2 * Common Block IO controller cgroup interface
4 * Based on ideas and code from CFQ, CFS and BFQ:
5 * Copyright (C) 2003 Jens Axboe <axboe@kernel.dk>
7 * Copyright (C) 2008 Fabio Checconi <fabio@gandalf.sssup.it>
8 * Paolo Valente <paolo.valente@unimore.it>
10 * Copyright (C) 2009 Vivek Goyal <vgoyal@redhat.com>
11 * Nauman Rafique <nauman@google.com>
13 #include <linux/ioprio.h>
14 #include <linux/kdev_t.h>
15 #include <linux/module.h>
16 #include <linux/err.h>
17 #include <linux/blkdev.h>
18 #include <linux/slab.h>
19 #include <linux/genhd.h>
20 #include <linux/delay.h>
21 #include <linux/atomic.h>
22 #include "blk-cgroup.h"
25 #define MAX_KEY_LEN 100
27 static DEFINE_MUTEX(blkcg_pol_mutex);
29 struct blkcg blkcg_root = { .cfq_weight = 2 * CFQ_WEIGHT_DEFAULT };
30 EXPORT_SYMBOL_GPL(blkcg_root);
32 static struct blkcg_policy *blkcg_policy[BLKCG_MAX_POLS];
34 struct blkcg *cgroup_to_blkcg(struct cgroup *cgroup)
36 return container_of(cgroup_subsys_state(cgroup, blkio_subsys_id),
39 EXPORT_SYMBOL_GPL(cgroup_to_blkcg);
41 static struct blkcg *task_blkcg(struct task_struct *tsk)
43 return container_of(task_subsys_state(tsk, blkio_subsys_id),
47 struct blkcg *bio_blkcg(struct bio *bio)
49 if (bio && bio->bi_css)
50 return container_of(bio->bi_css, struct blkcg, css);
51 return task_blkcg(current);
53 EXPORT_SYMBOL_GPL(bio_blkcg);
55 static bool blkcg_policy_enabled(struct request_queue *q,
56 const struct blkcg_policy *pol)
58 return pol && test_bit(pol->plid, q->blkcg_pols);
62 * blkg_free - free a blkg
65 * Free @blkg which may be partially allocated.
67 static void blkg_free(struct blkcg_gq *blkg)
74 for (i = 0; i < BLKCG_MAX_POLS; i++) {
75 struct blkcg_policy *pol = blkcg_policy[i];
76 struct blkg_policy_data *pd = blkg->pd[i];
81 if (pol && pol->pd_exit_fn)
82 pol->pd_exit_fn(blkg);
91 * blkg_alloc - allocate a blkg
92 * @blkcg: block cgroup the new blkg is associated with
93 * @q: request_queue the new blkg is associated with
95 * Allocate a new blkg assocating @blkcg and @q.
97 static struct blkcg_gq *blkg_alloc(struct blkcg *blkcg, struct request_queue *q)
99 struct blkcg_gq *blkg;
102 /* alloc and init base part */
103 blkg = kzalloc_node(sizeof(*blkg), GFP_ATOMIC, q->node);
108 INIT_LIST_HEAD(&blkg->q_node);
112 for (i = 0; i < BLKCG_MAX_POLS; i++) {
113 struct blkcg_policy *pol = blkcg_policy[i];
114 struct blkg_policy_data *pd;
116 if (!blkcg_policy_enabled(q, pol))
119 /* alloc per-policy data and attach it to blkg */
120 pd = kzalloc_node(pol->pd_size, GFP_ATOMIC, q->node);
130 /* invoke per-policy init */
131 for (i = 0; i < BLKCG_MAX_POLS; i++) {
132 struct blkcg_policy *pol = blkcg_policy[i];
134 if (blkcg_policy_enabled(blkg->q, pol))
135 pol->pd_init_fn(blkg);
141 static struct blkcg_gq *__blkg_lookup(struct blkcg *blkcg,
142 struct request_queue *q)
144 struct blkcg_gq *blkg;
145 struct hlist_node *n;
147 hlist_for_each_entry_rcu(blkg, n, &blkcg->blkg_list, blkcg_node)
154 * blkg_lookup - lookup blkg for the specified blkcg - q pair
155 * @blkcg: blkcg of interest
156 * @q: request_queue of interest
158 * Lookup blkg for the @blkcg - @q pair. This function should be called
159 * under RCU read lock and is guaranteed to return %NULL if @q is bypassing
160 * - see blk_queue_bypass_start() for details.
