fs/super.c

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This source file includes following definitions.
super_cache_scan
super_cache_count
destroy_super_work
destroy_super_rcu
destroy_unused_super
alloc_super
__put_super
put_super
deactivate_locked_super
deactivate_super
grab_super
trylock_super
generic_shutdown_super
mount_capable
sget_fc
sget
drop_super
drop_super_exclusive
__iterate_supers
iterate_supers
iterate_supers_type
__get_super
get_super
__get_super_thawed
get_super_thawed
get_super_exclusive_thawed
get_active_super
user_get_super
reconfigure_super
do_emergency_remount_callback
do_emergency_remount
emergency_remount
do_thaw_all_callback
do_thaw_all
emergency_thaw_all
get_anon_bdev
free_anon_bdev
set_anon_super
kill_anon_super
kill_litter_super
set_anon_super_fc
test_keyed_super
test_single_super
vfs_get_super
get_tree_nodev
get_tree_single
get_tree_single_reconf
get_tree_keyed
set_bdev_super
set_bdev_super_fc
test_bdev_super_fc
get_tree_bdev
test_bdev_super
mount_bdev
kill_block_super
mount_nodev
reconfigure_single
compare_single
mount_single
vfs_get_tree
super_setup_bdi_name
super_setup_bdi
__sb_end_write
__sb_start_write
sb_wait_write
lockdep_sb_freeze_release
lockdep_sb_freeze_acquire
sb_freeze_unlock
freeze_super
thaw_super_locked
thaw_super
   1 // SPDX-License-Identifier: GPL-2.0
   2 /*
   3  *  linux/fs/super.c
   4  *
   5  *  Copyright (C) 1991, 1992  Linus Torvalds
   6  *
   7  *  super.c contains code to handle: - mount structures
   8  *                                   - super-block tables
   9  *                                   - filesystem drivers list
  10  *                                   - mount system call
  11  *                                   - umount system call
  12  *                                   - ustat system call
  13  *
  14  * GK 2/5/95  -  Changed to support mounting the root fs via NFS
  15  *
  16  *  Added kerneld support: Jacques Gelinas and Bjorn Ekwall
  17  *  Added change_root: Werner Almesberger & Hans Lermen, Feb '96
  18  *  Added options to /proc/mounts:
  19  *    Torbjörn Lindh (torbjorn.lindh@gopta.se), April 14, 1996.
  20  *  Added devfs support: Richard Gooch <rgooch@atnf.csiro.au>, 13-JAN-1998
  21  *  Heavily rewritten for 'one fs - one tree' dcache architecture. AV, Mar 2000
  22  */
  23 
  24 #include <linux/export.h>
  25 #include <linux/slab.h>
  26 #include <linux/blkdev.h>
  27 #include <linux/mount.h>
  28 #include <linux/security.h>
  29 #include <linux/writeback.h>            /* for the emergency remount stuff */
  30 #include <linux/idr.h>
  31 #include <linux/mutex.h>
  32 #include <linux/backing-dev.h>
  33 #include <linux/rculist_bl.h>
  34 #include <linux/cleancache.h>
  35 #include <linux/fscrypt.h>
  36 #include <linux/fsnotify.h>
  37 #include <linux/lockdep.h>
  38 #include <linux/user_namespace.h>
  39 #include <linux/fs_context.h>
  40 #include <uapi/linux/mount.h>
  41 #include "internal.h"
  42 
  43 static int thaw_super_locked(struct super_block *sb);
  44 
  45 static LIST_HEAD(super_blocks);
  46 static DEFINE_SPINLOCK(sb_lock);
  47 
  48 static char *sb_writers_name[SB_FREEZE_LEVELS] = {
  49         "sb_writers",
  50         "sb_pagefaults",
  51         "sb_internal",
  52 };
  53 
  54 /*
  55  * One thing we have to be careful of with a per-sb shrinker is that we don't
  56  * drop the last active reference to the superblock from within the shrinker.
  57  * If that happens we could trigger unregistering the shrinker from within the
  58  * shrinker path and that leads to deadlock on the shrinker_rwsem. Hence we
  59  * take a passive reference to the superblock to avoid this from occurring.
  60  */
  61 static unsigned long super_cache_scan(struct shrinker *shrink,
  62                                       struct shrink_control *sc)
  63 {
  64         struct super_block *sb;
  65         long    fs_objects = 0;
  66         long    total_objects;
  67         long    freed = 0;
  68         long    dentries;
  69         long    inodes;
  70 
  71         sb = container_of(shrink, struct super_block, s_shrink);
  72 
  73         /*
  74          * Deadlock avoidance.  We may hold various FS locks, and we don't want
  75          * to recurse into the FS that called us in clear_inode() and friends..
  76          */
  77         if (!(sc->gfp_mask & __GFP_FS))
  78                 return SHRINK_STOP;
  79 
  80         if (!trylock_super(sb))
  81                 return SHRINK_STOP;
  82 
  83         if (sb->s_op->nr_cached_objects)
  84                 fs_objects = sb->s_op->nr_cached_objects(sb, sc);
  85 
  86         inodes = list_lru_shrink_count(&sb->s_inode_lru, sc);
  87         dentries = list_lru_shrink_count(&sb->s_dentry_lru, sc);
  88         total_objects = dentries + inodes + fs_objects + 1;
  89         if (!total_objects)
  90                 total_objects = 1;
  91 
  92         /* proportion the scan between the caches */
  93         dentries = mult_frac(sc->nr_to_scan, dentries, total_objects);
  94         inodes = mult_frac(sc->nr_to_scan, inodes, total_objects);
  95         fs_objects = mult_frac(sc->nr_to_scan, fs_objects, total_objects);
  96 
  97         /*
  98          * prune the dcache first as the icache is pinned by it, then
  99          * prune the icache, followed by the filesystem specific caches
 100          *
 101          * Ensure that we always scan at least one object - memcg kmem
 102          * accounting uses this to fully empty the caches.
 103          */
 104         sc->nr_to_scan = dentries + 1;
 105         freed = prune_dcache_sb(sb, sc);
 106         sc->nr_to_scan = inodes + 1;
 107         freed += prune_icache_sb(sb, sc);
 108 
 109         if (fs_objects) {
 110                 sc->nr_to_scan = fs_objects + 1;
 111                 freed += sb->s_op->free_cached_objects(sb, sc);
 112         }
 113 
 114         up_read(&sb->s_umount);
 115         return freed;
 116 }
 117 
 118 static unsigned long super_cache_count(struct shrinker *shrink,
 119                                        struct shrink_control *sc)
 120 {
 121         struct super_block *sb;
 122         long    total_objects = 0;
 123 
 124         sb = container_of(shrink, struct super_block, s_shrink);
 125 
 126         /*
 127          * We don't call trylock_super() here as it is a scalability bottleneck,
 128          * so we're exposed to partial setup state. The shrinker rwsem does not
 129          * protect filesystem operations backing list_lru_shrink_count() or
 130          * s_op->nr_cached_objects(). Counts can change between
 131          * super_cache_count and super_cache_scan, so we really don't need locks
 132          * here.
 133          *
 134          * However, if we are currently mounting the superblock, the underlying
 135          * filesystem might be in a state of partial construction and hence it
 136          * is dangerous to access it.  trylock_super() uses a SB_BORN check to
 137          * avoid this situation, so do the same here. The memory barrier is
 138          * matched with the one in mount_fs() as we don't hold locks here.
 139          */
 140         if (!(sb->s_flags & SB_BORN))
 141                 return 0;
 142         smp_rmb();
 143 
 144         if (sb->s_op && sb->s_op->nr_cached_objects)
 145                 total_objects = sb->s_op->nr_cached_objects(sb, sc);
 146 
 147         total_objects += list_lru_shrink_count(&sb->s_dentry_lru, sc);
 148         total_objects += list_lru_shrink_count(&sb->s_inode_lru, sc);
 149 
 150         if (!total_objects)
 151                 return SHRINK_EMPTY;
 152 
 153         total_objects = vfs_pressure_ratio(total_objects);
 154         return total_objects;
 155 }
 156 
 157 static void destroy_super_work(struct work_struct *work)
 158 {
 159         struct super_block *s = container_of(work, struct super_block,
 160                                                         destroy_work);
 161         int i;
 162 
 163         for (i = 0; i < SB_FREEZE_LEVELS; i++)
 164                 percpu_free_rwsem(&s->s_writers.rw_sem[i]);
 165         kfree(s);
 166 }
 167 
 168 static void destroy_super_rcu(struct rcu_head *head)
 169 {
 170         struct super_block *s = container_of(head, struct super_block, rcu);
 171         INIT_WORK(&s->destroy_work, destroy_super_work);
 172         schedule_work(&s->destroy_work);
 173 }
 174 
 175 /* Free a superblock that has never been seen by anyone */
 176 static void destroy_unused_super(struct super_block *s)
 177 {
 178         if (!s)
 179                 return;
 180         up_write(&s->s_umount);
 181         list_lru_destroy(&s->s_dentry_lru);
 182         list_lru_destroy(&s->s_inode_lru);
 183         security_sb_free(s);
 184         put_user_ns(s->s_user_ns);
 185         kfree(s->s_subtype);
 186         free_prealloced_shrinker(&s->s_shrink);
 187         /* no delays needed */
 188         destroy_super_work(&s->destroy_work);
 189 }
 190 
 191 /**
 192  *      alloc_super     -       create new superblock
 193  *      @type:  filesystem type superblock should belong to
 194  *      @flags: the mount flags
 195  *      @user_ns: User namespace for the super_block
 196  *
 197  *      Allocates and initializes a new &struct super_block.  alloc_super()
 198  *      returns a pointer new superblock or %NULL if allocation had failed.
