset, hlist)
1763                         list_move_tail(&cset->e_cset_node[ss->id],
1764                                        &dcgrp->e_csets[ss->id]);
1765                 spin_unlock_irq(&css_set_lock);
1766 
1767                 /* default hierarchy doesn't enable controllers by default */
1768                 dst_root->subsys_mask |= 1 << ssid;
1769                 if (dst_root == &cgrp_dfl_root) {
1770                         static_branch_enable(cgroup_subsys_on_dfl_key[ssid]);
1771                 } else {
1772                         dcgrp->subtree_control |= 1 << ssid;
1773                         static_branch_disable(cgroup_subsys_on_dfl_key[ssid]);
1774                 }
1775 
1776                 ret = cgroup_apply_control(dcgrp);
1777                 if (ret)
1778                         pr_warn("partial failure to rebind %s controller (err=%d)\n",
1779                                 ss->name, ret);
1780 
1781                 if (ss->bind)
1782                         ss->bind(css);
1783         } while_each_subsys_mask();
1784 
1785         kernfs_activate(dcgrp->kn);
1786         return 0;
1787 }
1788 
1789 int cgroup_show_path(struct seq_file *sf, struct kernfs_node *kf_node,
1790                      struct kernfs_root *kf_root)
1791 {
1792         int len = 0;
1793         char *buf = NULL;
1794         struct cgroup_root *kf_cgroot = cgroup_root_from_kf(kf_root);
1795         struct cgroup *ns_cgroup;
1796 
1797         buf = kmalloc(PATH_MAX, GFP_KERNEL);
1798         if (!buf)
1799                 return -ENOMEM;
1800 
1801         spin_lock_irq(&css_set_lock);
1802         ns_cgroup = current_cgns_cgroup_from_root(kf_cgroot);
1803         len = kernfs_path_from_node(kf_node, ns_cgroup->kn, buf, PATH_MAX);
1804         spin_unlock_irq(&css_set_lock);
1805 
1806         if (len >= PATH_MAX)
1807                 len = -ERANGE;
1808         else if (len > 0) {
1809                 seq_escape(sf, buf, " \t\n\\");
1810                 len = 0;
1811         }
1812         kfree(buf);
1813         return len;
1814 }
1815 
1816 enum cgroup2_param {
1817         Opt_nsdelegate,
1818         Opt_memory_localevents,
1819         nr__cgroup2_params
1820 };
1821 
1822 static const struct fs_parameter_spec cgroup2_param_specs[] = {
1823         fsparam_flag("nsdelegate",              Opt_nsdelegate),
1824         fsparam_flag("memory_localevents",      Opt_memory_localevents),
1825         {}
1826 };
1827 
1828 static const struct fs_parameter_description cgroup2_fs_parameters = {
1829         .name           = "cgroup2",
1830         .specs          = cgroup2_param_specs,
1831 };
1832 
1833 static int cgroup2_parse_param(struct fs_context *fc, struct fs_parameter *param)
1834 {
1835         struct cgroup_fs_context *ctx = cgroup_fc2context(fc);
1836         struct fs_parse_result result;
1837         int opt;
1838 
1839         opt = fs_parse(fc, &cgroup2_fs_parameters, param, &result);
1840         if (opt < 0)
1841                 return opt;
1842 
1843         switch (opt) {
1844         case Opt_nsdelegate:
1845                 ctx->flags |= CGRP_ROOT_NS_DELEGATE;
1846                 return 0;
1847         case Opt_memory_localevents:
1848                 ctx->flags |= CGRP_ROOT_MEMORY_LOCAL_EVENTS;
1849                 return 0;
1850         }
1851         return -EINVAL;
1852 }
1853 
1854 static void apply_cgroup_root_flags(unsigned int root_flags)
1855 {
1856         if (current->nsproxy->cgroup_ns == &init_cgroup_ns) {
1857                 if (root_flags & CGRP_ROOT_NS_DELEGATE)
1858                         cgrp_dfl_root.flags |= CGRP_ROOT_NS_DELEGATE;
1859                 else
1860                         cgrp_dfl_root.flags &= ~CGRP_ROOT_NS_DELEGATE;
1861 
1862                 if (root_flags & CGRP_ROOT_MEMORY_LOCAL_EVENTS)
1863                         cgrp_dfl_root.flags |= CGRP_ROOT_MEMORY_LOCAL_EVENTS;
1864                 else
1865                         cgrp_dfl_root.flags &= ~CGRP_ROOT_MEMORY_LOCAL_EVENTS;
1866         }
1867 }
1868 
1869 static int cgroup_show_options(struct seq_file *seq, struct kernfs_root *kf_root)
1870 {
1871         if (cgrp_dfl_root.flags & CGRP_ROOT_NS_DELEGATE)
1872                 seq_puts(seq, ",nsdelegate");
1873         if (cgrp_dfl_root.flags & CGRP_ROOT_MEMORY_LOCAL_EVENTS)
1874                 seq_puts(seq, ",memory_localevents");
1875         return 0;
1876 }
1877 
1878 static int cgroup_reconfigure(struct fs_context *fc)
1879 {
1880         struct cgroup_fs_context *ctx = cgroup_fc2context(fc);
1881 
1882         apply_cgroup_root_flags(ctx->flags);
1883         return 0;
1884 }
1885 
1886 /*
1887  * To reduce the fork() overhead for systems that are not actually using
1888  * their cgroups capability, we don't maintain the lists running through
1889  * each css_set to its tasks until we see the list actually used - in other
1890  * words after the first mount.
1891  */
1892 static bool use_task_css_set_links __read_mostly;
1893 
1894 void cgroup_enable_task_cg_lists(void)
1895 {
1896         struct task_struct *p, *g;
1897 
1898         /*
1899          * We need tasklist_lock because RCU is not safe against
1900          * while_each_thread(). Besides, a forking task that has passed
1901          * cgroup_post_fork() without seeing use_task_css_set_links = 1
1902          * is not guaranteed to have its child immediately visible in the
1903          * tasklist if we walk through it with RCU.
1904          */
1905         read_lock(&tasklist_lock);
1906         spin_lock_irq(&css_set_lock);
1907 
1908         if (use_task_css_set_links)
1909                 goto out_unlock;
1910 
1911         use_task_css_set_links = true;
1912 
1913         do_each_thread(g, p) {
1914                 WARN_ON_ONCE(!list_empty(&p->cg_list) ||
1915                              task_css_set(p) != &init_css_set);
1916 
1917                 /*
1918                  * We should check if the process is exiting, otherwise
1919                  * it will race with cgroup_exit() in that the list
1920                  * entry won't be deleted though the process has exited.
1921                  * Do it while holding siglock so that we don't end up
1922                  * racing against cgroup_exit().
1923                  *
1924                  * Interrupts were already disabled while acquiring
1925                  * the css_set_lock, so we do not need to disable it
1926                  * again when acquiring the sighand->siglock here.
1927                  */
1928                 spin_lock(&p->sighand->siglock);
1929                 if (!(p->flags & PF_EXITING)) {
1930                         struct css_set *cset = task_css_set(p);
1931 
1932                         if (!css_set_populated(cset))
1933                                 css_set_update_populated(cset, true);
1934                         list_add_tail(&p->cg_list, &cset->tasks);
1935                         get_css_set(cset);
1936                         cset->nr_tasks++;
1937                 }
1938                 spin_unlock(&p->sighand->siglock);
1939         } while_each_thread(g, p);
1940 out_unlock:
1941         spin_unlock_irq(&css_set_lock);
1942         read_unlock(&tasklist_lock);
1943 }
1944 
1945 static void init_cgroup_housekeeping(struct cgroup *cgrp)
1946 {
1947         struct cgroup_subsys *ss;
1948         int ssid;
1949 
1950         INIT_LIST_HEAD(&cgrp->self.sibling);
1951         INIT_LIST_HEAD(&cgrp->self.children);
1952         INIT_LIST_HEAD(&cgrp->cset_links);
1953         INIT_LIST_HEAD(&cgrp->pidlists);
1954         mutex_init(&cgrp->pidlist_mutex);
1955         cgrp->self.cgroup = cgrp;
1956         cgrp->self.flags |= CSS_ONLINE;
1957         cgrp->dom_cgrp = cgrp;
1958         cgrp->max_descendants = INT_MAX;
1959         cgrp->max_depth = INT_MAX;
1960         INIT_LIST_HEAD(&cgrp->rstat_css_list);
1961         prev_cputime_init(&cgrp->prev_cputime);
1962 
1963         for_each_subsys(ss, ssid)
1964                 INIT_LIST_HEAD(&cgrp->e_csets[ssid]);
1965 
1966         init_waitqueue_head(&cgrp->offline_waitq);
1967         INIT_WORK(&cgrp->release_agent_work, cgroup1_release_agent);
1968 }
1969 
1970 void init_cgroup_root(struct cgroup_fs_context *ctx)
1971 {
1972         struct cgroup_root *root = ctx->root;
1973         struct cgroup *cgrp = &root->cgrp;
1974 
1975         INIT_LIST_HEAD(&root->root_list);
1976         atomic_set(&root->nr_cgrps, 1);
1977         cgrp->root = root;
1978         init_cgroup_housekeeping(cgrp);
1979         idr_init(&root->cgroup_idr);
1980 
1981         root->flags = ctx->flags;
1982         if (ctx->release_agent)
1983                 strscpy(root->release_agent_path, ctx->release_agent, PATH_MAX);
1984         if (ctx->name)
1985                 strscpy(root->name, ctx->name, MAX_CGROUP_ROOT_NAMELEN);
1986         if (ctx->cpuset_clone_children)
1987                 set_bit(CGRP_CPUSET_CLONE_CHILDREN, &root->cgrp.flags);
1988 }
1989 
1990 int cgroup_setup_root(struct cgroup_root *root, u16 ss_mask)
1991 {
1992         LIST_HEAD(tmp_links);
1993         struct cgroup *root_cgrp = &root->cgrp;
1994         struct kernfs_syscall_ops *kf_sops;
1995         struct css_set *cset;
1996         int i, ret;
1997 
1998         lockdep_assert_held(&cgroup_mutex);
1999 
2000         ret = cgroup_idr_alloc(&root->cgroup_idr, root_cgrp, 1, 2, GFP_KERNEL);
2001         if (ret < 0)
2002                 goto out;
2003         root_cgrp->id = ret;
2004         root_cgrp->ancestor_ids[0] = ret;
2005 
2006         ret = percpu_ref_init(&root_cgrp->self.refcnt, css_release,
2007                               0, GFP_KERNEL);
2008         if (ret)
2009                 goto out;
2010 
2011         /*
2012          * We're accessing css_set_count without locking css_set_lock here,
2013          * but that's OK - it can only be increased by someone holding
2014          * cgroup_lock, and that's us.  Later rebinding may disable
2015          * controllers on the default hierarchy and thus create new csets,
2016          * which can't be more than the existing ones.  Allocate 2x.
2017          */
2018         ret = allocate_cgrp_cset_links(2 * css_set_count, &tmp_links);
2019         if (ret)
2020                 goto cancel_ref;
2021 
2022         ret = cgroup_init_root_id(root);
2023         if (ret)
2024                 goto cancel_ref;
2025 
2026         kf_sops = root == &cgrp_dfl_root ?
2027                 &cgroup_kf_syscall_ops : &cgroup1_kf_syscall_ops;
2028 
2029         root->kf_root = kernfs_create_root(kf_sops,
2030                                            KERNFS_ROOT_CREATE_DEACTIVATED |
2031                                            KERNFS_ROOT_SUPPORT_EXPORTOP,
2032                                            root_cgrp);
2033         if (IS_ERR(root->kf_root)) {
2034                 ret = PTR_ERR(root->kf_root);
2035                 goto exit_root_id;
2036         }
2037         root_cgrp->kn = root->kf_root->kn;
2038 
2039         ret = css_populate_dir(&root_cgrp->self);
2040         if (ret)
2041                 goto destroy_root;
2042 
2043         ret = rebind_subsystems(root, ss_mask);
2044         if (ret)
2045                 goto destroy_root;
2046 
2047         ret = cgroup_bpf_inherit(root_cgrp);
2048         WARN_ON_ONCE(ret);
2049 
2050         trace_cgroup_setup_root(root);
2051 
2052         /*
2053          * There must be no failure case after here, since rebinding takes
2054          * care of subsystems' refcounts, which are explicitly dropped in
2055          * the failure exit path.
2056          */
2057         list_add(&root->root_list, &cgroup_roots);
2058         cgroup_root_count++;
2059 
2060         /*
2061          * Link the root cgroup in this hierarchy into all the css_set
2062          * objects.
2063          */
2064         spin_lock_irq(&css_set_lock);
2065         hash_for_each(css_set_table, i, cset, hlist) {
2066                 link_css_set(&tmp_links, cset, root_cgrp);
2067                 if (css_set_populated(cset))
2068                         cgroup_update_populated(root_cgrp, true);
2069         }
2070         spin_unlock_irq(&css_set_lock);
2071 
2072         BUG_ON(!list_empty(&root_cgrp->self.children));
2073         BUG_ON(atomic_read(&root->nr_cgrps) != 1);
2074 
2075         kernfs_activate(root_cgrp->kn);
2076         ret = 0;
2077         goto out;
2078 
2079 destroy_root:
2080         kernfs_destroy_root(root->kf_root);
2081         root->kf_root = NULL;
2082 exit_root_id:
2083         cgroup_exit_root_id(root);
2084 cancel_ref:
2085         percpu_ref_exit(&root_cgrp->self.refcnt);
2086 out:
2087         free_cgrp_cset_links(&tmp_links);
2088         return ret;
2089 }
2090 
2091 int cgroup_do_get_tree(struct fs_context *fc)
2092 {
2093         struct cgroup_fs_context *ctx = cgroup_fc2context(fc);
2094         int ret;
2095 
2096         ctx->kfc.root = ctx->root->kf_root;
2097         if (fc->fs_type == &cgroup2_fs_type)
2098                 ctx->kfc.magic = CGROUP2_SUPER_MAGIC;
2099         else
2100                 ctx->kfc.magic = CGROUP_SUPER_MAGIC;
2101         ret = kernfs_get_tree(fc);
2102 
2103         /*
2104          * In non-init cgroup namespace, instead of root cgroup's dentry,
2105          * we return the dentry corresponding to the cgroupns->root_cgrp.
2106          */
2107         if (!ret && ctx->ns != &init_cgroup_ns) {
2108                 struct dentry *nsdentry;
2109                 struct super_block *sb = fc->root->d_sb;
2110                 struct cgroup *cgrp;
2111 
2112                 mutex_lock(&cgroup_mutex);
2113                 spin_lock_irq(&css_set_lock);
2114 
2115                 cgrp = cset_cgroup_from_root(ctx->ns->root_cset, ctx->root);
2116 
2117                 spin_unlock_irq(&css_set_lock);
2118                 mutex_unlock(&cgroup_mutex);
2119 
2120                 nsdentry = kernfs_node_dentry(cgrp->kn, sb);
2121                 dput(fc->root);
2122                 if (IS_ERR(nsdentry)) {
2123                         deactivate_locked_super(sb);
2124                         ret = PTR_ERR(nsdentry);
2125                         nsdentry = NULL;
2126                 }
2127                 fc->root = nsdentry;
2128         }
2129 
2130         if (!ctx->kfc.new_sb_created)
2131                 cgroup_put(&ctx->root->cgrp);
2132 
2133         return ret;
2134 }
2135 
2136 /*
2137  * Destroy a cgroup filesystem context.
2138  */
2139 static void cgroup_fs_context_free(struct fs_context *fc)
2140 {
2141         struct cgroup_fs_context *ctx = cgroup_fc2context(fc);
2142 
2143         kfree(ctx->name);
2144         kfree(ctx->release_agent);
2145         put_cgroup_ns(ctx->ns);
2146         kernfs_free_fs_context(fc);
2147         kfree(ctx);
2148 }
2149 
2150 static int cgroup_get_tree(struct fs_context *fc)
2151 {
2152         struct cgroup_fs_context *ctx = cgroup_fc2context(fc);
2153         int ret;
2154 
2155         cgrp_dfl_visible = true;
2156         cgroup_get_live(&cgrp_dfl_root.cgrp);
2157         ctx->root = &cgrp_dfl_root;
2158 
2159         ret = cgroup_do_get_tree(fc);
2160         if (!ret)
2161                 apply_cgroup_root_flags(ctx->flags);
2162         return ret;
2163 }
2164 
2165 static const struct fs_context_operations cgroup_fs_context_ops = {
2166         .free           = cgroup_fs_context_free,
2167         .parse_param    = cgroup2_parse_param,
2168         .get_tree       = cgroup_get_tree,
2169         .reconfigure    = cgroup_reconfigure,
2170 };
2171 
2172 static const struct fs_context_operations cgroup1_fs_context_ops = {
2173         .free           = cgroup_fs_context_free,
2174         .parse_param    = cgroup1_parse_param,
2175         .get_tree       = cgroup1_get_tree,
2176         .reconfigure    = cgroup1_reconfigure,
2177 };
2178 
2179 /*
2180  * Initialise the cgroup filesystem creation/reconfiguration context.  Notably,
2181  * we select the namespace we're going to use.
2182  */
2183 static int cgroup_init_fs_context(struct fs_context *fc)
2184 {
2185         struct cgroup_fs_context *ctx;
2186 
2187         ctx = kzalloc(sizeof(struct cgroup_fs_context), GFP_KERNEL);
2188         if (!ctx)
2189                 return -ENOMEM;
2190 
2191         /*
2192          * The first time anyone tries to mount a cgroup, enable the list
2193          * linking each css_set to its tasks and fix up all existing tasks.
2194          */
2195         if (!use_task_css_set_links)
2196                 cgroup_enable_task_cg_lists();
2197 
2198         ctx->ns = current->nsproxy->cgroup_ns;
2199         get_cgroup_ns(ctx->ns);
2200         fc->fs_private = &ctx->kfc;
2201         if (fc->fs_type == &cgroup2_fs_type)
2202                 fc->ops = &cgroup_fs_context_ops;
2203         else
2204                 fc->ops = &cgroup1_fs_context_ops;
2205         put_user_ns(fc->user_ns);
2206         fc->user_ns = get_user_ns(ctx->ns->user_ns);
2207         fc->global = true;
2208         return 0;
2209 }
2210 
2211 static void cgroup_kill_sb(struct super_block *sb)
2212 {
2213         struct kernfs_root *kf_root = kernfs_root_from_sb(sb);
2214         struct cgroup_root *root = cgroup_root_from_kf(kf_root);
2215 
2216         /*
2217          * If @root doesn't have any children, start killing it.
2218          * This prevents new mounts by disabling percpu_ref_tryget_live().
2219          * cgroup_mount() may wait for @root's release.
2220          *
2221          * And don't kill the default root.
2222          */
2223         if (list_empty(&root->cgrp.self.children) && root != &cgrp_dfl_root &&
2224             !percpu_ref_is_dying(&root->cgrp.self.refcnt))
2225                 percpu_ref_kill(&root->cgrp.self.refcnt);
2226         cgroup_put(&root->cgrp);
2227         kernfs_kill_sb(sb);
2228 }
2229 
2230 struct file_system_type cgroup_fs_type = {
2231         .name                   = "cgroup",
2232         .init_fs_context        = cgroup_init_fs_context,
2233         .parameters             = &cgroup1_fs_parameters,
2234         .kill_sb                = cgroup_kill_sb,
2235         .fs_flags               = FS_USERNS_MOUNT,
2236 };
2237 
2238 static struct file_system_type cgroup2_fs_type = {
2239         .name                   = "cgroup2",
2240         .init_fs_context        = cgroup_init_fs_context,
2241         .parameters             = &cgroup2_fs_parameters,
2242         .kill_sb                = cgroup_kill_sb,
2243         .fs_flags               = FS_USERNS_MOUNT,
2244 };
2245 
2246 #ifdef CONFIG_CPUSETS
2247 static const struct fs_context_operations cpuset_fs_context_ops = {
2248         .get_tree       = cgroup1_get_tree,
2249         .free           = cgroup_fs_context_free,
2250 };
2251 
2252 /*
2253  * This is ugly, but preserves the userspace API for existing cpuset
2254  * users. If someone tries to mount the "cpuset" filesystem, we
2255  * silently switch it to mount "cgroup" instead
2256  */
2257 static int cpuset_init_fs_context(struct fs_context *fc)
2258 {
2259         char *agent = kstrdup("/sbin/cpuset_release_agent", GFP_USER);
2260         struct cgroup_fs_context *ctx;
2261         int err;
2262 
2263         err = cgroup_init_fs_context(fc);
2264         if (err) {
2265                 kfree(agent);
2266                 return err;
2267         }
2268 
2269         fc->ops = &cpuset_fs_context_ops;
2270 
2271         ctx = cgroup_fc2context(fc);
2272         ctx->subsys_mask = 1 << cpuset_cgrp_id;
2273         ctx->flags |= CGRP_ROOT_NOPREFIX;
2274         ctx->release_agent = agent;
2275 
2276         get_filesystem(&cgroup_fs_type);
2277         put_filesystem(fc->fs_type);
2278         fc->fs_type = &cgroup_fs_type;
2279 
2280         return 0;
2281 }
2282 
2283 static struct file_system_type cpuset_fs_type = {
2284         .name                   = "cpuset",
2285         .init_fs_context        = cpuset_init_fs_context,
2286         .fs_flags               = FS_USERNS_MOUNT,
2287 };
2288 #endif
2289 
2290 int cgroup_path_ns_locked(struct cgroup *cgrp, char *buf, size_t buflen,
2291                           struct cgroup_namespace *ns)
2292 {
2293         struct cgroup *root = cset_cgroup_from_root(ns->root_cset, cgrp->root);
2294 
2295         return kernfs_path_from_node(cgrp->kn, root->kn, buf, buflen);
2296 }
2297 
2298 int cgroup_path_ns(struct cgroup *cgrp, char *buf, size_t buflen,
2299                    struct cgroup_namespace *ns)
2300 {
2301         int ret;
2302 
2303         mutex_lock(&cgroup_mutex);
2304         spin_lock_irq(&css_set_lock);
2305 
2306         ret = cgroup_path_ns_locked(cgrp, buf, buflen, ns);
2307 
2308         spin_unlock_irq(&css_set_lock);
2309         mutex_unlock(&cgroup_mutex);
2310 
2311         return ret;
2312 }
2313 EXPORT_SYMBOL_GPL(cgroup_path_ns);
2314 
2315 /**
2316  * task_cgroup_path - cgroup path of a task in the first cgroup hierarchy
2317  * @task: target task
2318  * @buf: the buffer to write the path into
2319  * @buflen: the length of the buffer
2320  *
2321  * Determine @task's cgroup on the first (the one with the lowest non-zero
2322  * hierarchy_id) cgroup hierarchy and copy its path into @buf.  This
2323  * function grabs cgroup_mutex and shouldn't be used inside locks used by
2324  * cgroup controller callbacks.
2325  *
2326  * Return value is the same as kernfs_path().
