Merge tag 'linux-kselftest-kunit-5.12-rc1' of git://git.kernel.org/pub/scm/linux...
[linux-2.6-microblaze.git] / block / blk-cgroup.c
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 /*
36  * blkcg_pol_mutex protects blkcg_policy[] and policy [de]activation.
37  * blkcg_pol_register_mutex nests outside of it and synchronizes entire
38  * policy [un]register operations including cgroup file additions /
39  * removals.  Putting cgroup file registration outside blkcg_pol_mutex
40  * allows grabbing it from cgroup callbacks.
41  */
42 static DEFINE_MUTEX(blkcg_pol_register_mutex);
43 static DEFINE_MUTEX(blkcg_pol_mutex);
44
45 struct blkcg blkcg_root;
46 EXPORT_SYMBOL_GPL(blkcg_root);
47
48 struct cgroup_subsys_state * const blkcg_root_css = &blkcg_root.css;
49 EXPORT_SYMBOL_GPL(blkcg_root_css);
50
51 static struct blkcg_policy *blkcg_policy[BLKCG_MAX_POLS];
52
53 static LIST_HEAD(all_blkcgs);           /* protected by blkcg_pol_mutex */
54
55 bool blkcg_debug_stats = false;
56 static struct workqueue_struct *blkcg_punt_bio_wq;
57
58 static bool blkcg_policy_enabled(struct request_queue *q,
59                                  const struct blkcg_policy *pol)
60 {
61         return pol && test_bit(pol->plid, q->blkcg_pols);
62 }
63
64 /**
65  * blkg_free - free a blkg
66  * @blkg: blkg to free
67  *
68  * Free @blkg which may be partially allocated.
69  */
70 static void blkg_free(struct blkcg_gq *blkg)
71 {
72         int i;
73
74         if (!blkg)
75                 return;
76
77         for (i = 0; i < BLKCG_MAX_POLS; i++)
78                 if (blkg->pd[i])
79                         blkcg_policy[i]->pd_free_fn(blkg->pd[i]);
80
81         free_percpu(blkg->iostat_cpu);
82         percpu_ref_exit(&blkg->refcnt);
83         kfree(blkg);
84 }
85
86 static void __blkg_release(struct rcu_head *rcu)
87 {
88         struct blkcg_gq *blkg = container_of(rcu, struct blkcg_gq, rcu_head);
89
90         WARN_ON(!bio_list_empty(&blkg->async_bios));
91
92         /* release the blkcg and parent blkg refs this blkg has been holding */
93         css_put(&blkg->blkcg->css);
94         if (blkg->parent)
95                 blkg_put(blkg->parent);
96         blkg_free(blkg);
97 }
98
99 /*
100  * A group is RCU protected, but having an rcu lock does not mean that one
101  * can access all the fields of blkg and assume these are valid.  For
102  * example, don't try to follow throtl_data and request queue links.
103  *
104  * Having a reference to blkg under an rcu allows accesses to only values
105  * local to groups like group stats and group rate limits.
106  */
107 static void blkg_release(struct percpu_ref *ref)
108 {
109         struct blkcg_gq *blkg = container_of(ref, struct blkcg_gq, refcnt);
110
111         call_rcu(&blkg->rcu_head, __blkg_release);
112 }
113
114 static void blkg_async_bio_workfn(struct work_struct *work)
115 {
116         struct blkcg_gq *blkg = container_of(work, struct blkcg_gq,
117                                              async_bio_work);
118         struct bio_list bios = BIO_EMPTY_LIST;
119         struct bio *bio;
120         struct blk_plug plug;
121         bool need_plug = false;
122
123         /* as long as there are pending bios, @blkg can't go away */
124         spin_lock_bh(&blkg->async_bio_lock);
125         bio_list_merge(&bios, &blkg->async_bios);
126         bio_list_init(&blkg->async_bios);
127         spin_unlock_bh(&blkg->async_bio_lock);
128
129         /* start plug only when bio_list contains at least 2 bios */
130         if (bios.head && bios.head->bi_next) {
131                 need_plug = true;
132                 blk_start_plug(&plug);
133         }
134         while ((bio = bio_list_pop(&bios)))
135                 submit_bio(bio);
136         if (need_plug)
137                 blk_finish_plug(&plug);
138 }
139
140 /**
141  * blkg_alloc - allocate a blkg
142  * @blkcg: block cgroup the new blkg is associated with
143  * @q: request_queue the new blkg is associated with
144  * @gfp_mask: allocation mask to use
145  *
146  * Allocate a new blkg assocating @blkcg and @q.
147  */
148 static struct blkcg_gq *blkg_alloc(struct blkcg *blkcg, struct request_queue *q,
149                                    gfp_t gfp_mask)
150 {
151         struct blkcg_gq *blkg;
152         int i, cpu;
153
154         /* alloc and init base part */
155         blkg = kzalloc_node(sizeof(*blkg), gfp_mask, q->node);
156         if (!blkg)
157                 return NULL;
158
159         if (percpu_ref_init(&blkg->refcnt, blkg_release, 0, gfp_mask))
160                 goto err_free;
161
162         blkg->iostat_cpu = alloc_percpu_gfp(struct blkg_iostat_set, gfp_mask);
163         if (!blkg->iostat_cpu)
164                 goto err_free;
165
166         blkg->q = q;
167         INIT_LIST_HEAD(&blkg->q_node);
168         spin_lock_init(&blkg->async_bio_lock);
169         bio_list_init(&blkg->async_bios);
170         INIT_WORK(&blkg->async_bio_work, blkg_async_bio_workfn);
171         blkg->blkcg = blkcg;
172
173         u64_stats_init(&blkg->iostat.sync);
174         for_each_possible_cpu(cpu)
175                 u64_stats_init(&per_cpu_ptr(blkg->iostat_cpu, cpu)->sync);
176
177         for (i = 0; i < BLKCG_MAX_POLS; i++) {
178                 struct blkcg_policy *pol = blkcg_policy[i];
179                 struct blkg_policy_data *pd;
180
181                 if (!blkcg_policy_enabled(q, pol))
182                         continue;
183
184                 /* alloc per-policy data and attach it to blkg */
185                 pd = pol->pd_alloc_fn(gfp_mask, q, blkcg);
186                 if (!pd)
187                         goto err_free;
188
189                 blkg->pd[i] = pd;
190                 pd->blkg = blkg;
191                 pd->plid = i;
192         }
193
194         return blkg;
195
196 err_free:
197         blkg_free(blkg);
198         return NULL;
199 }
200
201 struct blkcg_gq *blkg_lookup_slowpath(struct blkcg *blkcg,
202                                       struct request_queue *q, bool update_hint)
203 {
204         struct blkcg_gq *blkg;
205
206         /*
207          * Hint didn't match.  Look up from the radix tree.  Note that the
208          * hint can only be updated under queue_lock as otherwise @blkg
209          * could have already been removed from blkg_tree.  The caller is
210          * responsible for grabbing queue_lock if @update_hint.
211          */
212         blkg = radix_tree_lookup(&blkcg->blkg_tree, q->id);
213         if (blkg && blkg->q == q) {
214                 if (update_hint) {
215                         lockdep_assert_held(&q->queue_lock);
216                         rcu_assign_pointer(blkcg->blkg_hint, blkg);
217                 }
218                 return blkg;
219         }
220
221         return NULL;
222 }
223 EXPORT_SYMBOL_GPL(blkg_lookup_slowpath);
224
225 /*
226  * If @new_blkg is %NULL, this function tries to allocate a new one as
227  * necessary using %GFP_NOWAIT.  @new_blkg is always consumed on return.