162 struct blkcg_gq *blkg_lookup(struct blkcg *blkcg, struct request_queue *q)
164 WARN_ON_ONCE(!rcu_read_lock_held());
166 if (unlikely(blk_queue_bypass(q)))
168 return __blkg_lookup(blkcg, q);
170 EXPORT_SYMBOL_GPL(blkg_lookup);
172 static struct blkcg_gq *__blkg_lookup_create(struct blkcg *blkcg,
173 struct request_queue *q)
174 __releases(q->queue_lock) __acquires(q->queue_lock)
176 struct blkcg_gq *blkg;
179 WARN_ON_ONCE(!rcu_read_lock_held());
180 lockdep_assert_held(q->queue_lock);
182 blkg = __blkg_lookup(blkcg, q);
186 /* blkg holds a reference to blkcg */
187 if (!css_tryget(&blkcg->css))
188 return ERR_PTR(-EINVAL);
192 blkg = blkg_alloc(blkcg, q);
197 spin_lock(&blkcg->lock);
198 hlist_add_head_rcu(&blkg->blkcg_node, &blkcg->blkg_list);
199 list_add(&blkg->q_node, &q->blkg_list);
200 spin_unlock(&blkcg->lock);
204 css_put(&blkcg->css);
208 struct blkcg_gq *blkg_lookup_create(struct blkcg *blkcg,
209 struct request_queue *q)
212 * This could be the first entry point of blkcg implementation and
213 * we shouldn't allow anything to go through for a bypassing queue.
215 if (unlikely(blk_queue_bypass(q)))
216 return ERR_PTR(blk_queue_dead(q) ? -EINVAL : -EBUSY);
217 return __blkg_lookup_create(blkcg, q);
219 EXPORT_SYMBOL_GPL(blkg_lookup_create);
221 static void blkg_destroy(struct blkcg_gq *blkg)
223 struct request_queue *q = blkg->q;
224 struct blkcg *blkcg = blkg->blkcg;
226 lockdep_assert_held(q->queue_lock);
227 lockdep_assert_held(&blkcg->lock);
229 /* Something wrong if we are trying to remove same group twice */
230 WARN_ON_ONCE(list_empty(&blkg->q_node));
231 WARN_ON_ONCE(hlist_unhashed(&blkg->blkcg_node));
232 list_del_init(&blkg->q_node);
233 hlist_del_init_rcu(&blkg->blkcg_node);
236 * Put the reference taken at the time of creation so that when all
237 * queues are gone, group can be destroyed.
243 * blkg_destroy_all - destroy all blkgs associated with a request_queue
244 * @q: request_queue of interest
246 * Destroy all blkgs associated with @q.
248 static void blkg_destroy_all(struct request_queue *q)
250 struct blkcg_gq *blkg, *n;
252 lockdep_assert_held(q->queue_lock);
254 list_for_each_entry_safe(blkg, n, &q->blkg_list, q_node) {
255 struct blkcg *blkcg = blkg->blkcg;
257 spin_lock(&blkcg->lock);
259 spin_unlock(&blkcg->lock);
263 static void blkg_rcu_free(struct rcu_head *rcu_head)
265 blkg_free(container_of(rcu_head, struct blkcg_gq, rcu_head));
268 void __blkg_release(struct blkcg_gq *blkg)
270 /* release the extra blkcg reference this blkg has been holding */
271 css_put(&blkg->blkcg->css);
274 * A group is freed in rcu manner. But having an rcu lock does not
275 * mean that one can access all the fields of blkg and assume these
276 * are valid. For example, don't try to follow throtl_data and
277 * request queue links.
279 * Having a reference to blkg under an rcu allows acess to only
280 * values local to groups like group stats and group rate limits
282 call_rcu(&blkg->rcu_head, blkg_rcu_free);
284 EXPORT_SYMBOL_GPL(__blkg_release);
286 static int blkcg_reset_stats(struct cgroup *cgroup, struct cftype *cftype,
289 struct blkcg *blkcg = cgroup_to_blkcg(cgroup);
290 struct blkcg_gq *blkg;
291 struct hlist_node *n;
294 mutex_lock(&blkcg_pol_mutex);
295 spin_lock_irq(&blkcg->lock);
298 * Note that stat reset is racy - it doesn't synchronize against
299 * stat updates. This is a debug feature which shouldn't exist
300 * anyway. If you get hit by a race, retry.