2327  */
2328 int task_cgroup_path(struct task_struct *task, char *buf, size_t buflen)
2329 {
2330         struct cgroup_root *root;
2331         struct cgroup *cgrp;
2332         int hierarchy_id = 1;
2333         int ret;
2334 
2335         mutex_lock(&cgroup_mutex);
2336         spin_lock_irq(&css_set_lock);
2337 
2338         root = idr_get_next(&cgroup_hierarchy_idr, &hierarchy_id);
2339 
2340         if (root) {
2341                 cgrp = task_cgroup_from_root(task, root);
2342                 ret = cgroup_path_ns_locked(cgrp, buf, buflen, &init_cgroup_ns);
2343         } else {
2344                 /* if no hierarchy exists, everyone is in "/" */
2345                 ret = strlcpy(buf, "/", buflen);
2346         }
2347 
2348         spin_unlock_irq(&css_set_lock);
2349         mutex_unlock(&cgroup_mutex);
2350         return ret;
2351 }
2352 EXPORT_SYMBOL_GPL(task_cgroup_path);
2353 
2354 /**
2355  * cgroup_migrate_add_task - add a migration target task to a migration context
2356  * @task: target task
2357  * @mgctx: target migration context
2358  *
2359  * Add @task, which is a migration target, to @mgctx->tset.  This function
2360  * becomes noop if @task doesn't need to be migrated.  @task's css_set
2361  * should have been added as a migration source and @task->cg_list will be
2362  * moved from the css_set's tasks list to mg_tasks one.
2363  */
2364 static void cgroup_migrate_add_task(struct task_struct *task,
2365                                     struct cgroup_mgctx *mgctx)
2366 {
2367         struct css_set *cset;
2368 
2369         lockdep_assert_held(&css_set_lock);
2370 
2371         /* @task either already exited or can't exit until the end */
2372         if (task->flags & PF_EXITING)
2373                 return;
2374 
2375         /* leave @task alone if post_fork() hasn't linked it yet */
2376         if (list_empty(&task->cg_list))
2377                 return;
2378 
2379         cset = task_css_set(task);
2380         if (!cset->mg_src_cgrp)
2381                 return;
2382 
2383         mgctx->tset.nr_tasks++;
2384 
2385         list_move_tail(&task->cg_list, &cset->mg_tasks);
2386         if (list_empty(&cset->mg_node))
2387                 list_add_tail(&cset->mg_node,
2388                               &mgctx->tset.src_csets);
2389         if (list_empty(&cset->mg_dst_cset->mg_node))
2390                 list_add_tail(&cset->mg_dst_cset->mg_node,
2391                               &mgctx->tset.dst_csets);
2392 }
2393 
2394 /**
2395  * cgroup_taskset_first - reset taskset and return the first task
2396  * @tset: taskset of interest
2397  * @dst_cssp: output variable for the destination css
2398  *
2399  * @tset iteration is initialized and the first task is returned.
2400  */
2401 struct task_struct *cgroup_taskset_first(struct cgroup_taskset *tset,
2402                                          struct cgroup_subsys_state **dst_cssp)
2403 {
2404         tset->cur_cset = list_first_entry(tset->csets, struct css_set, mg_node);
2405         tset->cur_task = NULL;
2406 
2407         return cgroup_taskset_next(tset, dst_cssp);
2408 }
2409 
2410 /**
2411  * cgroup_taskset_next - iterate to the next task in taskset
2412  * @tset: taskset of interest
2413  * @dst_cssp: output variable for the destination css
2414  *
2415  * Return the next task in @tset.  Iteration must have been initialized
2416  * with cgroup_taskset_first().
2417  */
2418 struct task_struct *cgroup_taskset_next(struct cgroup_taskset *tset,
2419                                         struct cgroup_subsys_state **dst_cssp)
2420 {
2421         struct css_set *cset = tset->cur_cset;
2422         struct task_struct *task = tset->cur_task;
2423 
2424         while (&cset->mg_node != tset->csets) {
2425                 if (!task)
2426                         task = list_first_entry(&cset->mg_tasks,
2427                                                 struct task_struct, cg_list);
2428                 else
2429                         task = list_next_entry(task, cg_list);
2430 
2431                 if (&task->cg_list != &cset->mg_tasks) {
2432                         tset->cur_cset = cset;
2433                         tset->cur_task = task;
2434 
2435                         /*
2436                          * This function may be called both before and
2437                          * after cgroup_taskset_migrate().  The two cases
2438                          * can be distinguished by looking at whether @cset
2439                          * has its ->mg_dst_cset set.
2440                          */
2441                         if (cset->mg_dst_cset)
2442                                 *dst_cssp = cset->mg_dst_cset->subsys[tset->ssid];
2443                         else
2444                                 *dst_cssp = cset->subsys[tset->ssid];
2445 
2446                         return task;
2447                 }
2448 
2449                 cset = list_next_entry(cset, mg_node);
2450                 task = NULL;
2451         }
2452 
2453         return NULL;
2454 }
2455 
2456 /**
2457  * cgroup_taskset_migrate - migrate a taskset
2458  * @mgctx: migration context
2459  *
2460  * Migrate tasks in @mgctx as setup by migration preparation functions.
2461  * This function fails iff one of the ->can_attach callbacks fails and
2462  * guarantees that either all or none of the tasks in @mgctx are migrated.
2463  * @mgctx is consumed regardless of success.
2464  */
2465 static int cgroup_migrate_execute(struct cgroup_mgctx *mgctx)
2466 {
2467         struct cgroup_taskset *tset = &mgctx->tset;
2468         struct cgroup_subsys *ss;
2469         struct task_struct *task, *tmp_task;
2470         struct css_set *cset, *tmp_cset;
2471         int ssid, failed_ssid, ret;
2472 
2473         /* check that we can legitimately attach to the cgroup */
2474         if (tset->nr_tasks) {
2475                 do_each_subsys_mask(ss, ssid, mgctx->ss_mask) {
2476                         if (ss->can_attach) {
2477                                 tset->ssid = ssid;
2478                                 ret = ss->can_attach(tset);
2479                                 if (ret) {
2480                                         failed_ssid = ssid;
2481                                         goto out_cancel_attach;
2482                                 }
2483                         }
2484                 } while_each_subsys_mask();
2485         }
2486 
2487         /*
2488          * Now that we're guaranteed success, proceed to move all tasks to
2489          * the new cgroup.  There are no failure cases after here, so this
2490          * is the commit point.
2491          */
2492         spin_lock_irq(&css_set_lock);
2493         list_for_each_entry(cset, &tset->src_csets, mg_node) {
2494                 list_for_each_entry_safe(task, tmp_task, &cset->mg_tasks, cg_list) {
2495                         struct css_set *from_cset = task_css_set(task);
2496                         struct css_set *to_cset = cset->mg_dst_cset;
2497 
2498                         get_css_set(to_cset);
2499                         to_cset->nr_tasks++;
2500                         css_set_move_task(task, from_cset, to_cset, true);
2501                         from_cset->nr_tasks--;
2502                         /*
2503                          * If the source or destination cgroup is frozen,
2504                          * the task might require to change its state.
2505                          */
2506                         cgroup_freezer_migrate_task(task, from_cset->dfl_cgrp,
2507                                                     to_cset->dfl_cgrp);
2508                         put_css_set_locked(from_cset);
2509 
2510                 }
2511         }
2512         spin_unlock_irq(&css_set_lock);
2513 
2514         /*
2515          * Migration is committed, all target tasks are now on dst_csets.
2516          * Nothing is sensitive to fork() after this point.  Notify
2517          * controllers that migration is complete.
2518          */
2519         tset->csets = &tset->dst_csets;
2520 
2521         if (tset->nr_tasks) {
2522                 do_each_subsys_mask(ss, ssid, mgctx->ss_mask) {
2523                         if (ss->attach) {
2524                                 tset->ssid = ssid;
2525                                 ss->attach(tset);
2526                         }
2527                 } while_each_subsys_mask();
2528         }
2529 
2530         ret = 0;
2531         goto out_release_tset;
2532 
2533 out_cancel_attach:
2534         if (tset->nr_tasks) {
2535                 do_each_subsys_mask(ss, ssid, mgctx->ss_mask) {
2536                         if (ssid == failed_ssid)
2537                                 break;
2538                         if (ss->cancel_attach) {
2539                                 tset->ssid = ssid;
2540                                 ss->cancel_attach(tset);
2541                         }
2542                 } while_each_subsys_mask();
2543         }
2544 out_release_tset:
2545         spin_lock_irq(&css_set_lock);
2546         list_splice_init(&tset->dst_csets, &tset->src_csets);
2547         list_for_each_entry_safe(cset, tmp_cset, &tset->src_csets, mg_node) {
2548                 list_splice_tail_init(&cset->mg_tasks, &cset->tasks);
2549                 list_del_init(&cset->mg_node);
2550         }
2551         spin_unlock_irq(&css_set_lock);
2552 
2553         /*
2554          * Re-initialize the cgroup_taskset structure in case it is reused
2555          * again in another cgroup_migrate_add_task()/cgroup_migrate_execute()
2556          * iteration.
2557          */
2558         tset->nr_tasks = 0;
2559         tset->csets    = &tset->src_csets;
2560         return ret;
2561 }
2562 
2563 /**
2564  * cgroup_migrate_vet_dst - verify whether a cgroup can be migration destination
2565  * @dst_cgrp: destination cgroup to test
2566  *
2567  * On the default hierarchy, except for the mixable, (possible) thread root
2568  * and threaded cgroups, subtree_control must be zero for migration
2569  * destination cgroups with tasks so that child cgroups don't compete
2570  * against tasks.
2571  */
2572 int cgroup_migrate_vet_dst(struct cgroup *dst_cgrp)
2573 {
2574         /* v1 doesn't have any restriction */
2575         if (!cgroup_on_dfl(dst_cgrp))
2576                 return 0;
2577 
2578         /* verify @dst_cgrp can host resources */
2579         if (!cgroup_is_valid_domain(dst_cgrp->dom_cgrp))
2580                 return -EOPNOTSUPP;
2581 
2582         /* mixables don't care */
2583         if (cgroup_is_mixable(dst_cgrp))
2584                 return 0;
2585 
2586         /*
2587          * If @dst_cgrp is already or can become a thread root or is
2588          * threaded, it doesn't matter.
2589          */
2590         if (cgroup_can_be_thread_root(dst_cgrp) || cgroup_is_threaded(dst_cgrp))
2591                 return 0;
2592 
2593         /* apply no-internal-process constraint */
2594         if (dst_cgrp->subtree_control)
2595                 return -EBUSY;
2596 
2597         return 0;
2598 }
2599 
2600 /**
2601  * cgroup_migrate_finish - cleanup after attach
2602  * @mgctx: migration context
2603  *
2604  * Undo cgroup_migrate_add_src() and cgroup_migrate_prepare_dst().  See
2605  * those functions for details.
2606  */
2607 void cgroup_migrate_finish(struct cgroup_mgctx *mgctx)
2608 {
2609         LIST_HEAD(preloaded);
2610         struct css_set *cset, *tmp_cset;
2611 
2612         lockdep_assert_held(&cgroup_mutex);
2613 
2614         spin_lock_irq(&css_set_lock);
2615 
2616         list_splice_tail_init(&mgctx->preloaded_src_csets, &preloaded);
2617         list_splice_tail_init(&mgctx->preloaded_dst_csets, &preloaded);
2618 
2619         list_for_each_entry_safe(cset, tmp_cset, &preloaded, mg_preload_node) {
2620                 cset->mg_src_cgrp = NULL;
2621                 cset->mg_dst_cgrp = NULL;
2622                 cset->mg_dst_cset = NULL;
2623                 list_del_init(&cset->mg_preload_node);
2624                 put_css_set_locked(cset);
2625         }
2626 
2627         spin_unlock_irq(&css_set_lock);
2628 }
2629 
2630 /**
2631  * cgroup_migrate_add_src - add a migration source css_set
2632  * @src_cset: the source css_set to add
2633  * @dst_cgrp: the destination cgroup
2634  * @mgctx: migration context
2635  *
2636  * Tasks belonging to @src_cset are about to be migrated to @dst_cgrp.  Pin
2637  * @src_cset and add it to @mgctx->src_csets, which should later be cleaned
2638  * up by cgroup_migrate_finish().
2639  *
2640  * This function may be called without holding cgroup_threadgroup_rwsem
2641  * even if the target is a process.  Threads may be created and destroyed
2642  * but as long as cgroup_mutex is not dropped, no new css_set can be put
2643  * into play and the preloaded css_sets are guaranteed to cover all
2644  * migrations.
2645  */
2646 void cgroup_migrate_add_src(struct css_set *src_cset,
2647                             struct cgroup *dst_cgrp,
2648                             struct cgroup_mgctx *mgctx)
2649 {
2650         struct cgroup *src_cgrp;
2651 
2652         lockdep_assert_held(&cgroup_mutex);
2653         lockdep_assert_held(&css_set_lock);
2654 
2655         /*
2656          * If ->dead, @src_set is associated with one or more dead cgroups
2657          * and doesn't contain any migratable tasks.  Ignore it early so
2658          * that the rest of migration path doesn't get confused by it.
2659          */
2660         if (src_cset->dead)
2661                 return;
2662 
2663         src_cgrp = cset_cgroup_from_root(src_cset, dst_cgrp->root);
2664 
2665         if (!list_empty(&src_cset->mg_preload_node))
2666                 return;
2667 
2668         WARN_ON(src_cset->mg_src_cgrp);
2669         WARN_ON(src_cset->mg_dst_cgrp);
2670         WARN_ON(!list_empty(&src_cset->mg_tasks));
2671         WARN_ON(!list_empty(&src_cset->mg_node));
2672 
2673         src_cset->mg_src_cgrp = src_cgrp;
2674         src_cset->mg_dst_cgrp = dst_cgrp;
2675         get_css_set(src_cset);
2676         list_add_tail(&src_cset->mg_preload_node, &mgctx->preloaded_src_csets);
2677 }
2678 
2679 /**
2680  * cgroup_migrate_prepare_dst - prepare destination css_sets for migration
2681  * @mgctx: migration context
2682  *
2683  * Tasks are about to be moved and all the source css_sets have been
2684  * preloaded to @mgctx->preloaded_src_csets.  This function looks up and
2685  * pins all destination css_sets, links each to its source, and append them
2686  * to @mgctx->preloaded_dst_csets.
2687  *
2688  * This function must be called after cgroup_migrate_add_src() has been
2689  * called on each migration source css_set.  After migration is performed
2690  * using cgroup_migrate(), cgroup_migrate_finish() must be called on
2691  * @mgctx.
2692  */
2693 int cgroup_migrate_prepare_dst(struct cgroup_mgctx *mgctx)
2694 {
2695         struct css_set *src_cset, *tmp_cset;
2696 
2697         lockdep_assert_held(&cgroup_mutex);
2698 
2699         /* look up the dst cset for each src cset and link it to src */
2700         list_for_each_entry_safe(src_cset, tmp_cset, &mgctx->preloaded_src_csets,
2701                                  mg_preload_node) {
2702                 struct css_set *dst_cset;
2703                 struct cgroup_subsys *ss;
2704                 int ssid;
2705 
2706                 dst_cset = find_css_set(src_cset, src_cset->mg_dst_cgrp);
2707                 if (!dst_cset)
2708                         return -ENOMEM;
2709 
2710                 WARN_ON_ONCE(src_cset->mg_dst_cset || dst_cset->mg_dst_cset);
2711 
2712                 /*
2713                  * If src cset equals dst, it's noop.  Drop the src.
2714                  * cgroup_migrate() will skip the cset too.  Note that we
2715                  * can't handle src == dst as some nodes are used by both.
2716                  */
2717                 if (src_cset == dst_cset) {
2718                         src_cset->mg_src_cgrp = NULL;
2719                         src_cset->mg_dst_cgrp = NULL;
2720                         list_del_init(&src_cset->mg_preload_node);
2721                         put_css_set(src_cset);
2722                         put_css_set(dst_cset);
2723                         continue;
2724                 }
2725 
2726                 src_cset->mg_dst_cset = dst_cset;
2727 
2728                 if (list_empty(&dst_cset->mg_preload_node))
2729                         list_add_tail(&dst_cset->mg_preload_node,
2730                                       &mgctx->preloaded_dst_csets);
2731                 else
2732                         put_css_set(dst_cset);
2733 
2734                 for_each_subsys(ss, ssid)
2735                         if (src_cset->subsys[ssid] != dst_cset->subsys[ssid])
2736                                 mgctx->ss_mask |= 1 << ssid;
2737         }
2738 
2739         return 0;
2740 }
2741 
2742 /**
2743  * cgroup_migrate - migrate a process or task to a cgroup
2744  * @leader: the leader of the process or the task to migrate
2745  * @threadgroup: whether @leader points to the whole process or a single task
2746  * @mgctx: migration context
2747  *
2748  * Migrate a process or task denoted by @leader.  If migrating a process,
2749  * the caller must be holding cgroup_threadgroup_rwsem.  The caller is also
2750  * responsible for invoking cgroup_migrate_add_src() and
2751  * cgroup_migrate_prepare_dst() on the targets before invoking this
2752  * function and following up with cgroup_migrate_finish().
2753  *
2754  * As long as a controller's ->can_attach() doesn't fail, this function is
2755  * guaranteed to succeed.  This means that, excluding ->can_attach()
2756  * failure, when migrating multiple targets, the success or failure can be
2757  * decided for all targets by invoking group_migrate_prepare_dst() before
2758  * actually starting migrating.
2759  */
2760 int cgroup_migrate(struct task_struct *leader, bool threadgroup,
2761                    struct cgroup_mgctx *mgctx)
2762 {
2763         struct task_struct *task;
2764 
2765         /*
2766          * Prevent freeing of tasks while we take a snapshot. Tasks that are
2767          * already PF_EXITING could be freed from underneath us unless we
2768          * take an rcu_read_lock.
2769          */
2770         spin_lock_irq(&css_set_lock);
2771         rcu_read_lock();
2772         task = leader;
2773         do {
2774                 cgroup_migrate_add_task(task, mgctx);
2775                 if (!threadgroup)
2776                         break;
2777         } while_each_thread(leader, task);
2778         rcu_read_unlock();
2779         spin_unlock_irq(&css_set_lock);
2780 
2781         return cgroup_migrate_execute(mgctx);
2782 }
2783 
2784 /**
2785  * cgroup_attach_task - attach a task or a whole threadgroup to a cgroup
2786  * @dst_cgrp: the cgroup to attach to
2787  * @leader: the task or the leader of the threadgroup to be attached
2788  * @threadgroup: attach the whole threadgroup?
2789  *
2790  * Call holding cgroup_mutex and cgroup_threadgroup_rwsem.
2791  */
2792 int cgroup_attach_task(struct cgroup *dst_cgrp, struct task_struct *leader,
2793                        bool threadgroup)
2794 {
2795         DEFINE_CGROUP_MGCTX(mgctx);
2796         struct task_struct *task;
2797         int ret;
2798 
2799         ret = cgroup_migrate_vet_dst(dst_cgrp);
2800         if (ret)
2801                 return ret;
2802 
2803         /* look up all src csets */
2804         spin_lock_irq(&css_set_lock);
2805         rcu_read_lock();
2806         task = leader;
2807         do {
2808                 cgroup_migrate_add_src(task_css_set(task), dst_cgrp, &mgctx);
2809                 if (!threadgroup)
2810                         break;
2811         } while_each_thread(leader, task);
2812         rcu_read_unlock();
2813         spin_unlock_irq(&css_set_lock);
2814 
2815         /* prepare dst csets and commit */
2816         ret = cgroup_migrate_prepare_dst(&mgctx);
2817         if (!ret)
2818                 ret = cgroup_migrate(leader, threadgroup, &mgctx);
2819 
2820         cgroup_migrate_finish(&mgctx);
2821 
2822         if (!ret)
2823                 TRACE_CGROUP_PATH(attach_task, dst_cgrp, leader, threadgroup);
2824 
2825         return ret;
2826 }
2827 
2828 struct task_struct *cgroup_procs_write_start(char *buf, bool threadgroup)
2829         __acquires(&cgroup_threadgroup_rwsem)
2830 {
2831         struct task_struct *tsk;
2832         pid_t pid;
2833 
2834         if (kstrtoint(strstrip(buf), 0, &pid) || pid < 0)
2835                 return ERR_PTR(-EINVAL);
2836 
2837         percpu_down_write(&cgroup_threadgroup_rwsem);
2838 
2839         rcu_read_lock();
2840         if (pid) {
2841                 tsk = find_task_by_vpid(pid);
2842                 if (!tsk) {
2843                         tsk = ERR_PTR(-ESRCH);
2844                         goto out_unlock_threadgroup;
2845                 }
2846         } else {
2847                 tsk = current;
2848         }
2849 
2850         if (threadgroup)
2851                 tsk = tsk->group_leader;
2852 
2853         /*
2854          * kthreads may acquire PF_NO_SETAFFINITY during initialization.
2855          * If userland migrates such a kthread to a non-root cgroup, it can
2856          * become trapped in a cpuset, or RT kthread may be born in a
2857          * cgroup with no rt_runtime allocated.  Just say no.
2858          */
2859         if (tsk->no_cgroup_migration || (tsk->flags & PF_NO_SETAFFINITY)) {
2860                 tsk = ERR_PTR(-EINVAL);
2861                 goto out_unlock_threadgroup;
2862         }
2863 
2864         get_task_struct(tsk);
2865         goto out_unlock_rcu;
2866 
2867 out_unlock_threadgroup:
2868         percpu_up_write(&cgroup_threadgroup_rwsem);
2869 out_unlock_rcu:
2870         rcu_read_unlock();
2871         return tsk;
2872 }
2873 
2874 void cgroup_procs_write_finish(struct task_struct *task)
2875         __releases(&cgroup_threadgroup_rwsem)
2876 {
2877         struct cgroup_subsys *ss;
2878         int ssid;
2879 
2880         /* release reference from cgroup_procs_write_start() */
2881         put_task_struct(task);
2882 
2883         percpu_up_write(&cgroup_threadgroup_rwsem);
2884         for_each_subsys(ss, ssid)
2885                 if (ss->post_attach)
2886                         ss->post_attach();
2887 }
2888 
2889 static void cgroup_print_ss_mask(struct seq_file *seq, u16 ss_mask)
2890 {
2891         struct cgroup_subsys *ss;
2892         bool printed = false;
2893         int ssid;
2894 
2895         do_each_subsys_mask(ss, ssid, ss_mask) {
2896                 if (printed)
2897                         seq_putc(seq, ' ');
2898                 seq_puts(seq, ss->name);
2899                 printed = true;
2900         } while_each_subsys_mask();
2901         if (printed)
2902                 seq_putc(seq, '\n');
2903 }
2904 
2905 /* show controllers which are enabled from the parent */
2906 static int cgroup_controllers_show(struct seq_file *seq, void *v)
2907 {
2908         struct cgroup *cgrp = seq_css(seq)->cgroup;
2909 
2910         cgroup_print_ss_mask(seq, cgroup_control(cgrp));
2911         return 0;
2912 }
2913 
2914 /* show controllers which are enabled for a given cgroup's children */
2915 static int cgroup_subtree_control_show(struct seq_file *seq, void *v)
2916 {
2917         struct cgroup *cgrp = seq_css(seq)->cgroup;
2918 
2919         cgroup_print_ss_mask(seq, cgrp->subtree_control);
2920         return 0;
2921 }
2922 
2923 /**
2924  * cgroup_update_dfl_csses - update css assoc of a subtree in default hierarchy
2925  * @cgrp: root of the subtree to update csses for
2926  *
2927  * @cgrp's control masks have changed and its subtree's css associations
2928  * need to be updated accordingly.  This function looks up all css_sets
2929  * which are attached to the subtree, creates the matching updated css_sets
2930  * and migrates the tasks to the new ones.