228  */
229 static struct blkcg_gq *blkg_create(struct blkcg *blkcg,
230                                     struct request_queue *q,
231                                     struct blkcg_gq *new_blkg)
232 {
233         struct blkcg_gq *blkg;
234         int i, ret;
235
236         WARN_ON_ONCE(!rcu_read_lock_held());
237         lockdep_assert_held(&q->queue_lock);
238
239         /* request_queue is dying, do not create/recreate a blkg */
240         if (blk_queue_dying(q)) {
241                 ret = -ENODEV;
242                 goto err_free_blkg;
243         }
244
245         /* blkg holds a reference to blkcg */
246         if (!css_tryget_online(&blkcg->css)) {
247                 ret = -ENODEV;
248                 goto err_free_blkg;
249         }
250
251         /* allocate */
252         if (!new_blkg) {
253                 new_blkg = blkg_alloc(blkcg, q, GFP_NOWAIT | __GFP_NOWARN);
254                 if (unlikely(!new_blkg)) {
255                         ret = -ENOMEM;
256                         goto err_put_css;
257                 }
258         }
259         blkg = new_blkg;
260
261         /* link parent */
262         if (blkcg_parent(blkcg)) {
263                 blkg->parent = __blkg_lookup(blkcg_parent(blkcg), q, false);
264                 if (WARN_ON_ONCE(!blkg->parent)) {
265                         ret = -ENODEV;
266                         goto err_put_css;
267                 }
268                 blkg_get(blkg->parent);
269         }
270
271         /* invoke per-policy init */
272         for (i = 0; i < BLKCG_MAX_POLS; i++) {
273                 struct blkcg_policy *pol = blkcg_policy[i];
274
275                 if (blkg->pd[i] && pol->pd_init_fn)
276                         pol->pd_init_fn(blkg->pd[i]);
277         }
278
279         /* insert */
280         spin_lock(&blkcg->lock);
281         ret = radix_tree_insert(&blkcg->blkg_tree, q->id, blkg);
282         if (likely(!ret)) {
283                 hlist_add_head_rcu(&blkg->blkcg_node, &blkcg->blkg_list);
284                 list_add(&blkg->q_node, &q->blkg_list);
285
286                 for (i = 0; i < BLKCG_MAX_POLS; i++) {
287                         struct blkcg_policy *pol = blkcg_policy[i];
288
289                         if (blkg->pd[i] && pol->pd_online_fn)
290                                 pol->pd_online_fn(blkg->pd[i]);
291                 }
292         }
293         blkg->online = true;
294         spin_unlock(&blkcg->lock);
295
296         if (!ret)
297                 return blkg;
298
299         /* @blkg failed fully initialized, use the usual release path */
300         blkg_put(blkg);
301         return ERR_PTR(ret);
302
303 err_put_css:
304         css_put(&blkcg->css);
305 err_free_blkg:
306         blkg_free(new_blkg);
307         return ERR_PTR(ret);
308 }
309
310 /**
311  * blkg_lookup_create - lookup blkg, try to create one if not there
312  * @blkcg: blkcg of interest
313  * @q: request_queue of interest
314  *
315  * Lookup blkg for the @blkcg - @q pair.  If it doesn't exist, try to
316  * create one.  blkg creation is performed recursively from blkcg_root such
317  * that all non-root blkg's have access to the parent blkg.  This function
318  * should be called under RCU read lock and takes @q->queue_lock.
319  *
320  * Returns the blkg or the closest blkg if blkg_create() fails as it walks
321  * down from root.
322  */
323 static struct blkcg_gq *blkg_lookup_create(struct blkcg *blkcg,
324                 struct request_queue *q)
325 {
326         struct blkcg_gq *blkg;
327         unsigned long flags;
328
329         WARN_ON_ONCE(!rcu_read_lock_held());
330
331         blkg = blkg_lookup(blkcg, q);
332         if (blkg)
333                 return blkg;
334
335         spin_lock_irqsave(&q->queue_lock, flags);
336         blkg = __blkg_lookup(blkcg, q, true);
337         if (blkg)
338                 goto found;
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                         blkg = ret_blkg;
364                         break;
365                 }
366                 if (pos == blkcg)
367                         break;
368         }
369
370 found:
371         spin_unlock_irqrestore(&q->queue_lock, flags);
372         return blkg;
373 }
374
375 static void blkg_destroy(struct blkcg_gq *blkg)
376 {
377         struct blkcg *blkcg = blkg->blkcg;
378         int i;
379
380         lockdep_assert_held(&blkg->q->queue_lock);
381         lockdep_assert_held(&blkcg->lock);
382
383         /* Something wrong if we are trying to remove same group twice */
384         WARN_ON_ONCE(list_empty(&blkg->q_node));
385         WARN_ON_ONCE(hlist_unhashed(&blkg->blkcg_node));
386
387         for (i = 0; i < BLKCG_MAX_POLS; i++) {
388                 struct blkcg_policy *pol = blkcg_policy[i];
389
390                 if (blkg->pd[i] && pol->pd_offline_fn)
391                         pol->pd_offline_fn(blkg->pd[i]);
392         }
393
394         blkg->online = false;
395
396         radix_tree_delete(&blkcg->blkg_tree, blkg->q->id);
397         list_del_init(&blkg->q_node);
398         hlist_del_init_rcu(&blkg->blkcg_node);
399
400         /*
401          * Both setting lookup hint to and clearing it from @blkg are done
402          * under queue_lock.  If it's not pointing to @blkg now, it never
403          * will.  Hint assignment itself can race safely.
404          */
405         if (rcu_access_pointer(blkcg->blkg_hint) == blkg)
406                 rcu_assign_pointer(blkcg->blkg_hint, NULL);
407
408         /*
409          * Put the reference taken at the time of creation so that when all
410          * queues are gone, group can be destroyed.
411          */
412         percpu_ref_kill(&blkg->refcnt);
413 }
414
415 /**
416  * blkg_destroy_all - destroy all blkgs associated with a request_queue
417  * @q: request_queue of interest
418  *
419  * Destroy all blkgs associated with @q.
420  */
421 static void blkg_destroy_all(struct request_queue *q)
422 {
423         struct blkcg_gq *blkg, *n;
424
425         spin_lock_irq(&q->queue_lock);
426         list_for_each_entry_safe(blkg, n, &q->blkg_list, q_node) {
427                 struct blkcg *blkcg = blkg->blkcg;
428
429                 spin_lock(&blkcg->lock);
430                 blkg_destroy(blkg);
431                 spin_unlock(&blkcg->lock);
432         }
433
434         q->root_blkg = NULL;
435         spin_unlock_irq(&q->queue_lock);
436 }
437
438 static int blkcg_reset_stats(struct cgroup_subsys_state *css,
439                              struct cftype *cftype, u64 val)
440 {
441         struct blkcg *blkcg = css_to_blkcg(css);
442         struct blkcg_gq *blkg;
443         int i, cpu;
444
445         mutex_lock(&blkcg_pol_mutex);
446         spin_lock_irq(&blkcg->lock);
447
448         /*
449          * Note that stat reset is racy - it doesn't synchronize against
450          * stat updates.  This is a debug feature which shouldn't exist
451          * anyway.  If you get hit by a race, retry.
452          */
453         hlist_for_each_entry(blkg, &blkcg->blkg_list, blkcg_node) {
454                 for_each_possible_cpu(cpu) {
455                         struct blkg_iostat_set *bis =
456                                 per_cpu_ptr(blkg->iostat_cpu, cpu);
457                         memset(bis, 0, sizeof(*bis));
458                 }
459                 memset(&blkg->iostat, 0, sizeof(blkg->iostat));
460
461                 for (i = 0; i < BLKCG_MAX_POLS; i++) {
462                         struct blkcg_policy *pol = blkcg_policy[i];
463
464                         if (blkg->pd[i] && pol->pd_reset_stats_fn)
465                                 pol->pd_reset_stats_fn(blkg->pd[i]);
466                 }
467         }
468
469         spin_unlock_irq(&blkcg->lock);
470         mutex_unlock(&blkcg_pol_mutex);
471         return 0;
472 }
473
474 const char *blkg_dev_name(struct blkcg_gq *blkg)
475 {
476         /* some drivers (floppy) instantiate a queue w/o disk registered */
477         if (blkg->q->backing_dev_info->dev)
478                 return bdi_dev_name(blkg->q->backing_dev_info);
479         return NULL;
480 }
481
482 /**
483  * blkcg_print_blkgs - helper for printing per-blkg data
484  * @sf: seq_file to print to
485  * @blkcg: blkcg of interest
486  * @prfill: fill function to print out a blkg
487  * @pol: policy in question
488  * @data: data to be passed to @prfill
489  * @show_total: to print out sum of prfill return values or not
490  *
491  * This function invokes @prfill on each blkg of @blkcg if pd for the
492  * policy specified by @pol exists.  @prfill is invoked with @sf, the
493  * policy data and @data and the matching queue lock held.  If @show_total
494  * is %true, the sum of the return values from @prfill is printed with
495  * "Total" label at the end.
