block/blk-cgroup.c

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This source file includes following definitions.
blkcg_policy_enabled
blkg_free
__blkg_release
blkg_release
blkg_async_bio_workfn
blkg_alloc
blkg_lookup_slowpath
blkg_create
__blkg_lookup_create
blkg_lookup_create
blkg_destroy
blkg_destroy_all
blkcg_reset_stats
blkg_dev_name
blkcg_print_blkgs
__blkg_prfill_u64
__blkg_prfill_rwstat
blkg_prfill_rwstat
blkg_prfill_rwstat_field
blkg_print_stat_bytes
blkg_print_stat_ios
blkg_prfill_rwstat_field_recursive
blkg_print_stat_bytes_recursive
blkg_print_stat_ios_recursive
blkg_rwstat_recursive_sum
blkg_lookup_check
blkcg_conf_get_disk
blkg_conf_prep
blkg_conf_finish
blkcg_print_stat
blkcg_css_offline
blkcg_destroy_blkgs
blkcg_css_free
blkcg_css_alloc
blkcg_init_queue
blkcg_drain_queue
blkcg_exit_queue
blkcg_can_attach
blkcg_bind
blkcg_exit
blkcg_activate_policy
blkcg_deactivate_policy
blkcg_policy_register
blkcg_policy_unregister
__blkcg_punt_bio_submit
blkcg_scale_delay
blkcg_maybe_throttle_blkg
blkcg_maybe_throttle_current
blkcg_schedule_throttle
blkcg_add_delay
blkcg_init
   1 // SPDX-License-Identifier: GPL-2.0
   2 /*
   3  * Common Block IO controller cgroup interface
   4  *
   5  * Based on ideas and code from CFQ, CFS and BFQ:
   6  * Copyright (C) 2003 Jens Axboe <axboe@kernel.dk>
   7  *
   8  * Copyright (C) 2008 Fabio Checconi <fabio@gandalf.sssup.it>
   9  *                    Paolo Valente <paolo.valente@unimore.it>
  10  *
  11  * Copyright (C) 2009 Vivek Goyal <vgoyal@redhat.com>
  12  *                    Nauman Rafique <nauman@google.com>
  13  *
  14  * For policy-specific per-blkcg data:
  15  * Copyright (C) 2015 Paolo Valente <paolo.valente@unimore.it>
  16  *                    Arianna Avanzini <avanzini.arianna@gmail.com>
  17  */
  18 #include <linux/ioprio.h>
  19 #include <linux/kdev_t.h>
  20 #include <linux/module.h>
  21 #include <linux/sched/signal.h>
  22 #include <linux/err.h>
  23 #include <linux/blkdev.h>
  24 #include <linux/backing-dev.h>
  25 #include <linux/slab.h>
  26 #include <linux/genhd.h>
  27 #include <linux/delay.h>
  28 #include <linux/atomic.h>
  29 #include <linux/ctype.h>
  30 #include <linux/blk-cgroup.h>
  31 #include <linux/tracehook.h>
  32 #include <linux/psi.h>
  33 #include "blk.h"
  34 
  35 #define MAX_KEY_LEN 100
  36 
  37 /*
  38  * blkcg_pol_mutex protects blkcg_policy[] and policy [de]activation.
  39  * blkcg_pol_register_mutex nests outside of it and synchronizes entire
  40  * policy [un]register operations including cgroup file additions /
  41  * removals.  Putting cgroup file registration outside blkcg_pol_mutex
  42  * allows grabbing it from cgroup callbacks.
  43  */
  44 static DEFINE_MUTEX(blkcg_pol_register_mutex);
  45 static DEFINE_MUTEX(blkcg_pol_mutex);
  46 
  47 struct blkcg blkcg_root;
  48 EXPORT_SYMBOL_GPL(blkcg_root);
  49 
  50 struct cgroup_subsys_state * const blkcg_root_css = &blkcg_root.css;
  51 EXPORT_SYMBOL_GPL(blkcg_root_css);
  52 
  53 static struct blkcg_policy *blkcg_policy[BLKCG_MAX_POLS];
  54 
  55 static LIST_HEAD(all_blkcgs);           /* protected by blkcg_pol_mutex */
  56 
  57 bool blkcg_debug_stats = false;
  58 static struct workqueue_struct *blkcg_punt_bio_wq;
  59 
  60 static bool blkcg_policy_enabled(struct request_queue *q,
  61                                  const struct blkcg_policy *pol)
  62 {
  63         return pol && test_bit(pol->plid, q->blkcg_pols);
  64 }
  65 
  66 /**
  67  * blkg_free - free a blkg
  68  * @blkg: blkg to free
  69  *
  70  * Free @blkg which may be partially allocated.
  71  */
  72 static void blkg_free(struct blkcg_gq *blkg)
  73 {
  74         int i;
  75 
  76         if (!blkg)
  77                 return;
  78 
  79         for (i = 0; i < BLKCG_MAX_POLS; i++)
  80                 if (blkg->pd[i])
  81                         blkcg_policy[i]->pd_free_fn(blkg->pd[i]);
  82 
  83         blkg_rwstat_exit(&blkg->stat_ios);
  84         blkg_rwstat_exit(&blkg->stat_bytes);
  85         percpu_ref_exit(&blkg->refcnt);
  86         kfree(blkg);
  87 }
  88 
  89 static void __blkg_release(struct rcu_head *rcu)
  90 {
  91         struct blkcg_gq *blkg = container_of(rcu, struct blkcg_gq, rcu_head);
  92 
  93         WARN_ON(!bio_list_empty(&blkg->async_bios));
  94 
  95         /* release the blkcg and parent blkg refs this blkg has been holding */
  96         css_put(&blkg->blkcg->css);
  97         if (blkg->parent)
  98                 blkg_put(blkg->parent);
  99 
 100         wb_congested_put(blkg->wb_congested);
 101 
 102         blkg_free(blkg);
 103 }
 104 
 105 /*
 106  * A group is RCU protected, but having an rcu lock does not mean that one
 107  * can access all the fields of blkg and assume these are valid.  For
 108  * example, don't try to follow throtl_data and request queue links.
 109  *
 110  * Having a reference to blkg under an rcu allows accesses to only values
 111  * local to groups like group stats and group rate limits.
 112  */
 113 static void blkg_release(struct percpu_ref *ref)
 114 {
 115         struct blkcg_gq *blkg = container_of(ref, struct blkcg_gq, refcnt);
 116 
 117         call_rcu(&blkg->rcu_head, __blkg_release);
 118 }
 119 
 120 static void blkg_async_bio_workfn(struct work_struct *work)
 121 {
 122         struct blkcg_gq *blkg = container_of(work, struct blkcg_gq,
 123                                              async_bio_work);
 124         struct bio_list bios = BIO_EMPTY_LIST;
 125         struct bio *bio;
 126 
 127         /* as long as there are pending bios, @blkg can't go away */
 128         spin_lock_bh(&blkg->async_bio_lock);
 129         bio_list_merge(&bios, &blkg->async_bios);
 130         bio_list_init(&blkg->async_bios);
 131         spin_unlock_bh(&blkg->async_bio_lock);
 132 
 133         while ((bio = bio_list_pop(&bios)))
 134                 submit_bio(bio);
 135 }
 136 
 137 /**
 138  * blkg_alloc - allocate a blkg
 139  * @blkcg: block cgroup the new blkg is associated with
 140  * @q: request_queue the new blkg is associated with
 141  * @gfp_mask: allocation mask to use
 142  *
 143  * Allocate a new blkg assocating @blkcg and @q.
 144  */
 145 static struct blkcg_gq *blkg_alloc(struct blkcg *blkcg, struct request_queue *q,
 146                                    gfp_t gfp_mask)
 147 {
 148         struct blkcg_gq *blkg;
 149         int i;
 150 
 151         /* alloc and init base part */
 152         blkg = kzalloc_node(sizeof(*blkg), gfp_mask, q->node);
 153         if (!blkg)
 154                 return NULL;
 155 
 156         if (percpu_ref_init(&blkg->refcnt, blkg_release, 0, gfp_mask))
 157                 goto err_free;
 158 
 159         if (blkg_rwstat_init(&blkg->stat_bytes, gfp_mask) ||
 160             blkg_rwstat_init(&blkg->stat_ios, gfp_mask))
 161                 goto err_free;
 162 
 163         blkg->q = q;
 164         INIT_LIST_HEAD(&blkg->q_node);
 165         spin_lock_init(&blkg->async_bio_lock);
 166         bio_list_init(&blkg->async_bios);
 167         INIT_WORK(&blkg->async_bio_work, blkg_async_bio_workfn);
 168         blkg->blkcg = blkcg;
 169 
 170         for (i = 0; i < BLKCG_MAX_POLS; i++) {
 171                 struct blkcg_policy *pol = blkcg_policy[i];
 172                 struct blkg_policy_data *pd;
 173 
 174                 if (!blkcg_policy_enabled(q, pol))
 175                         continue;
 176 
 177                 /* alloc per-policy data and attach it to blkg */
 178                 pd = pol->pd_alloc_fn(gfp_mask, q, blkcg);
 179                 if (!pd)
 180                         goto err_free;
 181 
 182                 blkg->pd[i] = pd;
 183                 pd->blkg = blkg;
 184                 pd->plid = i;
 185         }
 186 
 187         return blkg;
 188 
 189 err_free:
 190         blkg_free(blkg);
 191         return NULL;
 192 }
 193 
 194 struct blkcg_gq *blkg_lookup_slowpath(struct blkcg *blkcg,
 195                                       struct request_queue *q, bool update_hint)
 196 {
 197         struct blkcg_gq *blkg;
 198 
 199         /*
 200          * Hint didn't match.  Look up from the radix tree.  Note that the
 201          * hint can only be updated under queue_lock as otherwise @blkg
 202          * could have already been removed from blkg_tree.  The caller is
 203          * responsible for grabbing queue_lock if @update_hint.