 199  */
 200 static struct super_block *alloc_super(struct file_system_type *type, int flags,
 201                                        struct user_namespace *user_ns)
 202 {
 203         struct super_block *s = kzalloc(sizeof(struct super_block),  GFP_USER);
 204         static const struct super_operations default_op;
 205         int i;
 206 
 207         if (!s)
 208                 return NULL;
 209 
 210         INIT_LIST_HEAD(&s->s_mounts);
 211         s->s_user_ns = get_user_ns(user_ns);
 212         init_rwsem(&s->s_umount);
 213         lockdep_set_class(&s->s_umount, &type->s_umount_key);
 214         /*
 215          * sget() can have s_umount recursion.
 216          *
 217          * When it cannot find a suitable sb, it allocates a new
 218          * one (this one), and tries again to find a suitable old
 219          * one.
 220          *
 221          * In case that succeeds, it will acquire the s_umount
 222          * lock of the old one. Since these are clearly distrinct
 223          * locks, and this object isn't exposed yet, there's no
 224          * risk of deadlocks.
 225          *
 226          * Annotate this by putting this lock in a different
 227          * subclass.
 228          */
 229         down_write_nested(&s->s_umount, SINGLE_DEPTH_NESTING);
 230 
 231         if (security_sb_alloc(s))
 232                 goto fail;
 233 
 234         for (i = 0; i < SB_FREEZE_LEVELS; i++) {
 235                 if (__percpu_init_rwsem(&s->s_writers.rw_sem[i],
 236                                         sb_writers_name[i],
 237                                         &type->s_writers_key[i]))
 238                         goto fail;
 239         }
 240         init_waitqueue_head(&s->s_writers.wait_unfrozen);
 241         s->s_bdi = &noop_backing_dev_info;
 242         s->s_flags = flags;
 243         if (s->s_user_ns != &init_user_ns)
 244                 s->s_iflags |= SB_I_NODEV;
 245         INIT_HLIST_NODE(&s->s_instances);
 246         INIT_HLIST_BL_HEAD(&s->s_roots);
 247         mutex_init(&s->s_sync_lock);
 248         INIT_LIST_HEAD(&s->s_inodes);
 249         spin_lock_init(&s->s_inode_list_lock);
 250         INIT_LIST_HEAD(&s->s_inodes_wb);
 251         spin_lock_init(&s->s_inode_wblist_lock);
 252 
 253         s->s_count = 1;
 254         atomic_set(&s->s_active, 1);
 255         mutex_init(&s->s_vfs_rename_mutex);
 256         lockdep_set_class(&s->s_vfs_rename_mutex, &type->s_vfs_rename_key);
 257         init_rwsem(&s->s_dquot.dqio_sem);
 258         s->s_maxbytes = MAX_NON_LFS;
 259         s->s_op = &default_op;
 260         s->s_time_gran = 1000000000;
 261         s->s_time_min = TIME64_MIN;
 262         s->s_time_max = TIME64_MAX;
 263         s->cleancache_poolid = CLEANCACHE_NO_POOL;
 264 
 265         s->s_shrink.seeks = DEFAULT_SEEKS;
 266         s->s_shrink.scan_objects = super_cache_scan;
 267         s->s_shrink.count_objects = super_cache_count;
 268         s->s_shrink.batch = 1024;
 269         s->s_shrink.flags = SHRINKER_NUMA_AWARE | SHRINKER_MEMCG_AWARE;
 270         if (prealloc_shrinker(&s->s_shrink))
 271                 goto fail;
 272         if (list_lru_init_memcg(&s->s_dentry_lru, &s->s_shrink))
 273                 goto fail;
 274         if (list_lru_init_memcg(&s->s_inode_lru, &s->s_shrink))
 275                 goto fail;
 276         return s;
 277 
 278 fail:
 279         destroy_unused_super(s);
 280         return NULL;
 281 }
 282 
 283 /* Superblock refcounting  */
 284 
 285 /*
 286  * Drop a superblock's refcount.  The caller must hold sb_lock.
 287  */
 288 static void __put_super(struct super_block *s)
 289 {
 290         if (!--s->s_count) {
 291                 list_del_init(&s->s_list);
 292                 WARN_ON(s->s_dentry_lru.node);
 293                 WARN_ON(s->s_inode_lru.node);
 294                 WARN_ON(!list_empty(&s->s_mounts));
 295                 security_sb_free(s);
 296                 fscrypt_sb_free(s);
 297                 put_user_ns(s->s_user_ns);
 298                 kfree(s->s_subtype);
 299                 call_rcu(&s->rcu, destroy_super_rcu);
 300         }
 301 }
 302 
 303 /**
 304  *      put_super       -       drop a temporary reference to superblock
 305  *      @sb: superblock in question
 306  *
 307  *      Drops a temporary reference, frees superblock if there's no
 308  *      references left.
 309  */
 310 static void put_super(struct super_block *sb)
 311 {
 312         spin_lock(&sb_lock);
 313         __put_super(sb);
 314         spin_unlock(&sb_lock);
 315 }
 316 
 317 
 318 /**
 319  *      deactivate_locked_super -       drop an active reference to superblock
 320  *      @s: superblock to deactivate
 321  *
 322  *      Drops an active reference to superblock, converting it into a temporary
 323  *      one if there is no other active references left.  In that case we
 324  *      tell fs driver to shut it down and drop the temporary reference we
 325  *      had just acquired.
 326  *
 327  *      Caller holds exclusive lock on superblock; that lock is released.
 328  */
 329 void deactivate_locked_super(struct super_block *s)
 330 {
 331         struct file_system_type *fs = s->s_type;
 332         if (atomic_dec_and_test(&s->s_active)) {
 333                 cleancache_invalidate_fs(s);
 334                 unregister_shrinker(&s->s_shrink);
 335                 fs->kill_sb(s);
 336 
 337                 /*
 338                  * Since list_lru_destroy() may sleep, we cannot call it from
 339                  * put_super(), where we hold the sb_lock. Therefore we destroy
 340                  * the lru lists right now.
 341                  */
 342                 list_lru_destroy(&s->s_dentry_lru);
 343                 list_lru_destroy(&s->s_inode_lru);
 344 
 345                 put_filesystem(fs);
 346                 put_super(s);
 347         } else {
 348                 up_write(&s->s_umount);
 349         }
 350 }
 351 
 352 EXPORT_SYMBOL(deactivate_locked_super);
 353 
 354 /**
 355  *      deactivate_super        -       drop an active reference to superblock
 356  *      @s: superblock to deactivate
 357  *
 358  *      Variant of deactivate_locked_super(), except that superblock is *not*
 359  *      locked by caller.  If we are going to drop the final active reference,
 360  *      lock will be acquired prior to that.
 361  */
 362 void deactivate_super(struct super_block *s)
 363 {
 364         if (!atomic_add_unless(&s->s_active, -1, 1)) {
 365                 down_write(&s->s_umount);
 366                 deactivate_locked_super(s);
 367         }
 368 }
 369 
 370 EXPORT_SYMBOL(deactivate_super);
 371 
 372 /**
 373  *      grab_super - acquire an active reference
 374  *      @s: reference we are trying to make active
 375  *
 376  *      Tries to acquire an active reference.  grab_super() is used when we
 377  *      had just found a superblock in super_blocks or fs_type->fs_supers
 378  *      and want to turn it into a full-blown active reference.  grab_super()
 379  *      is called with sb_lock held and drops it.  Returns 1 in case of
 380  *      success, 0 if we had failed (superblock contents was already dead or
 381  *      dying when grab_super() had been called).  Note that this is only
 382  *      called for superblocks not in rundown mode (== ones still on ->fs_supers
 383  *      of their type), so increment of ->s_count is OK here.
 384  */
 385 static int grab_super(struct super_block *s) __releases(sb_lock)
 386 {
 387         s->s_count++;
 388         spin_unlock(&sb_lock);
 389         down_write(&s->s_umount);
 390         if ((s->s_flags & SB_BORN) && atomic_inc_not_zero(&s->s_active)) {
 391                 put_super(s);
 392                 return 1;
 393         }
 394         up_write(&s->s_umount);
 395         put_super(s);
 396         return 0;
 397 }
 398 
 399 /*
 400  *      trylock_super - try to grab ->s_umount shared
 401  *      @sb: reference we are trying to grab
 402  *
 403  *      Try to prevent fs shutdown.  This is used in places where we
 404  *      cannot take an active reference but we need to ensure that the
 405  *      filesystem is not shut down while we are working on it. It returns
 406  *      false if we cannot acquire s_umount or if we lose the race and
 407  *      filesystem already got into shutdown, and returns true with the s_umount
 408  *      lock held in read mode in case of success. On successful return,
 409  *      the caller must drop the s_umount lock when done.