496  *
497  * This is to be used to construct print functions for
498  * cftype->read_seq_string method.
499  */
500 void blkcg_print_blkgs(struct seq_file *sf, struct blkcg *blkcg,
501                        u64 (*prfill)(struct seq_file *,
502                                      struct blkg_policy_data *, int),
503                        const struct blkcg_policy *pol, int data,
504                        bool show_total)
505 {
506         struct blkcg_gq *blkg;
507         u64 total = 0;
508
509         rcu_read_lock();
510         hlist_for_each_entry_rcu(blkg, &blkcg->blkg_list, blkcg_node) {
511                 spin_lock_irq(&blkg->q->queue_lock);
512                 if (blkcg_policy_enabled(blkg->q, pol))
513                         total += prfill(sf, blkg->pd[pol->plid], data);
514                 spin_unlock_irq(&blkg->q->queue_lock);
515         }
516         rcu_read_unlock();
517
518         if (show_total)
519                 seq_printf(sf, "Total %llu\n", (unsigned long long)total);
520 }
521 EXPORT_SYMBOL_GPL(blkcg_print_blkgs);
522
523 /**
524  * __blkg_prfill_u64 - prfill helper for a single u64 value
525  * @sf: seq_file to print to
526  * @pd: policy private data of interest
527  * @v: value to print
528  *
529  * Print @v to @sf for the device assocaited with @pd.
530  */
531 u64 __blkg_prfill_u64(struct seq_file *sf, struct blkg_policy_data *pd, u64 v)
532 {
533         const char *dname = blkg_dev_name(pd->blkg);
534
535         if (!dname)
536                 return 0;
537
538         seq_printf(sf, "%s %llu\n", dname, (unsigned long long)v);
539         return v;
540 }
541 EXPORT_SYMBOL_GPL(__blkg_prfill_u64);
542
543 /* Performs queue bypass and policy enabled checks then looks up blkg. */
544 static struct blkcg_gq *blkg_lookup_check(struct blkcg *blkcg,
545                                           const struct blkcg_policy *pol,
546                                           struct request_queue *q)
547 {
548         WARN_ON_ONCE(!rcu_read_lock_held());
549         lockdep_assert_held(&q->queue_lock);
550
551         if (!blkcg_policy_enabled(q, pol))
552                 return ERR_PTR(-EOPNOTSUPP);
553         return __blkg_lookup(blkcg, q, true /* update_hint */);
554 }
555
556 /**
557  * blkcg_conf_open_bdev - parse and open bdev for per-blkg config update
558  * @inputp: input string pointer
559  *
560  * Parse the device node prefix part, MAJ:MIN, of per-blkg config update
561  * from @input and get and return the matching bdev.  *@inputp is
562  * updated to point past the device node prefix.  Returns an ERR_PTR()
563  * value on error.
564  *
565  * Use this function iff blkg_conf_prep() can't be used for some reason.
566  */
567 struct block_device *blkcg_conf_open_bdev(char **inputp)
568 {
569         char *input = *inputp;
570         unsigned int major, minor;
571         struct block_device *bdev;
572         int key_len;
573
574         if (sscanf(input, "%u:%u%n", &major, &minor, &key_len) != 2)
575                 return ERR_PTR(-EINVAL);
576
577         input += key_len;
578         if (!isspace(*input))
579                 return ERR_PTR(-EINVAL);
580         input = skip_spaces(input);
581
582         bdev = blkdev_get_no_open(MKDEV(major, minor));
583         if (!bdev)
584                 return ERR_PTR(-ENODEV);
585         if (bdev_is_partition(bdev)) {
586                 blkdev_put_no_open(bdev);
587                 return ERR_PTR(-ENODEV);
588         }
589
590         *inputp = input;
591         return bdev;
592 }
593
594 /**
595  * blkg_conf_prep - parse and prepare for per-blkg config update
596  * @blkcg: target block cgroup
597  * @pol: target policy
598  * @input: input string
599  * @ctx: blkg_conf_ctx to be filled
600  *
601  * Parse per-blkg config update from @input and initialize @ctx with the
602  * result.  @ctx->blkg points to the blkg to be updated and @ctx->body the
603  * part of @input following MAJ:MIN.  This function returns with RCU read
604  * lock and queue lock held and must be paired with blkg_conf_finish().
605  */
606 int blkg_conf_prep(struct blkcg *blkcg, const struct blkcg_policy *pol,
607                    char *input, struct blkg_conf_ctx *ctx)
608         __acquires(rcu) __acquires(&bdev->bd_disk->queue->queue_lock)
609 {
610         struct block_device *bdev;
611         struct request_queue *q;
612         struct blkcg_gq *blkg;
613         int ret;
614
615         bdev = blkcg_conf_open_bdev(&input);
616         if (IS_ERR(bdev))
617                 return PTR_ERR(bdev);
618
619         q = bdev->bd_disk->queue;
620
621         rcu_read_lock();
622         spin_lock_irq(&q->queue_lock);
623
624         blkg = blkg_lookup_check(blkcg, pol, q);
625         if (IS_ERR(blkg)) {
626                 ret = PTR_ERR(blkg);
627                 goto fail_unlock;
628         }
629
630         if (blkg)
631                 goto success;
632
633         /*
634          * Create blkgs walking down from blkcg_root to @blkcg, so that all
635          * non-root blkgs have access to their parents.
636          */
637         while (true) {
638                 struct blkcg *pos = blkcg;
639                 struct blkcg *parent;
640                 struct blkcg_gq *new_blkg;
641
642                 parent = blkcg_parent(blkcg);
643                 while (parent && !__blkg_lookup(parent, q, false)) {
644                         pos = parent;
645                         parent = blkcg_parent(parent);
646                 }
647
648                 /* Drop locks to do new blkg allocation with GFP_KERNEL. */
649                 spin_unlock_irq(&q->queue_lock);
650                 rcu_read_unlock();
651
652                 new_blkg = blkg_alloc(pos, q, GFP_KERNEL);
653                 if (unlikely(!new_blkg)) {
654                         ret = -ENOMEM;
655                         goto fail;
656                 }
657
658                 if (radix_tree_preload(GFP_KERNEL)) {
659                         blkg_free(new_blkg);
660                         ret = -ENOMEM;
661                         goto fail;
662                 }
663
664                 rcu_read_lock();
665                 spin_lock_irq(&q->queue_lock);
666
667                 blkg = blkg_lookup_check(pos, pol, q);
668                 if (IS_ERR(blkg)) {
669                         ret = PTR_ERR(blkg);
670                         blkg_free(new_blkg);
671                         goto fail_preloaded;
672                 }
673
674                 if (blkg) {
675                         blkg_free(new_blkg);
676                 } else {
677                         blkg = blkg_create(pos, q, new_blkg);
678                         if (IS_ERR(blkg)) {
679                                 ret = PTR_ERR(blkg);
680                                 goto fail_preloaded;
681                         }
682                 }
683
684                 radix_tree_preload_end();
685
686                 if (pos == blkcg)
687                         goto success;
688         }
689 success:
690         ctx->bdev = bdev;
691         ctx->blkg = blkg;
692         ctx->body = input;
693         return 0;
694
695 fail_preloaded:
696         radix_tree_preload_end();
697 fail_unlock:
698         spin_unlock_irq(&q->queue_lock);
699         rcu_read_unlock();
700 fail:
701         blkdev_put_no_open(bdev);
702         /*
703          * If queue was bypassing, we should retry.  Do so after a
704          * short msleep().  It isn't strictly necessary but queue
705          * can be bypassing for some time and it's always nice to
706          * avoid busy looping.
707          */
708         if (ret == -EBUSY) {
709                 msleep(10);
710                 ret = restart_syscall();
711         }
712         return ret;
713 }
714 EXPORT_SYMBOL_GPL(blkg_conf_prep);
715
716 /**
717  * blkg_conf_finish - finish up per-blkg config update
718  * @ctx: blkg_conf_ctx intiailized by blkg_conf_prep()
719  *
720  * Finish up after per-blkg config update.  This function must be paired
721  * with blkg_conf_prep().