 204          */
 205         blkg = radix_tree_lookup(&blkcg->blkg_tree, q->id);
 206         if (blkg && blkg->q == q) {
 207                 if (update_hint) {
 208                         lockdep_assert_held(&q->queue_lock);
 209                         rcu_assign_pointer(blkcg->blkg_hint, blkg);
 210                 }
 211                 return blkg;
 212         }
 213 
 214         return NULL;
 215 }
 216 EXPORT_SYMBOL_GPL(blkg_lookup_slowpath);
 217 
 218 /*
 219  * If @new_blkg is %NULL, this function tries to allocate a new one as
 220  * necessary using %GFP_NOWAIT.  @new_blkg is always consumed on return.
 221  */
 222 static struct blkcg_gq *blkg_create(struct blkcg *blkcg,
 223                                     struct request_queue *q,
 224                                     struct blkcg_gq *new_blkg)
 225 {
 226         struct blkcg_gq *blkg;
 227         struct bdi_writeback_congested *wb_congested;
 228         int i, ret;
 229 
 230         WARN_ON_ONCE(!rcu_read_lock_held());
 231         lockdep_assert_held(&q->queue_lock);
 232 
 233         /* request_queue is dying, do not create/recreate a blkg */
 234         if (blk_queue_dying(q)) {
 235                 ret = -ENODEV;
 236                 goto err_free_blkg;
 237         }
 238 
 239         /* blkg holds a reference to blkcg */
 240         if (!css_tryget_online(&blkcg->css)) {
 241                 ret = -ENODEV;
 242                 goto err_free_blkg;
 243         }
 244 
 245         wb_congested = wb_congested_get_create(q->backing_dev_info,
 246                                                blkcg->css.id,
 247                                                GFP_NOWAIT | __GFP_NOWARN);
 248         if (!wb_congested) {
 249                 ret = -ENOMEM;
 250                 goto err_put_css;
 251         }
 252 
 253         /* allocate */
 254         if (!new_blkg) {
 255                 new_blkg = blkg_alloc(blkcg, q, GFP_NOWAIT | __GFP_NOWARN);
 256                 if (unlikely(!new_blkg)) {
 257                         ret = -ENOMEM;
 258                         goto err_put_congested;
 259                 }
 260         }
 261         blkg = new_blkg;
 262         blkg->wb_congested = wb_congested;
 263 
 264         /* link parent */
 265         if (blkcg_parent(blkcg)) {
 266                 blkg->parent = __blkg_lookup(blkcg_parent(blkcg), q, false);
 267                 if (WARN_ON_ONCE(!blkg->parent)) {
 268                         ret = -ENODEV;
 269                         goto err_put_congested;
 270                 }
 271                 blkg_get(blkg->parent);
 272         }
 273 
 274         /* invoke per-policy init */
 275         for (i = 0; i < BLKCG_MAX_POLS; i++) {
 276                 struct blkcg_policy *pol = blkcg_policy[i];
 277 
 278                 if (blkg->pd[i] && pol->pd_init_fn)
 279                         pol->pd_init_fn(blkg->pd[i]);
 280         }
 281 
 282         /* insert */
 283         spin_lock(&blkcg->lock);
 284         ret = radix_tree_insert(&blkcg->blkg_tree, q->id, blkg);
 285         if (likely(!ret)) {
 286                 hlist_add_head_rcu(&blkg->blkcg_node, &blkcg->blkg_list);
 287                 list_add(&blkg->q_node, &q->blkg_list);
 288 
 289                 for (i = 0; i < BLKCG_MAX_POLS; i++) {
 290                         struct blkcg_policy *pol = blkcg_policy[i];
 291 
 292                         if (blkg->pd[i] && pol->pd_online_fn)
 293                                 pol->pd_online_fn(blkg->pd[i]);
 294                 }
 295         }
 296         blkg->online = true;
 297         spin_unlock(&blkcg->lock);
 298 
 299         if (!ret)
 300                 return blkg;
 301 
 302         /* @blkg failed fully initialized, use the usual release path */
 303         blkg_put(blkg);
 304         return ERR_PTR(ret);
 305 
 306 err_put_congested:
 307         wb_congested_put(wb_congested);
 308 err_put_css:
 309         css_put(&blkcg->css);
 310 err_free_blkg:
 311         blkg_free(new_blkg);
 312         return ERR_PTR(ret);
 313 }
 314 
 315 /**
 316  * __blkg_lookup_create - lookup blkg, try to create one if not there
 317  * @blkcg: blkcg of interest
 318  * @q: request_queue of interest
 319  *
 320  * Lookup blkg for the @blkcg - @q pair.  If it doesn't exist, try to
 321  * create one.  blkg creation is performed recursively from blkcg_root such
 322  * that all non-root blkg's have access to the parent blkg.  This function
 323  * should be called under RCU read lock and @q->queue_lock.
 324  *
 325  * Returns the blkg or the closest blkg if blkg_create() fails as it walks
 326  * down from root.
 327  */
 328 struct blkcg_gq *__blkg_lookup_create(struct blkcg *blkcg,
 329                                       struct request_queue *q)
 330 {
 331         struct blkcg_gq *blkg;
 332 
 333         WARN_ON_ONCE(!rcu_read_lock_held());
 334         lockdep_assert_held(&q->queue_lock);
 335 
 336         blkg = __blkg_lookup(blkcg, q, true);
 337         if (blkg)
 338                 return blkg;
 339 
 340         /*
 341          * Create blkgs walking down from blkcg_root to @blkcg, so that all
 342          * non-root blkgs have access to their parents.  Returns the closest
 343          * blkg to the intended blkg should blkg_create() fail.
 344          */
 345         while (true) {
 346                 struct blkcg *pos = blkcg;
 347                 struct blkcg *parent = blkcg_parent(blkcg);
 348                 struct blkcg_gq *ret_blkg = q->root_blkg;
 349 
 350                 while (parent) {
 351                         blkg = __blkg_lookup(parent, q, false);
 352                         if (blkg) {
 353                                 /* remember closest blkg */
 354                                 ret_blkg = blkg;
 355                                 break;
 356                         }
 357                         pos = parent;
 358                         parent = blkcg_parent(parent);
 359                 }
 360 
 361                 blkg = blkg_create(pos, q, NULL);
 362                 if (IS_ERR(blkg))
 363                         return ret_blkg;
 364                 if (pos == blkcg)
 365                         return blkg;
 366         }
 367 }
 368 
 369 /**
 370  * blkg_lookup_create - find or create a blkg
 371  * @blkcg: target block cgroup
 372  * @q: target request_queue
 373  *
 374  * This looks up or creates the blkg representing the unique pair
 375  * of the blkcg and the request_queue.
 376  */
 377 struct blkcg_gq *blkg_lookup_create(struct blkcg *blkcg,
 378                                     struct request_queue *q)
 379 {
 380         struct blkcg_gq *blkg = blkg_lookup(blkcg, q);
 381 
 382         if (unlikely(!blkg)) {
 383                 unsigned long flags;
 384 
 385                 spin_lock_irqsave(&q->queue_lock, flags);
 386                 blkg = __blkg_lookup_create(blkcg, q);
 387                 spin_unlock_irqrestore(&q->queue_lock, flags);
 388         }
 389 
 390         return blkg;
 391 }
 392 
 393 static void blkg_destroy(struct blkcg_gq *blkg)
 394 {
 395         struct blkcg *blkcg = blkg->blkcg;
 396         struct blkcg_gq *parent = blkg->parent;
 397         int i;
 398 
 399         lockdep_assert_held(&blkg->q->queue_lock);
 400         lockdep_assert_held(&blkcg->lock);
 401 
 402         /* Something wrong if we are trying to remove same group twice */
 403         WARN_ON_ONCE(list_empty(&blkg->q_node));
 404         WARN_ON_ONCE(hlist_unhashed(&blkg->blkcg_node));
 405 
 406         for (i = 0; i < BLKCG_MAX_POLS; i++) {
 407                 struct blkcg_policy *pol = blkcg_policy[i];
 408 
 409                 if (blkg->pd[i] && pol->pd_offline_fn)
 410                         pol->pd_offline_fn(blkg->pd[i]);
 411         }
 412 
 413         if (parent) {
 414                 blkg_rwstat_add_aux(&parent->stat_bytes, &blkg->stat_bytes);
 415                 blkg_rwstat_add_aux(&parent->stat_ios, &blkg->stat_ios);
 416         }
 417 
 418         blkg->online = false;
 419 
 420         radix_tree_delete(&blkcg->blkg_tree, blkg->q->id);
 421         list_del_init(&blkg->q_node);
 422         hlist_del_init_rcu(&blkg->blkcg_node);
 423 
 424         /*
 425          * Both setting lookup hint to and clearing it from @blkg are done
 426          * under queue_lock.  If it's not pointing to @blkg now, it never
 427          * will.  Hint assignment itself can race safely.
 428          */
 429         if (rcu_access_pointer(blkcg->blkg_hint) == blkg)
 430                 rcu_assign_pointer(blkcg->blkg_hint, NULL);
 431 
 432         /*
 433          * Put the reference taken at the time of creation so that when all
 434          * queues are gone, group can be destroyed.
 435          */
 436         percpu_ref_kill(&blkg->refcnt);
 437 }
 438 
 439 /**
 440  * blkg_destroy_all - destroy all blkgs associated with a request_queue
 441  * @q: request_queue of interest
 442  *
 443  * Destroy all blkgs associated with @q.