2931  */
2932 static int cgroup_update_dfl_csses(struct cgroup *cgrp)
2933 {
2934         DEFINE_CGROUP_MGCTX(mgctx);
2935         struct cgroup_subsys_state *d_css;
2936         struct cgroup *dsct;
2937         struct css_set *src_cset;
2938         int ret;
2939 
2940         lockdep_assert_held(&cgroup_mutex);
2941 
2942         percpu_down_write(&cgroup_threadgroup_rwsem);
2943 
2944         /* look up all csses currently attached to @cgrp's subtree */
2945         spin_lock_irq(&css_set_lock);
2946         cgroup_for_each_live_descendant_pre(dsct, d_css, cgrp) {
2947                 struct cgrp_cset_link *link;
2948 
2949                 list_for_each_entry(link, &dsct->cset_links, cset_link)
2950                         cgroup_migrate_add_src(link->cset, dsct, &mgctx);
2951         }
2952         spin_unlock_irq(&css_set_lock);
2953 
2954         /* NULL dst indicates self on default hierarchy */
2955         ret = cgroup_migrate_prepare_dst(&mgctx);
2956         if (ret)
2957                 goto out_finish;
2958 
2959         spin_lock_irq(&css_set_lock);
2960         list_for_each_entry(src_cset, &mgctx.preloaded_src_csets, mg_preload_node) {
2961                 struct task_struct *task, *ntask;
2962 
2963                 /* all tasks in src_csets need to be migrated */
2964                 list_for_each_entry_safe(task, ntask, &src_cset->tasks, cg_list)
2965                         cgroup_migrate_add_task(task, &mgctx);
2966         }
2967         spin_unlock_irq(&css_set_lock);
2968 
2969         ret = cgroup_migrate_execute(&mgctx);
2970 out_finish:
2971         cgroup_migrate_finish(&mgctx);
2972         percpu_up_write(&cgroup_threadgroup_rwsem);
2973         return ret;
2974 }
2975 
2976 /**
2977  * cgroup_lock_and_drain_offline - lock cgroup_mutex and drain offlined csses
2978  * @cgrp: root of the target subtree
2979  *
2980  * Because css offlining is asynchronous, userland may try to re-enable a
2981  * controller while the previous css is still around.  This function grabs
2982  * cgroup_mutex and drains the previous css instances of @cgrp's subtree.
2983  */
2984 void cgroup_lock_and_drain_offline(struct cgroup *cgrp)
2985         __acquires(&cgroup_mutex)
2986 {
2987         struct cgroup *dsct;
2988         struct cgroup_subsys_state *d_css;
2989         struct cgroup_subsys *ss;
2990         int ssid;
2991 
2992 restart:
2993         mutex_lock(&cgroup_mutex);
2994 
2995         cgroup_for_each_live_descendant_post(dsct, d_css, cgrp) {
2996                 for_each_subsys(ss, ssid) {
2997                         struct cgroup_subsys_state *css = cgroup_css(dsct, ss);
2998                         DEFINE_WAIT(wait);
2999 
3000                         if (!css || !percpu_ref_is_dying(&css->refcnt))
3001                                 continue;
3002 
3003                         cgroup_get_live(dsct);
3004                         prepare_to_wait(&dsct->offline_waitq, &wait,
3005                                         TASK_UNINTERRUPTIBLE);
3006 
3007                         mutex_unlock(&cgroup_mutex);
3008                         schedule();
3009                         finish_wait(&dsct->offline_waitq, &wait);
3010 
3011                         cgroup_put(dsct);
3012                         goto restart;
3013                 }
3014         }
3015 }
3016 
3017 /**
3018  * cgroup_save_control - save control masks and dom_cgrp of a subtree
3019  * @cgrp: root of the target subtree
3020  *
3021  * Save ->subtree_control, ->subtree_ss_mask and ->dom_cgrp to the
3022  * respective old_ prefixed fields for @cgrp's subtree including @cgrp
3023  * itself.
3024  */
3025 static void cgroup_save_control(struct cgroup *cgrp)
3026 {
3027         struct cgroup *dsct;
3028         struct cgroup_subsys_state *d_css;
3029 
3030         cgroup_for_each_live_descendant_pre(dsct, d_css, cgrp) {
3031                 dsct->old_subtree_control = dsct->subtree_control;
3032                 dsct->old_subtree_ss_mask = dsct->subtree_ss_mask;
3033                 dsct->old_dom_cgrp = dsct->dom_cgrp;
3034         }
3035 }
3036 
3037 /**
3038  * cgroup_propagate_control - refresh control masks of a subtree
3039  * @cgrp: root of the target subtree
3040  *
3041  * For @cgrp and its subtree, ensure ->subtree_ss_mask matches
3042  * ->subtree_control and propagate controller availability through the
3043  * subtree so that descendants don't have unavailable controllers enabled.
3044  */
3045 static void cgroup_propagate_control(struct cgroup *cgrp)
3046 {
3047         struct cgroup *dsct;
3048         struct cgroup_subsys_state *d_css;
3049 
3050         cgroup_for_each_live_descendant_pre(dsct, d_css, cgrp) {
3051                 dsct->subtree_control &= cgroup_control(dsct);
3052                 dsct->subtree_ss_mask =
3053                         cgroup_calc_subtree_ss_mask(dsct->subtree_control,
3054                                                     cgroup_ss_mask(dsct));
3055         }
3056 }
3057 
3058 /**
3059  * cgroup_restore_control - restore control masks and dom_cgrp of a subtree
3060  * @cgrp: root of the target subtree
3061  *
3062  * Restore ->subtree_control, ->subtree_ss_mask and ->dom_cgrp from the
3063  * respective old_ prefixed fields for @cgrp's subtree including @cgrp
3064  * itself.
3065  */
3066 static void cgroup_restore_control(struct cgroup *cgrp)
3067 {
3068         struct cgroup *dsct;
3069         struct cgroup_subsys_state *d_css;
3070 
3071         cgroup_for_each_live_descendant_post(dsct, d_css, cgrp) {
3072                 dsct->subtree_control = dsct->old_subtree_control;
3073                 dsct->subtree_ss_mask = dsct->old_subtree_ss_mask;
3074                 dsct->dom_cgrp = dsct->old_dom_cgrp;
3075         }
3076 }
3077 
3078 static bool css_visible(struct cgroup_subsys_state *css)
3079 {
3080         struct cgroup_subsys *ss = css->ss;
3081         struct cgroup *cgrp = css->cgroup;
3082 
3083         if (cgroup_control(cgrp) & (1 << ss->id))
3084                 return true;
3085         if (!(cgroup_ss_mask(cgrp) & (1 << ss->id)))
3086                 return false;
3087         return cgroup_on_dfl(cgrp) && ss->implicit_on_dfl;
3088 }
3089 
3090 /**
3091  * cgroup_apply_control_enable - enable or show csses according to control
3092  * @cgrp: root of the target subtree
3093  *
3094  * Walk @cgrp's subtree and create new csses or make the existing ones
3095  * visible.  A css is created invisible if it's being implicitly enabled
3096  * through dependency.  An invisible css is made visible when the userland
3097  * explicitly enables it.
3098  *
3099  * Returns 0 on success, -errno on failure.  On failure, csses which have
3100  * been processed already aren't cleaned up.  The caller is responsible for
3101  * cleaning up with cgroup_apply_control_disable().
3102  */
3103 static int cgroup_apply_control_enable(struct cgroup *cgrp)
3104 {
3105         struct cgroup *dsct;
3106         struct cgroup_subsys_state *d_css;
3107         struct cgroup_subsys *ss;
3108         int ssid, ret;
3109 
3110         cgroup_for_each_live_descendant_pre(dsct, d_css, cgrp) {
3111                 for_each_subsys(ss, ssid) {
3112                         struct cgroup_subsys_state *css = cgroup_css(dsct, ss);
3113 
3114                         if (!(cgroup_ss_mask(dsct) & (1 << ss->id)))
3115                                 continue;
3116 
3117                         if (!css) {
3118                                 css = css_create(dsct, ss);
3119                                 if (IS_ERR(css))
3120                                         return PTR_ERR(css);
3121                         }
3122 
3123                         WARN_ON_ONCE(percpu_ref_is_dying(&css->refcnt));
3124 
3125                         if (css_visible(css)) {
3126                                 ret = css_populate_dir(css);
3127                                 if (ret)
3128                                         return ret;
3129                         }
3130                 }
3131         }
3132 
3133         return 0;
3134 }
3135 
3136 /**
3137  * cgroup_apply_control_disable - kill or hide csses according to control
3138  * @cgrp: root of the target subtree
3139  *
3140  * Walk @cgrp's subtree and kill and hide csses so that they match
3141  * cgroup_ss_mask() and cgroup_visible_mask().
3142  *
3143  * A css is hidden when the userland requests it to be disabled while other
3144  * subsystems are still depending on it.  The css must not actively control
3145  * resources and be in the vanilla state if it's made visible again later.
3146  * Controllers which may be depended upon should provide ->css_reset() for
3147  * this purpose.
3148  */
3149 static void cgroup_apply_control_disable(struct cgroup *cgrp)
3150 {
3151         struct cgroup *dsct;
3152         struct cgroup_subsys_state *d_css;
3153         struct cgroup_subsys *ss;
3154         int ssid;
3155 
3156         cgroup_for_each_live_descendant_post(dsct, d_css, cgrp) {
3157                 for_each_subsys(ss, ssid) {
3158                         struct cgroup_subsys_state *css = cgroup_css(dsct, ss);
3159 
3160                         if (!css)
3161                                 continue;
3162 
3163                         WARN_ON_ONCE(percpu_ref_is_dying(&css->refcnt));
3164 
3165                         if (css->parent &&
3166                             !(cgroup_ss_mask(dsct) & (1 << ss->id))) {
3167                                 kill_css(css);
3168                         } else if (!css_visible(css)) {
3169                                 css_clear_dir(css);
3170                                 if (ss->css_reset)
3171                                         ss->css_reset(css);
3172                         }
3173                 }
3174         }
3175 }
3176 
3177 /**
3178  * cgroup_apply_control - apply control mask updates to the subtree
3179  * @cgrp: root of the target subtree
3180  *
3181  * subsystems can be enabled and disabled in a subtree using the following
3182  * steps.
3183  *
3184  * 1. Call cgroup_save_control() to stash the current state.
3185  * 2. Update ->subtree_control masks in the subtree as desired.
3186  * 3. Call cgroup_apply_control() to apply the changes.
3187  * 4. Optionally perform other related operations.
3188  * 5. Call cgroup_finalize_control() to finish up.
3189  *
3190  * This function implements step 3 and propagates the mask changes
3191  * throughout @cgrp's subtree, updates csses accordingly and perform
3192  * process migrations.
3193  */
3194 static int cgroup_apply_control(struct cgroup *cgrp)
3195 {
3196         int ret;
3197 
3198         cgroup_propagate_control(cgrp);
3199 
3200         ret = cgroup_apply_control_enable(cgrp);
3201         if (ret)
3202                 return ret;
3203 
3204         /*
3205          * At this point, cgroup_e_css_by_mask() results reflect the new csses
3206          * making the following cgroup_update_dfl_csses() properly update
3207          * css associations of all tasks in the subtree.
3208          */
3209         ret = cgroup_update_dfl_csses(cgrp);
3210         if (ret)
3211                 return ret;
3212 
3213         return 0;
3214 }
3215 
3216 /**
3217  * cgroup_finalize_control - finalize control mask update
3218  * @cgrp: root of the target subtree
3219  * @ret: the result of the update
3220  *
3221  * Finalize control mask update.  See cgroup_apply_control() for more info.
3222  */
3223 static void cgroup_finalize_control(struct cgroup *cgrp, int ret)
3224 {
3225         if (ret) {
3226                 cgroup_restore_control(cgrp);
3227                 cgroup_propagate_control(cgrp);
3228         }
3229 
3230         cgroup_apply_control_disable(cgrp);
3231 }
3232 
3233 static int cgroup_vet_subtree_control_enable(struct cgroup *cgrp, u16 enable)
3234 {
3235         u16 domain_enable = enable & ~cgrp_dfl_threaded_ss_mask;
3236 
3237         /* if nothing is getting enabled, nothing to worry about */
3238         if (!enable)
3239                 return 0;
3240 
3241         /* can @cgrp host any resources? */
3242         if (!cgroup_is_valid_domain(cgrp->dom_cgrp))
3243                 return -EOPNOTSUPP;
3244 
3245         /* mixables don't care */
3246         if (cgroup_is_mixable(cgrp))
3247                 return 0;
3248 
3249         if (domain_enable) {
3250                 /* can't enable domain controllers inside a thread subtree */
3251                 if (cgroup_is_thread_root(cgrp) || cgroup_is_threaded(cgrp))
3252                         return -EOPNOTSUPP;
3253         } else {
3254                 /*
3255                  * Threaded controllers can handle internal competitions
3256                  * and are always allowed inside a (prospective) thread
3257                  * subtree.
3258                  */
3259                 if (cgroup_can_be_thread_root(cgrp) || cgroup_is_threaded(cgrp))
3260                         return 0;
3261         }
3262 
3263         /*
3264          * Controllers can't be enabled for a cgroup with tasks to avoid
3265          * child cgroups competing against tasks.
3266          */
3267         if (cgroup_has_tasks(cgrp))
3268                 return -EBUSY;
3269 
3270         return 0;
3271 }
3272 
3273 /* change the enabled child controllers for a cgroup in the default hierarchy */
3274 static ssize_t cgroup_subtree_control_write(struct kernfs_open_file *of,
3275                                             char *buf, size_t nbytes,
3276                                             loff_t off)
3277 {
3278         u16 enable = 0, disable = 0;
3279         struct cgroup *cgrp, *child;
3280         struct cgroup_subsys *ss;
3281         char *tok;
3282         int ssid, ret;
3283 
3284         /*
3285          * Parse input - space separated list of subsystem names prefixed
3286          * with either + or -.
3287          */
3288         buf = strstrip(buf);
3289         while ((tok = strsep(&buf, " "))) {
3290                 if (tok[0] == '\0')
3291                         continue;
3292                 do_each_subsys_mask(ss, ssid, ~cgrp_dfl_inhibit_ss_mask) {
3293                         if (!cgroup_ssid_enabled(ssid) ||
3294                             strcmp(tok + 1, ss->name))
3295                                 continue;
3296 
3297                         if (*tok == '+') {
3298                                 enable |= 1 << ssid;
3299                                 disable &= ~(1 << ssid);
3300                         } else if (*tok == '-') {
3301                                 disable |= 1 << ssid;
3302                                 enable &= ~(1 << ssid);
3303                         } else {
3304                                 return -EINVAL;
3305                         }
3306                         break;
3307                 } while_each_subsys_mask();
3308                 if (ssid == CGROUP_SUBSYS_COUNT)
3309                         return -EINVAL;
3310         }
3311 
3312         cgrp = cgroup_kn_lock_live(of->kn, true);
3313         if (!cgrp)
3314                 return -ENODEV;
3315 
3316         for_each_subsys(ss, ssid) {
3317                 if (enable & (1 << ssid)) {
3318                         if (cgrp->subtree_control & (1 << ssid)) {
3319                                 enable &= ~(1 << ssid);
3320                                 continue;
3321                         }
3322 
3323                         if (!(cgroup_control(cgrp) & (1 << ssid))) {
3324                                 ret = -ENOENT;
3325                                 goto out_unlock;
3326                         }
3327                 } else if (disable & (1 << ssid)) {
3328                         if (!(cgrp->subtree_control & (1 << ssid))) {
3329                                 disable &= ~(1 << ssid);
3330                                 continue;
3331                         }
3332 
3333                         /* a child has it enabled? */
3334                         cgroup_for_each_live_child(child, cgrp) {
3335                                 if (child->subtree_control & (1 << ssid)) {
3336                                         ret = -EBUSY;
3337                                         goto out_unlock;
3338                                 }
3339                         }
3340                 }
3341         }
3342 
3343         if (!enable && !disable) {
3344                 ret = 0;
3345                 goto out_unlock;
3346         }
3347 
3348         ret = cgroup_vet_subtree_control_enable(cgrp, enable);
3349         if (ret)
3350                 goto out_unlock;
3351 
3352         /* save and update control masks and prepare csses */
3353         cgroup_save_control(cgrp);
3354 
3355         cgrp->subtree_control |= enable;
3356         cgrp->subtree_control &= ~disable;
3357 
3358         ret = cgroup_apply_control(cgrp);
3359         cgroup_finalize_control(cgrp, ret);
3360         if (ret)
3361                 goto out_unlock;
3362 
3363         kernfs_activate(cgrp->kn);
3364 out_unlock:
3365         cgroup_kn_unlock(of->kn);
3366         return ret ?: nbytes;
3367 }
3368 
3369 /**
3370  * cgroup_enable_threaded - make @cgrp threaded
3371  * @cgrp: the target cgroup
3372  *
3373  * Called when "threaded" is written to the cgroup.type interface file and
3374  * tries to make @cgrp threaded and join the parent's resource domain.
3375  * This function is never called on the root cgroup as cgroup.type doesn't
3376  * exist on it.
3377  */
3378 static int cgroup_enable_threaded(struct cgroup *cgrp)
3379 {
3380         struct cgroup *parent = cgroup_parent(cgrp);
3381         struct cgroup *dom_cgrp = parent->dom_cgrp;
3382         struct cgroup *dsct;
3383         struct cgroup_subsys_state *d_css;
3384         int ret;
3385 
3386         lockdep_assert_held(&cgroup_mutex);
3387 
3388         /* noop if already threaded */
3389         if (cgroup_is_threaded(cgrp))
3390                 return 0;
3391 
3392         /*
3393          * If @cgroup is populated or has domain controllers enabled, it
3394          * can't be switched.  While the below cgroup_can_be_thread_root()
3395          * test can catch the same conditions, that's only when @parent is
3396          * not mixable, so let's check it explicitly.
3397          */
3398         if (cgroup_is_populated(cgrp) ||
3399             cgrp->subtree_control & ~cgrp_dfl_threaded_ss_mask)
3400                 return -EOPNOTSUPP;
3401 
3402         /* we're joining the parent's domain, ensure its validity */
3403         if (!cgroup_is_valid_domain(dom_cgrp) ||
3404             !cgroup_can_be_thread_root(dom_cgrp))
3405                 return -EOPNOTSUPP;
3406 
3407         /*
3408          * The following shouldn't cause actual migrations and should
3409          * always succeed.