722  */
723 void blkg_conf_finish(struct blkg_conf_ctx *ctx)
724         __releases(&ctx->bdev->bd_disk->queue->queue_lock) __releases(rcu)
725 {
726         spin_unlock_irq(&ctx->bdev->bd_disk->queue->queue_lock);
727         rcu_read_unlock();
728         blkdev_put_no_open(ctx->bdev);
729 }
730 EXPORT_SYMBOL_GPL(blkg_conf_finish);
731
732 static void blkg_iostat_set(struct blkg_iostat *dst, struct blkg_iostat *src)
733 {
734         int i;
735
736         for (i = 0; i < BLKG_IOSTAT_NR; i++) {
737                 dst->bytes[i] = src->bytes[i];
738                 dst->ios[i] = src->ios[i];
739         }
740 }
741
742 static void blkg_iostat_add(struct blkg_iostat *dst, struct blkg_iostat *src)
743 {
744         int i;
745
746         for (i = 0; i < BLKG_IOSTAT_NR; i++) {
747                 dst->bytes[i] += src->bytes[i];
748                 dst->ios[i] += src->ios[i];
749         }
750 }
751
752 static void blkg_iostat_sub(struct blkg_iostat *dst, struct blkg_iostat *src)
753 {
754         int i;
755
756         for (i = 0; i < BLKG_IOSTAT_NR; i++) {
757                 dst->bytes[i] -= src->bytes[i];
758                 dst->ios[i] -= src->ios[i];
759         }
760 }
761
762 static void blkcg_rstat_flush(struct cgroup_subsys_state *css, int cpu)
763 {
764         struct blkcg *blkcg = css_to_blkcg(css);
765         struct blkcg_gq *blkg;
766
767         rcu_read_lock();
768
769         hlist_for_each_entry_rcu(blkg, &blkcg->blkg_list, blkcg_node) {
770                 struct blkcg_gq *parent = blkg->parent;
771                 struct blkg_iostat_set *bisc = per_cpu_ptr(blkg->iostat_cpu, cpu);
772                 struct blkg_iostat cur, delta;
773                 unsigned int seq;
774
775                 /* fetch the current per-cpu values */
776                 do {
777                         seq = u64_stats_fetch_begin(&bisc->sync);
778                         blkg_iostat_set(&cur, &bisc->cur);
779                 } while (u64_stats_fetch_retry(&bisc->sync, seq));
780
781                 /* propagate percpu delta to global */
782                 u64_stats_update_begin(&blkg->iostat.sync);
783                 blkg_iostat_set(&delta, &cur);
784                 blkg_iostat_sub(&delta, &bisc->last);
785                 blkg_iostat_add(&blkg->iostat.cur, &delta);
786                 blkg_iostat_add(&bisc->last, &delta);
787                 u64_stats_update_end(&blkg->iostat.sync);
788
789                 /* propagate global delta to parent */
790                 if (parent) {
791                         u64_stats_update_begin(&parent->iostat.sync);
792                         blkg_iostat_set(&delta, &blkg->iostat.cur);
793                         blkg_iostat_sub(&delta, &blkg->iostat.last);
794                         blkg_iostat_add(&parent->iostat.cur, &delta);
795                         blkg_iostat_add(&blkg->iostat.last, &delta);
796                         u64_stats_update_end(&parent->iostat.sync);
797                 }
798         }
799
800         rcu_read_unlock();
801 }
802
803 /*
804  * The rstat algorithms intentionally don't handle the root cgroup to avoid
805  * incurring overhead when no cgroups are defined. For that reason,
806  * cgroup_rstat_flush in blkcg_print_stat does not actually fill out the
807  * iostat in the root cgroup's blkcg_gq.
808  *
809  * However, we would like to re-use the printing code between the root and
810  * non-root cgroups to the extent possible. For that reason, we simulate
811  * flushing the root cgroup's stats by explicitly filling in the iostat
812  * with disk level statistics.
813  */
814 static void blkcg_fill_root_iostats(void)
815 {
816         struct class_dev_iter iter;
817         struct device *dev;
818
819         class_dev_iter_init(&iter, &block_class, NULL, &disk_type);
820         while ((dev = class_dev_iter_next(&iter))) {
821                 struct block_device *bdev = dev_to_bdev(dev);
822                 struct blkcg_gq *blkg =
823                         blk_queue_root_blkg(bdev->bd_disk->queue);
824                 struct blkg_iostat tmp;
825                 int cpu;
826
827                 memset(&tmp, 0, sizeof(tmp));
828                 for_each_possible_cpu(cpu) {
829                         struct disk_stats *cpu_dkstats;
830
831                         cpu_dkstats = per_cpu_ptr(bdev->bd_stats, cpu);
832                         tmp.ios[BLKG_IOSTAT_READ] +=
833                                 cpu_dkstats->ios[STAT_READ];
834                         tmp.ios[BLKG_IOSTAT_WRITE] +=
835                                 cpu_dkstats->ios[STAT_WRITE];
836                         tmp.ios[BLKG_IOSTAT_DISCARD] +=
837                                 cpu_dkstats->ios[STAT_DISCARD];
838                         // convert sectors to bytes
839                         tmp.bytes[BLKG_IOSTAT_READ] +=
840                                 cpu_dkstats->sectors[STAT_READ] << 9;
841                         tmp.bytes[BLKG_IOSTAT_WRITE] +=
842                                 cpu_dkstats->sectors[STAT_WRITE] << 9;
843                         tmp.bytes[BLKG_IOSTAT_DISCARD] +=
844                                 cpu_dkstats->sectors[STAT_DISCARD] << 9;
845
846                         u64_stats_update_begin(&blkg->iostat.sync);
847                         blkg_iostat_set(&blkg->iostat.cur, &tmp);
848                         u64_stats_update_end(&blkg->iostat.sync);
849                 }
850         }
851 }
852
853 static int blkcg_print_stat(struct seq_file *sf, void *v)
854 {
855         struct blkcg *blkcg = css_to_blkcg(seq_css(sf));
856         struct blkcg_gq *blkg;
857
858         if (!seq_css(sf)->parent)
859                 blkcg_fill_root_iostats();
860         else
861                 cgroup_rstat_flush(blkcg->css.cgroup);
862
863         rcu_read_lock();
864
865         hlist_for_each_entry_rcu(blkg, &blkcg->blkg_list, blkcg_node) {
866                 struct blkg_iostat_set *bis = &blkg->iostat;
867                 const char *dname;
868                 char *buf;
869                 u64 rbytes, wbytes, rios, wios, dbytes, dios;
870                 size_t size = seq_get_buf(sf, &buf), off = 0;
871                 int i;
872                 bool has_stats = false;
873                 unsigned seq;
874
875                 spin_lock_irq(&blkg->q->queue_lock);
876
877                 if (!blkg->online)
878                         goto skip;
879
880                 dname = blkg_dev_name(blkg);
881                 if (!dname)
882                         goto skip;
883
884                 /*
885                  * Hooray string manipulation, count is the size written NOT
886                  * INCLUDING THE \0, so size is now count+1 less than what we
887                  * had before, but we want to start writing the next bit from
888                  * the \0 so we only add count to buf.