 444  */
 445 static void blkg_destroy_all(struct request_queue *q)
 446 {
 447         struct blkcg_gq *blkg, *n;
 448 
 449         spin_lock_irq(&q->queue_lock);
 450         list_for_each_entry_safe(blkg, n, &q->blkg_list, q_node) {
 451                 struct blkcg *blkcg = blkg->blkcg;
 452 
 453                 spin_lock(&blkcg->lock);
 454                 blkg_destroy(blkg);
 455                 spin_unlock(&blkcg->lock);
 456         }
 457 
 458         q->root_blkg = NULL;
 459         spin_unlock_irq(&q->queue_lock);
 460 }
 461 
 462 static int blkcg_reset_stats(struct cgroup_subsys_state *css,
 463                              struct cftype *cftype, u64 val)
 464 {
 465         struct blkcg *blkcg = css_to_blkcg(css);
 466         struct blkcg_gq *blkg;
 467         int i;
 468 
 469         mutex_lock(&blkcg_pol_mutex);
 470         spin_lock_irq(&blkcg->lock);
 471 
 472         /*
 473          * Note that stat reset is racy - it doesn't synchronize against
 474          * stat updates.  This is a debug feature which shouldn't exist
 475          * anyway.  If you get hit by a race, retry.
 476          */
 477         hlist_for_each_entry(blkg, &blkcg->blkg_list, blkcg_node) {
 478                 blkg_rwstat_reset(&blkg->stat_bytes);
 479                 blkg_rwstat_reset(&blkg->stat_ios);
 480 
 481                 for (i = 0; i < BLKCG_MAX_POLS; i++) {
 482                         struct blkcg_policy *pol = blkcg_policy[i];
 483 
 484                         if (blkg->pd[i] && pol->pd_reset_stats_fn)
 485                                 pol->pd_reset_stats_fn(blkg->pd[i]);
 486                 }
 487         }
 488 
 489         spin_unlock_irq(&blkcg->lock);
 490         mutex_unlock(&blkcg_pol_mutex);
 491         return 0;
 492 }
 493 
 494 const char *blkg_dev_name(struct blkcg_gq *blkg)
 495 {
 496         /* some drivers (floppy) instantiate a queue w/o disk registered */
 497         if (blkg->q->backing_dev_info->dev)
 498                 return dev_name(blkg->q->backing_dev_info->dev);
 499         return NULL;
 500 }
 501 
 502 /**
 503  * blkcg_print_blkgs - helper for printing per-blkg data
 504  * @sf: seq_file to print to
 505  * @blkcg: blkcg of interest
 506  * @prfill: fill function to print out a blkg
 507  * @pol: policy in question
 508  * @data: data to be passed to @prfill
 509  * @show_total: to print out sum of prfill return values or not
 510  *
 511  * This function invokes @prfill on each blkg of @blkcg if pd for the
 512  * policy specified by @pol exists.  @prfill is invoked with @sf, the
 513  * policy data and @data and the matching queue lock held.  If @show_total
 514  * is %true, the sum of the return values from @prfill is printed with
 515  * "Total" label at the end.
 516  *
 517  * This is to be used to construct print functions for
 518  * cftype->read_seq_string method.
 519  */
 520 void blkcg_print_blkgs(struct seq_file *sf, struct blkcg *blkcg,
 521                        u64 (*prfill)(struct seq_file *,
 522                                      struct blkg_policy_data *, int),
 523                        const struct blkcg_policy *pol, int data,
 524                        bool show_total)
 525 {
 526         struct blkcg_gq *blkg;
 527         u64 total = 0;
 528 
 529         rcu_read_lock();
 530         hlist_for_each_entry_rcu(blkg, &blkcg->blkg_list, blkcg_node) {
 531                 spin_lock_irq(&blkg->q->queue_lock);
 532                 if (blkcg_policy_enabled(blkg->q, pol))
 533                         total += prfill(sf, blkg->pd[pol->plid], data);
 534                 spin_unlock_irq(&blkg->q->queue_lock);
 535         }
 536         rcu_read_unlock();
 537 
 538         if (show_total)
 539                 seq_printf(sf, "Total %llu\n", (unsigned long long)total);
 540 }
 541 EXPORT_SYMBOL_GPL(blkcg_print_blkgs);
 542 
 543 /**
 544  * __blkg_prfill_u64 - prfill helper for a single u64 value
 545  * @sf: seq_file to print to
 546  * @pd: policy private data of interest
 547  * @v: value to print
 548  *
 549  * Print @v to @sf for the device assocaited with @pd.
 550  */
 551 u64 __blkg_prfill_u64(struct seq_file *sf, struct blkg_policy_data *pd, u64 v)
 552 {
 553         const char *dname = blkg_dev_name(pd->blkg);
 554 
 555         if (!dname)
 556                 return 0;
 557 
 558         seq_printf(sf, "%s %llu\n", dname, (unsigned long long)v);
 559         return v;
 560 }
 561 EXPORT_SYMBOL_GPL(__blkg_prfill_u64);
 562 
 563 /**
 564  * __blkg_prfill_rwstat - prfill helper for a blkg_rwstat
 565  * @sf: seq_file to print to
 566  * @pd: policy private data of interest
 567  * @rwstat: rwstat to print
 568  *
 569  * Print @rwstat to @sf for the device assocaited with @pd.
 570  */
 571 u64 __blkg_prfill_rwstat(struct seq_file *sf, struct blkg_policy_data *pd,
 572                          const struct blkg_rwstat_sample *rwstat)
 573 {
 574         static const char *rwstr[] = {
 575                 [BLKG_RWSTAT_READ]      = "Read",
 576                 [BLKG_RWSTAT_WRITE]     = "Write",
 577                 [BLKG_RWSTAT_SYNC]      = "Sync",
 578                 [BLKG_RWSTAT_ASYNC]     = "Async",
 579                 [BLKG_RWSTAT_DISCARD]   = "Discard",
 580         };
 581         const char *dname = blkg_dev_name(pd->blkg);
 582         u64 v;
 583         int i;
 584 
 585         if (!dname)
 586                 return 0;
 587 
 588         for (i = 0; i < BLKG_RWSTAT_NR; i++)
 589                 seq_printf(sf, "%s %s %llu\n", dname, rwstr[i],
 590                            rwstat->cnt[i]);
 591 
 592         v = rwstat->cnt[BLKG_RWSTAT_READ] +
 593                 rwstat->cnt[BLKG_RWSTAT_WRITE] +
 594                 rwstat->cnt[BLKG_RWSTAT_DISCARD];
 595         seq_printf(sf, "%s Total %llu\n", dname, v);
 596         return v;
 597 }
 598 EXPORT_SYMBOL_GPL(__blkg_prfill_rwstat);
 599 
 600 /**
 601  * blkg_prfill_rwstat - prfill callback for blkg_rwstat
 602  * @sf: seq_file to print to
 603  * @pd: policy private data of interest
 604  * @off: offset to the blkg_rwstat in @pd
 605  *
 606  * prfill callback for printing a blkg_rwstat.
 607  */
 608 u64 blkg_prfill_rwstat(struct seq_file *sf, struct blkg_policy_data *pd,
 609                        int off)
 610 {
 611         struct blkg_rwstat_sample rwstat = { };
 612 
 613         blkg_rwstat_read((void *)pd + off, &rwstat);
 614         return __blkg_prfill_rwstat(sf, pd, &rwstat);
 615 }
 616 EXPORT_SYMBOL_GPL(blkg_prfill_rwstat);
 617 
 618 static u64 blkg_prfill_rwstat_field(struct seq_file *sf,
 619                                     struct blkg_policy_data *pd, int off)
 620 {
 621         struct blkg_rwstat_sample rwstat = { };
 622 
 623         blkg_rwstat_read((void *)pd->blkg + off, &rwstat);
 624         return __blkg_prfill_rwstat(sf, pd, &rwstat);
 625 }
 626 
 627 /**
 628  * blkg_print_stat_bytes - seq_show callback for blkg->stat_bytes
 629  * @sf: seq_file to print to
 630  * @v: unused
 631  *
 632  * To be used as cftype->seq_show to print blkg->stat_bytes.
 633  * cftype->private must be set to the blkcg_policy.
 634  */
 635 int blkg_print_stat_bytes(struct seq_file *sf, void *v)
 636 {
 637         blkcg_print_blkgs(sf, css_to_blkcg(seq_css(sf)),
 638                           blkg_prfill_rwstat_field, (void *)seq_cft(sf)->private,
 639                           offsetof(struct blkcg_gq, stat_bytes), true);
 640         return 0;
 641 }
 642 EXPORT_SYMBOL_GPL(blkg_print_stat_bytes);
 643 
 644 /**
 645  * blkg_print_stat_bytes - seq_show callback for blkg->stat_ios
 646  * @sf: seq_file to print to
 647  * @v: unused
 648  *
 649  * To be used as cftype->seq_show to print blkg->stat_ios.  cftype->private
 650  * must be set to the blkcg_policy.