3410          */
3411         cgroup_save_control(cgrp);
3412 
3413         cgroup_for_each_live_descendant_pre(dsct, d_css, cgrp)
3414                 if (dsct == cgrp || cgroup_is_threaded(dsct))
3415                         dsct->dom_cgrp = dom_cgrp;
3416 
3417         ret = cgroup_apply_control(cgrp);
3418         if (!ret)
3419                 parent->nr_threaded_children++;
3420 
3421         cgroup_finalize_control(cgrp, ret);
3422         return ret;
3423 }
3424 
3425 static int cgroup_type_show(struct seq_file *seq, void *v)
3426 {
3427         struct cgroup *cgrp = seq_css(seq)->cgroup;
3428 
3429         if (cgroup_is_threaded(cgrp))
3430                 seq_puts(seq, "threaded\n");
3431         else if (!cgroup_is_valid_domain(cgrp))
3432                 seq_puts(seq, "domain invalid\n");
3433         else if (cgroup_is_thread_root(cgrp))
3434                 seq_puts(seq, "domain threaded\n");
3435         else
3436                 seq_puts(seq, "domain\n");
3437 
3438         return 0;
3439 }
3440 
3441 static ssize_t cgroup_type_write(struct kernfs_open_file *of, char *buf,
3442                                  size_t nbytes, loff_t off)
3443 {
3444         struct cgroup *cgrp;
3445         int ret;
3446 
3447         /* only switching to threaded mode is supported */
3448         if (strcmp(strstrip(buf), "threaded"))
3449                 return -EINVAL;
3450 
3451         /* drain dying csses before we re-apply (threaded) subtree control */
3452         cgrp = cgroup_kn_lock_live(of->kn, true);
3453         if (!cgrp)
3454                 return -ENOENT;
3455 
3456         /* threaded can only be enabled */
3457         ret = cgroup_enable_threaded(cgrp);
3458 
3459         cgroup_kn_unlock(of->kn);
3460         return ret ?: nbytes;
3461 }
3462 
3463 static int cgroup_max_descendants_show(struct seq_file *seq, void *v)
3464 {
3465         struct cgroup *cgrp = seq_css(seq)->cgroup;
3466         int descendants = READ_ONCE(cgrp->max_descendants);
3467 
3468         if (descendants == INT_MAX)
3469                 seq_puts(seq, "max\n");
3470         else
3471                 seq_printf(seq, "%d\n", descendants);
3472 
3473         return 0;
3474 }
3475 
3476 static ssize_t cgroup_max_descendants_write(struct kernfs_open_file *of,
3477                                            char *buf, size_t nbytes, loff_t off)
3478 {
3479         struct cgroup *cgrp;
3480         int descendants;
3481         ssize_t ret;
3482 
3483         buf = strstrip(buf);
3484         if (!strcmp(buf, "max")) {
3485                 descendants = INT_MAX;
3486         } else {
3487                 ret = kstrtoint(buf, 0, &descendants);
3488                 if (ret)
3489                         return ret;
3490         }
3491 
3492         if (descendants < 0)
3493                 return -ERANGE;
3494 
3495         cgrp = cgroup_kn_lock_live(of->kn, false);
3496         if (!cgrp)
3497                 return -ENOENT;
3498 
3499         cgrp->max_descendants = descendants;
3500 
3501         cgroup_kn_unlock(of->kn);
3502 
3503         return nbytes;
3504 }
3505 
3506 static int cgroup_max_depth_show(struct seq_file *seq, void *v)
3507 {
3508         struct cgroup *cgrp = seq_css(seq)->cgroup;
3509         int depth = READ_ONCE(cgrp->max_depth);
3510 
3511         if (depth == INT_MAX)
3512                 seq_puts(seq, "max\n");
3513         else
3514                 seq_printf(seq, "%d\n", depth);
3515 
3516         return 0;
3517 }
3518 
3519 static ssize_t cgroup_max_depth_write(struct kernfs_open_file *of,
3520                                       char *buf, size_t nbytes, loff_t off)
3521 {
3522         struct cgroup *cgrp;
3523         ssize_t ret;
3524         int depth;
3525 
3526         buf = strstrip(buf);
3527         if (!strcmp(buf, "max")) {
3528                 depth = INT_MAX;
3529         } else {
3530                 ret = kstrtoint(buf, 0, &depth);
3531                 if (ret)
3532                         return ret;
3533         }
3534 
3535         if (depth < 0)
3536                 return -ERANGE;
3537 
3538         cgrp = cgroup_kn_lock_live(of->kn, false);
3539         if (!cgrp)
3540                 return -ENOENT;
3541 
3542         cgrp->max_depth = depth;
3543 
3544         cgroup_kn_unlock(of->kn);
3545 
3546         return nbytes;
3547 }
3548 
3549 static int cgroup_events_show(struct seq_file *seq, void *v)
3550 {
3551         struct cgroup *cgrp = seq_css(seq)->cgroup;
3552 
3553         seq_printf(seq, "populated %d\n", cgroup_is_populated(cgrp));
3554         seq_printf(seq, "frozen %d\n", test_bit(CGRP_FROZEN, &cgrp->flags));
3555 
3556         return 0;
3557 }
3558 
3559 static int cgroup_stat_show(struct seq_file *seq, void *v)
3560 {
3561         struct cgroup *cgroup = seq_css(seq)->cgroup;
3562 
3563         seq_printf(seq, "nr_descendants %d\n",
3564                    cgroup->nr_descendants);
3565         seq_printf(seq, "nr_dying_descendants %d\n",
3566                    cgroup->nr_dying_descendants);
3567 
3568         return 0;
3569 }
3570 
3571 static int __maybe_unused cgroup_extra_stat_show(struct seq_file *seq,
3572                                                  struct cgroup *cgrp, int ssid)
3573 {
3574         struct cgroup_subsys *ss = cgroup_subsys[ssid];
3575         struct cgroup_subsys_state *css;
3576         int ret;
3577 
3578         if (!ss->css_extra_stat_show)
3579                 return 0;
3580 
3581         css = cgroup_tryget_css(cgrp, ss);
3582         if (!css)
3583                 return 0;
3584 
3585         ret = ss->css_extra_stat_show(seq, css);
3586         css_put(css);
3587         return ret;
3588 }
3589 
3590 static int cpu_stat_show(struct seq_file *seq, void *v)
3591 {
3592         struct cgroup __maybe_unused *cgrp = seq_css(seq)->cgroup;
3593         int ret = 0;
3594 
3595         cgroup_base_stat_cputime_show(seq);
3596 #ifdef CONFIG_CGROUP_SCHED
3597         ret = cgroup_extra_stat_show(seq, cgrp, cpu_cgrp_id);
3598 #endif
3599         return ret;
3600 }
3601 
3602 #ifdef CONFIG_PSI
3603 static int cgroup_io_pressure_show(struct seq_file *seq, void *v)
3604 {
3605         struct cgroup *cgroup = seq_css(seq)->cgroup;
3606         struct psi_group *psi = cgroup->id == 1 ? &psi_system : &cgroup->psi;
3607 
3608         return psi_show(seq, psi, PSI_IO);
3609 }
3610 static int cgroup_memory_pressure_show(struct seq_file *seq, void *v)
3611 {
3612         struct cgroup *cgroup = seq_css(seq)->cgroup;
3613         struct psi_group *psi = cgroup->id == 1 ? &psi_system : &cgroup->psi;
3614 
3615         return psi_show(seq, psi, PSI_MEM);
3616 }
3617 static int cgroup_cpu_pressure_show(struct seq_file *seq, void *v)
3618 {
3619         struct cgroup *cgroup = seq_css(seq)->cgroup;
3620         struct psi_group *psi = cgroup->id == 1 ? &psi_system : &cgroup->psi;
3621 
3622         return psi_show(seq, psi, PSI_CPU);
3623 }
3624 
3625 static ssize_t cgroup_pressure_write(struct kernfs_open_file *of, char *buf,
3626                                           size_t nbytes, enum psi_res res)
3627 {
3628         struct psi_trigger *new;
3629         struct cgroup *cgrp;
3630 
3631         cgrp = cgroup_kn_lock_live(of->kn, false);
3632         if (!cgrp)
3633                 return -ENODEV;
3634 
3635         cgroup_get(cgrp);
3636         cgroup_kn_unlock(of->kn);
3637 
3638         new = psi_trigger_create(&cgrp->psi, buf, nbytes, res);
3639         if (IS_ERR(new)) {
3640                 cgroup_put(cgrp);
3641                 return PTR_ERR(new);
3642         }
3643 
3644         psi_trigger_replace(&of->priv, new);
3645 
3646         cgroup_put(cgrp);
3647 
3648         return nbytes;
3649 }
3650 
3651 static ssize_t cgroup_io_pressure_write(struct kernfs_open_file *of,
3652                                           char *buf, size_t nbytes,
3653                                           loff_t off)
3654 {
3655         return cgroup_pressure_write(of, buf, nbytes, PSI_IO);
3656 }
3657 
3658 static ssize_t cgroup_memory_pressure_write(struct kernfs_open_file *of,
3659                                           char *buf, size_t nbytes,
3660                                           loff_t off)
3661 {
3662         return cgroup_pressure_write(of, buf, nbytes, PSI_MEM);
3663 }
3664 
3665 static ssize_t cgroup_cpu_pressure_write(struct kernfs_open_file *of,
3666                                           char *buf, size_t nbytes,
3667                                           loff_t off)
3668 {
3669         return cgroup_pressure_write(of, buf, nbytes, PSI_CPU);
3670 }
3671 
3672 static __poll_t cgroup_pressure_poll(struct kernfs_open_file *of,
3673                                           poll_table *pt)
3674 {
3675         return psi_trigger_poll(&of->priv, of->file, pt);
3676 }
3677 
3678 static void cgroup_pressure_release(struct kernfs_open_file *of)
3679 {
3680         psi_trigger_replace(&of->priv, NULL);
3681 }
3682 #endif /* CONFIG_PSI */
3683 
3684 static int cgroup_freeze_show(struct seq_file *seq, void *v)
3685 {
3686         struct cgroup *cgrp = seq_css(seq)->cgroup;
3687 
3688         seq_printf(seq, "%d\n", cgrp->freezer.freeze);
3689 
3690         return 0;
3691 }
3692 
3693 static ssize_t cgroup_freeze_write(struct kernfs_open_file *of,
3694                                    char *buf, size_t nbytes, loff_t off)
3695 {
3696         struct cgroup *cgrp;
3697         ssize_t ret;
3698         int freeze;
3699 
3700         ret = kstrtoint(strstrip(buf), 0, &freeze);
3701         if (ret)
3702                 return ret;
3703 
3704         if (freeze < 0 || freeze > 1)
3705                 return -ERANGE;
3706 
3707         cgrp = cgroup_kn_lock_live(of->kn, false);
3708         if (!cgrp)
3709                 return -ENOENT;
3710 
3711         cgroup_freeze(cgrp, freeze);
3712 
3713         cgroup_kn_unlock(of->kn);
3714 
3715         return nbytes;
3716 }
3717 
3718 static int cgroup_file_open(struct kernfs_open_file *of)
3719 {
3720         struct cftype *cft = of->kn->priv;
3721 
3722         if (cft->open)
3723                 return cft->open(of);
3724         return 0;
3725 }
3726 
3727 static void cgroup_file_release(struct kernfs_open_file *of)
3728 {
3729         struct cftype *cft = of->kn->priv;
3730 
3731         if (cft->release)
3732                 cft->release(of);
3733 }
3734 
3735 static ssize_t cgroup_file_write(struct kernfs_open_file *of, char *buf,
3736                                  size_t nbytes, loff_t off)
3737 {
3738         struct cgroup_namespace *ns = current->nsproxy->cgroup_ns;
3739         struct cgroup *cgrp = of->kn->parent->priv;
3740         struct cftype *cft = of->kn->priv;
3741         struct cgroup_subsys_state *css;
3742         int ret;
3743 
3744         /*
3745          * If namespaces are delegation boundaries, disallow writes to
3746          * files in an non-init namespace root from inside the namespace
3747          * except for the files explicitly marked delegatable -
3748          * cgroup.procs and cgroup.subtree_control.
3749          */
3750         if ((cgrp->root->flags & CGRP_ROOT_NS_DELEGATE) &&
3751             !(cft->flags & CFTYPE_NS_DELEGATABLE) &&
3752             ns != &init_cgroup_ns && ns->root_cset->dfl_cgrp == cgrp)
3753                 return -EPERM;
3754 
3755         if (cft->write)
3756                 return cft->write(of, buf, nbytes, off);
3757 
3758         /*
3759          * kernfs guarantees that a file isn't deleted with operations in
3760          * flight, which means that the matching css is and stays alive and
3761          * doesn't need to be pinned.  The RCU locking is not necessary
3762          * either.  It's just for the convenience of using cgroup_css().
3763          */
3764         rcu_read_lock();
3765         css = cgroup_css(cgrp, cft->ss);
3766         rcu_read_unlock();
3767 
3768         if (cft->write_u64) {
3769                 unsigned long long v;
3770                 ret = kstrtoull(buf, 0, &v);
3771                 if (!ret)
3772                         ret = cft->write_u64(css, cft, v);
3773         } else if (cft->write_s64) {
3774                 long long v;
3775                 ret = kstrtoll(buf, 0, &v);
3776                 if (!ret)
3777                         ret = cft->write_s64(css, cft, v);
3778         } else {
3779                 ret = -EINVAL;
3780         }
3781 
3782         return ret ?: nbytes;
3783 }
3784 
3785 static __poll_t cgroup_file_poll(struct kernfs_open_file *of, poll_table *pt)
3786 {
3787         struct cftype *cft = of->kn->priv;
3788 
3789         if (cft->poll)
3790                 return cft->poll(of, pt);
3791 
3792         return kernfs_generic_poll(of, pt);
3793 }
3794 
3795 static void *cgroup_seqfile_start(struct seq_file *seq, loff_t *ppos)
3796 {
3797         return seq_cft(seq)->seq_start(seq, ppos);
3798 }
3799 
3800 static void *cgroup_seqfile_next(struct seq_file *seq, void *v, loff_t *ppos)
3801 {
3802         return seq_cft(seq)->seq_next(seq, v, ppos);
3803 }
3804 
3805 static void cgroup_seqfile_stop(struct seq_file *seq, void *v)
3806 {
3807         if (seq_cft(seq)->seq_stop)
3808                 seq_cft(seq)->seq_stop(seq, v);
3809 }
3810 
3811 static int cgroup_seqfile_show(struct seq_file *m, void *arg)
3812 {
3813         struct cftype *cft = seq_cft(m);
3814         struct cgroup_subsys_state *css = seq_css(m);
3815 
3816         if (cft->seq_show)
3817                 return cft->seq_show(m, arg);
3818 
3819         if (cft->read_u64)
3820                 seq_printf(m, "%llu\n", cft->read_u64(css, cft));
3821         else if (cft->read_s64)
3822                 seq_printf(m, "%lld\n", cft->read_s64(css, cft));
3823         else
3824                 return -EINVAL;
3825         return 0;
3826 }
3827 
3828 static struct kernfs_ops cgroup_kf_single_ops = {
3829         .atomic_write_len       = PAGE_SIZE,
3830         .open                   = cgroup_file_open,
3831         .release                = cgroup_file_release,
3832         .write                  = cgroup_file_write,
3833         .poll                   = cgroup_file_poll,
3834         .seq_show               = cgroup_seqfile_show,
3835 };
3836 
3837 static struct kernfs_ops cgroup_kf_ops = {
3838         .atomic_write_len       = PAGE_SIZE,
3839         .open                   = cgroup_file_open,
3840         .release                = cgroup_file_release,
3841         .write                  = cgroup_file_write,
3842         .poll                   = cgroup_file_poll,
3843         .seq_start              = cgroup_seqfile_start,
3844         .seq_next               = cgroup_seqfile_next,
3845         .seq_stop               = cgroup_seqfile_stop,
3846         .seq_show               = cgroup_seqfile_show,
3847 };
3848 
3849 /* set uid and gid of cgroup dirs and files to that of the creator */
3850 static int cgroup_kn_set_ugid(struct kernfs_node *kn)
3851 {
3852         struct iattr iattr = { .ia_valid = ATTR_UID | ATTR_GID,
3853                                .ia_uid = current_fsuid(),
3854                                .ia_gid = current_fsgid(), };
3855 
3856         if (uid_eq(iattr.ia_uid, GLOBAL_ROOT_UID) &&
3857             gid_eq(iattr.ia_gid, GLOBAL_ROOT_GID))
3858                 return 0;
3859 
3860         return kernfs_setattr(kn, &iattr);
3861 }
3862 
3863 static void cgroup_file_notify_timer(struct timer_list *timer)
3864 {
3865         cgroup_file_notify(container_of(timer, struct cgroup_file,
3866                                         notify_timer));
3867 }
3868 
3869 static int cgroup_add_file(struct cgroup_subsys_state *css, struct cgroup *cgrp,
3870                            struct cftype *cft)
3871 {
3872         char name[CGROUP_FILE_NAME_MAX];
3873         struct kernfs_node *kn;
3874         struct lock_class_key *key = NULL;
3875         int ret;
3876 
3877 #ifdef CONFIG_DEBUG_LOCK_ALLOC
3878         key = &cft->lockdep_key;
3879 #endif
3880         kn = __kernfs_create_file(cgrp->kn, cgroup_file_name(cgrp, cft, name),
3881                                   cgroup_file_mode(cft),
3882                                   GLOBAL_ROOT_UID, GLOBAL_ROOT_GID,
3883                                   0, cft->kf_ops, cft,
3884                                   NULL, key);
3885         if (IS_ERR(kn))
3886                 return PTR_ERR(kn);
3887 
3888         ret = cgroup_kn_set_ugid(kn);
3889         if (ret) {
3890                 kernfs_remove(kn);
3891                 return ret;
3892         }
3893 
3894         if (cft->file_offset) {
3895                 struct cgroup_file *cfile = (void *)css + cft->file_offset;
3896 
3897                 timer_setup(&cfile->notify_timer, cgroup_file_notify_timer, 0);
3898 
3899                 spin_lock_irq(&cgroup_file_kn_lock);
3900                 cfile->kn = kn;
3901                 spin_unlock_irq(&cgroup_file_kn_lock);
3902         }
3903 
3904         return 0;
3905 }
3906 
3907 /**
3908  * cgroup_addrm_files - add or remove files to a cgroup directory
3909  * @css: the target css
3910  * @cgrp: the target cgroup (usually css->cgroup)
3911  * @cfts: array of cftypes to be added
3912  * @is_add: whether to add or remove
3913  *
3914  * Depending on @is_add, add or remove files defined by @cfts on @cgrp.
3915  * For removals, this function never fails.
3916  */
3917 static int cgroup_addrm_files(struct cgroup_subsys_state *css,
3918                               struct cgroup *cgrp, struct cftype cfts[],
3919                               bool is_add)
3920 {
3921         struct cftype *cft, *cft_end = NULL;
3922         int ret = 0;
3923 
3924         lockdep_assert_held(&cgroup_mutex);
3925 
3926 restart:
3927         for (cft = cfts; cft != cft_end && cft->name[0] != '\0'; cft++) {
3928                 /* does cft->flags tell us to skip this file on @cgrp? */
3929                 if ((cft->flags & __CFTYPE_ONLY_ON_DFL) && !cgroup_on_dfl(cgrp))
3930                         continue;
3931                 if ((cft->flags & __CFTYPE_NOT_ON_DFL) && cgroup_on_dfl(cgrp))
3932                         continue;
3933                 if ((cft->flags & CFTYPE_NOT_ON_ROOT) && !cgroup_parent(cgrp))
3934                         continue;
3935                 if ((cft->flags & CFTYPE_ONLY_ON_ROOT) && cgroup_parent(cgrp))
3936                         continue;
3937                 if ((cft->flags & CFTYPE_DEBUG) && !cgroup_debug)
3938                         continue;
3939                 if (is_add) {
3940                         ret = cgroup_add_file(css, cgrp, cft);
3941                         if (ret) {
3942                                 pr_warn("%s: failed to add %s, err=%d\n",
3943                                         __func__, cft->name, ret);
3944                                 cft_end = cft;
3945                                 is_add = false;
3946                                 goto restart;
3947                         }
3948                 } else {
3949                         cgroup_rm_file(cgrp, cft);
3950                 }
3951         }
3952         return ret;
3953 }
3954 
3955 static int cgroup_apply_cftypes(struct cftype *cfts, bool is_add)
3956 {
3957         struct cgroup_subsys *ss = cfts[0].ss;
3958         struct cgroup *root = &ss->root->cgrp;
3959         struct cgroup_subsys_state *css;
3960         int ret = 0;
3961 
3962         lockdep_assert_held(&cgroup_mutex);
3963 
3964         /* add/rm files for all cgroups created before */
3965         css_for_each_descendant_pre(css, cgroup_css(root, ss)) {
3966                 struct cgroup *cgrp = css->cgroup;
3967 
3968                 if (!(css->flags & CSS_VISIBLE))
3969                         continue;
3970 
3971                 ret = cgroup_addrm_files(css, cgrp, cfts, is_add);
3972                 if (ret)
3973                         break;
3974         }
3975 
3976         if (is_add && !ret)
3977                 kernfs_activate(root->kn);
3978         return ret;
3979 }
3980 
3981 static void cgroup_exit_cftypes(struct cftype *cfts)
3982 {
3983         struct cftype *cft;
3984 
3985         for (cft = cfts; cft->name[0] != '\0'; cft++) {
3986                 /* free copy for custom atomic_write_len, see init_cftypes() */
3987                 if (cft->max_write_len && cft->max_write_len != PAGE_SIZE)
3988                         kfree(cft->kf_ops);
3989                 cft->kf_ops = NULL;
3990                 cft->ss = NULL;
3991 
3992                 /* revert flags set by cgroup core while adding @cfts */
3993                 cft->flags &= ~(__CFTYPE_ONLY_ON_DFL | __CFTYPE_NOT_ON_DFL);
3994         }
3995 }
3996 
3997 static int cgroup_init_cftypes(struct cgroup_subsys *ss, struct cftype *cfts)
3998 {
3999         struct cftype *cft;
4000 
4001         for (cft = cfts; cft->name[0] != '\0'; cft++) {
4002                 struct kernfs_ops *kf_ops;
4003 
4004                 WARN_ON(cft->ss || cft->kf_ops);
4005 
4006                 if (cft->seq_start)
4007                         kf_ops = &cgroup_kf_ops;
4008                 else
4009                         kf_ops = &cgroup_kf_single_ops;
4010 
4011                 /*
4012                  * Ugh... if @cft wants a custom max_write_len, we need to
4013                  * make a copy of kf_ops to set its atomic_write_len.
4014                  */
4015                 if (cft->max_write_len && cft->max_write_len != PAGE_SIZE) {
4016                         kf_ops = kmemdup(kf_ops, sizeof(*kf_ops), GFP_KERNEL);
4017                         if (!kf_ops) {
4018                                 cgroup_exit_cftypes(cfts);
4019                                 return -ENOMEM;
4020                         }
4021                         kf_ops->atomic_write_len = cft->max_write_len;
4022                 }
4023 
4024                 cft->kf_ops = kf_ops;
4025                 cft->ss = ss;
4026         }
4027 
4028         return 0;
4029 }
4030 
4031 static int cgroup_rm_cftypes_locked(struct cftype *cfts)
4032 {
4033         lockdep_assert_held(&cgroup_mutex);
4034 
4035         if (!cfts || !cfts[0].ss)
4036                 return -ENOENT;
4037 
4038         list_del(&cfts->node);
4039         cgroup_apply_cftypes(cfts, false);
4040         cgroup_exit_cftypes(cfts);
4041         return 0;
4042 }
4043 
4044 /**
4045  * cgroup_rm_cftypes - remove an array of cftypes from a subsystem
4046  * @cfts: zero-length name terminated array of cftypes
4047  *
4048  * Unregister @cfts.  Files described by @cfts are removed from all
4049  * existing cgroups and all future cgroups won't have them either.  This
4050  * function can be called anytime whether @cfts' subsys is attached or not.
4051  *
4052  * Returns 0 on successful unregistration, -ENOENT if @cfts is not
4053  * registered.
4054  */
4055 int cgroup_rm_cftypes(struct cftype *cfts)
4056 {
4057         int ret;
4058 
4059         mutex_lock(&cgroup_mutex);
4060         ret = cgroup_rm_cftypes_locked(cfts);
4061         mutex_unlock(&cgroup_mutex);
4062         return ret;
4063 }
4064 
4065 /**
4066  * cgroup_add_cftypes - add an array of cftypes to a subsystem
4067  * @ss: target cgroup subsystem
4068  * @cfts: zero-length name terminated array of cftypes
4069  *
4070  * Register @cfts to @ss.  Files described by @cfts are created for all
4071  * existing cgroups to which @ss is attached and all future cgroups will
4072  * have them too.  This function can be called anytime whether @ss is
4073  * attached or not.
4074  *
4075  * Returns 0 on successful registration, -errno on failure.  Note that this
4076  * function currently returns 0 as long as @cfts registration is successful
4077  * even if some file creation attempts on existing cgroups fail.
4078  */
4079 static int cgroup_add_cftypes(struct cgroup_subsys *ss, struct cftype *cfts)
4080 {
4081         int ret;
4082 
4083         if (!cgroup_ssid_enabled(ss->id))
4084                 return 0;
4085 
4086         if (!cfts || cfts[0].name[0] == '\0')
4087                 return 0;
4088 
4089         ret = cgroup_init_cftypes(ss, cfts);
4090         if (ret)
4091                 return ret;
4092 
4093         mutex_lock(&cgroup_mutex);
4094 
4095         list_add_tail(&cfts->node, &ss->cfts);
4096         ret = cgroup_apply_cftypes(cfts, true);
4097         if (ret)
4098                 cgroup_rm_cftypes_locked(cfts);
4099 
4100         mutex_unlock(&cgroup_mutex);
4101         return ret;
4102 }
4103 
4104 /**
4105  * cgroup_add_dfl_cftypes - add an array of cftypes for default hierarchy
4106  * @ss: target cgroup subsystem
4107  * @cfts: zero-length name terminated array of cftypes
4108  *
4109  * Similar to cgroup_add_cftypes() but the added files are only used for
4110  * the default hierarchy.
4111  */
4112 int cgroup_add_dfl_cftypes(struct cgroup_subsys *ss, struct cftype *cfts)
4113 {
4114         struct cftype *cft;
4115 
4116         for (cft = cfts; cft && cft->name[0] != '\0'; cft++)
4117                 cft->flags |= __CFTYPE_ONLY_ON_DFL;
4118         return cgroup_add_cftypes(ss, cfts);
4119 }
4120 
4121 /**
4122  * cgroup_add_legacy_cftypes - add an array of cftypes for legacy hierarchies
4123  * @ss: target cgroup subsystem
4124  * @cfts: zero-length name terminated array of cftypes
4125  *
4126  * Similar to cgroup_add_cftypes() but the added files are only used for
4127  * the legacy hierarchies.