302 hlist_for_each_entry(blkg, n, &blkcg->blkg_list, blkcg_node) {
303 for (i = 0; i < BLKCG_MAX_POLS; i++) {
304 struct blkcg_policy *pol = blkcg_policy[i];
306 if (blkcg_policy_enabled(blkg->q, pol) &&
307 pol->pd_reset_stats_fn)
308 pol->pd_reset_stats_fn(blkg);
312 spin_unlock_irq(&blkcg->lock);
313 mutex_unlock(&blkcg_pol_mutex);
317 static const char *blkg_dev_name(struct blkcg_gq *blkg)
319 /* some drivers (floppy) instantiate a queue w/o disk registered */
320 if (blkg->q->backing_dev_info.dev)
321 return dev_name(blkg->q->backing_dev_info.dev);
326 * blkcg_print_blkgs - helper for printing per-blkg data
327 * @sf: seq_file to print to
328 * @blkcg: blkcg of interest
329 * @prfill: fill function to print out a blkg
330 * @pol: policy in question
331 * @data: data to be passed to @prfill
332 * @show_total: to print out sum of prfill return values or not
334 * This function invokes @prfill on each blkg of @blkcg if pd for the
335 * policy specified by @pol exists. @prfill is invoked with @sf, the
336 * policy data and @data. If @show_total is %true, the sum of the return
337 * values from @prfill is printed with "Total" label at the end.
339 * This is to be used to construct print functions for
340 * cftype->read_seq_string method.
342 void blkcg_print_blkgs(struct seq_file *sf, struct blkcg *blkcg,
343 u64 (*prfill)(struct seq_file *,
344 struct blkg_policy_data *, int),
345 const struct blkcg_policy *pol, int data,
348 struct blkcg_gq *blkg;
349 struct hlist_node *n;
352 spin_lock_irq(&blkcg->lock);
353 hlist_for_each_entry(blkg, n, &blkcg->blkg_list, blkcg_node)
354 if (blkcg_policy_enabled(blkg->q, pol))
355 total += prfill(sf, blkg->pd[pol->plid], data);
356 spin_unlock_irq(&blkcg->lock);
359 seq_printf(sf, "Total %llu\n", (unsigned long long)total);
361 EXPORT_SYMBOL_GPL(blkcg_print_blkgs);
364 * __blkg_prfill_u64 - prfill helper for a single u64 value
365 * @sf: seq_file to print to
366 * @pd: policy private data of interest
369 * Print @v to @sf for the device assocaited with @pd.
371 u64 __blkg_prfill_u64(struct seq_file *sf, struct blkg_policy_data *pd, u64 v)
373 const char *dname = blkg_dev_name(pd->blkg);
378 seq_printf(sf, "%s %llu\n", dname, (unsigned long long)v);
381 EXPORT_SYMBOL_GPL(__blkg_prfill_u64);
384 * __blkg_prfill_rwstat - prfill helper for a blkg_rwstat
385 * @sf: seq_file to print to
386 * @pd: policy private data of interest
387 * @rwstat: rwstat to print
389 * Print @rwstat to @sf for the device assocaited with @pd.
391 u64 __blkg_prfill_rwstat(struct seq_file *sf, struct blkg_policy_data *pd,
392 const struct blkg_rwstat *rwstat)
394 static const char *rwstr[] = {
395 [BLKG_RWSTAT_READ] = "Read",
396 [BLKG_RWSTAT_WRITE] = "Write",
397 [BLKG_RWSTAT_SYNC] = "Sync",
398 [BLKG_RWSTAT_ASYNC] = "Async",
400 const char *dname = blkg_dev_name(pd->blkg);
407 for (i = 0; i < BLKG_RWSTAT_NR; i++)
408 seq_printf(sf, "%s %s %llu\n", dname, rwstr[i],
409 (unsigned long long)rwstat->cnt[i]);
411 v = rwstat->cnt[BLKG_RWSTAT_READ] + rwstat->cnt[BLKG_RWSTAT_WRITE];
412 seq_printf(sf, "%s Total %llu\n", dname, (unsigned long long)v);
417 * blkg_prfill_stat - prfill callback for blkg_stat
418 * @sf: seq_file to print to
419 * @pd: policy private data of interest
420 * @off: offset to the blkg_stat in @pd
422 * prfill callback for printing a blkg_stat.