 651  */
 652 int blkg_print_stat_ios(struct seq_file *sf, void *v)
 653 {
 654         blkcg_print_blkgs(sf, css_to_blkcg(seq_css(sf)),
 655                           blkg_prfill_rwstat_field, (void *)seq_cft(sf)->private,
 656                           offsetof(struct blkcg_gq, stat_ios), true);
 657         return 0;
 658 }
 659 EXPORT_SYMBOL_GPL(blkg_print_stat_ios);
 660 
 661 static u64 blkg_prfill_rwstat_field_recursive(struct seq_file *sf,
 662                                               struct blkg_policy_data *pd,
 663                                               int off)
 664 {
 665         struct blkg_rwstat_sample rwstat;
 666 
 667         blkg_rwstat_recursive_sum(pd->blkg, NULL, off, &rwstat);
 668         return __blkg_prfill_rwstat(sf, pd, &rwstat);
 669 }
 670 
 671 /**
 672  * blkg_print_stat_bytes_recursive - recursive version of blkg_print_stat_bytes
 673  * @sf: seq_file to print to
 674  * @v: unused
 675  */
 676 int blkg_print_stat_bytes_recursive(struct seq_file *sf, void *v)
 677 {
 678         blkcg_print_blkgs(sf, css_to_blkcg(seq_css(sf)),
 679                           blkg_prfill_rwstat_field_recursive,
 680                           (void *)seq_cft(sf)->private,
 681                           offsetof(struct blkcg_gq, stat_bytes), true);
 682         return 0;
 683 }
 684 EXPORT_SYMBOL_GPL(blkg_print_stat_bytes_recursive);
 685 
 686 /**
 687  * blkg_print_stat_ios_recursive - recursive version of blkg_print_stat_ios
 688  * @sf: seq_file to print to
 689  * @v: unused
 690  */
 691 int blkg_print_stat_ios_recursive(struct seq_file *sf, void *v)
 692 {
 693         blkcg_print_blkgs(sf, css_to_blkcg(seq_css(sf)),
 694                           blkg_prfill_rwstat_field_recursive,
 695                           (void *)seq_cft(sf)->private,
 696                           offsetof(struct blkcg_gq, stat_ios), true);
 697         return 0;
 698 }
 699 EXPORT_SYMBOL_GPL(blkg_print_stat_ios_recursive);
 700 
 701 /**
 702  * blkg_rwstat_recursive_sum - collect hierarchical blkg_rwstat
 703  * @blkg: blkg of interest
 704  * @pol: blkcg_policy which contains the blkg_rwstat
 705  * @off: offset to the blkg_rwstat in blkg_policy_data or @blkg
 706  * @sum: blkg_rwstat_sample structure containing the results
 707  *
 708  * Collect the blkg_rwstat specified by @blkg, @pol and @off and all its
 709  * online descendants and their aux counts.  The caller must be holding the
 710  * queue lock for online tests.
 711  *
 712  * If @pol is NULL, blkg_rwstat is at @off bytes into @blkg; otherwise, it
 713  * is at @off bytes into @blkg's blkg_policy_data of the policy.
 714  */
 715 void blkg_rwstat_recursive_sum(struct blkcg_gq *blkg, struct blkcg_policy *pol,
 716                 int off, struct blkg_rwstat_sample *sum)
 717 {
 718         struct blkcg_gq *pos_blkg;
 719         struct cgroup_subsys_state *pos_css;
 720         unsigned int i;
 721 
 722         lockdep_assert_held(&blkg->q->queue_lock);
 723 
 724         rcu_read_lock();
 725         blkg_for_each_descendant_pre(pos_blkg, pos_css, blkg) {
 726                 struct blkg_rwstat *rwstat;
 727 
 728                 if (!pos_blkg->online)
 729                         continue;
 730 
 731                 if (pol)
 732                         rwstat = (void *)blkg_to_pd(pos_blkg, pol) + off;
 733                 else
 734                         rwstat = (void *)pos_blkg + off;
 735 
 736                 for (i = 0; i < BLKG_RWSTAT_NR; i++)
 737                         sum->cnt[i] = blkg_rwstat_read_counter(rwstat, i);
 738         }
 739         rcu_read_unlock();
 740 }
 741 EXPORT_SYMBOL_GPL(blkg_rwstat_recursive_sum);
 742 
 743 /* Performs queue bypass and policy enabled checks then looks up blkg. */
 744 static struct blkcg_gq *blkg_lookup_check(struct blkcg *blkcg,
 745                                           const struct blkcg_policy *pol,
 746                                           struct request_queue *q)
 747 {
 748         WARN_ON_ONCE(!rcu_read_lock_held());
 749         lockdep_assert_held(&q->queue_lock);
 750 
 751         if (!blkcg_policy_enabled(q, pol))
 752                 return ERR_PTR(-EOPNOTSUPP);
 753         return __blkg_lookup(blkcg, q, true /* update_hint */);
 754 }
 755 
 756 /**
 757  * blkg_conf_prep - parse and prepare for per-blkg config update
 758  * @inputp: input string pointer
 759  *
 760  * Parse the device node prefix part, MAJ:MIN, of per-blkg config update
 761  * from @input and get and return the matching gendisk.  *@inputp is
 762  * updated to point past the device node prefix.  Returns an ERR_PTR()
 763  * value on error.
 764  *
 765  * Use this function iff blkg_conf_prep() can't be used for some reason.
 766  */
 767 struct gendisk *blkcg_conf_get_disk(char **inputp)
 768 {
 769         char *input = *inputp;
 770         unsigned int major, minor;
 771         struct gendisk *disk;
 772         int key_len, part;
 773 
 774         if (sscanf(input, "%u:%u%n", &major, &minor, &key_len) != 2)
 775                 return ERR_PTR(-EINVAL);
 776 
 777         input += key_len;
 778         if (!isspace(*input))
 779                 return ERR_PTR(-EINVAL);
 780         input = skip_spaces(input);
 781 
 782         disk = get_gendisk(MKDEV(major, minor), &part);
 783         if (!disk)
 784                 return ERR_PTR(-ENODEV);
 785         if (part) {
 786                 put_disk_and_module(disk);
 787                 return ERR_PTR(-ENODEV);
 788         }
 789 
 790         *inputp = input;
 791         return disk;
 792 }
 793 
 794 /**
 795  * blkg_conf_prep - parse and prepare for per-blkg config update
 796  * @blkcg: target block cgroup
 797  * @pol: target policy
 798  * @input: input string
 799  * @ctx: blkg_conf_ctx to be filled
 800  *
 801  * Parse per-blkg config update from @input and initialize @ctx with the
 802  * result.  @ctx->blkg points to the blkg to be updated and @ctx->body the
 803  * part of @input following MAJ:MIN.  This function returns with RCU read
 804  * lock and queue lock held and must be paired with blkg_conf_finish().
 805  */
 806 int blkg_conf_prep(struct blkcg *blkcg, const struct blkcg_policy *pol,
 807                    char *input, struct blkg_conf_ctx *ctx)
 808         __acquires(rcu) __acquires(&disk->queue->queue_lock)
 809 {
 810         struct gendisk *disk;
 811         struct request_queue *q;
 812         struct blkcg_gq *blkg;
 813         int ret;
 814 
 815         disk = blkcg_conf_get_disk(&input);
 816         if (IS_ERR(disk))
 817                 return PTR_ERR(disk);
 818 
 819         q = disk->queue;
 820 
 821         rcu_read_lock();
 822         spin_lock_irq(&q->queue_lock);
 823 
 824         blkg = blkg_lookup_check(blkcg, pol, q);
 825         if (IS_ERR(blkg)) {
 826                 ret = PTR_ERR(blkg);
 827                 goto fail_unlock;
 828         }
 829 
 830         if (blkg)
 831                 goto success;
 832 
 833         /*
 834          * Create blkgs walking down from blkcg_root to @blkcg, so that all
 835          * non-root blkgs have access to their parents.
 836          */
 837         while (true) {
 838                 struct blkcg *pos = blkcg;
 839                 struct blkcg *parent;
 840                 struct blkcg_gq *new_blkg;
 841 
 842                 parent = blkcg_parent(blkcg);
 843                 while (parent && !__blkg_lookup(parent, q, false)) {
 844                         pos = parent;
 845                         parent = blkcg_parent(parent);
 846                 }
 847 
 848                 /* Drop locks to do new blkg allocation with GFP_KERNEL. */
 849                 spin_unlock_irq(&q->queue_lock);
 850                 rcu_read_unlock();
 851 
 852                 new_blkg = blkg_alloc(pos, q, GFP_KERNEL);
 853                 if (unlikely(!new_blkg)) {
 854                         ret = -ENOMEM;
 855                         goto fail;
 856                 }
 857 
 858                 rcu_read_lock();
 859                 spin_lock_irq(&q->queue_lock);
 860 
 861                 blkg = blkg_lookup_check(pos, pol, q);
 862                 if (IS_ERR(blkg)) {
 863                         ret = PTR_ERR(blkg);
 864                         goto fail_unlock;
 865                 }
 866 
 867                 if (blkg) {
 868                         blkg_free(new_blkg);
 869                 } else {
 870                         blkg = blkg_create(pos, q, new_blkg);
 871                         if (IS_ERR(blkg)) {
 872                                 ret = PTR_ERR(blkg);
 873                                 goto fail_unlock;
 874                         }
 875                 }
 876 
 877                 if (pos == blkcg)
 878                         goto success;
 879         }
 880 success:
 881         ctx->disk = disk;
 882         ctx->blkg = blkg;
 883         ctx->body = input;
 884         return 0;
 885 
 886 fail_unlock:
 887         spin_unlock_irq(&q->queue_lock);
 888         rcu_read_unlock();
 889 fail:
 890         put_disk_and_module(disk);
 891         /*
 892          * If queue was bypassing, we should retry.  Do so after a
 893          * short msleep().  It isn't strictly necessary but queue
 894          * can be bypassing for some time and it's always nice to
 895          * avoid busy looping.