889                  */
890                 off += scnprintf(buf+off, size-off, "%s ", dname);
891
892                 do {
893                         seq = u64_stats_fetch_begin(&bis->sync);
894
895                         rbytes = bis->cur.bytes[BLKG_IOSTAT_READ];
896                         wbytes = bis->cur.bytes[BLKG_IOSTAT_WRITE];
897                         dbytes = bis->cur.bytes[BLKG_IOSTAT_DISCARD];
898                         rios = bis->cur.ios[BLKG_IOSTAT_READ];
899                         wios = bis->cur.ios[BLKG_IOSTAT_WRITE];
900                         dios = bis->cur.ios[BLKG_IOSTAT_DISCARD];
901                 } while (u64_stats_fetch_retry(&bis->sync, seq));
902
903                 if (rbytes || wbytes || rios || wios) {
904                         has_stats = true;
905                         off += scnprintf(buf+off, size-off,
906                                          "rbytes=%llu wbytes=%llu rios=%llu wios=%llu dbytes=%llu dios=%llu",
907                                          rbytes, wbytes, rios, wios,
908                                          dbytes, dios);
909                 }
910
911                 if (blkcg_debug_stats && atomic_read(&blkg->use_delay)) {
912                         has_stats = true;
913                         off += scnprintf(buf+off, size-off,
914                                          " use_delay=%d delay_nsec=%llu",
915                                          atomic_read(&blkg->use_delay),
916                                         (unsigned long long)atomic64_read(&blkg->delay_nsec));
917                 }
918
919                 for (i = 0; i < BLKCG_MAX_POLS; i++) {
920                         struct blkcg_policy *pol = blkcg_policy[i];
921                         size_t written;
922
923                         if (!blkg->pd[i] || !pol->pd_stat_fn)
924                                 continue;
925
926                         written = pol->pd_stat_fn(blkg->pd[i], buf+off, size-off);
927                         if (written)
928                                 has_stats = true;
929                         off += written;
930                 }
931
932                 if (has_stats) {
933                         if (off < size - 1) {
934                                 off += scnprintf(buf+off, size-off, "\n");
935                                 seq_commit(sf, off);
936                         } else {
937                                 seq_commit(sf, -1);
938                         }
939                 }
940         skip:
941                 spin_unlock_irq(&blkg->q->queue_lock);
942         }
943
944         rcu_read_unlock();
945         return 0;
946 }
947
948 static struct cftype blkcg_files[] = {
949         {
950                 .name = "stat",
951                 .seq_show = blkcg_print_stat,
952         },
953         { }     /* terminate */
954 };
955
956 static struct cftype blkcg_legacy_files[] = {
957         {
958                 .name = "reset_stats",
959                 .write_u64 = blkcg_reset_stats,
960         },
961         { }     /* terminate */
962 };
963
964 /*
965  * blkcg destruction is a three-stage process.
966  *
967  * 1. Destruction starts.  The blkcg_css_offline() callback is invoked
968  *    which offlines writeback.  Here we tie the next stage of blkg destruction
969  *    to the completion of writeback associated with the blkcg.  This lets us
970  *    avoid punting potentially large amounts of outstanding writeback to root
971  *    while maintaining any ongoing policies.  The next stage is triggered when
972  *    the nr_cgwbs count goes to zero.
973  *
974  * 2. When the nr_cgwbs count goes to zero, blkcg_destroy_blkgs() is called
975  *    and handles the destruction of blkgs.  Here the css reference held by
976  *    the blkg is put back eventually allowing blkcg_css_free() to be called.
977  *    This work may occur in cgwb_release_workfn() on the cgwb_release
978  *    workqueue.  Any submitted ios that fail to get the blkg ref will be
979  *    punted to the root_blkg.
980  *
981  * 3. Once the blkcg ref count goes to zero, blkcg_css_free() is called.
982  *    This finally frees the blkcg.
983  */
984
985 /**
986  * blkcg_css_offline - cgroup css_offline callback
987  * @css: css of interest
988  *
989  * This function is called when @css is about to go away.  Here the cgwbs are
990  * offlined first and only once writeback associated with the blkcg has
991  * finished do we start step 2 (see above).
992  */
993 static void blkcg_css_offline(struct cgroup_subsys_state *css)
994 {
995         struct blkcg *blkcg = css_to_blkcg(css);
996
997         /* this prevents anyone from attaching or migrating to this blkcg */
998         wb_blkcg_offline(blkcg);
999
1000         /* put the base online pin allowing step 2 to be triggered */
1001         blkcg_unpin_online(blkcg);
1002 }
1003
1004 /**
1005  * blkcg_destroy_blkgs - responsible for shooting down blkgs
1006  * @blkcg: blkcg of interest
1007  *
1008  * blkgs should be removed while holding both q and blkcg locks.  As blkcg lock
1009  * is nested inside q lock, this function performs reverse double lock dancing.
1010  * Destroying the blkgs releases the reference held on the blkcg's css allowing
1011  * blkcg_css_free to eventually be called.
1012  *
1013  * This is the blkcg counterpart of ioc_release_fn().
1014  */
1015 void blkcg_destroy_blkgs(struct blkcg *blkcg)
1016 {
1017         might_sleep();
1018
1019         spin_lock_irq(&blkcg->lock);
1020
1021         while (!hlist_empty(&blkcg->blkg_list)) {
1022                 struct blkcg_gq *blkg = hlist_entry(blkcg->blkg_list.first,
1023                                                 struct blkcg_gq, blkcg_node);
1024                 struct request_queue *q = blkg->q;
1025
1026                 if (need_resched() || !spin_trylock(&q->queue_lock)) {
1027                         /*
1028                          * Given that the system can accumulate a huge number
1029                          * of blkgs in pathological cases, check to see if we
1030                          * need to rescheduling to avoid softlockup.
1031                          */
1032                         spin_unlock_irq(&blkcg->lock);
1033                         cond_resched();
1034                         spin_lock_irq(&blkcg->lock);
1035                         continue;
1036                 }
1037
1038                 blkg_destroy(blkg);
1039                 spin_unlock(&q->queue_lock);
1040         }
1041
1042         spin_unlock_irq(&blkcg->lock);
1043 }
1044
1045 static void blkcg_css_free(struct cgroup_subsys_state *css)
1046 {
1047         struct blkcg *blkcg = css_to_blkcg(css);
1048         int i;
1049
1050         mutex_lock(&blkcg_pol_mutex);
1051
1052         list_del(&blkcg->all_blkcgs_node);
1053
1054         for (i = 0; i < BLKCG_MAX_POLS; i++)
1055                 if (blkcg->cpd[i])
1056                         blkcg_policy[i]->cpd_free_fn(blkcg->cpd[i]);
1057
1058         mutex_unlock(&blkcg_pol_mutex);
1059
1060         kfree(blkcg);
1061 }
1062
1063 static struct cgroup_subsys_state *
1064 blkcg_css_alloc(struct cgroup_subsys_state *parent_css)
1065 {
1066         struct blkcg *blkcg;
1067         struct cgroup_subsys_state *ret;
1068         int i;
1069
1070         mutex_lock(&blkcg_pol_mutex);
1071
1072         if (!parent_css) {
1073                 blkcg = &blkcg_root;
1074         } else {
1075                 blkcg = kzalloc(sizeof(*blkcg), GFP_KERNEL);
1076                 if (!blkcg) {
1077                         ret = ERR_PTR(-ENOMEM);
1078                         goto unlock;
1079                 }
1080         }
1081
1082         for (i = 0; i < BLKCG_MAX_POLS ; i++) {
1083                 struct blkcg_policy *pol = blkcg_policy[i];
1084                 struct blkcg_policy_data *cpd;
1085
1086                 /*
1087                  * If the policy hasn't been attached yet, wait for it
1088                  * to be attached before doing anything else. Otherwise,
1089                  * check if the policy requires any specific per-cgroup
1090                  * data: if it does, allocate and initialize it.
1091                  */
1092                 if (!pol || !pol->cpd_alloc_fn)
1093                         continue;
1094
1095                 cpd = pol->cpd_alloc_fn(GFP_KERNEL);
1096                 if (!cpd) {
1097                         ret = ERR_PTR(-ENOMEM);
1098                         goto free_pd_blkcg;
1099                 }
1100                 blkcg->cpd[i] = cpd;
1101                 cpd->blkcg = blkcg;
1102                 cpd->plid = i;
1103                 if (pol->cpd_init_fn)
1104                         pol->cpd_init_fn(cpd);
1105         }
1106
1107         spin_lock_init(&blkcg->lock);
1108         refcount_set(&blkcg->online_pin, 1);
1109         INIT_RADIX_TREE(&blkcg->blkg_tree, GFP_NOWAIT | __GFP_NOWARN);
1110         INIT_HLIST_HEAD(&blkcg->blkg_list);
1111 #ifdef CONFIG_CGROUP_WRITEBACK
1112         INIT_LIST_HEAD(&blkcg->cgwb_list);
1113 #endif
1114         list_add_tail(&blkcg->all_blkcgs_node, &all_blkcgs);
1115
1116         mutex_unlock(&blkcg_pol_mutex);
1117         return &blkcg->css;
1118
1119 free_pd_blkcg:
1120         for (i--; i >= 0; i--)
1121                 if (blkcg->cpd[i])
1122                         blkcg_policy[i]->cpd_free_fn(blkcg->cpd[i]);
1123
1124         if (blkcg != &blkcg_root)
1125                 kfree(blkcg);
1126 unlock:
1127         mutex_unlock(&blkcg_pol_mutex);
1128         return ret;
1129 }
1130
1131 static int blkcg_css_online(struct cgroup_subsys_state *css)
1132 {
1133         struct blkcg *blkcg = css_to_blkcg(css);
1134         struct blkcg *parent = blkcg_parent(blkcg);
1135
1136         /*
1137          * blkcg_pin_online() is used to delay blkcg offline so that blkgs
1138          * don't go offline while cgwbs are still active on them.  Pin the
1139          * parent so that offline always happens towards the root.