 410  *
 411  *      Note that unlike get_super() et.al. this one does *not* bump ->s_count.
 412  *      The reason why it's safe is that we are OK with doing trylock instead
 413  *      of down_read().  There's a couple of places that are OK with that, but
 414  *      it's very much not a general-purpose interface.
 415  */
 416 bool trylock_super(struct super_block *sb)
 417 {
 418         if (down_read_trylock(&sb->s_umount)) {
 419                 if (!hlist_unhashed(&sb->s_instances) &&
 420                     sb->s_root && (sb->s_flags & SB_BORN))
 421                         return true;
 422                 up_read(&sb->s_umount);
 423         }
 424 
 425         return false;
 426 }
 427 
 428 /**
 429  *      generic_shutdown_super  -       common helper for ->kill_sb()
 430  *      @sb: superblock to kill
 431  *
 432  *      generic_shutdown_super() does all fs-independent work on superblock
 433  *      shutdown.  Typical ->kill_sb() should pick all fs-specific objects
 434  *      that need destruction out of superblock, call generic_shutdown_super()
 435  *      and release aforementioned objects.  Note: dentries and inodes _are_
 436  *      taken care of and do not need specific handling.
 437  *
 438  *      Upon calling this function, the filesystem may no longer alter or
 439  *      rearrange the set of dentries belonging to this super_block, nor may it
 440  *      change the attachments of dentries to inodes.
 441  */
 442 void generic_shutdown_super(struct super_block *sb)
 443 {
 444         const struct super_operations *sop = sb->s_op;
 445 
 446         if (sb->s_root) {
 447                 shrink_dcache_for_umount(sb);
 448                 sync_filesystem(sb);
 449                 sb->s_flags &= ~SB_ACTIVE;
 450 
 451                 cgroup_writeback_umount();
 452 
 453                 /* evict all inodes with zero refcount */
 454                 evict_inodes(sb);
 455                 /* only nonzero refcount inodes can have marks */
 456                 fsnotify_sb_delete(sb);
 457 
 458                 if (sb->s_dio_done_wq) {
 459                         destroy_workqueue(sb->s_dio_done_wq);
 460                         sb->s_dio_done_wq = NULL;
 461                 }
 462 
 463                 if (sop->put_super)
 464                         sop->put_super(sb);
 465 
 466                 if (!list_empty(&sb->s_inodes)) {
 467                         printk("VFS: Busy inodes after unmount of %s. "
 468                            "Self-destruct in 5 seconds.  Have a nice day...\n",
 469                            sb->s_id);
 470                 }
 471         }
 472         spin_lock(&sb_lock);
 473         /* should be initialized for __put_super_and_need_restart() */
 474         hlist_del_init(&sb->s_instances);
 475         spin_unlock(&sb_lock);
 476         up_write(&sb->s_umount);
 477         if (sb->s_bdi != &noop_backing_dev_info) {
 478                 bdi_put(sb->s_bdi);
 479                 sb->s_bdi = &noop_backing_dev_info;
 480         }
 481 }
 482 
 483 EXPORT_SYMBOL(generic_shutdown_super);
 484 
 485 bool mount_capable(struct fs_context *fc)
 486 {
 487         if (!(fc->fs_type->fs_flags & FS_USERNS_MOUNT))
 488                 return capable(CAP_SYS_ADMIN);
 489         else
 490                 return ns_capable(fc->user_ns, CAP_SYS_ADMIN);
 491 }
 492 
 493 /**
 494  * sget_fc - Find or create a superblock
 495  * @fc: Filesystem context.
 496  * @test: Comparison callback
 497  * @set: Setup callback
 498  *
 499  * Find or create a superblock using the parameters stored in the filesystem
 500  * context and the two callback functions.
 501  *
 502  * If an extant superblock is matched, then that will be returned with an
 503  * elevated reference count that the caller must transfer or discard.
 504  *
 505  * If no match is made, a new superblock will be allocated and basic
 506  * initialisation will be performed (s_type, s_fs_info and s_id will be set and
 507  * the set() callback will be invoked), the superblock will be published and it
 508  * will be returned in a partially constructed state with SB_BORN and SB_ACTIVE
 509  * as yet unset.
 510  */
 511 struct super_block *sget_fc(struct fs_context *fc,
 512                             int (*test)(struct super_block *, struct fs_context *),
 513                             int (*set)(struct super_block *, struct fs_context *))
 514 {
 515         struct super_block *s = NULL;
 516         struct super_block *old;
 517         struct user_namespace *user_ns = fc->global ? &init_user_ns : fc->user_ns;
 518         int err;
 519 
 520 retry:
 521         spin_lock(&sb_lock);
 522         if (test) {
 523                 hlist_for_each_entry(old, &fc->fs_type->fs_supers, s_instances) {
 524                         if (test(old, fc))
 525                                 goto share_extant_sb;
 526                 }
 527         }
 528         if (!s) {
 529                 spin_unlock(&sb_lock);
 530                 s = alloc_super(fc->fs_type, fc->sb_flags, user_ns);
 531                 if (!s)
 532                         return ERR_PTR(-ENOMEM);
 533                 goto retry;
 534         }
 535 
 536         s->s_fs_info = fc->s_fs_info;
 537         err = set(s, fc);
 538         if (err) {
 539                 s->s_fs_info = NULL;
 540                 spin_unlock(&sb_lock);
 541                 destroy_unused_super(s);
 542                 return ERR_PTR(err);
 543         }
 544         fc->s_fs_info = NULL;
 545         s->s_type = fc->fs_type;
 546         s->s_iflags |= fc->s_iflags;
 547         strlcpy(s->s_id, s->s_type->name, sizeof(s->s_id));
 548         list_add_tail(&s->s_list, &super_blocks);
 549         hlist_add_head(&s->s_instances, &s->s_type->fs_supers);
 550         spin_unlock(&sb_lock);
 551         get_filesystem(s->s_type);
 552         register_shrinker_prepared(&s->s_shrink);
 553         return s;
 554 
 555 share_extant_sb:
 556         if (user_ns != old->s_user_ns) {
 557                 spin_unlock(&sb_lock);
 558                 destroy_unused_super(s);
 559                 return ERR_PTR(-EBUSY);
 560         }
 561         if (!grab_super(old))
 562                 goto retry;
 563         destroy_unused_super(s);
 564         return old;
 565 }
 566 EXPORT_SYMBOL(sget_fc);
 567 
 568 /**
 569  *      sget    -       find or create a superblock
 570  *      @type:    filesystem type superblock should belong to
 571  *      @test:    comparison callback
 572  *      @set:     setup callback
 573  *      @flags:   mount flags
 574  *      @data:    argument to each of them
 575  */
 576 struct super_block *sget(struct file_system_type *type,
 577                         int (*test)(struct super_block *,void *),
 578                         int (*set)(struct super_block *,void *),
 579                         int flags,
 580                         void *data)
 581 {
 582         struct user_namespace *user_ns = current_user_ns();
 583         struct super_block *s = NULL;
 584         struct super_block *old;
 585         int err;
 586 
 587         /* We don't yet pass the user namespace of the parent
 588          * mount through to here so always use &init_user_ns
 589          * until that changes.
 590          */
 591         if (flags & SB_SUBMOUNT)
 592                 user_ns = &init_user_ns;
 593 
 594 retry:
 595         spin_lock(&sb_lock);
 596         if (test) {
 597                 hlist_for_each_entry(old, &type->fs_supers, s_instances) {
 598                         if (!test(old, data))
 599                                 continue;
 600                         if (user_ns != old->s_user_ns) {
 601                                 spin_unlock(&sb_lock);
 602                                 destroy_unused_super(s);
 603                                 return ERR_PTR(-EBUSY);
 604                         }
 605                         if (!grab_super(old))
 606                                 goto retry;
 607                         destroy_unused_super(s);
 608                         return old;
 609                 }
 610         }
 611         if (!s) {
 612                 spin_unlock(&sb_lock);
 613                 s = alloc_super(type, (flags & ~SB_SUBMOUNT), user_ns);
 614                 if (!s)
 615                         return ERR_PTR(-ENOMEM);
 616                 goto retry;
 617         }
 618 
 619         err = set(s, data);
 620         if (err) {
 621                 spin_unlock(&sb_lock);
 622                 destroy_unused_super(s);
 623                 return ERR_PTR(err);
 624         }
 625         s->s_type = type;
 626         strlcpy(s->s_id, type->name, sizeof(s->s_id));
 627         list_add_tail(&s->s_list, &super_blocks);
 628         hlist_add_head(&s->s_instances, &type->fs_supers);
 629         spin_unlock(&sb_lock);
 630         get_filesystem(type);
 631         register_shrinker_prepared(&s->s_shrink);
 632         return s;
 633 }
 634 EXPORT_SYMBOL(sget);
 635 
 636 void drop_super(struct super_block *sb)
 637 {
 638         up_read(&sb->s_umount);
 639         put_super(sb);
 640 }
 641 
 642 EXPORT_SYMBOL(drop_super);
 643 
 644 void drop_super_exclusive(struct super_block *sb)
 645 {
 646         up_write(&sb->s_umount);
 647         put_super(sb);
 648 }
 649 EXPORT_SYMBOL(drop_super_exclusive);
 650 
 651 static void __iterate_supers(void (*f)(struct super_block *))
 652 {
 653         struct super_block *sb, *p = NULL;
 654 
 655         spin_lock(&sb_lock);
 656         list_for_each_entry(sb, &super_blocks, s_list) {
 657                 if (hlist_unhashed(&sb->s_instances))
 658                         continue;
 659                 sb->s_count++;
 660                 spin_unlock(&sb_lock);
 661 
 662                 f(sb);
 663 
 664                 spin_lock(&sb_lock);
 665                 if (p)
 666                         __put_super(p);
 667                 p = sb;
 668         }
 669         if (p)
 670                 __put_super(p);
 671         spin_unlock(&sb_lock);
 672 }
 673 /**
 674  *      iterate_supers - call function for all active superblocks
 675  *      @f: function to call
 676  *      @arg: argument to pass to it
 677  *
 678  *      Scans the superblock list and calls given function, passing it
 679  *      locked superblock and given argument.