 896          */
 897         if (ret == -EBUSY) {
 898                 msleep(10);
 899                 ret = restart_syscall();
 900         }
 901         return ret;
 902 }
 903 EXPORT_SYMBOL_GPL(blkg_conf_prep);
 904 
 905 /**
 906  * blkg_conf_finish - finish up per-blkg config update
 907  * @ctx: blkg_conf_ctx intiailized by blkg_conf_prep()
 908  *
 909  * Finish up after per-blkg config update.  This function must be paired
 910  * with blkg_conf_prep().
 911  */
 912 void blkg_conf_finish(struct blkg_conf_ctx *ctx)
 913         __releases(&ctx->disk->queue->queue_lock) __releases(rcu)
 914 {
 915         spin_unlock_irq(&ctx->disk->queue->queue_lock);
 916         rcu_read_unlock();
 917         put_disk_and_module(ctx->disk);
 918 }
 919 EXPORT_SYMBOL_GPL(blkg_conf_finish);
 920 
 921 static int blkcg_print_stat(struct seq_file *sf, void *v)
 922 {
 923         struct blkcg *blkcg = css_to_blkcg(seq_css(sf));
 924         struct blkcg_gq *blkg;
 925 
 926         rcu_read_lock();
 927 
 928         hlist_for_each_entry_rcu(blkg, &blkcg->blkg_list, blkcg_node) {
 929                 const char *dname;
 930                 char *buf;
 931                 struct blkg_rwstat_sample rwstat;
 932                 u64 rbytes, wbytes, rios, wios, dbytes, dios;
 933                 size_t size = seq_get_buf(sf, &buf), off = 0;
 934                 int i;
 935                 bool has_stats = false;
 936 
 937                 spin_lock_irq(&blkg->q->queue_lock);
 938 
 939                 if (!blkg->online)
 940                         goto skip;
 941 
 942                 dname = blkg_dev_name(blkg);
 943                 if (!dname)
 944                         goto skip;
 945 
 946                 /*
 947                  * Hooray string manipulation, count is the size written NOT
 948                  * INCLUDING THE \0, so size is now count+1 less than what we
 949                  * had before, but we want to start writing the next bit from
 950                  * the \0 so we only add count to buf.
 951                  */
 952                 off += scnprintf(buf+off, size-off, "%s ", dname);
 953 
 954                 blkg_rwstat_recursive_sum(blkg, NULL,
 955                                 offsetof(struct blkcg_gq, stat_bytes), &rwstat);
 956                 rbytes = rwstat.cnt[BLKG_RWSTAT_READ];
 957                 wbytes = rwstat.cnt[BLKG_RWSTAT_WRITE];
 958                 dbytes = rwstat.cnt[BLKG_RWSTAT_DISCARD];
 959 
 960                 blkg_rwstat_recursive_sum(blkg, NULL,
 961                                         offsetof(struct blkcg_gq, stat_ios), &rwstat);
 962                 rios = rwstat.cnt[BLKG_RWSTAT_READ];
 963                 wios = rwstat.cnt[BLKG_RWSTAT_WRITE];
 964                 dios = rwstat.cnt[BLKG_RWSTAT_DISCARD];
 965 
 966                 if (rbytes || wbytes || rios || wios) {
 967                         has_stats = true;
 968                         off += scnprintf(buf+off, size-off,
 969                                          "rbytes=%llu wbytes=%llu rios=%llu wios=%llu dbytes=%llu dios=%llu",
 970                                          rbytes, wbytes, rios, wios,
 971                                          dbytes, dios);
 972                 }
 973 
 974                 if (blkcg_debug_stats && atomic_read(&blkg->use_delay)) {
 975                         has_stats = true;
 976                         off += scnprintf(buf+off, size-off,
 977                                          " use_delay=%d delay_nsec=%llu",
 978                                          atomic_read(&blkg->use_delay),
 979                                         (unsigned long long)atomic64_read(&blkg->delay_nsec));
 980                 }
 981 
 982                 for (i = 0; i < BLKCG_MAX_POLS; i++) {
 983                         struct blkcg_policy *pol = blkcg_policy[i];
 984                         size_t written;
 985 
 986                         if (!blkg->pd[i] || !pol->pd_stat_fn)
 987                                 continue;
 988 
 989                         written = pol->pd_stat_fn(blkg->pd[i], buf+off, size-off);
 990                         if (written)
 991                                 has_stats = true;
 992                         off += written;
 993                 }
 994 
 995                 if (has_stats) {
 996                         if (off < size - 1) {
 997                                 off += scnprintf(buf+off, size-off, "\n");
 998                                 seq_commit(sf, off);
 999                         } else {
1000                                 seq_commit(sf, -1);
1001                         }
1002                 }
1003         skip:
1004                 spin_unlock_irq(&blkg->q->queue_lock);
1005         }
1006 
1007         rcu_read_unlock();
1008         return 0;
1009 }
1010 
1011 static struct cftype blkcg_files[] = {
1012         {
1013                 .name = "stat",
1014                 .flags = CFTYPE_NOT_ON_ROOT,
1015                 .seq_show = blkcg_print_stat,
1016         },
1017         { }     /* terminate */
1018 };
1019 
1020 static struct cftype blkcg_legacy_files[] = {
1021         {
1022                 .name = "reset_stats",
1023                 .write_u64 = blkcg_reset_stats,
1024         },
1025         { }     /* terminate */
1026 };
1027 
1028 /*
1029  * blkcg destruction is a three-stage process.
1030  *
1031  * 1. Destruction starts.  The blkcg_css_offline() callback is invoked
1032  *    which offlines writeback.  Here we tie the next stage of blkg destruction
1033  *    to the completion of writeback associated with the blkcg.  This lets us
1034  *    avoid punting potentially large amounts of outstanding writeback to root
1035  *    while maintaining any ongoing policies.  The next stage is triggered when
1036  *    the nr_cgwbs count goes to zero.
1037  *
1038  * 2. When the nr_cgwbs count goes to zero, blkcg_destroy_blkgs() is called
1039  *    and handles the destruction of blkgs.  Here the css reference held by
1040  *    the blkg is put back eventually allowing blkcg_css_free() to be called.
1041  *    This work may occur in cgwb_release_workfn() on the cgwb_release
1042  *    workqueue.  Any submitted ios that fail to get the blkg ref will be
1043  *    punted to the root_blkg.
1044  *
1045  * 3. Once the blkcg ref count goes to zero, blkcg_css_free() is called.
1046  *    This finally frees the blkcg.
1047  */
1048 
1049 /**
1050  * blkcg_css_offline - cgroup css_offline callback
1051  * @css: css of interest
1052  *
1053  * This function is called when @css is about to go away.  Here the cgwbs are
1054  * offlined first and only once writeback associated with the blkcg has
1055  * finished do we start step 2 (see above).
1056  */
1057 static void blkcg_css_offline(struct cgroup_subsys_state *css)
1058 {
1059         struct blkcg *blkcg = css_to_blkcg(css);
1060 
1061         /* this prevents anyone from attaching or migrating to this blkcg */
1062         wb_blkcg_offline(blkcg);
1063 
1064         /* put the base cgwb reference allowing step 2 to be triggered */
1065         blkcg_cgwb_put(blkcg);
1066 }
1067 
1068 /**
1069  * blkcg_destroy_blkgs - responsible for shooting down blkgs
1070  * @blkcg: blkcg of interest
1071  *
1072  * blkgs should be removed while holding both q and blkcg locks.  As blkcg lock
1073  * is nested inside q lock, this function performs reverse double lock dancing.
1074  * Destroying the blkgs releases the reference held on the blkcg's css allowing
1075  * blkcg_css_free to eventually be called.
1076  *
1077  * This is the blkcg counterpart of ioc_release_fn().
1078  */
1079 void blkcg_destroy_blkgs(struct blkcg *blkcg)
1080 {
1081         spin_lock_irq(&blkcg->lock);
1082 
1083         while (!hlist_empty(&blkcg->blkg_list)) {
1084                 struct blkcg_gq *blkg = hlist_entry(blkcg->blkg_list.first,
1085                                                 struct blkcg_gq, blkcg_node);
1086                 struct request_queue *q = blkg->q;
1087 
1088                 if (spin_trylock(&q->queue_lock)) {
1089                         blkg_destroy(blkg);
1090                         spin_unlock(&q->queue_lock);
1091                 } else {
1092                         spin_unlock_irq(&blkcg->lock);
1093                         cpu_relax();
1094                         spin_lock_irq(&blkcg->lock);
1095                 }
1096         }
1097 
1098         spin_unlock_irq(&blkcg->lock);
1099 }
1100 
1101 static void blkcg_css_free(struct cgroup_subsys_state *css)
1102 {
1103         struct blkcg *blkcg = css_to_blkcg(css);
1104         int i;
1105 
1106         mutex_lock(&blkcg_pol_mutex);
1107 
1108         list_del(&blkcg->all_blkcgs_node);
1109 
1110         for (i = 0; i < BLKCG_MAX_POLS; i++)
1111                 if (blkcg->cpd[i])
1112                         blkcg_policy[i]->cpd_free_fn(blkcg->cpd[i]);
1113 
1114         mutex_unlock(&blkcg_pol_mutex);
1115 
1116         kfree(blkcg);
1117 }
1118 
1119 static struct cgroup_subsys_state *
1120 blkcg_css_alloc(struct cgroup_subsys_state *parent_css)
1121 {
1122         struct blkcg *blkcg;
1123         struct cgroup_subsys_state *ret;
1124         int i;
1125 
1126         mutex_lock(&blkcg_pol_mutex);
1127 
1128         if (!parent_css) {
1129                 blkcg = &blkcg_root;
1130         } else {
1131                 blkcg = kzalloc(sizeof(*blkcg), GFP_KERNEL);
1132                 if (!blkcg) {
1133                         ret = ERR_PTR(-ENOMEM);
1134                         goto unlock;
1135                 }
1136         }
1137 
1138         for (i = 0; i < BLKCG_MAX_POLS ; i++) {
1139                 struct blkcg_policy *pol = blkcg_policy[i];
1140                 struct blkcg_policy_data *cpd;
1141 
1142                 /*
1143                  * If the policy hasn't been attached yet, wait for it
1144                  * to be attached before doing anything else. Otherwise,
1145                  * check if the policy requires any specific per-cgroup
1146                  * data: if it does, allocate and initialize it.