1140          */
1141         if (parent)
1142                 blkcg_pin_online(parent);
1143         return 0;
1144 }
1145
1146 /**
1147  * blkcg_init_queue - initialize blkcg part of request queue
1148  * @q: request_queue to initialize
1149  *
1150  * Called from blk_alloc_queue(). Responsible for initializing blkcg
1151  * part of new request_queue @q.
1152  *
1153  * RETURNS:
1154  * 0 on success, -errno on failure.
1155  */
1156 int blkcg_init_queue(struct request_queue *q)
1157 {
1158         struct blkcg_gq *new_blkg, *blkg;
1159         bool preloaded;
1160         int ret;
1161
1162         new_blkg = blkg_alloc(&blkcg_root, q, GFP_KERNEL);
1163         if (!new_blkg)
1164                 return -ENOMEM;
1165
1166         preloaded = !radix_tree_preload(GFP_KERNEL);
1167
1168         /* Make sure the root blkg exists. */
1169         rcu_read_lock();
1170         spin_lock_irq(&q->queue_lock);
1171         blkg = blkg_create(&blkcg_root, q, new_blkg);
1172         if (IS_ERR(blkg))
1173                 goto err_unlock;
1174         q->root_blkg = blkg;
1175         spin_unlock_irq(&q->queue_lock);
1176         rcu_read_unlock();
1177
1178         if (preloaded)
1179                 radix_tree_preload_end();
1180
1181         ret = blk_throtl_init(q);
1182         if (ret)
1183                 goto err_destroy_all;
1184
1185         ret = blk_iolatency_init(q);
1186         if (ret) {
1187                 blk_throtl_exit(q);
1188                 goto err_destroy_all;
1189         }
1190         return 0;
1191
1192 err_destroy_all:
1193         blkg_destroy_all(q);
1194         return ret;
1195 err_unlock:
1196         spin_unlock_irq(&q->queue_lock);
1197         rcu_read_unlock();
1198         if (preloaded)
1199                 radix_tree_preload_end();
1200         return PTR_ERR(blkg);
1201 }
1202
1203 /**
1204  * blkcg_exit_queue - exit and release blkcg part of request_queue
1205  * @q: request_queue being released
1206  *
1207  * Called from blk_exit_queue().  Responsible for exiting blkcg part.
1208  */
1209 void blkcg_exit_queue(struct request_queue *q)
1210 {
1211         blkg_destroy_all(q);
1212         blk_throtl_exit(q);
1213 }
1214
1215 /*
1216  * We cannot support shared io contexts, as we have no mean to support
1217  * two tasks with the same ioc in two different groups without major rework
1218  * of the main cic data structures.  For now we allow a task to change
1219  * its cgroup only if it's the only owner of its ioc.
1220  */
1221 static int blkcg_can_attach(struct cgroup_taskset *tset)
1222 {
1223         struct task_struct *task;
1224         struct cgroup_subsys_state *dst_css;
1225         struct io_context *ioc;
1226         int ret = 0;
1227
1228         /* task_lock() is needed to avoid races with exit_io_context() */
1229         cgroup_taskset_for_each(task, dst_css, tset) {
1230                 task_lock(task);
1231                 ioc = task->io_context;
1232                 if (ioc && atomic_read(&ioc->nr_tasks) > 1)
1233                         ret = -EINVAL;
1234                 task_unlock(task);
1235                 if (ret)
1236                         break;
1237         }
1238         return ret;
1239 }
1240
1241 static void blkcg_bind(struct cgroup_subsys_state *root_css)
1242 {
1243         int i;
1244
1245         mutex_lock(&blkcg_pol_mutex);
1246
1247         for (i = 0; i < BLKCG_MAX_POLS; i++) {
1248                 struct blkcg_policy *pol = blkcg_policy[i];
1249                 struct blkcg *blkcg;
1250
1251                 if (!pol || !pol->cpd_bind_fn)
1252                         continue;
1253
1254                 list_for_each_entry(blkcg, &all_blkcgs, all_blkcgs_node)
1255                         if (blkcg->cpd[pol->plid])
1256                                 pol->cpd_bind_fn(blkcg->cpd[pol->plid]);
1257         }
1258         mutex_unlock(&blkcg_pol_mutex);
1259 }
1260
1261 static void blkcg_exit(struct task_struct *tsk)
1262 {
1263         if (tsk->throttle_queue)
1264                 blk_put_queue(tsk->throttle_queue);
1265         tsk->throttle_queue = NULL;
1266 }
1267
1268 struct cgroup_subsys io_cgrp_subsys = {
1269         .css_alloc = blkcg_css_alloc,
1270         .css_online = blkcg_css_online,
1271         .css_offline = blkcg_css_offline,
1272         .css_free = blkcg_css_free,
1273         .can_attach = blkcg_can_attach,
1274         .css_rstat_flush = blkcg_rstat_flush,
1275         .bind = blkcg_bind,
1276         .dfl_cftypes = blkcg_files,
1277         .legacy_cftypes = blkcg_legacy_files,
1278         .legacy_name = "blkio",
1279         .exit = blkcg_exit,
1280 #ifdef CONFIG_MEMCG
1281         /*
1282          * This ensures that, if available, memcg is automatically enabled
1283          * together on the default hierarchy so that the owner cgroup can
1284          * be retrieved from writeback pages.
1285          */
1286         .depends_on = 1 << memory_cgrp_id,
1287 #endif
1288 };
1289 EXPORT_SYMBOL_GPL(io_cgrp_subsys);
1290
1291 /**
1292  * blkcg_activate_policy - activate a blkcg policy on a request_queue
1293  * @q: request_queue of interest
1294  * @pol: blkcg policy to activate
1295  *
1296  * Activate @pol on @q.  Requires %GFP_KERNEL context.  @q goes through
1297  * bypass mode to populate its blkgs with policy_data for @pol.
1298  *
1299  * Activation happens with @q bypassed, so nobody would be accessing blkgs
1300  * from IO path.  Update of each blkg is protected by both queue and blkcg
1301  * locks so that holding either lock and testing blkcg_policy_enabled() is
1302  * always enough for dereferencing policy data.
1303  *
1304  * The caller is responsible for synchronizing [de]activations and policy
1305  * [un]registerations.  Returns 0 on success, -errno on failure.
1306  */
1307 int blkcg_activate_policy(struct request_queue *q,
1308                           const struct blkcg_policy *pol)
1309 {
1310         struct blkg_policy_data *pd_prealloc = NULL;
1311         struct blkcg_gq *blkg, *pinned_blkg = NULL;
1312         int ret;
1313
1314         if (blkcg_policy_enabled(q, pol))
1315                 return 0;
1316
1317         if (queue_is_mq(q))
1318                 blk_mq_freeze_queue(q);
1319 retry:
1320         spin_lock_irq(&q->queue_lock);
1321
1322         /* blkg_list is pushed at the head, reverse walk to allocate parents first */
1323         list_for_each_entry_reverse(blkg, &q->blkg_list, q_node) {
1324                 struct blkg_policy_data *pd;
1325
1326                 if (blkg->pd[pol->plid])
1327                         continue;
1328
1329                 /* If prealloc matches, use it; otherwise try GFP_NOWAIT */
1330                 if (blkg == pinned_blkg) {
1331                         pd = pd_prealloc;
1332                         pd_prealloc = NULL;
1333                 } else {
1334                         pd = pol->pd_alloc_fn(GFP_NOWAIT | __GFP_NOWARN, q,
1335                                               blkg->blkcg);
1336                 }
1337
1338                 if (!pd) {
1339                         /*
1340                          * GFP_NOWAIT failed.  Free the existing one and
1341                          * prealloc for @blkg w/ GFP_KERNEL.