 680  */
 681 void iterate_supers(void (*f)(struct super_block *, void *), void *arg)
 682 {
 683         struct super_block *sb, *p = NULL;
 684 
 685         spin_lock(&sb_lock);
 686         list_for_each_entry(sb, &super_blocks, s_list) {
 687                 if (hlist_unhashed(&sb->s_instances))
 688                         continue;
 689                 sb->s_count++;
 690                 spin_unlock(&sb_lock);
 691 
 692                 down_read(&sb->s_umount);
 693                 if (sb->s_root && (sb->s_flags & SB_BORN))
 694                         f(sb, arg);
 695                 up_read(&sb->s_umount);
 696 
 697                 spin_lock(&sb_lock);
 698                 if (p)
 699                         __put_super(p);
 700                 p = sb;
 701         }
 702         if (p)
 703                 __put_super(p);
 704         spin_unlock(&sb_lock);
 705 }
 706 
 707 /**
 708  *      iterate_supers_type - call function for superblocks of given type
 709  *      @type: fs type
 710  *      @f: function to call
 711  *      @arg: argument to pass to it
 712  *
 713  *      Scans the superblock list and calls given function, passing it
 714  *      locked superblock and given argument.
 715  */
 716 void iterate_supers_type(struct file_system_type *type,
 717         void (*f)(struct super_block *, void *), void *arg)
 718 {
 719         struct super_block *sb, *p = NULL;
 720 
 721         spin_lock(&sb_lock);
 722         hlist_for_each_entry(sb, &type->fs_supers, s_instances) {
 723                 sb->s_count++;
 724                 spin_unlock(&sb_lock);
 725 
 726                 down_read(&sb->s_umount);
 727                 if (sb->s_root && (sb->s_flags & SB_BORN))
 728                         f(sb, arg);
 729                 up_read(&sb->s_umount);
 730 
 731                 spin_lock(&sb_lock);
 732                 if (p)
 733                         __put_super(p);
 734                 p = sb;
 735         }
 736         if (p)
 737                 __put_super(p);
 738         spin_unlock(&sb_lock);
 739 }
 740 
 741 EXPORT_SYMBOL(iterate_supers_type);
 742 
 743 static struct super_block *__get_super(struct block_device *bdev, bool excl)
 744 {
 745         struct super_block *sb;
 746 
 747         if (!bdev)
 748                 return NULL;
 749 
 750         spin_lock(&sb_lock);
 751 rescan:
 752         list_for_each_entry(sb, &super_blocks, s_list) {
 753                 if (hlist_unhashed(&sb->s_instances))
 754                         continue;
 755                 if (sb->s_bdev == bdev) {
 756                         sb->s_count++;
 757                         spin_unlock(&sb_lock);
 758                         if (!excl)
 759                                 down_read(&sb->s_umount);
 760                         else
 761                                 down_write(&sb->s_umount);
 762                         /* still alive? */
 763                         if (sb->s_root && (sb->s_flags & SB_BORN))
 764                                 return sb;
 765                         if (!excl)
 766                                 up_read(&sb->s_umount);
 767                         else
 768                                 up_write(&sb->s_umount);
 769                         /* nope, got unmounted */
 770                         spin_lock(&sb_lock);
 771                         __put_super(sb);
 772                         goto rescan;
 773                 }
 774         }
 775         spin_unlock(&sb_lock);
 776         return NULL;
 777 }
 778 
 779 /**
 780  *      get_super - get the superblock of a device
 781  *      @bdev: device to get the superblock for
 782  *
 783  *      Scans the superblock list and finds the superblock of the file system
 784  *      mounted on the device given. %NULL is returned if no match is found.
 785  */
 786 struct super_block *get_super(struct block_device *bdev)
 787 {
 788         return __get_super(bdev, false);
 789 }
 790 EXPORT_SYMBOL(get_super);
 791 
 792 static struct super_block *__get_super_thawed(struct block_device *bdev,
 793                                               bool excl)
 794 {
 795         while (1) {
 796                 struct super_block *s = __get_super(bdev, excl);
 797                 if (!s || s->s_writers.frozen == SB_UNFROZEN)
 798                         return s;
 799                 if (!excl)
 800                         up_read(&s->s_umount);
 801                 else
 802                         up_write(&s->s_umount);
 803                 wait_event(s->s_writers.wait_unfrozen,
 804                            s->s_writers.frozen == SB_UNFROZEN);
 805                 put_super(s);
 806         }
 807 }
 808 
 809 /**
 810  *      get_super_thawed - get thawed superblock of a device
 811  *      @bdev: device to get the superblock for
 812  *
 813  *      Scans the superblock list and finds the superblock of the file system
 814  *      mounted on the device. The superblock is returned once it is thawed
 815  *      (or immediately if it was not frozen). %NULL is returned if no match
 816  *      is found.
 817  */
 818 struct super_block *get_super_thawed(struct block_device *bdev)
 819 {
 820         return __get_super_thawed(bdev, false);
 821 }
 822 EXPORT_SYMBOL(get_super_thawed);
 823 
 824 /**
 825  *      get_super_exclusive_thawed - get thawed superblock of a device
 826  *      @bdev: device to get the superblock for
 827  *
 828  *      Scans the superblock list and finds the superblock of the file system
 829  *      mounted on the device. The superblock is returned once it is thawed
 830  *      (or immediately if it was not frozen) and s_umount semaphore is held
 831  *      in exclusive mode. %NULL is returned if no match is found.
 832  */
 833 struct super_block *get_super_exclusive_thawed(struct block_device *bdev)
 834 {
 835         return __get_super_thawed(bdev, true);
 836 }
 837 EXPORT_SYMBOL(get_super_exclusive_thawed);
 838 
 839 /**
 840  * get_active_super - get an active reference to the superblock of a device
 841  * @bdev: device to get the superblock for
 842  *
 843  * Scans the superblock list and finds the superblock of the file system
 844  * mounted on the device given.  Returns the superblock with an active
 845  * reference or %NULL if none was found.
 846  */
 847 struct super_block *get_active_super(struct block_device *bdev)
 848 {
 849         struct super_block *sb;
 850 
 851         if (!bdev)
 852                 return NULL;
 853 
 854 restart:
 855         spin_lock(&sb_lock);
 856         list_for_each_entry(sb, &super_blocks, s_list) {
 857                 if (hlist_unhashed(&sb->s_instances))
 858                         continue;
 859                 if (sb->s_bdev == bdev) {
 860                         if (!grab_super(sb))
 861                                 goto restart;
 862                         up_write(&sb->s_umount);
 863                         return sb;
 864                 }
 865         }
 866         spin_unlock(&sb_lock);
 867         return NULL;
 868 }
 869 
 870 struct super_block *user_get_super(dev_t dev)
 871 {
 872         struct super_block *sb;
 873 
 874         spin_lock(&sb_lock);
 875 rescan:
 876         list_for_each_entry(sb, &super_blocks, s_list) {
 877                 if (hlist_unhashed(&sb->s_instances))
 878                         continue;
 879                 if (sb->s_dev ==  dev) {
 880                         sb->s_count++;
 881                         spin_unlock(&sb_lock);
 882                         down_read(&sb->s_umount);
 883                         /* still alive? */
 884                         if (sb->s_root && (sb->s_flags & SB_BORN))
 885                                 return sb;
 886                         up_read(&sb->s_umount);
 887                         /* nope, got unmounted */
 888                         spin_lock(&sb_lock);
 889                         __put_super(sb);
 890                         goto rescan;
 891                 }
 892         }
 893         spin_unlock(&sb_lock);
 894         return NULL;
 895 }
 896 
 897 /**
 898  * reconfigure_super - asks filesystem to change superblock parameters
 899  * @fc: The superblock and configuration
 900  *
 901  * Alters the configuration parameters of a live superblock.