1147                  */
1148                 if (!pol || !pol->cpd_alloc_fn)
1149                         continue;
1150 
1151                 cpd = pol->cpd_alloc_fn(GFP_KERNEL);
1152                 if (!cpd) {
1153                         ret = ERR_PTR(-ENOMEM);
1154                         goto free_pd_blkcg;
1155                 }
1156                 blkcg->cpd[i] = cpd;
1157                 cpd->blkcg = blkcg;
1158                 cpd->plid = i;
1159                 if (pol->cpd_init_fn)
1160                         pol->cpd_init_fn(cpd);
1161         }
1162 
1163         spin_lock_init(&blkcg->lock);
1164         INIT_RADIX_TREE(&blkcg->blkg_tree, GFP_NOWAIT | __GFP_NOWARN);
1165         INIT_HLIST_HEAD(&blkcg->blkg_list);
1166 #ifdef CONFIG_CGROUP_WRITEBACK
1167         INIT_LIST_HEAD(&blkcg->cgwb_list);
1168         refcount_set(&blkcg->cgwb_refcnt, 1);
1169 #endif
1170         list_add_tail(&blkcg->all_blkcgs_node, &all_blkcgs);
1171 
1172         mutex_unlock(&blkcg_pol_mutex);
1173         return &blkcg->css;
1174 
1175 free_pd_blkcg:
1176         for (i--; i >= 0; i--)
1177                 if (blkcg->cpd[i])
1178                         blkcg_policy[i]->cpd_free_fn(blkcg->cpd[i]);
1179 
1180         if (blkcg != &blkcg_root)
1181                 kfree(blkcg);
1182 unlock:
1183         mutex_unlock(&blkcg_pol_mutex);
1184         return ret;
1185 }
1186 
1187 /**
1188  * blkcg_init_queue - initialize blkcg part of request queue
1189  * @q: request_queue to initialize
1190  *
1191  * Called from blk_alloc_queue_node(). Responsible for initializing blkcg
1192  * part of new request_queue @q.
1193  *
1194  * RETURNS:
1195  * 0 on success, -errno on failure.
1196  */
1197 int blkcg_init_queue(struct request_queue *q)
1198 {
1199         struct blkcg_gq *new_blkg, *blkg;
1200         bool preloaded;
1201         int ret;
1202 
1203         new_blkg = blkg_alloc(&blkcg_root, q, GFP_KERNEL);
1204         if (!new_blkg)
1205                 return -ENOMEM;
1206 
1207         preloaded = !radix_tree_preload(GFP_KERNEL);
1208 
1209         /* Make sure the root blkg exists. */
1210         rcu_read_lock();
1211         spin_lock_irq(&q->queue_lock);
1212         blkg = blkg_create(&blkcg_root, q, new_blkg);
1213         if (IS_ERR(blkg))
1214                 goto err_unlock;
1215         q->root_blkg = blkg;
1216         spin_unlock_irq(&q->queue_lock);
1217         rcu_read_unlock();
1218 
1219         if (preloaded)
1220                 radix_tree_preload_end();
1221 
1222         ret = blk_iolatency_init(q);
1223         if (ret)
1224                 goto err_destroy_all;
1225 
1226         ret = blk_throtl_init(q);
1227         if (ret)
1228                 goto err_destroy_all;
1229         return 0;
1230 
1231 err_destroy_all:
1232         blkg_destroy_all(q);
1233         return ret;
1234 err_unlock:
1235         spin_unlock_irq(&q->queue_lock);
1236         rcu_read_unlock();
1237         if (preloaded)
1238                 radix_tree_preload_end();
1239         return PTR_ERR(blkg);
1240 }
1241 
1242 /**
1243  * blkcg_drain_queue - drain blkcg part of request_queue
1244  * @q: request_queue to drain
1245  *
1246  * Called from blk_drain_queue().  Responsible for draining blkcg part.
1247  */
1248 void blkcg_drain_queue(struct request_queue *q)
1249 {
1250         lockdep_assert_held(&q->queue_lock);
1251 
1252         /*
1253          * @q could be exiting and already have destroyed all blkgs as
1254          * indicated by NULL root_blkg.  If so, don't confuse policies.
1255          */
1256         if (!q->root_blkg)
1257                 return;
1258 
1259         blk_throtl_drain(q);
1260 }
1261 
1262 /**
1263  * blkcg_exit_queue - exit and release blkcg part of request_queue
1264  * @q: request_queue being released
1265  *
1266  * Called from blk_exit_queue().  Responsible for exiting blkcg part.
1267  */
1268 void blkcg_exit_queue(struct request_queue *q)
1269 {
1270         blkg_destroy_all(q);
1271         blk_throtl_exit(q);
1272 }
1273 
1274 /*
1275  * We cannot support shared io contexts, as we have no mean to support
1276  * two tasks with the same ioc in two different groups without major rework
1277  * of the main cic data structures.  For now we allow a task to change
1278  * its cgroup only if it's the only owner of its ioc.
1279  */
1280 static int blkcg_can_attach(struct cgroup_taskset *tset)
1281 {
1282         struct task_struct *task;
1283         struct cgroup_subsys_state *dst_css;
1284         struct io_context *ioc;
1285         int ret = 0;
1286 
1287         /* task_lock() is needed to avoid races with exit_io_context() */
1288         cgroup_taskset_for_each(task, dst_css, tset) {
1289                 task_lock(task);
1290                 ioc = task->io_context;
1291                 if (ioc && atomic_read(&ioc->nr_tasks) > 1)
1292                         ret = -EINVAL;
1293                 task_unlock(task);
1294                 if (ret)
1295                         break;
1296         }
1297         return ret;
1298 }
1299 
1300 static void blkcg_bind(struct cgroup_subsys_state *root_css)
1301 {
1302         int i;
1303 
1304         mutex_lock(&blkcg_pol_mutex);
1305 
1306         for (i = 0; i < BLKCG_MAX_POLS; i++) {
1307                 struct blkcg_policy *pol = blkcg_policy[i];
1308                 struct blkcg *blkcg;
1309 
1310                 if (!pol || !pol->cpd_bind_fn)
1311                         continue;
1312 
1313                 list_for_each_entry(blkcg, &all_blkcgs, all_blkcgs_node)
1314                         if (blkcg->cpd[pol->plid])
1315                                 pol->cpd_bind_fn(blkcg->cpd[pol->plid]);
1316         }
1317         mutex_unlock(&blkcg_pol_mutex);
1318 }
1319 
1320 static void blkcg_exit(struct task_struct *tsk)
1321 {
1322         if (tsk->throttle_queue)
1323                 blk_put_queue(tsk->throttle_queue);
1324         tsk->throttle_queue = NULL;
1325 }
1326 
1327 struct cgroup_subsys io_cgrp_subsys = {
1328         .css_alloc = blkcg_css_alloc,
1329         .css_offline = blkcg_css_offline,
1330         .css_free = blkcg_css_free,
1331         .can_attach = blkcg_can_attach,
1332         .bind = blkcg_bind,
1333         .dfl_cftypes = blkcg_files,
1334         .legacy_cftypes = blkcg_legacy_files,
1335         .legacy_name = "blkio",
1336         .exit = blkcg_exit,
1337 #ifdef CONFIG_MEMCG
1338         /*
1339          * This ensures that, if available, memcg is automatically enabled
1340          * together on the default hierarchy so that the owner cgroup can
1341          * be retrieved from writeback pages.
1342          */
1343         .depends_on = 1 << memory_cgrp_id,
1344 #endif
1345 };
1346 EXPORT_SYMBOL_GPL(io_cgrp_subsys);
1347 
1348 /**
1349  * blkcg_activate_policy - activate a blkcg policy on a request_queue
1350  * @q: request_queue of interest
1351  * @pol: blkcg policy to activate
1352  *
1353  * Activate @pol on @q.  Requires %GFP_KERNEL context.  @q goes through
1354  * bypass mode to populate its blkgs with policy_data for @pol.
1355  *
1356  * Activation happens with @q bypassed, so nobody would be accessing blkgs
1357  * from IO path.  Update of each blkg is protected by both queue and blkcg
1358  * locks so that holding either lock and testing blkcg_policy_enabled() is
1359  * always enough for dereferencing policy data.
1360  *
1361  * The caller is responsible for synchronizing [de]activations and policy
1362  * [un]registerations.  Returns 0 on success, -errno on failure.
1363  */
1364 int blkcg_activate_policy(struct request_queue *q,
1365                           const struct blkcg_policy *pol)
1366 {
1367         struct blkg_policy_data *pd_prealloc = NULL;
1368         struct blkcg_gq *blkg, *pinned_blkg = NULL;
1369         int ret;
1370 
1371         if (blkcg_policy_enabled(q, pol))
1372                 return 0;
1373 
1374         if (queue_is_mq(q))
1375                 blk_mq_freeze_queue(q);
1376 retry:
1377         spin_lock_irq(&q->queue_lock);
1378 
1379         /* blkg_list is pushed at the head, reverse walk to allocate parents first */
1380         list_for_each_entry_reverse(blkg, &q->blkg_list, q_node) {
1381                 struct blkg_policy_data *pd;
1382 
1383                 if (blkg->pd[pol->plid])
1384                         continue;
1385 
1386                 /* If prealloc matches, use it; otherwise try GFP_NOWAIT */
1387                 if (blkg == pinned_blkg) {
1388                         pd = pd_prealloc;
1389                         pd_prealloc = NULL;
1390                 } else {
1391                         pd = pol->pd_alloc_fn(GFP_NOWAIT | __GFP_NOWARN, q,
1392                                               blkg->blkcg);
1393                 }
1394 
1395                 if (!pd) {
1396                         /*
1397                          * GFP_NOWAIT failed.  Free the existing one and
1398                          * prealloc for @blkg w/ GFP_KERNEL.