4128  */
4129 int cgroup_add_legacy_cftypes(struct cgroup_subsys *ss, struct cftype *cfts)
4130 {
4131         struct cftype *cft;
4132 
4133         for (cft = cfts; cft && cft->name[0] != '\0'; cft++)
4134                 cft->flags |= __CFTYPE_NOT_ON_DFL;
4135         return cgroup_add_cftypes(ss, cfts);
4136 }
4137 
4138 /**
4139  * cgroup_file_notify - generate a file modified event for a cgroup_file
4140  * @cfile: target cgroup_file
4141  *
4142  * @cfile must have been obtained by setting cftype->file_offset.
4143  */
4144 void cgroup_file_notify(struct cgroup_file *cfile)
4145 {
4146         unsigned long flags;
4147 
4148         spin_lock_irqsave(&cgroup_file_kn_lock, flags);
4149         if (cfile->kn) {
4150                 unsigned long last = cfile->notified_at;
4151                 unsigned long next = last + CGROUP_FILE_NOTIFY_MIN_INTV;
4152 
4153                 if (time_in_range(jiffies, last, next)) {
4154                         timer_reduce(&cfile->notify_timer, next);
4155                 } else {
4156                         kernfs_notify(cfile->kn);
4157                         cfile->notified_at = jiffies;
4158                 }
4159         }
4160         spin_unlock_irqrestore(&cgroup_file_kn_lock, flags);
4161 }
4162 
4163 /**
4164  * css_next_child - find the next child of a given css
4165  * @pos: the current position (%NULL to initiate traversal)
4166  * @parent: css whose children to walk
4167  *
4168  * This function returns the next child of @parent and should be called
4169  * under either cgroup_mutex or RCU read lock.  The only requirement is
4170  * that @parent and @pos are accessible.  The next sibling is guaranteed to
4171  * be returned regardless of their states.
4172  *
4173  * If a subsystem synchronizes ->css_online() and the start of iteration, a
4174  * css which finished ->css_online() is guaranteed to be visible in the
4175  * future iterations and will stay visible until the last reference is put.
4176  * A css which hasn't finished ->css_online() or already finished
4177  * ->css_offline() may show up during traversal.  It's each subsystem's
4178  * responsibility to synchronize against on/offlining.
4179  */
4180 struct cgroup_subsys_state *css_next_child(struct cgroup_subsys_state *pos,
4181                                            struct cgroup_subsys_state *parent)
4182 {
4183         struct cgroup_subsys_state *next;
4184 
4185         cgroup_assert_mutex_or_rcu_locked();
4186 
4187         /*
4188          * @pos could already have been unlinked from the sibling list.
4189          * Once a cgroup is removed, its ->sibling.next is no longer
4190          * updated when its next sibling changes.  CSS_RELEASED is set when
4191          * @pos is taken off list, at which time its next pointer is valid,
4192          * and, as releases are serialized, the one pointed to by the next
4193          * pointer is guaranteed to not have started release yet.  This
4194          * implies that if we observe !CSS_RELEASED on @pos in this RCU
4195          * critical section, the one pointed to by its next pointer is
4196          * guaranteed to not have finished its RCU grace period even if we
4197          * have dropped rcu_read_lock() inbetween iterations.
4198          *
4199          * If @pos has CSS_RELEASED set, its next pointer can't be
4200          * dereferenced; however, as each css is given a monotonically
4201          * increasing unique serial number and always appended to the
4202          * sibling list, the next one can be found by walking the parent's
4203          * children until the first css with higher serial number than
4204          * @pos's.  While this path can be slower, it happens iff iteration
4205          * races against release and the race window is very small.
4206          */
4207         if (!pos) {
4208                 next = list_entry_rcu(parent->children.next, struct cgroup_subsys_state, sibling);
4209         } else if (likely(!(pos->flags & CSS_RELEASED))) {
4210                 next = list_entry_rcu(pos->sibling.next, struct cgroup_subsys_state, sibling);
4211         } else {
4212                 list_for_each_entry_rcu(next, &parent->children, sibling)
4213                         if (next->serial_nr > pos->serial_nr)
4214                                 break;
4215         }
4216 
4217         /*
4218          * @next, if not pointing to the head, can be dereferenced and is
4219          * the next sibling.
4220          */
4221         if (&next->sibling != &parent->children)
4222                 return next;
4223         return NULL;
4224 }
4225 
4226 /**
4227  * css_next_descendant_pre - find the next descendant for pre-order walk
4228  * @pos: the current position (%NULL to initiate traversal)
4229  * @root: css whose descendants to walk
4230  *
4231  * To be used by css_for_each_descendant_pre().  Find the next descendant
4232  * to visit for pre-order traversal of @root's descendants.  @root is
4233  * included in the iteration and the first node to be visited.
4234  *
4235  * While this function requires cgroup_mutex or RCU read locking, it
4236  * doesn't require the whole traversal to be contained in a single critical
4237  * section.  This function will return the correct next descendant as long
4238  * as both @pos and @root are accessible and @pos is a descendant of @root.
4239  *
4240  * If a subsystem synchronizes ->css_online() and the start of iteration, a
4241  * css which finished ->css_online() is guaranteed to be visible in the
4242  * future iterations and will stay visible until the last reference is put.
4243  * A css which hasn't finished ->css_online() or already finished
4244  * ->css_offline() may show up during traversal.  It's each subsystem's
4245  * responsibility to synchronize against on/offlining.
4246  */
4247 struct cgroup_subsys_state *
4248 css_next_descendant_pre(struct cgroup_subsys_state *pos,
4249                         struct cgroup_subsys_state *root)
4250 {
4251         struct cgroup_subsys_state *next;
4252 
4253         cgroup_assert_mutex_or_rcu_locked();
4254 
4255         /* if first iteration, visit @root */
4256         if (!pos)
4257                 return root;
4258 
4259         /* visit the first child if exists */
4260         next = css_next_child(NULL, pos);
4261         if (next)
4262                 return next;
4263 
4264         /* no child, visit my or the closest ancestor's next sibling */
4265         while (pos != root) {
4266                 next = css_next_child(pos, pos->parent);
4267                 if (next)
4268                         return next;
4269                 pos = pos->parent;
4270         }
4271 
4272         return NULL;
4273 }
4274 EXPORT_SYMBOL_GPL(css_next_descendant_pre);
4275 
4276 /**
4277  * css_rightmost_descendant - return the rightmost descendant of a css
4278  * @pos: css of interest
4279  *
4280  * Return the rightmost descendant of @pos.  If there's no descendant, @pos
4281  * is returned.  This can be used during pre-order traversal to skip
4282  * subtree of @pos.
4283  *
4284  * While this function requires cgroup_mutex or RCU read locking, it
4285  * doesn't require the whole traversal to be contained in a single critical
4286  * section.  This function will return the correct rightmost descendant as
4287  * long as @pos is accessible.
4288  */
4289 struct cgroup_subsys_state *
4290 css_rightmost_descendant(struct cgroup_subsys_state *pos)
4291 {
4292         struct cgroup_subsys_state *last, *tmp;
4293 
4294         cgroup_assert_mutex_or_rcu_locked();
4295 
4296         do {
4297                 last = pos;
4298                 /* ->prev isn't RCU safe, walk ->next till the end */
4299                 pos = NULL;
4300                 css_for_each_child(tmp, last)
4301                         pos = tmp;
4302         } while (pos);
4303 
4304         return last;
4305 }
4306 
4307 static struct cgroup_subsys_state *
4308 css_leftmost_descendant(struct cgroup_subsys_state *pos)
4309 {
4310         struct cgroup_subsys_state *last;
4311 
4312         do {
4313                 last = pos;
4314                 pos = css_next_child(NULL, pos);
4315         } while (pos);
4316 
4317         return last;
4318 }
4319 
4320 /**
4321  * css_next_descendant_post - find the next descendant for post-order walk
4322  * @pos: the current position (%NULL to initiate traversal)
4323  * @root: css whose descendants to walk
4324  *
4325  * To be used by css_for_each_descendant_post().  Find the next descendant
4326  * to visit for post-order traversal of @root's descendants.  @root is
4327  * included in the iteration and the last node to be visited.
4328  *
4329  * While this function requires cgroup_mutex or RCU read locking, it
4330  * doesn't require the whole traversal to be contained in a single critical
4331  * section.  This function will return the correct next descendant as long
4332  * as both @pos and @cgroup are accessible and @pos is a descendant of
4333  * @cgroup.
4334  *
4335  * If a subsystem synchronizes ->css_online() and the start of iteration, a
4336  * css which finished ->css_online() is guaranteed to be visible in the
4337  * future iterations and will stay visible until the last reference is put.
4338  * A css which hasn't finished ->css_online() or already finished
4339  * ->css_offline() may show up during traversal.  It's each subsystem's
4340  * responsibility to synchronize against on/offlining.
4341  */
4342 struct cgroup_subsys_state *
4343 css_next_descendant_post(struct cgroup_subsys_state *pos,
4344                          struct cgroup_subsys_state *root)
4345 {
4346         struct cgroup_subsys_state *next;
4347 
4348         cgroup_assert_mutex_or_rcu_locked();
4349 
4350         /* if first iteration, visit leftmost descendant which may be @root */
4351         if (!pos)
4352                 return css_leftmost_descendant(root);
4353 
4354         /* if we visited @root, we're done */
4355         if (pos == root)
4356                 return NULL;
4357 
4358         /* if there's an unvisited sibling, visit its leftmost descendant */
4359         next = css_next_child(pos, pos->parent);
4360         if (next)
4361                 return css_leftmost_descendant(next);
4362 
4363         /* no sibling left, visit parent */
4364         return pos->parent;
4365 }
4366 
4367 /**
4368  * css_has_online_children - does a css have online children
4369  * @css: the target css
4370  *
4371  * Returns %true if @css has any online children; otherwise, %false.  This
4372  * function can be called from any context but the caller is responsible
4373  * for synchronizing against on/offlining as necessary.
4374  */
4375 bool css_has_online_children(struct cgroup_subsys_state *css)
4376 {
4377         struct cgroup_subsys_state *child;
4378         bool ret = false;
4379 
4380         rcu_read_lock();
4381         css_for_each_child(child, css) {
4382                 if (child->flags & CSS_ONLINE) {
4383                         ret = true;
4384                         break;
4385                 }
4386         }
4387         rcu_read_unlock();
4388         return ret;
4389 }
4390 
4391 static struct css_set *css_task_iter_next_css_set(struct css_task_iter *it)
4392 {
4393         struct list_head *l;
4394         struct cgrp_cset_link *link;
4395         struct css_set *cset;
4396 
4397         lockdep_assert_held(&css_set_lock);
4398 
4399         /* find the next threaded cset */
4400         if (it->tcset_pos) {
4401                 l = it->tcset_pos->next;
4402 
4403                 if (l != it->tcset_head) {
4404                         it->tcset_pos = l;
4405                         return container_of(l, struct css_set,
4406                                             threaded_csets_node);
4407                 }
4408 
4409                 it->tcset_pos = NULL;
4410         }
4411 
4412         /* find the next cset */
4413         l = it->cset_pos;
4414         l = l->next;
4415         if (l == it->cset_head) {
4416                 it->cset_pos = NULL;
4417                 return NULL;
4418         }
4419 
4420         if (it->ss) {
4421                 cset = container_of(l, struct css_set, e_cset_node[it->ss->id]);
4422         } else {
4423                 link = list_entry(l, struct cgrp_cset_link, cset_link);
4424                 cset = link->cset;
4425         }
4426 
4427         it->cset_pos = l;
4428 
4429         /* initialize threaded css_set walking */
4430         if (it->flags & CSS_TASK_ITER_THREADED) {
4431                 if (it->cur_dcset)
4432                         put_css_set_locked(it->cur_dcset);
4433                 it->cur_dcset = cset;
4434                 get_css_set(cset);
4435 
4436                 it->tcset_head = &cset->threaded_csets;
4437                 it->tcset_pos = &cset->threaded_csets;
4438         }
4439 
4440         return cset;
4441 }
4442 
4443 /**
4444  * css_task_iter_advance_css_set - advance a task itererator to the next css_set
4445  * @it: the iterator to advance
4446  *
4447  * Advance @it to the next css_set to walk.
4448  */
4449 static void css_task_iter_advance_css_set(struct css_task_iter *it)
4450 {
4451         struct css_set *cset;
4452 
4453         lockdep_assert_held(&css_set_lock);
4454 
4455         /* Advance to the next non-empty css_set */
4456         do {
4457                 cset = css_task_iter_next_css_set(it);
4458                 if (!cset) {
4459                         it->task_pos = NULL;
4460                         return;
4461                 }
4462         } while (!css_set_populated(cset) && list_empty(&cset->dying_tasks));
4463 
4464         if (!list_empty(&cset->tasks)) {
4465                 it->task_pos = cset->tasks.next;
4466                 it->cur_tasks_head = &cset->tasks;
4467         } else if (!list_empty(&cset->mg_tasks)) {
4468                 it->task_pos = cset->mg_tasks.next;
4469                 it->cur_tasks_head = &cset->mg_tasks;
4470         } else {
4471                 it->task_pos = cset->dying_tasks.next;
4472                 it->cur_tasks_head = &cset->dying_tasks;
4473         }
4474 
4475         it->tasks_head = &cset->tasks;
4476         it->mg_tasks_head = &cset->mg_tasks;
4477         it->dying_tasks_head = &cset->dying_tasks;
4478 
4479         /*
4480          * We don't keep css_sets locked across iteration steps and thus
4481          * need to take steps to ensure that iteration can be resumed after
4482          * the lock is re-acquired.  Iteration is performed at two levels -
4483          * css_sets and tasks in them.
4484          *
4485          * Once created, a css_set never leaves its cgroup lists, so a
4486          * pinned css_set is guaranteed to stay put and we can resume
4487          * iteration afterwards.
4488          *
4489          * Tasks may leave @cset across iteration steps.  This is resolved
4490          * by registering each iterator with the css_set currently being
4491          * walked and making css_set_move_task() advance iterators whose
4492          * next task is leaving.
4493          */
4494         if (it->cur_cset) {
4495                 list_del(&it->iters_node);
4496                 put_css_set_locked(it->cur_cset);
4497         }
4498         get_css_set(cset);
4499         it->cur_cset = cset;
4500         list_add(&it->iters_node, &cset->task_iters);
4501 }
4502 
4503 static void css_task_iter_skip(struct css_task_iter *it,
4504                                struct task_struct *task)
4505 {
4506         lockdep_assert_held(&css_set_lock);
4507 
4508         if (it->task_pos == &task->cg_list) {
4509                 it->task_pos = it->task_pos->next;
4510                 it->flags |= CSS_TASK_ITER_SKIPPED;
4511         }
4512 }
4513 
4514 static void css_task_iter_advance(struct css_task_iter *it)
4515 {
4516         struct task_struct *task;
4517 
4518         lockdep_assert_held(&css_set_lock);
4519 repeat:
4520         if (it->task_pos) {
4521                 /*
4522                  * Advance iterator to find next entry.  cset->tasks is
4523                  * consumed first and then ->mg_tasks.  After ->mg_tasks,
4524                  * we move onto the next cset.
4525                  */
4526                 if (it->flags & CSS_TASK_ITER_SKIPPED)
4527                         it->flags &= ~CSS_TASK_ITER_SKIPPED;
4528                 else
4529                         it->task_pos = it->task_pos->next;
4530 
4531                 if (it->task_pos == it->tasks_head) {
4532                         it->task_pos = it->mg_tasks_head->next;
4533                         it->cur_tasks_head = it->mg_tasks_head;
4534                 }
4535                 if (it->task_pos == it->mg_tasks_head) {
4536                         it->task_pos = it->dying_tasks_head->next;
4537                         it->cur_tasks_head = it->dying_tasks_head;
4538                 }
4539                 if (it->task_pos == it->dying_tasks_head)
4540                         css_task_iter_advance_css_set(it);
4541         } else {
4542                 /* called from start, proceed to the first cset */
4543                 css_task_iter_advance_css_set(it);
4544         }
4545 
4546         if (!it->task_pos)
4547                 return;
4548 
4549         task = list_entry(it->task_pos, struct task_struct, cg_list);
4550 
4551         if (it->flags & CSS_TASK_ITER_PROCS) {
4552                 /* if PROCS, skip over tasks which aren't group leaders */
4553                 if (!thread_group_leader(task))
4554                         goto repeat;
4555 
4556                 /* and dying leaders w/o live member threads */
4557                 if (it->cur_tasks_head == it->dying_tasks_head &&
4558                     !atomic_read(&task->signal->live))
4559                         goto repeat;
4560         } else {
4561                 /* skip all dying ones */
4562                 if (it->cur_tasks_head == it->dying_tasks_head)
4563                         goto repeat;
4564         }
4565 }
4566 
4567 /**
4568  * css_task_iter_start - initiate task iteration
4569  * @css: the css to walk tasks of
4570  * @flags: CSS_TASK_ITER_* flags
4571  * @it: the task iterator to use
4572  *
4573  * Initiate iteration through the tasks of @css.  The caller can call
4574  * css_task_iter_next() to walk through the tasks until the function
4575  * returns NULL.  On completion of iteration, css_task_iter_end() must be
4576  * called.
4577  */
4578 void css_task_iter_start(struct cgroup_subsys_state *css, unsigned int flags,
4579                          struct css_task_iter *it)
4580 {
4581         /* no one should try to iterate before mounting cgroups */
4582         WARN_ON_ONCE(!use_task_css_set_links);
4583 
4584         memset(it, 0, sizeof(*it));
4585 
4586         spin_lock_irq(&css_set_lock);
4587 
4588         it->ss = css->ss;
4589         it->flags = flags;
4590 
4591         if (it->ss)
4592                 it->cset_pos = &css->cgroup->e_csets[css->ss->id];
4593         else
4594                 it->cset_pos = &css->cgroup->cset_links;
4595 
4596         it->cset_head = it->cset_pos;
4597 
4598         css_task_iter_advance(it);
4599 
4600         spin_unlock_irq(&css_set_lock);
4601 }
4602 
4603 /**
4604  * css_task_iter_next - return the next task for the iterator
4605  * @it: the task iterator being iterated
4606  *
4607  * The "next" function for task iteration.  @it should have been
4608  * initialized via css_task_iter_start().  Returns NULL when the iteration
4609  * reaches the end.
4610  */
4611 struct task_struct *css_task_iter_next(struct css_task_iter *it)
4612 {
4613         if (it->cur_task) {
4614                 put_task_struct(it->cur_task);
4615                 it->cur_task = NULL;
4616         }
4617 
4618         spin_lock_irq(&css_set_lock);
4619 
4620         /* @it may be half-advanced by skips, finish advancing */
4621         if (it->flags & CSS_TASK_ITER_SKIPPED)
4622                 css_task_iter_advance(it);
4623 
4624         if (it->task_pos) {
4625                 it->cur_task = list_entry(it->task_pos, struct task_struct,
4626                                           cg_list);
4627                 get_task_struct(it->cur_task);
4628                 css_task_iter_advance(it);
4629         }
4630 
4631         spin_unlock_irq(&css_set_lock);
4632 
4633         return it->cur_task;
4634 }
4635 
4636 /**
4637  * css_task_iter_end - finish task iteration
4638  * @it: the task iterator to finish
4639  *
4640  * Finish task iteration started by css_task_iter_start().
4641  */
4642 void css_task_iter_end(struct css_task_iter *it)
4643 {
4644         if (it->cur_cset) {
4645                 spin_lock_irq(&css_set_lock);
4646                 list_del(&it->iters_node);
4647                 put_css_set_locked(it->cur_cset);
4648                 spin_unlock_irq(&css_set_lock);
4649         }
4650 
4651         if (it->cur_dcset)
4652                 put_css_set(it->cur_dcset);
4653 
4654         if (it->cur_task)
4655                 put_task_struct(it->cur_task);
4656 }
4657 
4658 static void cgroup_procs_release(struct kernfs_open_file *of)
4659 {
4660         if (of->priv) {
4661                 css_task_iter_end(of->priv);
4662                 kfree(of->priv);
4663         }
4664 }
4665 
4666 static void *cgroup_procs_next(struct seq_file *s, void *v, loff_t *pos)
4667 {
4668         struct kernfs_open_file *of = s->private;
4669         struct css_task_iter *it = of->priv;
4670 
4671         if (pos)
4672                 (*pos)++;
4673 
4674         return css_task_iter_next(it);
4675 }
4676 
4677 static void *__cgroup_procs_start(struct seq_file *s, loff_t *pos,
4678                                   unsigned int iter_flags)
4679 {
4680         struct kernfs_open_file *of = s->private;
4681         struct cgroup *cgrp = seq_css(s)->cgroup;
4682         struct css_task_iter *it = of->priv;
4683 
4684         /*
4685          * When a seq_file is seeked, it's always traversed sequentially
4686          * from position 0, so we can simply keep iterating on !0 *pos.
4687          */
4688         if (!it) {
4689                 if (WARN_ON_ONCE((*pos)))
4690                         return ERR_PTR(-EINVAL);
4691 
4692                 it = kzalloc(sizeof(*it), GFP_KERNEL);
4693                 if (!it)
4694                         return ERR_PTR(-ENOMEM);
4695                 of->priv = it;
4696                 css_task_iter_start(&cgrp->self, iter_flags, it);
4697         } else if (!(*pos)) {
4698                 css_task_iter_end(it);
4699                 css_task_iter_start(&cgrp->self, iter_flags, it);
4700         } else
4701                 return it->cur_task;
4702 
4703         return cgroup_procs_next(s, NULL, NULL);
4704 }
4705 
4706 static void *cgroup_procs_start(struct seq_file *s, loff_t *pos)
4707 {
4708         struct cgroup *cgrp = seq_css(s)->cgroup;
4709 
4710         /*
4711          * All processes of a threaded subtree belong to the domain cgroup
4712          * of the subtree.  Only threads can be distributed across the
4713          * subtree.  Reject reads on cgroup.procs in the subtree proper.
4714          * They're always empty anyway.
4715          */
4716         if (cgroup_is_threaded(cgrp))
4717                 return ERR_PTR(-EOPNOTSUPP);
4718 
4719         return __cgroup_procs_start(s, pos, CSS_TASK_ITER_PROCS |
4720                                             CSS_TASK_ITER_THREADED);
4721 }
4722 
4723 static int cgroup_procs_show(struct seq_file *s, void *v)
4724 {
4725         seq_printf(s, "%d\n", task_pid_vnr(v));
4726         return 0;
4727 }
4728 
4729 static int cgroup_procs_write_permission(struct cgroup *src_cgrp,
4730                                          struct cgroup *dst_cgrp,
4731                                          struct super_block *sb)
4732 {
4733         struct cgroup_namespace *ns = current->nsproxy->cgroup_ns;
4734         struct cgroup *com_cgrp = src_cgrp;
4735         struct inode *inode;
4736         int ret;
4737 
4738         lockdep_assert_held(&cgroup_mutex);
4739 
4740         /* find the common ancestor */
4741         while (!cgroup_is_descendant(dst_cgrp, com_cgrp))
4742                 com_cgrp = cgroup_parent(com_cgrp);
4743 
4744         /* %current should be authorized to migrate to the common ancestor */
4745         inode = kernfs_get_inode(sb, com_cgrp->procs_file.kn);
4746         if (!inode)
4747                 return -ENOMEM;
4748 
4749         ret = inode_permission(inode, MAY_WRITE);
4750         iput(inode);
4751         if (ret)
4752                 return ret;
4753 
4754         /*
4755          * If namespaces are delegation boundaries, %current must be able
4756          * to see both source and destination cgroups from its namespace.