 902  */
 903 int reconfigure_super(struct fs_context *fc)
 904 {
 905         struct super_block *sb = fc->root->d_sb;
 906         int retval;
 907         bool remount_ro = false;
 908         bool force = fc->sb_flags & SB_FORCE;
 909 
 910         if (fc->sb_flags_mask & ~MS_RMT_MASK)
 911                 return -EINVAL;
 912         if (sb->s_writers.frozen != SB_UNFROZEN)
 913                 return -EBUSY;
 914 
 915         retval = security_sb_remount(sb, fc->security);
 916         if (retval)
 917                 return retval;
 918 
 919         if (fc->sb_flags_mask & SB_RDONLY) {
 920 #ifdef CONFIG_BLOCK
 921                 if (!(fc->sb_flags & SB_RDONLY) && bdev_read_only(sb->s_bdev))
 922                         return -EACCES;
 923 #endif
 924 
 925                 remount_ro = (fc->sb_flags & SB_RDONLY) && !sb_rdonly(sb);
 926         }
 927 
 928         if (remount_ro) {
 929                 if (!hlist_empty(&sb->s_pins)) {
 930                         up_write(&sb->s_umount);
 931                         group_pin_kill(&sb->s_pins);
 932                         down_write(&sb->s_umount);
 933                         if (!sb->s_root)
 934                                 return 0;
 935                         if (sb->s_writers.frozen != SB_UNFROZEN)
 936                                 return -EBUSY;
 937                         remount_ro = !sb_rdonly(sb);
 938                 }
 939         }
 940         shrink_dcache_sb(sb);
 941 
 942         /* If we are reconfiguring to RDONLY and current sb is read/write,
 943          * make sure there are no files open for writing.
 944          */
 945         if (remount_ro) {
 946                 if (force) {
 947                         sb->s_readonly_remount = 1;
 948                         smp_wmb();
 949                 } else {
 950                         retval = sb_prepare_remount_readonly(sb);
 951                         if (retval)
 952                                 return retval;
 953                 }
 954         }
 955 
 956         if (fc->ops->reconfigure) {
 957                 retval = fc->ops->reconfigure(fc);
 958                 if (retval) {
 959                         if (!force)
 960                                 goto cancel_readonly;
 961                         /* If forced remount, go ahead despite any errors */
 962                         WARN(1, "forced remount of a %s fs returned %i\n",
 963                              sb->s_type->name, retval);
 964                 }
 965         }
 966 
 967         WRITE_ONCE(sb->s_flags, ((sb->s_flags & ~fc->sb_flags_mask) |
 968                                  (fc->sb_flags & fc->sb_flags_mask)));
 969         /* Needs to be ordered wrt mnt_is_readonly() */
 970         smp_wmb();
 971         sb->s_readonly_remount = 0;
 972 
 973         /*
 974          * Some filesystems modify their metadata via some other path than the
 975          * bdev buffer cache (eg. use a private mapping, or directories in
 976          * pagecache, etc). Also file data modifications go via their own
 977          * mappings. So If we try to mount readonly then copy the filesystem
 978          * from bdev, we could get stale data, so invalidate it to give a best
 979          * effort at coherency.
 980          */
 981         if (remount_ro && sb->s_bdev)
 982                 invalidate_bdev(sb->s_bdev);
 983         return 0;
 984 
 985 cancel_readonly:
 986         sb->s_readonly_remount = 0;
 987         return retval;
 988 }
 989 
 990 static void do_emergency_remount_callback(struct super_block *sb)
 991 {
 992         down_write(&sb->s_umount);
 993         if (sb->s_root && sb->s_bdev && (sb->s_flags & SB_BORN) &&
 994             !sb_rdonly(sb)) {
 995                 struct fs_context *fc;
 996 
 997                 fc = fs_context_for_reconfigure(sb->s_root,
 998                                         SB_RDONLY | SB_FORCE, SB_RDONLY);
 999                 if (!IS_ERR(fc)) {
1000                         if (parse_monolithic_mount_data(fc, NULL) == 0)
1001                                 (void)reconfigure_super(fc);
1002                         put_fs_context(fc);
1003                 }
1004         }
1005         up_write(&sb->s_umount);
1006 }
1007 
1008 static void do_emergency_remount(struct work_struct *work)
1009 {
1010         __iterate_supers(do_emergency_remount_callback);
1011         kfree(work);
1012         printk("Emergency Remount complete\n");
1013 }
1014 
1015 void emergency_remount(void)
1016 {
1017         struct work_struct *work;
1018 
1019         work = kmalloc(sizeof(*work), GFP_ATOMIC);
1020         if (work) {
1021                 INIT_WORK(work, do_emergency_remount);
1022                 schedule_work(work);
1023         }
1024 }
1025 
1026 static void do_thaw_all_callback(struct super_block *sb)
1027 {
1028         down_write(&sb->s_umount);
1029         if (sb->s_root && sb->s_flags & SB_BORN) {
1030                 emergency_thaw_bdev(sb);
1031                 thaw_super_locked(sb);
1032         } else {
1033                 up_write(&sb->s_umount);
1034         }
1035 }
1036 
1037 static void do_thaw_all(struct work_struct *work)
1038 {
1039         __iterate_supers(do_thaw_all_callback);
1040         kfree(work);
1041         printk(KERN_WARNING "Emergency Thaw complete\n");
1042 }
1043 
1044 /**
1045  * emergency_thaw_all -- forcibly thaw every frozen filesystem
1046  *
1047  * Used for emergency unfreeze of all filesystems via SysRq
1048  */
1049 void emergency_thaw_all(void)
1050 {
1051         struct work_struct *work;
1052 
1053         work = kmalloc(sizeof(*work), GFP_ATOMIC);
1054         if (work) {
1055                 INIT_WORK(work, do_thaw_all);
1056                 schedule_work(work);
1057         }
1058 }
1059 
1060 static DEFINE_IDA(unnamed_dev_ida);
1061 
1062 /**
1063  * get_anon_bdev - Allocate a block device for filesystems which don't have one.
1064  * @p: Pointer to a dev_t.
1065  *
1066  * Filesystems which don't use real block devices can call this function
1067  * to allocate a virtual block device.
1068  *
1069  * Context: Any context.  Frequently called while holding sb_lock.
1070  * Return: 0 on success, -EMFILE if there are no anonymous bdevs left
1071  * or -ENOMEM if memory allocation failed.
1072  */
1073 int get_anon_bdev(dev_t *p)
1074 {
1075         int dev;
1076 
1077         /*
1078          * Many userspace utilities consider an FSID of 0 invalid.
1079          * Always return at least 1 from get_anon_bdev.
1080          */
1081         dev = ida_alloc_range(&unnamed_dev_ida, 1, (1 << MINORBITS) - 1,
1082                         GFP_ATOMIC);
1083         if (dev == -ENOSPC)
1084                 dev = -EMFILE;
1085         if (dev < 0)
1086                 return dev;
1087 
1088         *p = MKDEV(0, dev);
1089         return 0;
1090 }
1091 EXPORT_SYMBOL(get_anon_bdev);
1092 
1093 void free_anon_bdev(dev_t dev)
1094 {
1095         ida_free(&unnamed_dev_ida, MINOR(dev));
1096 }
1097 EXPORT_SYMBOL(free_anon_bdev);
1098 
1099 int set_anon_super(struct super_block *s, void *data)
1100 {
1101         return get_anon_bdev(&s->s_dev);
1102 }
1103 EXPORT_SYMBOL(set_anon_super);
1104 
1105 void kill_anon_super(struct super_block *sb)
1106 {
1107         dev_t dev = sb->s_dev;
1108         generic_shutdown_super(sb);
1109         free_anon_bdev(dev);
1110 }
1111 EXPORT_SYMBOL(kill_anon_super);
1112 
1113 void kill_litter_super(struct super_block *sb)
1114 {
1115         if (sb->s_root)
1116                 d_genocide(sb->s_root);
1117         kill_anon_super(sb);
1118 }
1119 EXPORT_SYMBOL(kill_litter_super);
1120 
1121 int set_anon_super_fc(struct super_block *sb, struct fs_context *fc)
1122 {
1123         return set_anon_super(sb, NULL);
1124 }
1125 EXPORT_SYMBOL(set_anon_super_fc);
1126 
1127 static int test_keyed_super(struct super_block *sb, struct fs_context *fc)
1128 {
1129         return sb->s_fs_info == fc->s_fs_info;
1130 }
1131 
1132 static int test_single_super(struct super_block *s, struct fs_context *fc)
1133 {
1134         return 1;
1135 }
1136 
1137 /**
1138  * vfs_get_super - Get a superblock with a search key set in s_fs_info.
1139  * @fc: The filesystem context holding the parameters
1140  * @keying: How to distinguish superblocks
1141  * @fill_super: Helper to initialise a new superblock
1142  *
1143  * Search for a superblock and create a new one if not found.  The search
1144  * criterion is controlled by @keying.  If the search fails, a new superblock
1145  * is created and @fill_super() is called to initialise it.
1146  *
1147  * @keying can take one of a number of values:
1148  *
1149  * (1) vfs_get_single_super - Only one superblock of this type may exist on the
1150  *     system.  This is typically used for special system filesystems.