424 u64 blkg_prfill_stat(struct seq_file *sf, struct blkg_policy_data *pd, int off)
426 return __blkg_prfill_u64(sf, pd, blkg_stat_read((void *)pd + off));
428 EXPORT_SYMBOL_GPL(blkg_prfill_stat);
431 * blkg_prfill_rwstat - prfill callback for blkg_rwstat
432 * @sf: seq_file to print to
433 * @pd: policy private data of interest
434 * @off: offset to the blkg_rwstat in @pd
436 * prfill callback for printing a blkg_rwstat.
438 u64 blkg_prfill_rwstat(struct seq_file *sf, struct blkg_policy_data *pd,
441 struct blkg_rwstat rwstat = blkg_rwstat_read((void *)pd + off);
443 return __blkg_prfill_rwstat(sf, pd, &rwstat);
445 EXPORT_SYMBOL_GPL(blkg_prfill_rwstat);
448 * blkg_conf_prep - parse and prepare for per-blkg config update
449 * @blkcg: target block cgroup
450 * @pol: target policy
451 * @input: input string
452 * @ctx: blkg_conf_ctx to be filled
454 * Parse per-blkg config update from @input and initialize @ctx with the
455 * result. @ctx->blkg points to the blkg to be updated and @ctx->v the new
456 * value. This function returns with RCU read lock and queue lock held and
457 * must be paired with blkg_conf_finish().
459 int blkg_conf_prep(struct blkcg *blkcg, const struct blkcg_policy *pol,
460 const char *input, struct blkg_conf_ctx *ctx)
461 __acquires(rcu) __acquires(disk->queue->queue_lock)
463 struct gendisk *disk;
464 struct blkcg_gq *blkg;
465 unsigned int major, minor;
466 unsigned long long v;
469 if (sscanf(input, "%u:%u %llu", &major, &minor, &v) != 3)
472 disk = get_gendisk(MKDEV(major, minor), &part);
477 spin_lock_irq(disk->queue->queue_lock);
479 if (blkcg_policy_enabled(disk->queue, pol))
480 blkg = blkg_lookup_create(blkcg, disk->queue);
482 blkg = ERR_PTR(-EINVAL);
487 spin_unlock_irq(disk->queue->queue_lock);
490 * If queue was bypassing, we should retry. Do so after a
491 * short msleep(). It isn't strictly necessary but queue
492 * can be bypassing for some time and it's always nice to
493 * avoid busy looping.
497 ret = restart_syscall();
507 EXPORT_SYMBOL_GPL(blkg_conf_prep);
510 * blkg_conf_finish - finish up per-blkg config update
511 * @ctx: blkg_conf_ctx intiailized by blkg_conf_prep()
513 * Finish up after per-blkg config update. This function must be paired
514 * with blkg_conf_prep().
516 void blkg_conf_finish(struct blkg_conf_ctx *ctx)
517 __releases(ctx->disk->queue->queue_lock) __releases(rcu)
519 spin_unlock_irq(ctx->disk->queue->queue_lock);
523 EXPORT_SYMBOL_GPL(blkg_conf_finish);
525 struct cftype blkcg_files[] = {
527 .name = "reset_stats",
528 .write_u64 = blkcg_reset_stats,
534 * blkcg_pre_destroy - cgroup pre_destroy callback
535 * @cgroup: cgroup of interest
537 * This function is called when @cgroup is about to go away and responsible
538 * for shooting down all blkgs associated with @cgroup. blkgs should be
539 * removed while holding both q and blkcg locks. As blkcg lock is nested
540 * inside q lock, this function performs reverse double lock dancing.
542 * This is the blkcg counterpart of ioc_release_fn().