4757          */
4758         if ((cgrp_dfl_root.flags & CGRP_ROOT_NS_DELEGATE) &&
4759             (!cgroup_is_descendant(src_cgrp, ns->root_cset->dfl_cgrp) ||
4760              !cgroup_is_descendant(dst_cgrp, ns->root_cset->dfl_cgrp)))
4761                 return -ENOENT;
4762 
4763         return 0;
4764 }
4765 
4766 static ssize_t cgroup_procs_write(struct kernfs_open_file *of,
4767                                   char *buf, size_t nbytes, loff_t off)
4768 {
4769         struct cgroup *src_cgrp, *dst_cgrp;
4770         struct task_struct *task;
4771         ssize_t ret;
4772 
4773         dst_cgrp = cgroup_kn_lock_live(of->kn, false);
4774         if (!dst_cgrp)
4775                 return -ENODEV;
4776 
4777         task = cgroup_procs_write_start(buf, true);
4778         ret = PTR_ERR_OR_ZERO(task);
4779         if (ret)
4780                 goto out_unlock;
4781 
4782         /* find the source cgroup */
4783         spin_lock_irq(&css_set_lock);
4784         src_cgrp = task_cgroup_from_root(task, &cgrp_dfl_root);
4785         spin_unlock_irq(&css_set_lock);
4786 
4787         ret = cgroup_procs_write_permission(src_cgrp, dst_cgrp,
4788                                             of->file->f_path.dentry->d_sb);
4789         if (ret)
4790                 goto out_finish;
4791 
4792         ret = cgroup_attach_task(dst_cgrp, task, true);
4793 
4794 out_finish:
4795         cgroup_procs_write_finish(task);
4796 out_unlock:
4797         cgroup_kn_unlock(of->kn);
4798 
4799         return ret ?: nbytes;
4800 }
4801 
4802 static void *cgroup_threads_start(struct seq_file *s, loff_t *pos)
4803 {
4804         return __cgroup_procs_start(s, pos, 0);
4805 }
4806 
4807 static ssize_t cgroup_threads_write(struct kernfs_open_file *of,
4808                                     char *buf, size_t nbytes, loff_t off)
4809 {
4810         struct cgroup *src_cgrp, *dst_cgrp;
4811         struct task_struct *task;
4812         ssize_t ret;
4813 
4814         buf = strstrip(buf);
4815 
4816         dst_cgrp = cgroup_kn_lock_live(of->kn, false);
4817         if (!dst_cgrp)
4818                 return -ENODEV;
4819 
4820         task = cgroup_procs_write_start(buf, false);
4821         ret = PTR_ERR_OR_ZERO(task);
4822         if (ret)
4823                 goto out_unlock;
4824 
4825         /* find the source cgroup */
4826         spin_lock_irq(&css_set_lock);
4827         src_cgrp = task_cgroup_from_root(task, &cgrp_dfl_root);
4828         spin_unlock_irq(&css_set_lock);
4829 
4830         /* thread migrations follow the cgroup.procs delegation rule */
4831         ret = cgroup_procs_write_permission(src_cgrp, dst_cgrp,
4832                                             of->file->f_path.dentry->d_sb);
4833         if (ret)
4834                 goto out_finish;
4835 
4836         /* and must be contained in the same domain */
4837         ret = -EOPNOTSUPP;
4838         if (src_cgrp->dom_cgrp != dst_cgrp->dom_cgrp)
4839                 goto out_finish;
4840 
4841         ret = cgroup_attach_task(dst_cgrp, task, false);
4842 
4843 out_finish:
4844         cgroup_procs_write_finish(task);
4845 out_unlock:
4846         cgroup_kn_unlock(of->kn);
4847 
4848         return ret ?: nbytes;
4849 }
4850 
4851 /* cgroup core interface files for the default hierarchy */
4852 static struct cftype cgroup_base_files[] = {
4853         {
4854                 .name = "cgroup.type",
4855                 .flags = CFTYPE_NOT_ON_ROOT,
4856                 .seq_show = cgroup_type_show,
4857                 .write = cgroup_type_write,
4858         },
4859         {
4860                 .name = "cgroup.procs",
4861                 .flags = CFTYPE_NS_DELEGATABLE,
4862                 .file_offset = offsetof(struct cgroup, procs_file),
4863                 .release = cgroup_procs_release,
4864                 .seq_start = cgroup_procs_start,
4865                 .seq_next = cgroup_procs_next,
4866                 .seq_show = cgroup_procs_show,
4867                 .write = cgroup_procs_write,
4868         },
4869         {
4870                 .name = "cgroup.threads",
4871                 .flags = CFTYPE_NS_DELEGATABLE,
4872                 .release = cgroup_procs_release,
4873                 .seq_start = cgroup_threads_start,
4874                 .seq_next = cgroup_procs_next,
4875                 .seq_show = cgroup_procs_show,
4876                 .write = cgroup_threads_write,
4877         },
4878         {
4879                 .name = "cgroup.controllers",
4880                 .seq_show = cgroup_controllers_show,
4881         },
4882         {
4883                 .name = "cgroup.subtree_control",
4884                 .flags = CFTYPE_NS_DELEGATABLE,
4885                 .seq_show = cgroup_subtree_control_show,
4886                 .write = cgroup_subtree_control_write,
4887         },
4888         {
4889                 .name = "cgroup.events",
4890                 .flags = CFTYPE_NOT_ON_ROOT,
4891                 .file_offset = offsetof(struct cgroup, events_file),
4892                 .seq_show = cgroup_events_show,
4893         },
4894         {
4895                 .name = "cgroup.max.descendants",
4896                 .seq_show = cgroup_max_descendants_show,
4897                 .write = cgroup_max_descendants_write,
4898         },
4899         {
4900                 .name = "cgroup.max.depth",
4901                 .seq_show = cgroup_max_depth_show,
4902                 .write = cgroup_max_depth_write,
4903         },
4904         {
4905                 .name = "cgroup.stat",
4906                 .seq_show = cgroup_stat_show,
4907         },
4908         {
4909                 .name = "cgroup.freeze",
4910                 .flags = CFTYPE_NOT_ON_ROOT,
4911                 .seq_show = cgroup_freeze_show,
4912                 .write = cgroup_freeze_write,
4913         },
4914         {
4915                 .name = "cpu.stat",
4916                 .flags = CFTYPE_NOT_ON_ROOT,
4917                 .seq_show = cpu_stat_show,
4918         },
4919 #ifdef CONFIG_PSI
4920         {
4921                 .name = "io.pressure",
4922                 .seq_show = cgroup_io_pressure_show,
4923                 .write = cgroup_io_pressure_write,
4924                 .poll = cgroup_pressure_poll,
4925                 .release = cgroup_pressure_release,
4926         },
4927         {
4928                 .name = "memory.pressure",
4929                 .seq_show = cgroup_memory_pressure_show,
4930                 .write = cgroup_memory_pressure_write,
4931                 .poll = cgroup_pressure_poll,
4932                 .release = cgroup_pressure_release,
4933         },
4934         {
4935                 .name = "cpu.pressure",
4936                 .seq_show = cgroup_cpu_pressure_show,
4937                 .write = cgroup_cpu_pressure_write,
4938                 .poll = cgroup_pressure_poll,
4939                 .release = cgroup_pressure_release,
4940         },
4941 #endif /* CONFIG_PSI */
4942         { }     /* terminate */
4943 };
4944 
4945 /*
4946  * css destruction is four-stage process.
4947  *
4948  * 1. Destruction starts.  Killing of the percpu_ref is initiated.
4949  *    Implemented in kill_css().
4950  *
4951  * 2. When the percpu_ref is confirmed to be visible as killed on all CPUs
4952  *    and thus css_tryget_online() is guaranteed to fail, the css can be
4953  *    offlined by invoking offline_css().  After offlining, the base ref is
4954  *    put.  Implemented in css_killed_work_fn().
4955  *
4956  * 3. When the percpu_ref reaches zero, the only possible remaining
4957  *    accessors are inside RCU read sections.  css_release() schedules the
4958  *    RCU callback.
4959  *
4960  * 4. After the grace period, the css can be freed.  Implemented in
4961  *    css_free_work_fn().
4962  *
4963  * It is actually hairier because both step 2 and 4 require process context
4964  * and thus involve punting to css->destroy_work adding two additional
4965  * steps to the already complex sequence.
4966  */
4967 static void css_free_rwork_fn(struct work_struct *work)
4968 {
4969         struct cgroup_subsys_state *css = container_of(to_rcu_work(work),
4970                                 struct cgroup_subsys_state, destroy_rwork);
4971         struct cgroup_subsys *ss = css->ss;
4972         struct cgroup *cgrp = css->cgroup;
4973 
4974         percpu_ref_exit(&css->refcnt);
4975 
4976         if (ss) {
4977                 /* css free path */
4978                 struct cgroup_subsys_state *parent = css->parent;
4979                 int id = css->id;
4980 
4981                 ss->css_free(css);
4982                 cgroup_idr_remove(&ss->css_idr, id);
4983                 cgroup_put(cgrp);
4984 
4985                 if (parent)
4986                         css_put(parent);
4987         } else {
4988                 /* cgroup free path */
4989                 atomic_dec(&cgrp->root->nr_cgrps);
4990                 cgroup1_pidlist_destroy_all(cgrp);
4991                 cancel_work_sync(&cgrp->release_agent_work);
4992 
4993                 if (cgroup_parent(cgrp)) {
4994                         /*
4995                          * We get a ref to the parent, and put the ref when
4996                          * this cgroup is being freed, so it's guaranteed
4997                          * that the parent won't be destroyed before its
4998                          * children.
4999                          */
5000                         cgroup_put(cgroup_parent(cgrp));
5001                         kernfs_put(cgrp->kn);
5002                         psi_cgroup_free(cgrp);
5003                         if (cgroup_on_dfl(cgrp))
5004                                 cgroup_rstat_exit(cgrp);
5005                         kfree(cgrp);
5006                 } else {
5007                         /*
5008                          * This is root cgroup's refcnt reaching zero,
5009                          * which indicates that the root should be
5010                          * released.
5011                          */
5012                         cgroup_destroy_root(cgrp->root);
5013                 }
5014         }
5015 }
5016 
5017 static void css_release_work_fn(struct work_struct *work)
5018 {
5019         struct cgroup_subsys_state *css =
5020                 container_of(work, struct cgroup_subsys_state, destroy_work);
5021         struct cgroup_subsys *ss = css->ss;
5022         struct cgroup *cgrp = css->cgroup;
5023 
5024         mutex_lock(&cgroup_mutex);
5025 
5026         css->flags |= CSS_RELEASED;
5027         list_del_rcu(&css->sibling);
5028 
5029         if (ss) {
5030                 /* css release path */
5031                 if (!list_empty(&css->rstat_css_node)) {
5032                         cgroup_rstat_flush(cgrp);
5033                         list_del_rcu(&css->rstat_css_node);
5034                 }
5035 
5036                 cgroup_idr_replace(&ss->css_idr, NULL, css->id);
5037                 if (ss->css_released)
5038                         ss->css_released(css);
5039         } else {
5040                 struct cgroup *tcgrp;
5041 
5042                 /* cgroup release path */
5043                 TRACE_CGROUP_PATH(release, cgrp);
5044 
5045                 if (cgroup_on_dfl(cgrp))
5046                         cgroup_rstat_flush(cgrp);
5047 
5048                 spin_lock_irq(&css_set_lock);
5049                 for (tcgrp = cgroup_parent(cgrp); tcgrp;
5050                      tcgrp = cgroup_parent(tcgrp))
5051                         tcgrp->nr_dying_descendants--;
5052                 spin_unlock_irq(&css_set_lock);
5053 
5054                 cgroup_idr_remove(&cgrp->root->cgroup_idr, cgrp->id);
5055                 cgrp->id = -1;
5056 
5057                 /*
5058                  * There are two control paths which try to determine
5059                  * cgroup from dentry without going through kernfs -
5060                  * cgroupstats_build() and css_tryget_online_from_dir().
5061                  * Those are supported by RCU protecting clearing of
5062                  * cgrp->kn->priv backpointer.
5063                  */
5064                 if (cgrp->kn)
5065                         RCU_INIT_POINTER(*(void __rcu __force **)&cgrp->kn->priv,
5066                                          NULL);
5067         }
5068 
5069         mutex_unlock(&cgroup_mutex);
5070 
5071         INIT_RCU_WORK(&css->destroy_rwork, css_free_rwork_fn);
5072         queue_rcu_work(cgroup_destroy_wq, &css->destroy_rwork);
5073 }
5074 
5075 static void css_release(struct percpu_ref *ref)
5076 {
5077         struct cgroup_subsys_state *css =
5078                 container_of(ref, struct cgroup_subsys_state, refcnt);
5079 
5080         INIT_WORK(&css->destroy_work, css_release_work_fn);
5081         queue_work(cgroup_destroy_wq, &css->destroy_work);
5082 }
5083 
5084 static void init_and_link_css(struct cgroup_subsys_state *css,
5085                               struct cgroup_subsys *ss, struct cgroup *cgrp)
5086 {
5087         lockdep_assert_held(&cgroup_mutex);
5088 
5089         cgroup_get_live(cgrp);
5090 
5091         memset(css, 0, sizeof(*css));
5092         css->cgroup = cgrp;
5093         css->ss = ss;
5094         css->id = -1;
5095         INIT_LIST_HEAD(&css->sibling);
5096         INIT_LIST_HEAD(&css->children);
5097         INIT_LIST_HEAD(&css->rstat_css_node);
5098         css->serial_nr = css_serial_nr_next++;
5099         atomic_set(&css->online_cnt, 0);
5100 
5101         if (cgroup_parent(cgrp)) {
5102                 css->parent = cgroup_css(cgroup_parent(cgrp), ss);
5103                 css_get(css->parent);
5104         }
5105 
5106         if (cgroup_on_dfl(cgrp) && ss->css_rstat_flush)
5107                 list_add_rcu(&css->rstat_css_node, &cgrp->rstat_css_list);
5108 
5109         BUG_ON(cgroup_css(cgrp, ss));
5110 }
5111 
5112 /* invoke ->css_online() on a new CSS and mark it online if successful */
5113 static int online_css(struct cgroup_subsys_state *css)
5114 {
5115         struct cgroup_subsys *ss = css->ss;
5116         int ret = 0;
5117 
5118         lockdep_assert_held(&cgroup_mutex);
5119 
5120         if (ss->css_online)
5121                 ret = ss->css_online(css);
5122         if (!ret) {
5123                 css->flags |= CSS_ONLINE;
5124                 rcu_assign_pointer(css->cgroup->subsys[ss->id], css);
5125 
5126                 atomic_inc(&css->online_cnt);
5127                 if (css->parent)
5128                         atomic_inc(&css->parent->online_cnt);
5129         }
5130         return ret;
5131 }
5132 
5133 /* if the CSS is online, invoke ->css_offline() on it and mark it offline */
5134 static void offline_css(struct cgroup_subsys_state *css)
5135 {
5136         struct cgroup_subsys *ss = css->ss;
5137 
5138         lockdep_assert_held(&cgroup_mutex);
5139 
5140         if (!(css->flags & CSS_ONLINE))
5141                 return;
5142 
5143         if (ss->css_offline)
5144                 ss->css_offline(css);
5145 
5146         css->flags &= ~CSS_ONLINE;
5147         RCU_INIT_POINTER(css->cgroup->subsys[ss->id], NULL);
5148 
5149         wake_up_all(&css->cgroup->offline_waitq);
5150 }
5151 
5152 /**
5153  * css_create - create a cgroup_subsys_state
5154  * @cgrp: the cgroup new css will be associated with
5155  * @ss: the subsys of new css
5156  *
5157  * Create a new css associated with @cgrp - @ss pair.  On success, the new
5158  * css is online and installed in @cgrp.  This function doesn't create the
5159  * interface files.  Returns 0 on success, -errno on failure.
5160  */
5161 static struct cgroup_subsys_state *css_create(struct cgroup *cgrp,
5162                                               struct cgroup_subsys *ss)
5163 {
5164         struct cgroup *parent = cgroup_parent(cgrp);
5165         struct cgroup_subsys_state *parent_css = cgroup_css(parent, ss);
5166         struct cgroup_subsys_state *css;
5167         int err;
5168 
5169         lockdep_assert_held(&cgroup_mutex);
5170 
5171         css = ss->css_alloc(parent_css);
5172         if (!css)
5173                 css = ERR_PTR(-ENOMEM);
5174         if (IS_ERR(css))
5175                 return css;
5176 
5177         init_and_link_css(css, ss, cgrp);
5178 
5179         err = percpu_ref_init(&css->refcnt, css_release, 0, GFP_KERNEL);
5180         if (err)
5181                 goto err_free_css;
5182 
5183         err = cgroup_idr_alloc(&ss->css_idr, NULL, 2, 0, GFP_KERNEL);
5184         if (err < 0)
5185                 goto err_free_css;
5186         css->id = err;
5187 
5188         /* @css is ready to be brought online now, make it visible */
5189         list_add_tail_rcu(&css->sibling, &parent_css->children);
5190         cgroup_idr_replace(&ss->css_idr, css, css->id);
5191 
5192         err = online_css(css);
5193         if (err)
5194                 goto err_list_del;
5195 
5196         if (ss->broken_hierarchy && !ss->warned_broken_hierarchy &&
5197             cgroup_parent(parent)) {
5198                 pr_warn("%s (%d) created nested cgroup for controller \"%s\" which has incomplete hierarchy support. Nested cgroups may change behavior in the future.\n",
5199                         current->comm, current->pid, ss->name);
5200                 if (!strcmp(ss->name, "memory"))
5201                         pr_warn("\"memory\" requires setting use_hierarchy to 1 on the root\n");
5202                 ss->warned_broken_hierarchy = true;
5203         }
5204 
5205         return css;
5206 
5207 err_list_del:
5208         list_del_rcu(&css->sibling);
5209 err_free_css:
5210         list_del_rcu(&css->rstat_css_node);
5211         INIT_RCU_WORK(&css->destroy_rwork, css_free_rwork_fn);
5212         queue_rcu_work(cgroup_destroy_wq, &css->destroy_rwork);
5213         return ERR_PTR(err);
5214 }
5215 
5216 /*
5217  * The returned cgroup is fully initialized including its control mask, but
5218  * it isn't associated with its kernfs_node and doesn't have the control
5219  * mask applied.
5220  */
5221 static struct cgroup *cgroup_create(struct cgroup *parent)
5222 {
5223         struct cgroup_root *root = parent->root;
5224         struct cgroup *cgrp, *tcgrp;
5225         int level = parent->level + 1;
5226         int ret;
5227 
5228         /* allocate the cgroup and its ID, 0 is reserved for the root */
5229         cgrp = kzalloc(struct_size(cgrp, ancestor_ids, (level + 1)),
5230                        GFP_KERNEL);
5231         if (!cgrp)
5232                 return ERR_PTR(-ENOMEM);
5233 
5234         ret = percpu_ref_init(&cgrp->self.refcnt, css_release, 0, GFP_KERNEL);
5235         if (ret)
5236                 goto out_free_cgrp;
5237 
5238         if (cgroup_on_dfl(parent)) {
5239                 ret = cgroup_rstat_init(cgrp);
5240                 if (ret)
5241                         goto out_cancel_ref;
5242         }
5243 
5244         /*
5245          * Temporarily set the pointer to NULL, so idr_find() won't return
5246          * a half-baked cgroup.
5247          */
5248         cgrp->id = cgroup_idr_alloc(&root->cgroup_idr, NULL, 2, 0, GFP_KERNEL);
5249         if (cgrp->id < 0) {
5250                 ret = -ENOMEM;
5251                 goto out_stat_exit;
5252         }
5253 
5254         init_cgroup_housekeeping(cgrp);
5255 
5256         cgrp->self.parent = &parent->self;
5257         cgrp->root = root;
5258         cgrp->level = level;
5259 
5260         ret = psi_cgroup_alloc(cgrp);
5261         if (ret)
5262                 goto out_idr_free;
5263 
5264         ret = cgroup_bpf_inherit(cgrp);
5265         if (ret)
5266                 goto out_psi_free;
5267 
5268         /*
5269          * New cgroup inherits effective freeze counter, and
5270          * if the parent has to be frozen, the child has too.
5271          */
5272         cgrp->freezer.e_freeze = parent->freezer.e_freeze;
5273         if (cgrp->freezer.e_freeze) {
5274                 /*
5275                  * Set the CGRP_FREEZE flag, so when a process will be
5276                  * attached to the child cgroup, it will become frozen.
5277                  * At this point the new cgroup is unpopulated, so we can
5278                  * consider it frozen immediately.
5279                  */
5280                 set_bit(CGRP_FREEZE, &cgrp->flags);
5281                 set_bit(CGRP_FROZEN, &cgrp->flags);
5282         }
5283 
5284         spin_lock_irq(&css_set_lock);
5285         for (tcgrp = cgrp; tcgrp; tcgrp = cgroup_parent(tcgrp)) {
5286                 cgrp->ancestor_ids[tcgrp->level] = tcgrp->id;
5287 
5288                 if (tcgrp != cgrp) {
5289                         tcgrp->nr_descendants++;
5290 
5291                         /*
5292                          * If the new cgroup is frozen, all ancestor cgroups
5293                          * get a new frozen descendant, but their state can't
5294                          * change because of this.
5295                          */
5296                         if (cgrp->freezer.e_freeze)
5297                                 tcgrp->freezer.nr_frozen_descendants++;
5298                 }
5299         }
5300         spin_unlock_irq(&css_set_lock);
5301 
5302         if (notify_on_release(parent))
5303                 set_bit(CGRP_NOTIFY_ON_RELEASE, &cgrp->flags);
5304 
5305         if (test_bit(CGRP_CPUSET_CLONE_CHILDREN, &parent->flags))
5306                 set_bit(CGRP_CPUSET_CLONE_CHILDREN, &cgrp->flags);
5307 
5308         cgrp->self.serial_nr = css_serial_nr_next++;
5309 
5310         /* allocation complete, commit to creation */
5311         list_add_tail_rcu(&cgrp->self.sibling, &cgroup_parent(cgrp)->self.children);
5312         atomic_inc(&root->nr_cgrps);
5313         cgroup_get_live(parent);
5314 
5315         /*
5316          * @cgrp is now fully operational.  If something fails after this
5317          * point, it'll be released via the normal destruction path.
5318          */
5319         cgroup_idr_replace(&root->cgroup_idr, cgrp, cgrp->id);
5320 
5321         /*
5322          * On the default hierarchy, a child doesn't automatically inherit
5323          * subtree_control from the parent.  Each is configured manually.