1151  *
1152  * (2) vfs_get_keyed_super - Multiple superblocks may exist, but they must have
1153  *     distinct keys (where the key is in s_fs_info).  Searching for the same
1154  *     key again will turn up the superblock for that key.
1155  *
1156  * (3) vfs_get_independent_super - Multiple superblocks may exist and are
1157  *     unkeyed.  Each call will get a new superblock.
1158  *
1159  * A permissions check is made by sget_fc() unless we're getting a superblock
1160  * for a kernel-internal mount or a submount.
1161  */
1162 int vfs_get_super(struct fs_context *fc,
1163                   enum vfs_get_super_keying keying,
1164                   int (*fill_super)(struct super_block *sb,
1165                                     struct fs_context *fc))
1166 {
1167         int (*test)(struct super_block *, struct fs_context *);
1168         struct super_block *sb;
1169         int err;
1170 
1171         switch (keying) {
1172         case vfs_get_single_super:
1173         case vfs_get_single_reconf_super:
1174                 test = test_single_super;
1175                 break;
1176         case vfs_get_keyed_super:
1177                 test = test_keyed_super;
1178                 break;
1179         case vfs_get_independent_super:
1180                 test = NULL;
1181                 break;
1182         default:
1183                 BUG();
1184         }
1185 
1186         sb = sget_fc(fc, test, set_anon_super_fc);
1187         if (IS_ERR(sb))
1188                 return PTR_ERR(sb);
1189 
1190         if (!sb->s_root) {
1191                 err = fill_super(sb, fc);
1192                 if (err)
1193                         goto error;
1194 
1195                 sb->s_flags |= SB_ACTIVE;
1196                 fc->root = dget(sb->s_root);
1197         } else {
1198                 fc->root = dget(sb->s_root);
1199                 if (keying == vfs_get_single_reconf_super) {
1200                         err = reconfigure_super(fc);
1201                         if (err < 0) {
1202                                 dput(fc->root);
1203                                 fc->root = NULL;
1204                                 goto error;
1205                         }
1206                 }
1207         }
1208 
1209         return 0;
1210 
1211 error:
1212         deactivate_locked_super(sb);
1213         return err;
1214 }
1215 EXPORT_SYMBOL(vfs_get_super);
1216 
1217 int get_tree_nodev(struct fs_context *fc,
1218                   int (*fill_super)(struct super_block *sb,
1219                                     struct fs_context *fc))
1220 {
1221         return vfs_get_super(fc, vfs_get_independent_super, fill_super);
1222 }
1223 EXPORT_SYMBOL(get_tree_nodev);
1224 
1225 int get_tree_single(struct fs_context *fc,
1226                   int (*fill_super)(struct super_block *sb,
1227                                     struct fs_context *fc))
1228 {
1229         return vfs_get_super(fc, vfs_get_single_super, fill_super);
1230 }
1231 EXPORT_SYMBOL(get_tree_single);
1232 
1233 int get_tree_single_reconf(struct fs_context *fc,
1234                   int (*fill_super)(struct super_block *sb,
1235                                     struct fs_context *fc))
1236 {
1237         return vfs_get_super(fc, vfs_get_single_reconf_super, fill_super);
1238 }
1239 EXPORT_SYMBOL(get_tree_single_reconf);
1240 
1241 int get_tree_keyed(struct fs_context *fc,
1242                   int (*fill_super)(struct super_block *sb,
1243                                     struct fs_context *fc),
1244                 void *key)
1245 {
1246         fc->s_fs_info = key;
1247         return vfs_get_super(fc, vfs_get_keyed_super, fill_super);
1248 }
1249 EXPORT_SYMBOL(get_tree_keyed);
1250 
1251 #ifdef CONFIG_BLOCK
1252 
1253 static int set_bdev_super(struct super_block *s, void *data)
1254 {
1255         s->s_bdev = data;
1256         s->s_dev = s->s_bdev->bd_dev;
1257         s->s_bdi = bdi_get(s->s_bdev->bd_bdi);
1258 
1259         return 0;
1260 }
1261 
1262 static int set_bdev_super_fc(struct super_block *s, struct fs_context *fc)
1263 {
1264         return set_bdev_super(s, fc->sget_key);
1265 }
1266 
1267 static int test_bdev_super_fc(struct super_block *s, struct fs_context *fc)
1268 {
1269         return s->s_bdev == fc->sget_key;
1270 }
1271 
1272 /**
1273  * get_tree_bdev - Get a superblock based on a single block device
1274  * @fc: The filesystem context holding the parameters
1275  * @fill_super: Helper to initialise a new superblock
1276  */
1277 int get_tree_bdev(struct fs_context *fc,
1278                 int (*fill_super)(struct super_block *,
1279                                   struct fs_context *))
1280 {
1281         struct block_device *bdev;
1282         struct super_block *s;
1283         fmode_t mode = FMODE_READ | FMODE_EXCL;
1284         int error = 0;
1285 
1286         if (!(fc->sb_flags & SB_RDONLY))
1287                 mode |= FMODE_WRITE;
1288 
1289         if (!fc->source)
1290                 return invalf(fc, "No source specified");
1291 
1292         bdev = blkdev_get_by_path(fc->source, mode, fc->fs_type);
1293         if (IS_ERR(bdev)) {
1294                 errorf(fc, "%s: Can't open blockdev", fc->source);
1295                 return PTR_ERR(bdev);
1296         }
1297 
1298         /* Once the superblock is inserted into the list by sget_fc(), s_umount
1299          * will protect the lockfs code from trying to start a snapshot while
1300          * we are mounting
1301          */
1302         mutex_lock(&bdev->bd_fsfreeze_mutex);
1303         if (bdev->bd_fsfreeze_count > 0) {
1304                 mutex_unlock(&bdev->bd_fsfreeze_mutex);
1305                 warnf(fc, "%pg: Can't mount, blockdev is frozen", bdev);
1306                 blkdev_put(bdev, mode);
1307                 return -EBUSY;
1308         }
1309 
1310         fc->sb_flags |= SB_NOSEC;
1311         fc->sget_key = bdev;
1312         s = sget_fc(fc, test_bdev_super_fc, set_bdev_super_fc);
1313         mutex_unlock(&bdev->bd_fsfreeze_mutex);
1314         if (IS_ERR(s)) {
1315                 blkdev_put(bdev, mode);
1316                 return PTR_ERR(s);
1317         }
1318 
1319         if (s->s_root) {
1320                 /* Don't summarily change the RO/RW state. */
1321                 if ((fc->sb_flags ^ s->s_flags) & SB_RDONLY) {
1322                         warnf(fc, "%pg: Can't mount, would change RO state", bdev);
1323                         deactivate_locked_super(s);
1324                         blkdev_put(bdev, mode);
1325                         return -EBUSY;
1326                 }
1327 
1328                 /*
1329                  * s_umount nests inside bd_mutex during
1330                  * __invalidate_device().  blkdev_put() acquires
1331                  * bd_mutex and can't be called under s_umount.  Drop
1332                  * s_umount temporarily.  This is safe as we're
1333                  * holding an active reference.
1334                  */
1335                 up_write(&s->s_umount);
1336                 blkdev_put(bdev, mode);
1337                 down_write(&s->s_umount);
1338         } else {
1339                 s->s_mode = mode;
1340                 snprintf(s->s_id, sizeof(s->s_id), "%pg", bdev);
1341                 sb_set_blocksize(s, block_size(bdev));
1342                 error = fill_super(s, fc);
1343                 if (error) {
1344                         deactivate_locked_super(s);
1345                         return error;
1346                 }
1347 
1348                 s->s_flags |= SB_ACTIVE;
1349                 bdev->bd_super = s;
1350         }
1351 
1352         BUG_ON(fc->root);
1353         fc->root = dget(s->s_root);
1354         return 0;
1355 }
1356 EXPORT_SYMBOL(get_tree_bdev);
1357 
1358 static int test_bdev_super(struct super_block *s, void *data)
1359 {
1360         return (void *)s->s_bdev == data;
1361 }
1362 
1363 struct dentry *mount_bdev(struct file_system_type *fs_type,
1364         int flags, const char *dev_name, void *data,
1365         int (*fill_super)(struct super_block *, void *, int))
1366 {
1367         struct block_device *bdev;
1368         struct super_block *s;
1369         fmode_t mode = FMODE_READ | FMODE_EXCL;
1370         int error = 0;
1371 
1372         if (!(flags & SB_RDONLY))
1373                 mode |= FMODE_WRITE;
1374 
1375         bdev = blkdev_get_by_path(dev_name, mode, fs_type);
1376         if (IS_ERR(bdev))
1377                 return ERR_CAST(bdev);
1378 
1379         /*
1380          * once the super is inserted into the list by sget, s_umount
1381          * will protect the lockfs code from trying to start a snapshot
1382          * while we are mounting
1383          */
1384         mutex_lock(&bdev->bd_fsfreeze_mutex);
1385         if (bdev->bd_fsfreeze_count > 0) {
1386                 mutex_unlock(&bdev->bd_fsfreeze_mutex);
1387                 error = -EBUSY;
1388                 goto error_bdev;
1389         }
1390         s = sget(fs_type, test_bdev_super, set_bdev_super, flags | SB_NOSEC,
1391                  bdev);
1392         mutex_unlock(&bdev->bd_fsfreeze_mutex);
1393         if (IS_ERR(s))
1394                 goto error_s;
1395 
1396         if (s->s_root) {
1397                 if ((flags ^ s->s_flags) & SB_RDONLY) {
1398                         deactivate_locked_super(s);
1399                         error = -EBUSY;
1400                         goto error_bdev;
1401                 }
1402 
1403                 /*
1404                  * s_umount nests inside bd_mutex during
1405                  * __invalidate_device().  blkdev_put() acquires
1406                  * bd_mutex and can't be called under s_umount.  Drop
1407                  * s_umount temporarily.  This is safe as we're
1408                  * holding an active reference.