544 static int blkcg_pre_destroy(struct cgroup *cgroup)
546 struct blkcg *blkcg = cgroup_to_blkcg(cgroup);
548 spin_lock_irq(&blkcg->lock);
550 while (!hlist_empty(&blkcg->blkg_list)) {
551 struct blkcg_gq *blkg = hlist_entry(blkcg->blkg_list.first,
552 struct blkcg_gq, blkcg_node);
553 struct request_queue *q = blkg->q;
555 if (spin_trylock(q->queue_lock)) {
557 spin_unlock(q->queue_lock);
559 spin_unlock_irq(&blkcg->lock);
561 spin_lock_irq(&blkcg->lock);
565 spin_unlock_irq(&blkcg->lock);
569 static void blkcg_destroy(struct cgroup *cgroup)
571 struct blkcg *blkcg = cgroup_to_blkcg(cgroup);
573 if (blkcg != &blkcg_root)
577 static struct cgroup_subsys_state *blkcg_create(struct cgroup *cgroup)
579 static atomic64_t id_seq = ATOMIC64_INIT(0);
581 struct cgroup *parent = cgroup->parent;
588 blkcg = kzalloc(sizeof(*blkcg), GFP_KERNEL);
590 return ERR_PTR(-ENOMEM);
592 blkcg->cfq_weight = CFQ_WEIGHT_DEFAULT;
593 blkcg->id = atomic64_inc_return(&id_seq); /* root is 0, start from 1 */
595 spin_lock_init(&blkcg->lock);
596 INIT_HLIST_HEAD(&blkcg->blkg_list);
602 * blkcg_init_queue - initialize blkcg part of request queue
603 * @q: request_queue to initialize
605 * Called from blk_alloc_queue_node(). Responsible for initializing blkcg
606 * part of new request_queue @q.
609 * 0 on success, -errno on failure.
611 int blkcg_init_queue(struct request_queue *q)
615 return blk_throtl_init(q);
619 * blkcg_drain_queue - drain blkcg part of request_queue
620 * @q: request_queue to drain
622 * Called from blk_drain_queue(). Responsible for draining blkcg part.
624 void blkcg_drain_queue(struct request_queue *q)
626 lockdep_assert_held(q->queue_lock);
632 * blkcg_exit_queue - exit and release blkcg part of request_queue
633 * @q: request_queue being released
635 * Called from blk_release_queue(). Responsible for exiting blkcg part.
637 void blkcg_exit_queue(struct request_queue *q)
639 spin_lock_irq(q->queue_lock);
641 spin_unlock_irq(q->queue_lock);
647 * We cannot support shared io contexts, as we have no mean to support
648 * two tasks with the same ioc in two different groups without major rework
649 * of the main cic data structures. For now we allow a task to change
650 * its cgroup only if it's the only owner of its ioc.
652 static int blkcg_can_attach(struct cgroup *cgrp, struct cgroup_taskset *tset)
654 struct task_struct *task;
655 struct io_context *ioc;
658 /* task_lock() is needed to avoid races with exit_io_context() */
659 cgroup_taskset_for_each(task, cgrp, tset) {
661 ioc = task->io_context;
662 if (ioc && atomic_read(&ioc->nr_tasks) > 1)
671 struct cgroup_subsys blkio_subsys = {
673 .create = blkcg_create,
674 .can_attach = blkcg_can_attach,
675 .pre_destroy = blkcg_pre_destroy,
676 .destroy = blkcg_destroy,
677 .subsys_id = blkio_subsys_id,
678 .base_cftypes = blkcg_files,
679 .module = THIS_MODULE,
681 EXPORT_SYMBOL_GPL(blkio_subsys);
684 * blkcg_activate_policy - activate a blkcg policy on a request_queue
685 * @q: request_queue of interest
686 * @pol: blkcg policy to activate
688 * Activate @pol on @q. Requires %GFP_KERNEL context. @q goes through
689 * bypass mode to populate its blkgs with policy_data for @pol.
691 * Activation happens with @q bypassed, so nobody would be accessing blkgs
692 * from IO path. Update of each blkg is protected by both queue and blkcg
693 * locks so that holding either lock and testing blkcg_policy_enabled() is
694 * always enough for dereferencing policy data.
696 * The caller is responsible for synchronizing [de]activations and policy
697 * [un]registerations. Returns 0 on success, -errno on failure.
699 int blkcg_activate_policy(struct request_queue *q,
700 const struct blkcg_policy *pol)
703 struct blkcg_gq *blkg;
704 struct blkg_policy_data *pd, *n;
707 if (blkcg_policy_enabled(q, pol))
710 blk_queue_bypass_start(q);
712 /* make sure the root blkg exists and count the existing blkgs */
713 spin_lock_irq(q->queue_lock);
716 blkg = __blkg_lookup_create(&blkcg_root, q);
725 list_for_each_entry(blkg, &q->blkg_list, q_node)
728 spin_unlock_irq(q->queue_lock);
730 /* allocate policy_data for all existing blkgs */
732 pd = kzalloc_node(pol->pd_size, GFP_KERNEL, q->node);
737 list_add_tail(&pd->alloc_node, &pds);
741 * Install the allocated pds. With @q bypassing, no new blkg
742 * should have been created while the queue lock was dropped.