5324          */
5325         if (!cgroup_on_dfl(cgrp))
5326                 cgrp->subtree_control = cgroup_control(cgrp);
5327 
5328         cgroup_propagate_control(cgrp);
5329 
5330         return cgrp;
5331 
5332 out_psi_free:
5333         psi_cgroup_free(cgrp);
5334 out_idr_free:
5335         cgroup_idr_remove(&root->cgroup_idr, cgrp->id);
5336 out_stat_exit:
5337         if (cgroup_on_dfl(parent))
5338                 cgroup_rstat_exit(cgrp);
5339 out_cancel_ref:
5340         percpu_ref_exit(&cgrp->self.refcnt);
5341 out_free_cgrp:
5342         kfree(cgrp);
5343         return ERR_PTR(ret);
5344 }
5345 
5346 static bool cgroup_check_hierarchy_limits(struct cgroup *parent)
5347 {
5348         struct cgroup *cgroup;
5349         int ret = false;
5350         int level = 1;
5351 
5352         lockdep_assert_held(&cgroup_mutex);
5353 
5354         for (cgroup = parent; cgroup; cgroup = cgroup_parent(cgroup)) {
5355                 if (cgroup->nr_descendants >= cgroup->max_descendants)
5356                         goto fail;
5357 
5358                 if (level > cgroup->max_depth)
5359                         goto fail;
5360 
5361                 level++;
5362         }
5363 
5364         ret = true;
5365 fail:
5366         return ret;
5367 }
5368 
5369 int cgroup_mkdir(struct kernfs_node *parent_kn, const char *name, umode_t mode)
5370 {
5371         struct cgroup *parent, *cgrp;
5372         struct kernfs_node *kn;
5373         int ret;
5374 
5375         /* do not accept '\n' to prevent making /proc/<pid>/cgroup unparsable */
5376         if (strchr(name, '\n'))
5377                 return -EINVAL;
5378 
5379         parent = cgroup_kn_lock_live(parent_kn, false);
5380         if (!parent)
5381                 return -ENODEV;
5382 
5383         if (!cgroup_check_hierarchy_limits(parent)) {
5384                 ret = -EAGAIN;
5385                 goto out_unlock;
5386         }
5387 
5388         cgrp = cgroup_create(parent);
5389         if (IS_ERR(cgrp)) {
5390                 ret = PTR_ERR(cgrp);
5391                 goto out_unlock;
5392         }
5393 
5394         /* create the directory */
5395         kn = kernfs_create_dir(parent->kn, name, mode, cgrp);
5396         if (IS_ERR(kn)) {
5397                 ret = PTR_ERR(kn);
5398                 goto out_destroy;
5399         }
5400         cgrp->kn = kn;
5401 
5402         /*
5403          * This extra ref will be put in cgroup_free_fn() and guarantees
5404          * that @cgrp->kn is always accessible.
5405          */
5406         kernfs_get(kn);
5407 
5408         ret = cgroup_kn_set_ugid(kn);
5409         if (ret)
5410                 goto out_destroy;
5411 
5412         ret = css_populate_dir(&cgrp->self);
5413         if (ret)
5414                 goto out_destroy;
5415 
5416         ret = cgroup_apply_control_enable(cgrp);
5417         if (ret)
5418                 goto out_destroy;
5419 
5420         TRACE_CGROUP_PATH(mkdir, cgrp);
5421 
5422         /* let's create and online css's */
5423         kernfs_activate(kn);
5424 
5425         ret = 0;
5426         goto out_unlock;
5427 
5428 out_destroy:
5429         cgroup_destroy_locked(cgrp);
5430 out_unlock:
5431         cgroup_kn_unlock(parent_kn);
5432         return ret;
5433 }
5434 
5435 /*
5436  * This is called when the refcnt of a css is confirmed to be killed.
5437  * css_tryget_online() is now guaranteed to fail.  Tell the subsystem to
5438  * initate destruction and put the css ref from kill_css().
5439  */
5440 static void css_killed_work_fn(struct work_struct *work)
5441 {
5442         struct cgroup_subsys_state *css =
5443                 container_of(work, struct cgroup_subsys_state, destroy_work);
5444 
5445         mutex_lock(&cgroup_mutex);
5446 
5447         do {
5448                 offline_css(css);
5449                 css_put(css);
5450                 /* @css can't go away while we're holding cgroup_mutex */
5451                 css = css->parent;
5452         } while (css && atomic_dec_and_test(&css->online_cnt));
5453 
5454         mutex_unlock(&cgroup_mutex);
5455 }
5456 
5457 /* css kill confirmation processing requires process context, bounce */
5458 static void css_killed_ref_fn(struct percpu_ref *ref)
5459 {
5460         struct cgroup_subsys_state *css =
5461                 container_of(ref, struct cgroup_subsys_state, refcnt);
5462 
5463         if (atomic_dec_and_test(&css->online_cnt)) {
5464                 INIT_WORK(&css->destroy_work, css_killed_work_fn);
5465                 queue_work(cgroup_destroy_wq, &css->destroy_work);
5466         }
5467 }
5468 
5469 /**
5470  * kill_css - destroy a css
5471  * @css: css to destroy
5472  *
5473  * This function initiates destruction of @css by removing cgroup interface
5474  * files and putting its base reference.  ->css_offline() will be invoked
5475  * asynchronously once css_tryget_online() is guaranteed to fail and when
5476  * the reference count reaches zero, @css will be released.
5477  */
5478 static void kill_css(struct cgroup_subsys_state *css)
5479 {
5480         lockdep_assert_held(&cgroup_mutex);
5481 
5482         if (css->flags & CSS_DYING)
5483                 return;
5484 
5485         css->flags |= CSS_DYING;
5486 
5487         /*
5488          * This must happen before css is disassociated with its cgroup.
5489          * See seq_css() for details.
5490          */
5491         css_clear_dir(css);
5492 
5493         /*
5494          * Killing would put the base ref, but we need to keep it alive
5495          * until after ->css_offline().
5496          */
5497         css_get(css);
5498 
5499         /*
5500          * cgroup core guarantees that, by the time ->css_offline() is
5501          * invoked, no new css reference will be given out via
5502          * css_tryget_online().  We can't simply call percpu_ref_kill() and
5503          * proceed to offlining css's because percpu_ref_kill() doesn't
5504          * guarantee that the ref is seen as killed on all CPUs on return.
5505          *
5506          * Use percpu_ref_kill_and_confirm() to get notifications as each
5507          * css is confirmed to be seen as killed on all CPUs.
5508          */
5509         percpu_ref_kill_and_confirm(&css->refcnt, css_killed_ref_fn);
5510 }
5511 
5512 /**
5513  * cgroup_destroy_locked - the first stage of cgroup destruction
5514  * @cgrp: cgroup to be destroyed
5515  *
5516  * css's make use of percpu refcnts whose killing latency shouldn't be
5517  * exposed to userland and are RCU protected.  Also, cgroup core needs to
5518  * guarantee that css_tryget_online() won't succeed by the time
5519  * ->css_offline() is invoked.  To satisfy all the requirements,
5520  * destruction is implemented in the following two steps.
5521  *
5522  * s1. Verify @cgrp can be destroyed and mark it dying.  Remove all
5523  *     userland visible parts and start killing the percpu refcnts of
5524  *     css's.  Set up so that the next stage will be kicked off once all
5525  *     the percpu refcnts are confirmed to be killed.
5526  *
5527  * s2. Invoke ->css_offline(), mark the cgroup dead and proceed with the
5528  *     rest of destruction.  Once all cgroup references are gone, the
5529  *     cgroup is RCU-freed.
5530  *
5531  * This function implements s1.  After this step, @cgrp is gone as far as
5532  * the userland is concerned and a new cgroup with the same name may be
5533  * created.  As cgroup doesn't care about the names internally, this
5534  * doesn't cause any problem.
5535  */
5536 static int cgroup_destroy_locked(struct cgroup *cgrp)
5537         __releases(&cgroup_mutex) __acquires(&cgroup_mutex)
5538 {
5539         struct cgroup *tcgrp, *parent = cgroup_parent(cgrp);
5540         struct cgroup_subsys_state *css;
5541         struct cgrp_cset_link *link;
5542         int ssid;
5543 
5544         lockdep_assert_held(&cgroup_mutex);
5545 
5546         /*
5547          * Only migration can raise populated from zero and we're already
5548          * holding cgroup_mutex.
5549          */
5550         if (cgroup_is_populated(cgrp))
5551                 return -EBUSY;
5552 
5553         /*
5554          * Make sure there's no live children.  We can't test emptiness of
5555          * ->self.children as dead children linger on it while being
5556          * drained; otherwise, "rmdir parent/child parent" may fail.
5557          */
5558         if (css_has_online_children(&cgrp->self))
5559                 return -EBUSY;
5560 
5561         /*
5562          * Mark @cgrp and the associated csets dead.  The former prevents
5563          * further task migration and child creation by disabling
5564          * cgroup_lock_live_group().  The latter makes the csets ignored by
5565          * the migration path.
5566          */
5567         cgrp->self.flags &= ~CSS_ONLINE;
5568 
5569         spin_lock_irq(&css_set_lock);
5570         list_for_each_entry(link, &cgrp->cset_links, cset_link)
5571                 link->cset->dead = true;
5572         spin_unlock_irq(&css_set_lock);
5573 
5574         /* initiate massacre of all css's */
5575         for_each_css(css, ssid, cgrp)
5576                 kill_css(css);
5577 
5578         /* clear and remove @cgrp dir, @cgrp has an extra ref on its kn */
5579         css_clear_dir(&cgrp->self);
5580         kernfs_remove(cgrp->kn);
5581 
5582         if (parent && cgroup_is_threaded(cgrp))
5583                 parent->nr_threaded_children--;
5584 
5585         spin_lock_irq(&css_set_lock);
5586         for (tcgrp = cgroup_parent(cgrp); tcgrp; tcgrp = cgroup_parent(tcgrp)) {
5587                 tcgrp->nr_descendants--;
5588                 tcgrp->nr_dying_descendants++;
5589                 /*
5590                  * If the dying cgroup is frozen, decrease frozen descendants
5591                  * counters of ancestor cgroups.
5592                  */
5593                 if (test_bit(CGRP_FROZEN, &cgrp->flags))
5594                         tcgrp->freezer.nr_frozen_descendants--;
5595         }
5596         spin_unlock_irq(&css_set_lock);
5597 
5598         cgroup1_check_for_release(parent);
5599 
5600         cgroup_bpf_offline(cgrp);
5601 
5602         /* put the base reference */
5603         percpu_ref_kill(&cgrp->self.refcnt);
5604 
5605         return 0;
5606 };
5607 
5608 int cgroup_rmdir(struct kernfs_node *kn)
5609 {
5610         struct cgroup *cgrp;
5611         int ret = 0;
5612 
5613         cgrp = cgroup_kn_lock_live(kn, false);
5614         if (!cgrp)
5615                 return 0;
5616 
5617         ret = cgroup_destroy_locked(cgrp);
5618         if (!ret)
5619                 TRACE_CGROUP_PATH(rmdir, cgrp);
5620 
5621         cgroup_kn_unlock(kn);
5622         return ret;
5623 }
5624 
5625 static struct kernfs_syscall_ops cgroup_kf_syscall_ops = {
5626         .show_options           = cgroup_show_options,
5627         .mkdir                  = cgroup_mkdir,
5628         .rmdir                  = cgroup_rmdir,
5629         .show_path              = cgroup_show_path,
5630 };
5631 
5632 static void __init cgroup_init_subsys(struct cgroup_subsys *ss, bool early)
5633 {
5634         struct cgroup_subsys_state *css;
5635 
5636         pr_debug("Initializing cgroup subsys %s\n", ss->name);
5637 
5638         mutex_lock(&cgroup_mutex);
5639 
5640         idr_init(&ss->css_idr);
5641         INIT_LIST_HEAD(&ss->cfts);
5642 
5643         /* Create the root cgroup state for this subsystem */
5644         ss->root = &cgrp_dfl_root;
5645         css = ss->css_alloc(cgroup_css(&cgrp_dfl_root.cgrp, ss));
5646         /* We don't handle early failures gracefully */
5647         BUG_ON(IS_ERR(css));
5648         init_and_link_css(css, ss, &cgrp_dfl_root.cgrp);
5649 
5650         /*
5651          * Root csses are never destroyed and we can't initialize
5652          * percpu_ref during early init.  Disable refcnting.
5653          */
5654         css->flags |= CSS_NO_REF;
5655 
5656         if (early) {
5657                 /* allocation can't be done safely during early init */
5658                 css->id = 1;
5659         } else {
5660                 css->id = cgroup_idr_alloc(&ss->css_idr, css, 1, 2, GFP_KERNEL);
5661                 BUG_ON(css->id < 0);
5662         }
5663 
5664         /* Update the init_css_set to contain a subsys
5665          * pointer to this state - since the subsystem is
5666          * newly registered, all tasks and hence the
5667          * init_css_set is in the subsystem's root cgroup. */
5668         init_css_set.subsys[ss->id] = css;
5669 
5670         have_fork_callback |= (bool)ss->fork << ss->id;
5671         have_exit_callback |= (bool)ss->exit << ss->id;
5672         have_release_callback |= (bool)ss->release << ss->id;
5673         have_canfork_callback |= (bool)ss->can_fork << ss->id;
5674 
5675         /* At system boot, before all subsystems have been
5676          * registered, no tasks have been forked, so we don't
5677          * need to invoke fork callbacks here. */
5678         BUG_ON(!list_empty(&init_task.tasks));
5679 
5680         BUG_ON(online_css(css));
5681 
5682         mutex_unlock(&cgroup_mutex);
5683 }
5684 
5685 /**
5686  * cgroup_init_early - cgroup initialization at system boot
5687  *
5688  * Initialize cgroups at system boot, and initialize any
5689  * subsystems that request early init.
5690  */
5691 int __init cgroup_init_early(void)
5692 {
5693         static struct cgroup_fs_context __initdata ctx;
5694         struct cgroup_subsys *ss;
5695         int i;
5696 
5697         ctx.root = &cgrp_dfl_root;
5698         init_cgroup_root(&ctx);
5699         cgrp_dfl_root.cgrp.self.flags |= CSS_NO_REF;
5700 
5701         RCU_INIT_POINTER(init_task.cgroups, &init_css_set);
5702 
5703         for_each_subsys(ss, i) {
5704                 WARN(!ss->css_alloc || !ss->css_free || ss->name || ss->id,
5705                      "invalid cgroup_subsys %d:%s css_alloc=%p css_free=%p id:name=%d:%s\n",
5706                      i, cgroup_subsys_name[i], ss->css_alloc, ss->css_free,
5707                      ss->id, ss->name);
5708                 WARN(strlen(cgroup_subsys_name[i]) > MAX_CGROUP_TYPE_NAMELEN,
5709                      "cgroup_subsys_name %s too long\n", cgroup_subsys_name[i]);
5710 
5711                 ss->id = i;
5712                 ss->name = cgroup_subsys_name[i];
5713                 if (!ss->legacy_name)
5714                         ss->legacy_name = cgroup_subsys_name[i];
5715 
5716                 if (ss->early_init)
5717                         cgroup_init_subsys(ss, true);
5718         }
5719         return 0;
5720 }
5721 
5722 static u16 cgroup_disable_mask __initdata;
5723 
5724 /**
5725  * cgroup_init - cgroup initialization
5726  *
5727  * Register cgroup filesystem and /proc file, and initialize
5728  * any subsystems that didn't request early init.
5729  */
5730 int __init cgroup_init(void)
5731 {
5732         struct cgroup_subsys *ss;
5733         int ssid;
5734 
5735         BUILD_BUG_ON(CGROUP_SUBSYS_COUNT > 16);
5736         BUG_ON(cgroup_init_cftypes(NULL, cgroup_base_files));
5737         BUG_ON(cgroup_init_cftypes(NULL, cgroup1_base_files));
5738 
5739         cgroup_rstat_boot();
5740 
5741         /*
5742          * The latency of the synchronize_rcu() is too high for cgroups,
5743          * avoid it at the cost of forcing all readers into the slow path.
5744          */
5745         rcu_sync_enter_start(&cgroup_threadgroup_rwsem.rss);
5746 
5747         get_user_ns(init_cgroup_ns.user_ns);
5748 
5749         mutex_lock(&cgroup_mutex);
5750 
5751         /*
5752          * Add init_css_set to the hash table so that dfl_root can link to
5753          * it during init.
5754          */
5755         hash_add(css_set_table, &init_css_set.hlist,
5756                  css_set_hash(init_css_set.subsys));
5757 
5758         BUG_ON(cgroup_setup_root(&cgrp_dfl_root, 0));
5759 
5760         mutex_unlock(&cgroup_mutex);
5761 
5762         for_each_subsys(ss, ssid) {
5763                 if (ss->early_init) {
5764                         struct cgroup_subsys_state *css =
5765                                 init_css_set.subsys[ss->id];
5766 
5767                         css->id = cgroup_idr_alloc(&ss->css_idr, css, 1, 2,
5768                                                    GFP_KERNEL);
5769                         BUG_ON(css->id < 0);
5770                 } else {
5771                         cgroup_init_subsys(ss, false);
5772                 }
5773 
5774                 list_add_tail(&init_css_set.e_cset_node[ssid],
5775                               &cgrp_dfl_root.cgrp.e_csets[ssid]);
5776 
5777                 /*
5778                  * Setting dfl_root subsys_mask needs to consider the
5779                  * disabled flag and cftype registration needs kmalloc,
5780                  * both of which aren't available during early_init.
5781                  */
5782                 if (cgroup_disable_mask & (1 << ssid)) {
5783                         static_branch_disable(cgroup_subsys_enabled_key[ssid]);
5784                         printk(KERN_INFO "Disabling %s control group subsystem\n",
5785                                ss->name);
5786                         continue;
5787                 }
5788 
5789                 if (cgroup1_ssid_disabled(ssid))
5790                         printk(KERN_INFO "Disabling %s control group subsystem in v1 mounts\n",
5791                                ss->name);
5792 
5793                 cgrp_dfl_root.subsys_mask |= 1 << ss->id;
5794 
5795                 /* implicit controllers must be threaded too */
5796                 WARN_ON(ss->implicit_on_dfl && !ss->threaded);
5797 
5798                 if (ss->implicit_on_dfl)
5799                         cgrp_dfl_implicit_ss_mask |= 1 << ss->id;
5800                 else if (!ss->dfl_cftypes)
5801                         cgrp_dfl_inhibit_ss_mask |= 1 << ss->id;
5802 
5803                 if (ss->threaded)
5804                         cgrp_dfl_threaded_ss_mask |= 1 << ss->id;
5805 
5806                 if (ss->dfl_cftypes == ss->legacy_cftypes) {
5807                         WARN_ON(cgroup_add_cftypes(ss, ss->dfl_cftypes));
5808                 } else {
5809                         WARN_ON(cgroup_add_dfl_cftypes(ss, ss->dfl_cftypes));
5810                         WARN_ON(cgroup_add_legacy_cftypes(ss, ss->legacy_cftypes));
5811                 }
5812 
5813                 if (ss->bind)
5814                         ss->bind(init_css_set.subsys[ssid]);
5815 
5816                 mutex_lock(&cgroup_mutex);
5817                 css_populate_dir(init_css_set.subsys[ssid]);
5818                 mutex_unlock(&cgroup_mutex);
5819         }
5820 
5821         /* init_css_set.subsys[] has been updated, re-hash */
5822         hash_del(&init_css_set.hlist);
5823         hash_add(css_set_table, &init_css_set.hlist,
5824                  css_set_hash(init_css_set.subsys));
5825 
5826         WARN_ON(sysfs_create_mount_point(fs_kobj, "cgroup"));
5827         WARN_ON(register_filesystem(&cgroup_fs_type));
5828         WARN_ON(register_filesystem(&cgroup2_fs_type));
5829         WARN_ON(!proc_create_single("cgroups", 0, NULL, proc_cgroupstats_show));
5830 #ifdef CONFIG_CPUSETS
5831         WARN_ON(register_filesystem(&cpuset_fs_type));
5832 #endif
5833 
5834         return 0;
5835 }
5836 
5837 static int __init cgroup_wq_init(void)
5838 {
5839         /*
5840          * There isn't much point in executing destruction path in
5841          * parallel.  Good chunk is serialized with cgroup_mutex anyway.
5842          * Use 1 for @max_active.
5843          *
5844          * We would prefer to do this in cgroup_init() above, but that
5845          * is called before init_workqueues(): so leave this until after.
5846          */
5847         cgroup_destroy_wq = alloc_workqueue("cgroup_destroy", 0, 1);
5848         BUG_ON(!cgroup_destroy_wq);
5849         return 0;
5850 }
5851 core_initcall(cgroup_wq_init);
5852 
5853 void cgroup_path_from_kernfs_id(const union kernfs_node_id *id,
5854                                         char *buf, size_t buflen)
5855 {
5856         struct kernfs_node *kn;
5857 
5858         kn = kernfs_get_node_by_id(cgrp_dfl_root.kf_root, id);
5859         if (!kn)
5860                 return;
5861         kernfs_path(kn, buf, buflen);
5862         kernfs_put(kn);
5863 }
5864 
5865 /*
5866  * proc_cgroup_show()
5867  *  - Print task's cgroup paths into seq_file, one line for each hierarchy
5868  *  - Used for /proc/<pid>/cgroup.
5869  */
5870 int proc_cgroup_show(struct seq_file *m, struct pid_namespace *ns,
5871                      struct pid *pid, struct task_struct *tsk)
5872 {
5873         char *buf;
5874         int retval;
5875         struct cgroup_root *root;
5876 
5877         retval = -ENOMEM;
5878         buf = kmalloc(PATH_MAX, GFP_KERNEL);
5879         if (!buf)
5880                 goto out;
5881 
5882         mutex_lock(&cgroup_mutex);
5883         spin_lock_irq(&css_set_lock);
5884 
5885         for_each_root(root) {
5886                 struct cgroup_subsys *ss;
5887                 struct cgroup *cgrp;
5888                 int ssid, count = 0;
5889 
5890                 if (root == &cgrp_dfl_root && !cgrp_dfl_visible)
5891                         continue;
5892 
5893                 seq_printf(m, "%d:", root->hierarchy_id);
5894                 if (root != &cgrp_dfl_root)
5895                         for_each_subsys(ss, ssid)
5896                                 if (root->subsys_mask & (1 << ssid))
5897                                         seq_printf(m, "%s%s", count++ ? "," : "",
5898                                                    ss->legacy_name);
5899                 if (strlen(root->name))
5900                         seq_printf(m, "%sname=%s", count ? "," : "",
5901                                    root->name);
5902                 seq_putc(m, ':');
5903 
5904                 cgrp = task_cgroup_from_root(tsk, root);
5905 
5906                 /*
5907                  * On traditional hierarchies, all zombie tasks show up as
5908                  * belonging to the root cgroup.  On the default hierarchy,
5909                  * while a zombie doesn't show up in "cgroup.procs" and
5910                  * thus can't be migrated, its /proc/PID/cgroup keeps
5911                  * reporting the cgroup it belonged to before exiting.  If
5912                  * the cgroup is removed before the zombie is reaped,
5913                  * " (deleted)" is appended to the cgroup path.