1409                  */
1410                 up_write(&s->s_umount);
1411                 blkdev_put(bdev, mode);
1412                 down_write(&s->s_umount);
1413         } else {
1414                 s->s_mode = mode;
1415                 snprintf(s->s_id, sizeof(s->s_id), "%pg", bdev);
1416                 sb_set_blocksize(s, block_size(bdev));
1417                 error = fill_super(s, data, flags & SB_SILENT ? 1 : 0);
1418                 if (error) {
1419                         deactivate_locked_super(s);
1420                         goto error;
1421                 }
1422 
1423                 s->s_flags |= SB_ACTIVE;
1424                 bdev->bd_super = s;
1425         }
1426 
1427         return dget(s->s_root);
1428 
1429 error_s:
1430         error = PTR_ERR(s);
1431 error_bdev:
1432         blkdev_put(bdev, mode);
1433 error:
1434         return ERR_PTR(error);
1435 }
1436 EXPORT_SYMBOL(mount_bdev);
1437 
1438 void kill_block_super(struct super_block *sb)
1439 {
1440         struct block_device *bdev = sb->s_bdev;
1441         fmode_t mode = sb->s_mode;
1442 
1443         bdev->bd_super = NULL;
1444         generic_shutdown_super(sb);
1445         sync_blockdev(bdev);
1446         WARN_ON_ONCE(!(mode & FMODE_EXCL));
1447         blkdev_put(bdev, mode | FMODE_EXCL);
1448 }
1449 
1450 EXPORT_SYMBOL(kill_block_super);
1451 #endif
1452 
1453 struct dentry *mount_nodev(struct file_system_type *fs_type,
1454         int flags, void *data,
1455         int (*fill_super)(struct super_block *, void *, int))
1456 {
1457         int error;
1458         struct super_block *s = sget(fs_type, NULL, set_anon_super, flags, NULL);
1459 
1460         if (IS_ERR(s))
1461                 return ERR_CAST(s);
1462 
1463         error = fill_super(s, data, flags & SB_SILENT ? 1 : 0);
1464         if (error) {
1465                 deactivate_locked_super(s);
1466                 return ERR_PTR(error);
1467         }
1468         s->s_flags |= SB_ACTIVE;
1469         return dget(s->s_root);
1470 }
1471 EXPORT_SYMBOL(mount_nodev);
1472 
1473 static int reconfigure_single(struct super_block *s,
1474                               int flags, void *data)
1475 {
1476         struct fs_context *fc;
1477         int ret;
1478 
1479         /* The caller really need to be passing fc down into mount_single(),
1480          * then a chunk of this can be removed.  [Bollocks -- AV]
1481          * Better yet, reconfiguration shouldn't happen, but rather the second
1482          * mount should be rejected if the parameters are not compatible.
1483          */
1484         fc = fs_context_for_reconfigure(s->s_root, flags, MS_RMT_MASK);
1485         if (IS_ERR(fc))
1486                 return PTR_ERR(fc);
1487 
1488         ret = parse_monolithic_mount_data(fc, data);
1489         if (ret < 0)
1490                 goto out;
1491 
1492         ret = reconfigure_super(fc);
1493 out:
1494         put_fs_context(fc);
1495         return ret;
1496 }
1497 
1498 static int compare_single(struct super_block *s, void *p)
1499 {
1500         return 1;
1501 }
1502 
1503 struct dentry *mount_single(struct file_system_type *fs_type,
1504         int flags, void *data,
1505         int (*fill_super)(struct super_block *, void *, int))
1506 {
1507         struct super_block *s;
1508         int error;
1509 
1510         s = sget(fs_type, compare_single, set_anon_super, flags, NULL);
1511         if (IS_ERR(s))
1512                 return ERR_CAST(s);
1513         if (!s->s_root) {
1514                 error = fill_super(s, data, flags & SB_SILENT ? 1 : 0);
1515                 if (!error)
1516                         s->s_flags |= SB_ACTIVE;
1517         } else {
1518                 error = reconfigure_single(s, flags, data);
1519         }
1520         if (unlikely(error)) {
1521                 deactivate_locked_super(s);
1522                 return ERR_PTR(error);
1523         }
1524         return dget(s->s_root);
1525 }
1526 EXPORT_SYMBOL(mount_single);
1527 
1528 /**
1529  * vfs_get_tree - Get the mountable root
1530  * @fc: The superblock configuration context.
1531  *
1532  * The filesystem is invoked to get or create a superblock which can then later
1533  * be used for mounting.  The filesystem places a pointer to the root to be
1534  * used for mounting in @fc->root.
1535  */
1536 int vfs_get_tree(struct fs_context *fc)
1537 {
1538         struct super_block *sb;
1539         int error;
1540 
1541         if (fc->root)
1542                 return -EBUSY;
1543 
1544         /* Get the mountable root in fc->root, with a ref on the root and a ref
1545          * on the superblock.
1546          */
1547         error = fc->ops->get_tree(fc);
1548         if (error < 0)
1549                 return error;
1550 
1551         if (!fc->root) {
1552                 pr_err("Filesystem %s get_tree() didn't set fc->root\n",
1553                        fc->fs_type->name);
1554                 /* We don't know what the locking state of the superblock is -
1555                  * if there is a superblock.
1556                  */
1557                 BUG();
1558         }
1559 
1560         sb = fc->root->d_sb;
1561         WARN_ON(!sb->s_bdi);
1562 
1563         /*
1564          * Write barrier is for super_cache_count(). We place it before setting
1565          * SB_BORN as the data dependency between the two functions is the
1566          * superblock structure contents that we just set up, not the SB_BORN
1567          * flag.
1568          */
1569         smp_wmb();
1570         sb->s_flags |= SB_BORN;
1571 
1572         error = security_sb_set_mnt_opts(sb, fc->security, 0, NULL);
1573         if (unlikely(error)) {
1574                 fc_drop_locked(fc);
1575                 return error;
1576         }
1577 
1578         /*
1579          * filesystems should never set s_maxbytes larger than MAX_LFS_FILESIZE
1580          * but s_maxbytes was an unsigned long long for many releases. Throw
1581          * this warning for a little while to try and catch filesystems that
1582          * violate this rule.
1583          */
1584         WARN((sb->s_maxbytes < 0), "%s set sb->s_maxbytes to "
1585                 "negative value (%lld)\n", fc->fs_type->name, sb->s_maxbytes);
1586 
1587         return 0;
1588 }
1589 EXPORT_SYMBOL(vfs_get_tree);
1590 
1591 /*
1592  * Setup private BDI for given superblock. It gets automatically cleaned up
1593  * in generic_shutdown_super().
1594  */
1595 int super_setup_bdi_name(struct super_block *sb, char *fmt, ...)
1596 {
1597         struct backing_dev_info *bdi;
1598         int err;
1599         va_list args;
1600 
1601         bdi = bdi_alloc(GFP_KERNEL);
1602         if (!bdi)
1603                 return -ENOMEM;
1604 
1605         bdi->name = sb->s_type->name;
1606 
1607         va_start(args, fmt);
1608         err = bdi_register_va(bdi, fmt, args);
1609         va_end(args);
1610         if (err) {
1611                 bdi_put(bdi);
1612                 return err;
1613         }
1614         WARN_ON(sb->s_bdi != &noop_backing_dev_info);
1615         sb->s_bdi = bdi;
1616 
1617         return 0;
1618 }
1619 EXPORT_SYMBOL(super_setup_bdi_name);
1620 
1621 /*
1622  * Setup private BDI for given superblock. I gets automatically cleaned up
1623  * in generic_shutdown_super().
1624  */
1625 int super_setup_bdi(struct super_block *sb)
1626 {
1627         static atomic_long_t bdi_seq = ATOMIC_LONG_INIT(0);
1628 
1629         return super_setup_bdi_name(sb, "%.28s-%ld", sb->s_type->name,
1630                                     atomic_long_inc_return(&bdi_seq));
1631 }
1632 EXPORT_SYMBOL(super_setup_bdi);
1633 
1634 /*
1635  * This is an internal function, please use sb_end_{write,pagefault,intwrite}
1636  * instead.
1637  */
1638 void __sb_end_write(struct super_block *sb, int level)
1639 {
1640         percpu_up_read(sb->s_writers.rw_sem + level-1);
1641 }
1642 EXPORT_SYMBOL(__sb_end_write);
1643 
1644 /*
1645  * This is an internal function, please use sb_start_{write,pagefault,intwrite}
1646  * instead.