1399                          */
1400                         if (pinned_blkg)
1401                                 blkg_put(pinned_blkg);
1402                         blkg_get(blkg);
1403                         pinned_blkg = blkg;
1404 
1405                         spin_unlock_irq(&q->queue_lock);
1406 
1407                         if (pd_prealloc)
1408                                 pol->pd_free_fn(pd_prealloc);
1409                         pd_prealloc = pol->pd_alloc_fn(GFP_KERNEL, q,
1410                                                        blkg->blkcg);
1411                         if (pd_prealloc)
1412                                 goto retry;
1413                         else
1414                                 goto enomem;
1415                 }
1416 
1417                 blkg->pd[pol->plid] = pd;
1418                 pd->blkg = blkg;
1419                 pd->plid = pol->plid;
1420         }
1421 
1422         /* all allocated, init in the same order */
1423         if (pol->pd_init_fn)
1424                 list_for_each_entry_reverse(blkg, &q->blkg_list, q_node)
1425                         pol->pd_init_fn(blkg->pd[pol->plid]);
1426 
1427         __set_bit(pol->plid, q->blkcg_pols);
1428         ret = 0;
1429 
1430         spin_unlock_irq(&q->queue_lock);
1431 out:
1432         if (queue_is_mq(q))
1433                 blk_mq_unfreeze_queue(q);
1434         if (pinned_blkg)
1435                 blkg_put(pinned_blkg);
1436         if (pd_prealloc)
1437                 pol->pd_free_fn(pd_prealloc);
1438         return ret;
1439 
1440 enomem:
1441         /* alloc failed, nothing's initialized yet, free everything */
1442         spin_lock_irq(&q->queue_lock);
1443         list_for_each_entry(blkg, &q->blkg_list, q_node) {
1444                 if (blkg->pd[pol->plid]) {
1445                         pol->pd_free_fn(blkg->pd[pol->plid]);
1446                         blkg->pd[pol->plid] = NULL;
1447                 }
1448         }
1449         spin_unlock_irq(&q->queue_lock);
1450         ret = -ENOMEM;
1451         goto out;
1452 }
1453 EXPORT_SYMBOL_GPL(blkcg_activate_policy);
1454 
1455 /**
1456  * blkcg_deactivate_policy - deactivate a blkcg policy on a request_queue
1457  * @q: request_queue of interest
1458  * @pol: blkcg policy to deactivate
1459  *
1460  * Deactivate @pol on @q.  Follows the same synchronization rules as
1461  * blkcg_activate_policy().
1462  */
1463 void blkcg_deactivate_policy(struct request_queue *q,
1464                              const struct blkcg_policy *pol)
1465 {
1466         struct blkcg_gq *blkg;
1467 
1468         if (!blkcg_policy_enabled(q, pol))
1469                 return;
1470 
1471         if (queue_is_mq(q))
1472                 blk_mq_freeze_queue(q);
1473 
1474         spin_lock_irq(&q->queue_lock);
1475 
1476         __clear_bit(pol->plid, q->blkcg_pols);
1477 
1478         list_for_each_entry(blkg, &q->blkg_list, q_node) {
1479                 if (blkg->pd[pol->plid]) {
1480                         if (pol->pd_offline_fn)
1481                                 pol->pd_offline_fn(blkg->pd[pol->plid]);
1482                         pol->pd_free_fn(blkg->pd[pol->plid]);
1483                         blkg->pd[pol->plid] = NULL;
1484                 }
1485         }
1486 
1487         spin_unlock_irq(&q->queue_lock);
1488 
1489         if (queue_is_mq(q))
1490                 blk_mq_unfreeze_queue(q);
1491 }
1492 EXPORT_SYMBOL_GPL(blkcg_deactivate_policy);
1493 
1494 /**
1495  * blkcg_policy_register - register a blkcg policy
1496  * @pol: blkcg policy to register
1497  *
1498  * Register @pol with blkcg core.  Might sleep and @pol may be modified on
1499  * successful registration.  Returns 0 on success and -errno on failure.
1500  */
1501 int blkcg_policy_register(struct blkcg_policy *pol)
1502 {
1503         struct blkcg *blkcg;
1504         int i, ret;
1505 
1506         mutex_lock(&blkcg_pol_register_mutex);
1507         mutex_lock(&blkcg_pol_mutex);
1508 
1509         /* find an empty slot */
1510         ret = -ENOSPC;
1511         for (i = 0; i < BLKCG_MAX_POLS; i++)
1512                 if (!blkcg_policy[i])
1513                         break;
1514         if (i >= BLKCG_MAX_POLS) {
1515                 pr_warn("blkcg_policy_register: BLKCG_MAX_POLS too small\n");
1516                 goto err_unlock;
1517         }
1518 
1519         /* Make sure cpd/pd_alloc_fn and cpd/pd_free_fn in pairs */
1520         if ((!pol->cpd_alloc_fn ^ !pol->cpd_free_fn) ||
1521                 (!pol->pd_alloc_fn ^ !pol->pd_free_fn))
1522                 goto err_unlock;
1523 
1524         /* register @pol */
1525         pol->plid = i;
1526         blkcg_policy[pol->plid] = pol;
1527 
1528         /* allocate and install cpd's */
1529         if (pol->cpd_alloc_fn) {
1530                 list_for_each_entry(blkcg, &all_blkcgs, all_blkcgs_node) {
1531                         struct blkcg_policy_data *cpd;
1532 
1533                         cpd = pol->cpd_alloc_fn(GFP_KERNEL);
1534                         if (!cpd)
1535                                 goto err_free_cpds;
1536 
1537                         blkcg->cpd[pol->plid] = cpd;
1538                         cpd->blkcg = blkcg;
1539                         cpd->plid = pol->plid;
1540                         if (pol->cpd_init_fn)
1541                                 pol->cpd_init_fn(cpd);
1542                 }
1543         }
1544 
1545         mutex_unlock(&blkcg_pol_mutex);
1546 
1547         /* everything is in place, add intf files for the new policy */
1548         if (pol->dfl_cftypes)
1549                 WARN_ON(cgroup_add_dfl_cftypes(&io_cgrp_subsys,
1550                                                pol->dfl_cftypes));
1551         if (pol->legacy_cftypes)
1552                 WARN_ON(cgroup_add_legacy_cftypes(&io_cgrp_subsys,
1553                                                   pol->legacy_cftypes));
1554         mutex_unlock(&blkcg_pol_register_mutex);
1555         return 0;
1556 
1557 err_free_cpds:
1558         if (pol->cpd_free_fn) {
1559                 list_for_each_entry(blkcg, &all_blkcgs, all_blkcgs_node) {
1560                         if (blkcg->cpd[pol->plid]) {
1561                                 pol->cpd_free_fn(blkcg->cpd[pol->plid]);
1562                                 blkcg->cpd[pol->plid] = NULL;
1563                         }
1564                 }
1565         }
1566         blkcg_policy[pol->plid] = NULL;
1567 err_unlock:
1568         mutex_unlock(&blkcg_pol_mutex);
1569         mutex_unlock(&blkcg_pol_register_mutex);
1570         return ret;
1571 }
1572 EXPORT_SYMBOL_GPL(blkcg_policy_register);
1573 
1574 /**
1575  * blkcg_policy_unregister - unregister a blkcg policy
1576  * @pol: blkcg policy to unregister
1577  *
1578  * Undo blkcg_policy_register(@pol).  Might sleep.
1579  */
1580 void blkcg_policy_unregister(struct blkcg_policy *pol)
1581 {
1582         struct blkcg *blkcg;
1583 
1584         mutex_lock(&blkcg_pol_register_mutex);
1585 
1586         if (WARN_ON(blkcg_policy[pol->plid] != pol))
1587                 goto out_unlock;
1588 
1589         /* kill the intf files first */
1590         if (pol->dfl_cftypes)
1591                 cgroup_rm_cftypes(pol->dfl_cftypes);
1592         if (pol->legacy_cftypes)
1593                 cgroup_rm_cftypes(pol->legacy_cftypes);
1594 
1595         /* remove cpds and unregister */
1596         mutex_lock(&blkcg_pol_mutex);
1597 
1598         if (pol->cpd_free_fn) {
1599                 list_for_each_entry(blkcg, &all_blkcgs, all_blkcgs_node) {
1600                         if (blkcg->cpd[pol->plid]) {
1601                                 pol->cpd_free_fn(blkcg->cpd[pol->plid]);
1602                                 blkcg->cpd[pol->plid] = NULL;
1603                         }
1604                 }
1605         }
1606         blkcg_policy[pol->plid] = NULL;
1607 
1608         mutex_unlock(&blkcg_pol_mutex);
1609 out_unlock:
1610         mutex_unlock(&blkcg_pol_register_mutex);
1611 }
1612 EXPORT_SYMBOL_GPL(blkcg_policy_unregister);
1613 
1614 bool __blkcg_punt_bio_submit(struct bio *bio)
1615 {
1616         struct blkcg_gq *blkg = bio->bi_blkg;
1617 
1618         /* consume the flag first */
1619         bio->bi_opf &= ~REQ_CGROUP_PUNT;
1620 
1621         /* never bounce for the root cgroup */
1622         if (!blkg->parent)
1623                 return false;
1624 
1625         spin_lock_bh(&blkg->async_bio_lock);
1626         bio_list_add(&blkg->async_bios, bio);
1627         spin_unlock_bh(&blkg->async_bio_lock);
1628 
1629         queue_work(blkcg_punt_bio_wq, &blkg->async_bio_work);
1630         return true;
1631 }
1632 
1633 /*
1634  * Scale the accumulated delay based on how long it has been since we updated
1635  * the delay.  We only call this when we are adding delay, in case it's been a
1636  * while since we added delay, and when we are checking to see if we need to
1637  * delay a task, to account for any delays that may have occurred.