744 spin_lock_irq(q->queue_lock);
746 list_for_each_entry(blkg, &q->blkg_list, q_node) {
747 if (WARN_ON(list_empty(&pds))) {
748 /* umm... this shouldn't happen, just abort */
752 pd = list_first_entry(&pds, struct blkg_policy_data, alloc_node);
753 list_del_init(&pd->alloc_node);
755 /* grab blkcg lock too while installing @pd on @blkg */
756 spin_lock(&blkg->blkcg->lock);
758 blkg->pd[pol->plid] = pd;
760 pol->pd_init_fn(blkg);
762 spin_unlock(&blkg->blkcg->lock);
765 __set_bit(pol->plid, q->blkcg_pols);
768 spin_unlock_irq(q->queue_lock);
770 blk_queue_bypass_end(q);
771 list_for_each_entry_safe(pd, n, &pds, alloc_node)
775 EXPORT_SYMBOL_GPL(blkcg_activate_policy);
778 * blkcg_deactivate_policy - deactivate a blkcg policy on a request_queue
779 * @q: request_queue of interest
780 * @pol: blkcg policy to deactivate
782 * Deactivate @pol on @q. Follows the same synchronization rules as
783 * blkcg_activate_policy().
785 void blkcg_deactivate_policy(struct request_queue *q,
786 const struct blkcg_policy *pol)
788 struct blkcg_gq *blkg;
790 if (!blkcg_policy_enabled(q, pol))
793 blk_queue_bypass_start(q);
794 spin_lock_irq(q->queue_lock);
796 __clear_bit(pol->plid, q->blkcg_pols);
798 /* if no policy is left, no need for blkgs - shoot them down */
799 if (bitmap_empty(q->blkcg_pols, BLKCG_MAX_POLS))
802 list_for_each_entry(blkg, &q->blkg_list, q_node) {
803 /* grab blkcg lock too while removing @pd from @blkg */
804 spin_lock(&blkg->blkcg->lock);
807 pol->pd_exit_fn(blkg);
809 kfree(blkg->pd[pol->plid]);
810 blkg->pd[pol->plid] = NULL;
812 spin_unlock(&blkg->blkcg->lock);
815 spin_unlock_irq(q->queue_lock);
816 blk_queue_bypass_end(q);
818 EXPORT_SYMBOL_GPL(blkcg_deactivate_policy);
821 * blkcg_policy_register - register a blkcg policy
822 * @pol: blkcg policy to register
824 * Register @pol with blkcg core. Might sleep and @pol may be modified on
825 * successful registration. Returns 0 on success and -errno on failure.
827 int blkcg_policy_register(struct blkcg_policy *pol)
831 if (WARN_ON(pol->pd_size < sizeof(struct blkg_policy_data)))
834 mutex_lock(&blkcg_pol_mutex);
836 /* find an empty slot */
838 for (i = 0; i < BLKCG_MAX_POLS; i++)
839 if (!blkcg_policy[i])
841 if (i >= BLKCG_MAX_POLS)
844 /* register and update blkgs */
846 blkcg_policy[i] = pol;
848 /* everything is in place, add intf files for the new policy */
850 WARN_ON(cgroup_add_cftypes(&blkio_subsys, pol->cftypes));
853 mutex_unlock(&blkcg_pol_mutex);
856 EXPORT_SYMBOL_GPL(blkcg_policy_register);
859 * blkcg_policy_unregister - unregister a blkcg policy
860 * @pol: blkcg policy to unregister
862 * Undo blkcg_policy_register(@pol). Might sleep.
864 void blkcg_policy_unregister(struct blkcg_policy *pol)
866 mutex_lock(&blkcg_pol_mutex);
868 if (WARN_ON(blkcg_policy[pol->plid] != pol))
871 /* kill the intf files first */
873 cgroup_rm_cftypes(&blkio_subsys, pol->cftypes);
875 /* unregister and update blkgs */
876 blkcg_policy[pol->plid] = NULL;
878 mutex_unlock(&blkcg_pol_mutex);
880 EXPORT_SYMBOL_GPL(blkcg_policy_unregister);