1647  */
1648 int __sb_start_write(struct super_block *sb, int level, bool wait)
1649 {
1650         bool force_trylock = false;
1651         int ret = 1;
1652 
1653 #ifdef CONFIG_LOCKDEP
1654         /*
1655          * We want lockdep to tell us about possible deadlocks with freezing
1656          * but it's it bit tricky to properly instrument it. Getting a freeze
1657          * protection works as getting a read lock but there are subtle
1658          * problems. XFS for example gets freeze protection on internal level
1659          * twice in some cases, which is OK only because we already hold a
1660          * freeze protection also on higher level. Due to these cases we have
1661          * to use wait == F (trylock mode) which must not fail.
1662          */
1663         if (wait) {
1664                 int i;
1665 
1666                 for (i = 0; i < level - 1; i++)
1667                         if (percpu_rwsem_is_held(sb->s_writers.rw_sem + i)) {
1668                                 force_trylock = true;
1669                                 break;
1670                         }
1671         }
1672 #endif
1673         if (wait && !force_trylock)
1674                 percpu_down_read(sb->s_writers.rw_sem + level-1);
1675         else
1676                 ret = percpu_down_read_trylock(sb->s_writers.rw_sem + level-1);
1677 
1678         WARN_ON(force_trylock && !ret);
1679         return ret;
1680 }
1681 EXPORT_SYMBOL(__sb_start_write);
1682 
1683 /**
1684  * sb_wait_write - wait until all writers to given file system finish
1685  * @sb: the super for which we wait
1686  * @level: type of writers we wait for (normal vs page fault)
1687  *
1688  * This function waits until there are no writers of given type to given file
1689  * system.
1690  */
1691 static void sb_wait_write(struct super_block *sb, int level)
1692 {
1693         percpu_down_write(sb->s_writers.rw_sem + level-1);
1694 }
1695 
1696 /*
1697  * We are going to return to userspace and forget about these locks, the
1698  * ownership goes to the caller of thaw_super() which does unlock().
1699  */
1700 static void lockdep_sb_freeze_release(struct super_block *sb)
1701 {
1702         int level;
1703 
1704         for (level = SB_FREEZE_LEVELS - 1; level >= 0; level--)
1705                 percpu_rwsem_release(sb->s_writers.rw_sem + level, 0, _THIS_IP_);
1706 }
1707 
1708 /*
1709  * Tell lockdep we are holding these locks before we call ->unfreeze_fs(sb).
1710  */
1711 static void lockdep_sb_freeze_acquire(struct super_block *sb)
1712 {
1713         int level;
1714 
1715         for (level = 0; level < SB_FREEZE_LEVELS; ++level)
1716                 percpu_rwsem_acquire(sb->s_writers.rw_sem + level, 0, _THIS_IP_);
1717 }
1718 
1719 static void sb_freeze_unlock(struct super_block *sb)
1720 {
1721         int level;
1722 
1723         for (level = SB_FREEZE_LEVELS - 1; level >= 0; level--)
1724                 percpu_up_write(sb->s_writers.rw_sem + level);
1725 }
1726 
1727 /**
1728  * freeze_super - lock the filesystem and force it into a consistent state
1729  * @sb: the super to lock
1730  *
1731  * Syncs the super to make sure the filesystem is consistent and calls the fs's
1732  * freeze_fs.  Subsequent calls to this without first thawing the fs will return
1733  * -EBUSY.
1734  *
1735  * During this function, sb->s_writers.frozen goes through these values:
1736  *
1737  * SB_UNFROZEN: File system is normal, all writes progress as usual.
1738  *
1739  * SB_FREEZE_WRITE: The file system is in the process of being frozen.  New
1740  * writes should be blocked, though page faults are still allowed. We wait for
1741  * all writes to complete and then proceed to the next stage.
1742  *
1743  * SB_FREEZE_PAGEFAULT: Freezing continues. Now also page faults are blocked
1744  * but internal fs threads can still modify the filesystem (although they
1745  * should not dirty new pages or inodes), writeback can run etc. After waiting
1746  * for all running page faults we sync the filesystem which will clean all
1747  * dirty pages and inodes (no new dirty pages or inodes can be created when
1748  * sync is running).
1749  *
1750  * SB_FREEZE_FS: The file system is frozen. Now all internal sources of fs
1751  * modification are blocked (e.g. XFS preallocation truncation on inode
1752  * reclaim). This is usually implemented by blocking new transactions for
1753  * filesystems that have them and need this additional guard. After all
1754  * internal writers are finished we call ->freeze_fs() to finish filesystem
1755  * freezing. Then we transition to SB_FREEZE_COMPLETE state. This state is
1756  * mostly auxiliary for filesystems to verify they do not modify frozen fs.
1757  *
1758  * sb->s_writers.frozen is protected by sb->s_umount.
1759  */
1760 int freeze_super(struct super_block *sb)
1761 {
1762         int ret;
1763 
1764         atomic_inc(&sb->s_active);
1765         down_write(&sb->s_umount);
1766         if (sb->s_writers.frozen != SB_UNFROZEN) {
1767                 deactivate_locked_super(sb);
1768                 return -EBUSY;
1769         }
1770 
1771         if (!(sb->s_flags & SB_BORN)) {
1772                 up_write(&sb->s_umount);
1773                 return 0;       /* sic - it's "nothing to do" */
1774         }
1775 
1776         if (sb_rdonly(sb)) {
1777                 /* Nothing to do really... */
1778                 sb->s_writers.frozen = SB_FREEZE_COMPLETE;
1779                 up_write(&sb->s_umount);
1780                 return 0;
1781         }
1782 
1783         sb->s_writers.frozen = SB_FREEZE_WRITE;
1784         /* Release s_umount to preserve sb_start_write -> s_umount ordering */
1785         up_write(&sb->s_umount);
1786         sb_wait_write(sb, SB_FREEZE_WRITE);
1787         down_write(&sb->s_umount);
1788 
1789         /* Now we go and block page faults... */
1790         sb->s_writers.frozen = SB_FREEZE_PAGEFAULT;
1791         sb_wait_write(sb, SB_FREEZE_PAGEFAULT);
1792 
1793         /* All writers are done so after syncing there won't be dirty data */
1794         sync_filesystem(sb);
1795 
1796         /* Now wait for internal filesystem counter */
1797         sb->s_writers.frozen = SB_FREEZE_FS;
1798         sb_wait_write(sb, SB_FREEZE_FS);
1799 
1800         if (sb->s_op->freeze_fs) {
1801                 ret = sb->s_op->freeze_fs(sb);
1802                 if (ret) {
1803                         printk(KERN_ERR
1804                                 "VFS:Filesystem freeze failed\n");
1805                         sb->s_writers.frozen = SB_UNFROZEN;
1806                         sb_freeze_unlock(sb);
1807                         wake_up(&sb->s_writers.wait_unfrozen);
1808                         deactivate_locked_super(sb);
1809                         return ret;
1810                 }
1811         }
1812         /*
1813          * For debugging purposes so that fs can warn if it sees write activity
1814          * when frozen is set to SB_FREEZE_COMPLETE, and for thaw_super().
1815          */
1816         sb->s_writers.frozen = SB_FREEZE_COMPLETE;
1817         lockdep_sb_freeze_release(sb);
1818         up_write(&sb->s_umount);
1819         return 0;
1820 }
1821 EXPORT_SYMBOL(freeze_super);
1822 
1823 /**
1824  * thaw_super -- unlock filesystem
1825  * @sb: the super to thaw
1826  *
1827  * Unlocks the filesystem and marks it writeable again after freeze_super().
1828  */
1829 static int thaw_super_locked(struct super_block *sb)
1830 {
1831         int error;
1832 
1833         if (sb->s_writers.frozen != SB_FREEZE_COMPLETE) {
1834                 up_write(&sb->s_umount);
1835                 return -EINVAL;
1836         }
1837 
1838         if (sb_rdonly(sb)) {
1839                 sb->s_writers.frozen = SB_UNFROZEN;
1840                 goto out;
1841         }
1842 
1843         lockdep_sb_freeze_acquire(sb);
1844 
1845         if (sb->s_op->unfreeze_fs) {
1846                 error = sb->s_op->unfreeze_fs(sb);
1847                 if (error) {
1848                         printk(KERN_ERR
1849                                 "VFS:Filesystem thaw failed\n");
1850                         lockdep_sb_freeze_release(sb);
1851                         up_write(&sb->s_umount);
1852                         return error;
1853                 }
1854         }
1855 
1856         sb->s_writers.frozen = SB_UNFROZEN;
1857         sb_freeze_unlock(sb);
1858 out:
1859         wake_up(&sb->s_writers.wait_unfrozen);
1860         deactivate_locked_super(sb);
1861         return 0;
1862 }
1863 
1864 int thaw_super(struct super_block *sb)
1865 {
1866         down_write(&sb->s_umount);
1867         return thaw_super_locked(sb);
1868 }
1869 EXPORT_SYMBOL(thaw_super);
/* [<][>][^][v][top][bottom][index][help] */
root/fs/super.c

DEFINITIONS