1638  */
1639 static void blkcg_scale_delay(struct blkcg_gq *blkg, u64 now)
1640 {
1641         u64 old = atomic64_read(&blkg->delay_start);
1642 
1643         /*
1644          * We only want to scale down every second.  The idea here is that we
1645          * want to delay people for min(delay_nsec, NSEC_PER_SEC) in a certain
1646          * time window.  We only want to throttle tasks for recent delay that
1647          * has occurred, in 1 second time windows since that's the maximum
1648          * things can be throttled.  We save the current delay window in
1649          * blkg->last_delay so we know what amount is still left to be charged
1650          * to the blkg from this point onward.  blkg->last_use keeps track of
1651          * the use_delay counter.  The idea is if we're unthrottling the blkg we
1652          * are ok with whatever is happening now, and we can take away more of
1653          * the accumulated delay as we've already throttled enough that
1654          * everybody is happy with their IO latencies.
1655          */
1656         if (time_before64(old + NSEC_PER_SEC, now) &&
1657             atomic64_cmpxchg(&blkg->delay_start, old, now) == old) {
1658                 u64 cur = atomic64_read(&blkg->delay_nsec);
1659                 u64 sub = min_t(u64, blkg->last_delay, now - old);
1660                 int cur_use = atomic_read(&blkg->use_delay);
1661 
1662                 /*
1663                  * We've been unthrottled, subtract a larger chunk of our
1664                  * accumulated delay.
1665                  */
1666                 if (cur_use < blkg->last_use)
1667                         sub = max_t(u64, sub, blkg->last_delay >> 1);
1668 
1669                 /*
1670                  * This shouldn't happen, but handle it anyway.  Our delay_nsec
1671                  * should only ever be growing except here where we subtract out
1672                  * min(last_delay, 1 second), but lord knows bugs happen and I'd
1673                  * rather not end up with negative numbers.
1674                  */
1675                 if (unlikely(cur < sub)) {
1676                         atomic64_set(&blkg->delay_nsec, 0);
1677                         blkg->last_delay = 0;
1678                 } else {
1679                         atomic64_sub(sub, &blkg->delay_nsec);
1680                         blkg->last_delay = cur - sub;
1681                 }
1682                 blkg->last_use = cur_use;
1683         }
1684 }
1685 
1686 /*
1687  * This is called when we want to actually walk up the hierarchy and check to
1688  * see if we need to throttle, and then actually throttle if there is some
1689  * accumulated delay.  This should only be called upon return to user space so
1690  * we're not holding some lock that would induce a priority inversion.
1691  */
1692 static void blkcg_maybe_throttle_blkg(struct blkcg_gq *blkg, bool use_memdelay)
1693 {
1694         unsigned long pflags;
1695         u64 now = ktime_to_ns(ktime_get());
1696         u64 exp;
1697         u64 delay_nsec = 0;
1698         int tok;
1699 
1700         while (blkg->parent) {
1701                 if (atomic_read(&blkg->use_delay)) {
1702                         blkcg_scale_delay(blkg, now);
1703                         delay_nsec = max_t(u64, delay_nsec,
1704                                            atomic64_read(&blkg->delay_nsec));
1705                 }
1706                 blkg = blkg->parent;
1707         }
1708 
1709         if (!delay_nsec)
1710                 return;
1711 
1712         /*
1713          * Let's not sleep for all eternity if we've amassed a huge delay.
1714          * Swapping or metadata IO can accumulate 10's of seconds worth of
1715          * delay, and we want userspace to be able to do _something_ so cap the
1716          * delays at 1 second.  If there's 10's of seconds worth of delay then
1717          * the tasks will be delayed for 1 second for every syscall.
1718          */
1719         delay_nsec = min_t(u64, delay_nsec, 250 * NSEC_PER_MSEC);
1720 
1721         if (use_memdelay)
1722                 psi_memstall_enter(&pflags);
1723 
1724         exp = ktime_add_ns(now, delay_nsec);
1725         tok = io_schedule_prepare();
1726         do {
1727                 __set_current_state(TASK_KILLABLE);
1728                 if (!schedule_hrtimeout(&exp, HRTIMER_MODE_ABS))
1729                         break;
1730         } while (!fatal_signal_pending(current));
1731         io_schedule_finish(tok);
1732 
1733         if (use_memdelay)
1734                 psi_memstall_leave(&pflags);
1735 }
1736 
1737 /**
1738  * blkcg_maybe_throttle_current - throttle the current task if it has been marked
1739  *
1740  * This is only called if we've been marked with set_notify_resume().  Obviously
1741  * we can be set_notify_resume() for reasons other than blkcg throttling, so we
1742  * check to see if current->throttle_queue is set and if not this doesn't do
1743  * anything.  This should only ever be called by the resume code, it's not meant
1744  * to be called by people willy-nilly as it will actually do the work to
1745  * throttle the task if it is setup for throttling.
1746  */
1747 void blkcg_maybe_throttle_current(void)
1748 {
1749         struct request_queue *q = current->throttle_queue;
1750         struct cgroup_subsys_state *css;
1751         struct blkcg *blkcg;
1752         struct blkcg_gq *blkg;
1753         bool use_memdelay = current->use_memdelay;
1754 
1755         if (!q)
1756                 return;
1757 
1758         current->throttle_queue = NULL;
1759         current->use_memdelay = false;
1760 
1761         rcu_read_lock();
1762         css = kthread_blkcg();
1763         if (css)
1764                 blkcg = css_to_blkcg(css);
1765         else
1766                 blkcg = css_to_blkcg(task_css(current, io_cgrp_id));
1767 
1768         if (!blkcg)
1769                 goto out;
1770         blkg = blkg_lookup(blkcg, q);
1771         if (!blkg)
1772                 goto out;
1773         if (!blkg_tryget(blkg))
1774                 goto out;
1775         rcu_read_unlock();
1776 
1777         blkcg_maybe_throttle_blkg(blkg, use_memdelay);
1778         blkg_put(blkg);
1779         blk_put_queue(q);
1780         return;
1781 out:
1782         rcu_read_unlock();
1783         blk_put_queue(q);
1784 }
1785 
1786 /**
1787  * blkcg_schedule_throttle - this task needs to check for throttling
1788  * @q: the request queue IO was submitted on
1789  * @use_memdelay: do we charge this to memory delay for PSI
1790  *
1791  * This is called by the IO controller when we know there's delay accumulated
1792  * for the blkg for this task.  We do not pass the blkg because there are places
1793  * we call this that may not have that information, the swapping code for
1794  * instance will only have a request_queue at that point.  This set's the
1795  * notify_resume for the task to check and see if it requires throttling before
1796  * returning to user space.
1797  *
1798  * We will only schedule once per syscall.  You can call this over and over
1799  * again and it will only do the check once upon return to user space, and only
1800  * throttle once.  If the task needs to be throttled again it'll need to be
1801  * re-set at the next time we see the task.
1802  */
1803 void blkcg_schedule_throttle(struct request_queue *q, bool use_memdelay)
1804 {
1805         if (unlikely(current->flags & PF_KTHREAD))
1806                 return;
1807 
1808         if (!blk_get_queue(q))
1809                 return;
1810 
1811         if (current->throttle_queue)
1812                 blk_put_queue(current->throttle_queue);
1813         current->throttle_queue = q;
1814         if (use_memdelay)
1815                 current->use_memdelay = use_memdelay;
1816         set_notify_resume(current);
1817 }
1818 
1819 /**
1820  * blkcg_add_delay - add delay to this blkg
1821  * @blkg: blkg of interest
1822  * @now: the current time in nanoseconds
1823  * @delta: how many nanoseconds of delay to add
1824  *
1825  * Charge @delta to the blkg's current delay accumulation.  This is used to
1826  * throttle tasks if an IO controller thinks we need more throttling.
1827  */
1828 void blkcg_add_delay(struct blkcg_gq *blkg, u64 now, u64 delta)
1829 {
1830         blkcg_scale_delay(blkg, now);
1831         atomic64_add(delta, &blkg->delay_nsec);
1832 }
1833 
1834 static int __init blkcg_init(void)
1835 {
1836         blkcg_punt_bio_wq = alloc_workqueue("blkcg_punt_bio",
1837                                             WQ_MEM_RECLAIM | WQ_FREEZABLE |
1838                                             WQ_UNBOUND | WQ_SYSFS, 0);
1839         if (!blkcg_punt_bio_wq)
1840                 return -ENOMEM;
1841         return 0;
1842 }
1843 subsys_initcall(blkcg_init);
1844 
1845 module_param(blkcg_debug_stats, bool, 0644);
1846 MODULE_PARM_DESC(blkcg_debug_stats, "True if you want debug stats, false if not");
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root/block/blk-cgroup.c

DEFINITIONS