1342                          */
1343                         if (pinned_blkg)
1344                                 blkg_put(pinned_blkg);
1345                         blkg_get(blkg);
1346                         pinned_blkg = blkg;
1347
1348                         spin_unlock_irq(&q->queue_lock);
1349
1350                         if (pd_prealloc)
1351                                 pol->pd_free_fn(pd_prealloc);
1352                         pd_prealloc = pol->pd_alloc_fn(GFP_KERNEL, q,
1353                                                        blkg->blkcg);
1354                         if (pd_prealloc)
1355                                 goto retry;
1356                         else
1357                                 goto enomem;
1358                 }
1359
1360                 blkg->pd[pol->plid] = pd;
1361                 pd->blkg = blkg;
1362                 pd->plid = pol->plid;
1363         }
1364
1365         /* all allocated, init in the same order */
1366         if (pol->pd_init_fn)
1367                 list_for_each_entry_reverse(blkg, &q->blkg_list, q_node)
1368                         pol->pd_init_fn(blkg->pd[pol->plid]);
1369
1370         __set_bit(pol->plid, q->blkcg_pols);
1371         ret = 0;
1372
1373         spin_unlock_irq(&q->queue_lock);
1374 out:
1375         if (queue_is_mq(q))
1376                 blk_mq_unfreeze_queue(q);
1377         if (pinned_blkg)
1378                 blkg_put(pinned_blkg);
1379         if (pd_prealloc)
1380                 pol->pd_free_fn(pd_prealloc);
1381         return ret;
1382
1383 enomem:
1384         /* alloc failed, nothing's initialized yet, free everything */
1385         spin_lock_irq(&q->queue_lock);
1386         list_for_each_entry(blkg, &q->blkg_list, q_node) {
1387                 if (blkg->pd[pol->plid]) {
1388                         pol->pd_free_fn(blkg->pd[pol->plid]);
1389                         blkg->pd[pol->plid] = NULL;
1390                 }
1391         }
1392         spin_unlock_irq(&q->queue_lock);
1393         ret = -ENOMEM;
1394         goto out;
1395 }
1396 EXPORT_SYMBOL_GPL(blkcg_activate_policy);
1397
1398 /**
1399  * blkcg_deactivate_policy - deactivate a blkcg policy on a request_queue
1400  * @q: request_queue of interest
1401  * @pol: blkcg policy to deactivate
1402  *
1403  * Deactivate @pol on @q.  Follows the same synchronization rules as
1404  * blkcg_activate_policy().
1405  */
1406 void blkcg_deactivate_policy(struct request_queue *q,
1407                              const struct blkcg_policy *pol)
1408 {
1409         struct blkcg_gq *blkg;
1410
1411         if (!blkcg_policy_enabled(q, pol))
1412                 return;
1413
1414         if (queue_is_mq(q))
1415                 blk_mq_freeze_queue(q);
1416
1417         spin_lock_irq(&q->queue_lock);
1418
1419         __clear_bit(pol->plid, q->blkcg_pols);
1420
1421         list_for_each_entry(blkg, &q->blkg_list, q_node) {
1422                 if (blkg->pd[pol->plid]) {
1423                         if (pol->pd_offline_fn)
1424                                 pol->pd_offline_fn(blkg->pd[pol->plid]);
1425                         pol->pd_free_fn(blkg->pd[pol->plid]);
1426                         blkg->pd[pol->plid] = NULL;
1427                 }
1428         }
1429
1430         spin_unlock_irq(&q->queue_lock);
1431
1432         if (queue_is_mq(q))
1433                 blk_mq_unfreeze_queue(q);
1434 }
1435 EXPORT_SYMBOL_GPL(blkcg_deactivate_policy);
1436
1437 /**
1438  * blkcg_policy_register - register a blkcg policy
1439  * @pol: blkcg policy to register
1440  *
1441  * Register @pol with blkcg core.  Might sleep and @pol may be modified on
1442  * successful registration.  Returns 0 on success and -errno on failure.
1443  */
1444 int blkcg_policy_register(struct blkcg_policy *pol)
1445 {
1446         struct blkcg *blkcg;
1447         int i, ret;
1448
1449         mutex_lock(&blkcg_pol_register_mutex);
1450         mutex_lock(&blkcg_pol_mutex);
1451
1452         /* find an empty slot */
1453         ret = -ENOSPC;
1454         for (i = 0; i < BLKCG_MAX_POLS; i++)
1455                 if (!blkcg_policy[i])
1456                         break;
1457         if (i >= BLKCG_MAX_POLS) {
1458                 pr_warn("blkcg_policy_register: BLKCG_MAX_POLS too small\n");
1459                 goto err_unlock;
1460         }
1461
1462         /* Make sure cpd/pd_alloc_fn and cpd/pd_free_fn in pairs */
1463         if ((!pol->cpd_alloc_fn ^ !pol->cpd_free_fn) ||
1464                 (!pol->pd_alloc_fn ^ !pol->pd_free_fn))
1465                 goto err_unlock;
1466
1467         /* register @pol */
1468         pol->plid = i;
1469         blkcg_policy[pol->plid] = pol;
1470
1471         /* allocate and install cpd's */
1472         if (pol->cpd_alloc_fn) {
1473                 list_for_each_entry(blkcg, &all_blkcgs, all_blkcgs_node) {
1474                         struct blkcg_policy_data *cpd;
1475
1476                         cpd = pol->cpd_alloc_fn(GFP_KERNEL);
1477                         if (!cpd)
1478                                 goto err_free_cpds;
1479
1480                         blkcg->cpd[pol->plid] = cpd;
1481                         cpd->blkcg = blkcg;
1482                         cpd->plid = pol->plid;
1483                         if (pol->cpd_init_fn)
1484                                 pol->cpd_init_fn(cpd);
1485                 }
1486         }
1487
1488         mutex_unlock(&blkcg_pol_mutex);
1489
1490         /* everything is in place, add intf files for the new policy */
1491         if (pol->dfl_cftypes)
1492                 WARN_ON(cgroup_add_dfl_cftypes(&io_cgrp_subsys,
1493                                                pol->dfl_cftypes));
1494         if (pol->legacy_cftypes)
1495                 WARN_ON(cgroup_add_legacy_cftypes(&io_cgrp_subsys,
1496                                                   pol->legacy_cftypes));
1497         mutex_unlock(&blkcg_pol_register_mutex);
1498         return 0;
1499
1500 err_free_cpds:
1501         if (pol->cpd_free_fn) {
1502                 list_for_each_entry(blkcg, &all_blkcgs, all_blkcgs_node) {
1503                         if (blkcg->cpd[pol->plid]) {
1504                                 pol->cpd_free_fn(blkcg->cpd[pol->plid]);
1505                                 blkcg->cpd[pol->plid] = NULL;
1506                         }
1507                 }
1508         }
1509         blkcg_policy[pol->plid] = NULL;
1510 err_unlock:
1511         mutex_unlock(&blkcg_pol_mutex);
1512         mutex_unlock(&blkcg_pol_register_mutex);
1513         return ret;
1514 }
1515 EXPORT_SYMBOL_GPL(blkcg_policy_register);
1516
1517 /**
1518  * blkcg_policy_unregister - unregister a blkcg policy
1519  * @pol: blkcg policy to unregister
1520  *
1521  * Undo blkcg_policy_register(@pol).  Might sleep.