5914                  */
5915                 if (cgroup_on_dfl(cgrp) || !(tsk->flags & PF_EXITING)) {
5916                         retval = cgroup_path_ns_locked(cgrp, buf, PATH_MAX,
5917                                                 current->nsproxy->cgroup_ns);
5918                         if (retval >= PATH_MAX)
5919                                 retval = -ENAMETOOLONG;
5920                         if (retval < 0)
5921                                 goto out_unlock;
5922 
5923                         seq_puts(m, buf);
5924                 } else {
5925                         seq_puts(m, "/");
5926                 }
5927 
5928                 if (cgroup_on_dfl(cgrp) && cgroup_is_dead(cgrp))
5929                         seq_puts(m, " (deleted)\n");
5930                 else
5931                         seq_putc(m, '\n');
5932         }
5933 
5934         retval = 0;
5935 out_unlock:
5936         spin_unlock_irq(&css_set_lock);
5937         mutex_unlock(&cgroup_mutex);
5938         kfree(buf);
5939 out:
5940         return retval;
5941 }
5942 
5943 /**
5944  * cgroup_fork - initialize cgroup related fields during copy_process()
5945  * @child: pointer to task_struct of forking parent process.
5946  *
5947  * A task is associated with the init_css_set until cgroup_post_fork()
5948  * attaches it to the parent's css_set.  Empty cg_list indicates that
5949  * @child isn't holding reference to its css_set.
5950  */
5951 void cgroup_fork(struct task_struct *child)
5952 {
5953         RCU_INIT_POINTER(child->cgroups, &init_css_set);
5954         INIT_LIST_HEAD(&child->cg_list);
5955 }
5956 
5957 /**
5958  * cgroup_can_fork - called on a new task before the process is exposed
5959  * @child: the task in question.
5960  *
5961  * This calls the subsystem can_fork() callbacks. If the can_fork() callback
5962  * returns an error, the fork aborts with that error code. This allows for
5963  * a cgroup subsystem to conditionally allow or deny new forks.
5964  */
5965 int cgroup_can_fork(struct task_struct *child)
5966 {
5967         struct cgroup_subsys *ss;
5968         int i, j, ret;
5969 
5970         do_each_subsys_mask(ss, i, have_canfork_callback) {
5971                 ret = ss->can_fork(child);
5972                 if (ret)
5973                         goto out_revert;
5974         } while_each_subsys_mask();
5975 
5976         return 0;
5977 
5978 out_revert:
5979         for_each_subsys(ss, j) {
5980                 if (j >= i)
5981                         break;
5982                 if (ss->cancel_fork)
5983                         ss->cancel_fork(child);
5984         }
5985 
5986         return ret;
5987 }
5988 
5989 /**
5990  * cgroup_cancel_fork - called if a fork failed after cgroup_can_fork()
5991  * @child: the task in question
5992  *
5993  * This calls the cancel_fork() callbacks if a fork failed *after*
5994  * cgroup_can_fork() succeded.
5995  */
5996 void cgroup_cancel_fork(struct task_struct *child)
5997 {
5998         struct cgroup_subsys *ss;
5999         int i;
6000 
6001         for_each_subsys(ss, i)
6002                 if (ss->cancel_fork)
6003                         ss->cancel_fork(child);
6004 }
6005 
6006 /**
6007  * cgroup_post_fork - called on a new task after adding it to the task list
6008  * @child: the task in question
6009  *
6010  * Adds the task to the list running through its css_set if necessary and
6011  * call the subsystem fork() callbacks.  Has to be after the task is
6012  * visible on the task list in case we race with the first call to
6013  * cgroup_task_iter_start() - to guarantee that the new task ends up on its
6014  * list.
6015  */
6016 void cgroup_post_fork(struct task_struct *child)
6017 {
6018         struct cgroup_subsys *ss;
6019         int i;
6020 
6021         /*
6022          * This may race against cgroup_enable_task_cg_lists().  As that
6023          * function sets use_task_css_set_links before grabbing
6024          * tasklist_lock and we just went through tasklist_lock to add
6025          * @child, it's guaranteed that either we see the set
6026          * use_task_css_set_links or cgroup_enable_task_cg_lists() sees
6027          * @child during its iteration.
6028          *
6029          * If we won the race, @child is associated with %current's
6030          * css_set.  Grabbing css_set_lock guarantees both that the
6031          * association is stable, and, on completion of the parent's
6032          * migration, @child is visible in the source of migration or
6033          * already in the destination cgroup.  This guarantee is necessary
6034          * when implementing operations which need to migrate all tasks of
6035          * a cgroup to another.
6036          *
6037          * Note that if we lose to cgroup_enable_task_cg_lists(), @child
6038          * will remain in init_css_set.  This is safe because all tasks are
6039          * in the init_css_set before cg_links is enabled and there's no
6040          * operation which transfers all tasks out of init_css_set.
6041          */
6042         if (use_task_css_set_links) {
6043                 struct css_set *cset;
6044 
6045                 spin_lock_irq(&css_set_lock);
6046                 cset = task_css_set(current);
6047                 if (list_empty(&child->cg_list)) {
6048                         get_css_set(cset);
6049                         cset->nr_tasks++;
6050                         css_set_move_task(child, NULL, cset, false);
6051                 }
6052 
6053                 /*
6054                  * If the cgroup has to be frozen, the new task has too.
6055                  * Let's set the JOBCTL_TRAP_FREEZE jobctl bit to get
6056                  * the task into the frozen state.
6057                  */
6058                 if (unlikely(cgroup_task_freeze(child))) {
6059                         spin_lock(&child->sighand->siglock);
6060                         WARN_ON_ONCE(child->frozen);
6061                         child->jobctl |= JOBCTL_TRAP_FREEZE;
6062                         spin_unlock(&child->sighand->siglock);
6063 
6064                         /*
6065                          * Calling cgroup_update_frozen() isn't required here,
6066                          * because it will be called anyway a bit later
6067                          * from do_freezer_trap(). So we avoid cgroup's
6068                          * transient switch from the frozen state and back.
6069                          */
6070                 }
6071 
6072                 spin_unlock_irq(&css_set_lock);
6073         }
6074 
6075         /*
6076          * Call ss->fork().  This must happen after @child is linked on
6077          * css_set; otherwise, @child might change state between ->fork()
6078          * and addition to css_set.
6079          */
6080         do_each_subsys_mask(ss, i, have_fork_callback) {
6081                 ss->fork(child);
6082         } while_each_subsys_mask();
6083 }
6084 
6085 /**
6086  * cgroup_exit - detach cgroup from exiting task
6087  * @tsk: pointer to task_struct of exiting process
6088  *
6089  * Description: Detach cgroup from @tsk and release it.
6090  *
6091  * Note that cgroups marked notify_on_release force every task in
6092  * them to take the global cgroup_mutex mutex when exiting.
6093  * This could impact scaling on very large systems.  Be reluctant to
6094  * use notify_on_release cgroups where very high task exit scaling
6095  * is required on large systems.
6096  *
6097  * We set the exiting tasks cgroup to the root cgroup (top_cgroup).  We
6098  * call cgroup_exit() while the task is still competent to handle
6099  * notify_on_release(), then leave the task attached to the root cgroup in
6100  * each hierarchy for the remainder of its exit.  No need to bother with
6101  * init_css_set refcnting.  init_css_set never goes away and we can't race
6102  * with migration path - PF_EXITING is visible to migration path.
6103  */
6104 void cgroup_exit(struct task_struct *tsk)
6105 {
6106         struct cgroup_subsys *ss;
6107         struct css_set *cset;
6108         int i;
6109 
6110         /*
6111          * Unlink from @tsk from its css_set.  As migration path can't race
6112          * with us, we can check css_set and cg_list without synchronization.
6113          */
6114         cset = task_css_set(tsk);
6115 
6116         if (!list_empty(&tsk->cg_list)) {
6117                 spin_lock_irq(&css_set_lock);
6118                 css_set_move_task(tsk, cset, NULL, false);
6119                 list_add_tail(&tsk->cg_list, &cset->dying_tasks);
6120                 cset->nr_tasks--;
6121 
6122                 WARN_ON_ONCE(cgroup_task_frozen(tsk));
6123                 if (unlikely(cgroup_task_freeze(tsk)))
6124                         cgroup_update_frozen(task_dfl_cgroup(tsk));
6125 
6126                 spin_unlock_irq(&css_set_lock);
6127         } else {
6128                 get_css_set(cset);
6129         }
6130 
6131         /* see cgroup_post_fork() for details */
6132         do_each_subsys_mask(ss, i, have_exit_callback) {
6133                 ss->exit(tsk);
6134         } while_each_subsys_mask();
6135 }
6136 
6137 void cgroup_release(struct task_struct *task)
6138 {
6139         struct cgroup_subsys *ss;
6140         int ssid;
6141 
6142         do_each_subsys_mask(ss, ssid, have_release_callback) {
6143                 ss->release(task);
6144         } while_each_subsys_mask();
6145 
6146         if (use_task_css_set_links) {
6147                 spin_lock_irq(&css_set_lock);
6148                 css_set_skip_task_iters(task_css_set(task), task);
6149                 list_del_init(&task->cg_list);
6150                 spin_unlock_irq(&css_set_lock);
6151         }
6152 }
6153 
6154 void cgroup_free(struct task_struct *task)
6155 {
6156         struct css_set *cset = task_css_set(task);
6157         put_css_set(cset);
6158 }
6159 
6160 static int __init cgroup_disable(char *str)
6161 {
6162         struct cgroup_subsys *ss;
6163         char *token;
6164         int i;
6165 
6166         while ((token = strsep(&str, ",")) != NULL) {
6167                 if (!*token)
6168                         continue;
6169 
6170                 for_each_subsys(ss, i) {
6171                         if (strcmp(token, ss->name) &&
6172                             strcmp(token, ss->legacy_name))
6173                                 continue;
6174                         cgroup_disable_mask |= 1 << i;
6175                 }
6176         }
6177         return 1;
6178 }
6179 __setup("cgroup_disable=", cgroup_disable);
6180 
6181 void __init __weak enable_debug_cgroup(void) { }
6182 
6183 static int __init enable_cgroup_debug(char *str)
6184 {
6185         cgroup_debug = true;
6186         enable_debug_cgroup();
6187         return 1;
6188 }
6189 __setup("cgroup_debug", enable_cgroup_debug);
6190 
6191 /**
6192  * css_tryget_online_from_dir - get corresponding css from a cgroup dentry
6193  * @dentry: directory dentry of interest
6194  * @ss: subsystem of interest
6195  *
6196  * If @dentry is a directory for a cgroup which has @ss enabled on it, try
6197  * to get the corresponding css and return it.  If such css doesn't exist
6198  * or can't be pinned, an ERR_PTR value is returned.
6199  */
6200 struct cgroup_subsys_state *css_tryget_online_from_dir(struct dentry *dentry,
6201                                                        struct cgroup_subsys *ss)
6202 {
6203         struct kernfs_node *kn = kernfs_node_from_dentry(dentry);
6204         struct file_system_type *s_type = dentry->d_sb->s_type;
6205         struct cgroup_subsys_state *css = NULL;
6206         struct cgroup *cgrp;
6207 
6208         /* is @dentry a cgroup dir? */
6209         if ((s_type != &cgroup_fs_type && s_type != &cgroup2_fs_type) ||
6210             !kn || kernfs_type(kn) != KERNFS_DIR)
6211                 return ERR_PTR(-EBADF);
6212 
6213         rcu_read_lock();
6214 
6215         /*
6216          * This path doesn't originate from kernfs and @kn could already
6217          * have been or be removed at any point.  @kn->priv is RCU
6218          * protected for this access.  See css_release_work_fn() for details.
6219          */
6220         cgrp = rcu_dereference(*(void __rcu __force **)&kn->priv);
6221         if (cgrp)
6222                 css = cgroup_css(cgrp, ss);
6223 
6224         if (!css || !css_tryget_online(css))
6225                 css = ERR_PTR(-ENOENT);
6226 
6227         rcu_read_unlock();
6228         return css;
6229 }
6230 
6231 /**
6232  * css_from_id - lookup css by id
6233  * @id: the cgroup id
6234  * @ss: cgroup subsys to be looked into
6235  *
6236  * Returns the css if there's valid one with @id, otherwise returns NULL.
6237  * Should be called under rcu_read_lock().
6238  */
6239 struct cgroup_subsys_state *css_from_id(int id, struct cgroup_subsys *ss)
6240 {
6241         WARN_ON_ONCE(!rcu_read_lock_held());
6242         return idr_find(&ss->css_idr, id);
6243 }
6244 
6245 /**
6246  * cgroup_get_from_path - lookup and get a cgroup from its default hierarchy path
6247  * @path: path on the default hierarchy
6248  *
6249  * Find the cgroup at @path on the default hierarchy, increment its
6250  * reference count and return it.  Returns pointer to the found cgroup on
6251  * success, ERR_PTR(-ENOENT) if @path doens't exist and ERR_PTR(-ENOTDIR)
6252  * if @path points to a non-directory.
6253  */
6254 struct cgroup *cgroup_get_from_path(const char *path)
6255 {
6256         struct kernfs_node *kn;
6257         struct cgroup *cgrp;
6258 
6259         mutex_lock(&cgroup_mutex);
6260 
6261         kn = kernfs_walk_and_get(cgrp_dfl_root.cgrp.kn, path);
6262         if (kn) {
6263                 if (kernfs_type(kn) == KERNFS_DIR) {
6264                         cgrp = kn->priv;
6265                         cgroup_get_live(cgrp);
6266                 } else {
6267                         cgrp = ERR_PTR(-ENOTDIR);
6268                 }
6269                 kernfs_put(kn);
6270         } else {
6271                 cgrp = ERR_PTR(-ENOENT);
6272         }
6273 
6274         mutex_unlock(&cgroup_mutex);
6275         return cgrp;
6276 }
6277 EXPORT_SYMBOL_GPL(cgroup_get_from_path);
6278 
6279 /**
6280  * cgroup_get_from_fd - get a cgroup pointer from a fd
6281  * @fd: fd obtained by open(cgroup2_dir)
6282  *
6283  * Find the cgroup from a fd which should be obtained
6284  * by opening a cgroup directory.  Returns a pointer to the
6285  * cgroup on success. ERR_PTR is returned if the cgroup
6286  * cannot be found.
6287  */
6288 struct cgroup *cgroup_get_from_fd(int fd)
6289 {
6290         struct cgroup_subsys_state *css;
6291         struct cgroup *cgrp;
6292         struct file *f;
6293 
6294         f = fget_raw(fd);
6295         if (!f)
6296                 return ERR_PTR(-EBADF);
6297 
6298         css = css_tryget_online_from_dir(f->f_path.dentry, NULL);
6299         fput(f);
6300         if (IS_ERR(css))
6301                 return ERR_CAST(css);
6302 
6303         cgrp = css->cgroup;
6304         if (!cgroup_on_dfl(cgrp)) {
6305                 cgroup_put(cgrp);
6306                 return ERR_PTR(-EBADF);
6307         }
6308 
6309         return cgrp;
6310 }
6311 EXPORT_SYMBOL_GPL(cgroup_get_from_fd);
6312 
6313 static u64 power_of_ten(int power)
6314 {
6315         u64 v = 1;
6316         while (power--)
6317                 v *= 10;
6318         return v;
6319 }
6320 
6321 /**
6322  * cgroup_parse_float - parse a floating number
6323  * @input: input string
6324  * @dec_shift: number of decimal digits to shift
6325  * @v: output
6326  *
6327  * Parse a decimal floating point number in @input and store the result in
6328  * @v with decimal point right shifted @dec_shift times.  For example, if
6329  * @input is "12.3456" and @dec_shift is 3, *@v will be set to 12345.
6330  * Returns 0 on success, -errno otherwise.
6331  *
6332  * There's nothing cgroup specific about this function except that it's
6333  * currently the only user.
6334  */
6335 int cgroup_parse_float(const char *input, unsigned dec_shift, s64 *v)
6336 {
6337         s64 whole, frac = 0;
6338         int fstart = 0, fend = 0, flen;
6339 
6340         if (!sscanf(input, "%lld.%n%lld%n", &whole, &fstart, &frac, &fend))
6341                 return -EINVAL;
6342         if (frac < 0)
6343                 return -EINVAL;
6344 
6345         flen = fend > fstart ? fend - fstart : 0;
6346         if (flen < dec_shift)
6347                 frac *= power_of_ten(dec_shift - flen);
6348         else
6349                 frac = DIV_ROUND_CLOSEST_ULL(frac, power_of_ten(flen - dec_shift));
6350 
6351         *v = whole * power_of_ten(dec_shift) + frac;
6352         return 0;
6353 }
6354 
6355 /*
6356  * sock->sk_cgrp_data handling.  For more info, see sock_cgroup_data
6357  * definition in cgroup-defs.h.
6358  */
6359 #ifdef CONFIG_SOCK_CGROUP_DATA
6360 
6361 #if defined(CONFIG_CGROUP_NET_PRIO) || defined(CONFIG_CGROUP_NET_CLASSID)
6362 
6363 DEFINE_SPINLOCK(cgroup_sk_update_lock);
6364 static bool cgroup_sk_alloc_disabled __read_mostly;
6365 
6366 void cgroup_sk_alloc_disable(void)
6367 {
6368         if (cgroup_sk_alloc_disabled)
6369                 return;
6370         pr_info("cgroup: disabling cgroup2 socket matching due to net_prio or net_cls activation\n");
6371         cgroup_sk_alloc_disabled = true;
6372 }
6373 
6374 #else
6375 
6376 #define cgroup_sk_alloc_disabled        false
6377 
6378 #endif
6379 
6380 void cgroup_sk_alloc(struct sock_cgroup_data *skcd)
6381 {
6382         if (cgroup_sk_alloc_disabled)
6383                 return;
6384 
6385         /* Socket clone path */
6386         if (skcd->val) {
6387                 /*
6388                  * We might be cloning a socket which is left in an empty
6389                  * cgroup and the cgroup might have already been rmdir'd.
6390                  * Don't use cgroup_get_live().
6391                  */
6392                 cgroup_get(sock_cgroup_ptr(skcd));
6393                 cgroup_bpf_get(sock_cgroup_ptr(skcd));
6394                 return;
6395         }
6396 
6397         /* Don't associate the sock with unrelated interrupted task's cgroup. */
6398         if (in_interrupt())
6399                 return;
6400 
6401         rcu_read_lock();
6402 
6403         while (true) {
6404                 struct css_set *cset;
6405 
6406                 cset = task_css_set(current);
6407                 if (likely(cgroup_tryget(cset->dfl_cgrp))) {
6408                         skcd->val = (unsigned long)cset->dfl_cgrp;
6409                         cgroup_bpf_get(cset->dfl_cgrp);
6410                         break;
6411                 }
6412                 cpu_relax();
6413         }
6414 
6415         rcu_read_unlock();
6416 }
6417 
6418 void cgroup_sk_free(struct sock_cgroup_data *skcd)
6419 {
6420         struct cgroup *cgrp = sock_cgroup_ptr(skcd);
6421 
6422         cgroup_bpf_put(cgrp);
6423         cgroup_put(cgrp);
6424 }
6425 
6426 #endif  /* CONFIG_SOCK_CGROUP_DATA */
6427 
6428 #ifdef CONFIG_CGROUP_BPF
6429 int cgroup_bpf_attach(struct cgroup *cgrp, struct bpf_prog *prog,
6430                       enum bpf_attach_type type, u32 flags)
6431 {
6432         int ret;
6433 
6434         mutex_lock(&cgroup_mutex);
6435         ret = __cgroup_bpf_attach(cgrp, prog, type, flags);
6436         mutex_unlock(&cgroup_mutex);
6437         return ret;
6438 }
6439 int cgroup_bpf_detach(struct cgroup *cgrp, struct bpf_prog *prog,
6440                       enum bpf_attach_type type, u32 flags)
6441 {
6442         int ret;
6443 
6444         mutex_lock(&cgroup_mutex);
6445         ret = __cgroup_bpf_detach(cgrp, prog, type);
6446         mutex_unlock(&cgroup_mutex);
6447         return ret;
6448 }
6449 int cgroup_bpf_query(struct cgroup *cgrp, const union bpf_attr *attr,
6450                      union bpf_attr __user *uattr)
6451 {
6452         int ret;
6453 
6454         mutex_lock(&cgroup_mutex);
6455         ret = __cgroup_bpf_query(cgrp, attr, uattr);
6456         mutex_unlock(&cgroup_mutex);
6457         return ret;
6458 }
6459 #endif /* CONFIG_CGROUP_BPF */
6460 
6461 #ifdef CONFIG_SYSFS
6462 static ssize_t show_delegatable_files(struct cftype *files, char *buf,
6463                                       ssize_t size, const char *prefix)
6464 {
6465         struct cftype *cft;
6466         ssize_t ret = 0;
6467 
6468         for (cft = files; cft && cft->name[0] != '\0'; cft++) {
6469                 if (!(cft->flags & CFTYPE_NS_DELEGATABLE))
6470                         continue;
6471 
6472                 if (prefix)
6473                         ret += snprintf(buf + ret, size - ret, "%s.", prefix);
6474 
6475                 ret += snprintf(buf + ret, size - ret, "%s\n", cft->name);
6476 
6477                 if (WARN_ON(ret >= size))
6478                         break;
6479         }
6480 
6481         return ret;
6482 }
6483 
6484 static ssize_t delegate_show(struct kobject *kobj, struct kobj_attribute *attr,
6485                               char *buf)
6486 {
6487         struct cgroup_subsys *ss;
6488         int ssid;
6489         ssize_t ret = 0;
6490 
6491         ret = show_delegatable_files(cgroup_base_files, buf, PAGE_SIZE - ret,
6492                                      NULL);
6493 
6494         for_each_subsys(ss, ssid)
6495                 ret += show_delegatable_files(ss->dfl_cftypes, buf + ret,
6496                                               PAGE_SIZE - ret,
6497                                               cgroup_subsys_name[ssid]);
6498 
6499         return ret;
6500 }
6501 static struct kobj_attribute cgroup_delegate_attr = __ATTR_RO(delegate);
6502 
6503 static ssize_t features_show(struct kobject *kobj, struct kobj_attribute *attr,
6504                              char *buf)
6505 {
6506         return snprintf(buf, PAGE_SIZE, "nsdelegate\nmemory_localevents\n");
6507 }
6508 static struct kobj_attribute cgroup_features_attr = __ATTR_RO(features);
6509 
6510 static struct attribute *cgroup_sysfs_attrs[] = {
6511         &cgroup_delegate_attr.attr,
6512         &cgroup_features_attr.attr,
6513         NULL,
6514 };
6515 
6516 static const struct attribute_group cgroup_sysfs_attr_group = {
6517         .attrs = cgroup_sysfs_attrs,
6518         .name = "cgroup",
6519 };
6520 
6521 static int __init cgroup_sysfs_init(void)
6522 {
6523         return sysfs_create_group(kernel_kobj, &cgroup_sysfs_attr_group);
6524 }
6525 subsys_initcall(cgroup_sysfs_init);
6526 
6527 #endif /* CONFIG_SYSFS */
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root/kernel/cgroup/cgroup.c

DEFINITIONS