1522  */
1523 void blkcg_policy_unregister(struct blkcg_policy *pol)
1524 {
1525         struct blkcg *blkcg;
1526
1527         mutex_lock(&blkcg_pol_register_mutex);
1528
1529         if (WARN_ON(blkcg_policy[pol->plid] != pol))
1530                 goto out_unlock;
1531
1532         /* kill the intf files first */
1533         if (pol->dfl_cftypes)
1534                 cgroup_rm_cftypes(pol->dfl_cftypes);
1535         if (pol->legacy_cftypes)
1536                 cgroup_rm_cftypes(pol->legacy_cftypes);
1537
1538         /* remove cpds and unregister */
1539         mutex_lock(&blkcg_pol_mutex);
1540
1541         if (pol->cpd_free_fn) {
1542                 list_for_each_entry(blkcg, &all_blkcgs, all_blkcgs_node) {
1543                         if (blkcg->cpd[pol->plid]) {
1544                                 pol->cpd_free_fn(blkcg->cpd[pol->plid]);
1545                                 blkcg->cpd[pol->plid] = NULL;
1546                         }
1547                 }
1548         }
1549         blkcg_policy[pol->plid] = NULL;
1550
1551         mutex_unlock(&blkcg_pol_mutex);
1552 out_unlock:
1553         mutex_unlock(&blkcg_pol_register_mutex);
1554 }
1555 EXPORT_SYMBOL_GPL(blkcg_policy_unregister);
1556
1557 bool __blkcg_punt_bio_submit(struct bio *bio)
1558 {
1559         struct blkcg_gq *blkg = bio->bi_blkg;
1560
1561         /* consume the flag first */
1562         bio->bi_opf &= ~REQ_CGROUP_PUNT;
1563
1564         /* never bounce for the root cgroup */
1565         if (!blkg->parent)
1566                 return false;
1567
1568         spin_lock_bh(&blkg->async_bio_lock);
1569         bio_list_add(&blkg->async_bios, bio);
1570         spin_unlock_bh(&blkg->async_bio_lock);
1571
1572         queue_work(blkcg_punt_bio_wq, &blkg->async_bio_work);
1573         return true;
1574 }
1575
1576 /*
1577  * Scale the accumulated delay based on how long it has been since we updated
1578  * the delay.  We only call this when we are adding delay, in case it's been a
1579  * while since we added delay, and when we are checking to see if we need to
1580  * delay a task, to account for any delays that may have occurred.
1581  */
1582 static void blkcg_scale_delay(struct blkcg_gq *blkg, u64 now)
1583 {
1584         u64 old = atomic64_read(&blkg->delay_start);
1585
1586         /* negative use_delay means no scaling, see blkcg_set_delay() */
1587         if (atomic_read(&blkg->use_delay) < 0)
1588                 return;
1589
1590         /*
1591          * We only want to scale down every second.  The idea here is that we
1592          * want to delay people for min(delay_nsec, NSEC_PER_SEC) in a certain
1593          * time window.  We only want to throttle tasks for recent delay that
1594          * has occurred, in 1 second time windows since that's the maximum
1595          * things can be throttled.  We save the current delay window in
1596          * blkg->last_delay so we know what amount is still left to be charged
1597          * to the blkg from this point onward.  blkg->last_use keeps track of
1598          * the use_delay counter.  The idea is if we're unthrottling the blkg we
1599          * are ok with whatever is happening now, and we can take away more of
1600          * the accumulated delay as we've already throttled enough that
1601          * everybody is happy with their IO latencies.
1602          */
1603         if (time_before64(old + NSEC_PER_SEC, now) &&
1604             atomic64_cmpxchg(&blkg->delay_start, old, now) == old) {
1605                 u64 cur = atomic64_read(&blkg->delay_nsec);
1606                 u64 sub = min_t(u64, blkg->last_delay, now - old);
1607                 int cur_use = atomic_read(&blkg->use_delay);
1608
1609                 /*
1610                  * We've been unthrottled, subtract a larger chunk of our
1611                  * accumulated delay.
1612                  */
1613                 if (cur_use < blkg->last_use)
1614                         sub = max_t(u64, sub, blkg->last_delay >> 1);
1615
1616                 /*
1617                  * This shouldn't happen, but handle it anyway.  Our delay_nsec
1618                  * should only ever be growing except here where we subtract out
1619                  * min(last_delay, 1 second), but lord knows bugs happen and I'd
1620                  * rather not end up with negative numbers.
1621                  */
1622                 if (unlikely(cur < sub)) {
1623                         atomic64_set(&blkg->delay_nsec, 0);
1624                         blkg->last_delay = 0;
1625                 } else {
1626                         atomic64_sub(sub, &blkg->delay_nsec);
1627                         blkg->last_delay = cur - sub;
1628                 }
1629                 blkg->last_use = cur_use;
1630         }
1631 }
1632
1633 /*
1634  * This is called when we want to actually walk up the hierarchy and check to
1635  * see if we need to throttle, and then actually throttle if there is some
1636  * accumulated delay.  This should only be called upon return to user space so
1637  * we're not holding some lock that would induce a priority inversion.
1638  */
1639 static void blkcg_maybe_throttle_blkg(struct blkcg_gq *blkg, bool use_memdelay)
1640 {
1641         unsigned long pflags;
1642         bool clamp;
1643         u64 now = ktime_to_ns(ktime_get());
1644         u64 exp;
1645         u64 delay_nsec = 0;
1646         int tok;
1647
1648         while (blkg->parent) {
1649                 int use_delay = atomic_read(&blkg->use_delay);
1650
1651                 if (use_delay) {
1652                         u64 this_delay;
1653
1654                         blkcg_scale_delay(blkg, now);
1655                         this_delay = atomic64_read(&blkg->delay_nsec);
1656                         if (this_delay > delay_nsec) {
1657                                 delay_nsec = this_delay;
1658                                 clamp = use_delay > 0;
1659                         }
1660                 }
1661                 blkg = blkg->parent;
1662         }
1663
1664         if (!delay_nsec)
1665                 return;
1666
1667         /*
1668          * Let's not sleep for all eternity if we've amassed a huge delay.
1669          * Swapping or metadata IO can accumulate 10's of seconds worth of
1670          * delay, and we want userspace to be able to do _something_ so cap the
1671          * delays at 0.25s. If there's 10's of seconds worth of delay then the
1672          * tasks will be delayed for 0.25 second for every syscall. If
1673          * blkcg_set_delay() was used as indicated by negative use_delay, the
1674          * caller is responsible for regulating the range.
1675          */
1676         if (clamp)
1677                 delay_nsec = min_t(u64, delay_nsec, 250 * NSEC_PER_MSEC);
1678
1679         if (use_memdelay)
1680                 psi_memstall_enter(&pflags);
1681
1682         exp = ktime_add_ns(now, delay_nsec);
1683         tok = io_schedule_prepare();
1684         do {
1685                 __set_current_state(TASK_KILLABLE);
1686                 if (!schedule_hrtimeout(&exp, HRTIMER_MODE_ABS))
1687                         break;
1688         } while (!fatal_signal_pending(current));
1689         io_schedule_finish(tok);
1690
1691         if (use_memdelay)
1692                 psi_memstall_leave(&pflags);
1693 }
1694
1695 /**
1696  * blkcg_maybe_throttle_current - throttle the current task if it has been marked
1697  *
1698  * This is only called if we've been marked with set_notify_resume().  Obviously
1699  * we can be set_notify_resume() for reasons other than blkcg throttling, so we
1700  * check to see if current->throttle_queue is set and if not this doesn't do
1701  * anything.  This should only ever be called by the resume code, it's not meant
1702  * to be called by people willy-nilly as it will actually do the work to
1703  * throttle the task if it is setup for throttling.
1704  */
1705 void blkcg_maybe_throttle_current(void)
1706 {
1707         struct request_queue *q = current->throttle_queue;
1708         struct cgroup_subsys_state *css;
1709         struct blkcg *blkcg;
1710         struct blkcg_gq *blkg;
1711         bool use_memdelay = current->use_memdelay;
1712
1713         if (!q)
1714                 return;
1715
1716         current->throttle_queue = NULL;
1717         current->use_memdelay = false;
1718
1719         rcu_read_lock();
1720         css = kthread_blkcg();
1721         if (css)
1722                 blkcg = css_to_blkcg(css);
1723         else
1724                 blkcg = css_to_blkcg(task_css(current, io_cgrp_id));
1725
1726         if (!blkcg)
1727                 goto out;
1728         blkg = blkg_lookup(blkcg, q);
1729         if (!blkg)
1730                 goto out;
1731         if (!blkg_tryget(blkg))
1732                 goto out;
1733         rcu_read_unlock();
1734
1735         blkcg_maybe_throttle_blkg(blkg, use_memdelay);
1736         blkg_put(blkg);
1737         blk_put_queue(q);
1738         return;
1739 out:
1740         rcu_read_unlock();
1741         blk_put_queue(q);
1742 }
1743
1744 /**
1745  * blkcg_schedule_throttle - this task needs to check for throttling
1746  * @q: the request queue IO was submitted on
1747  * @use_memdelay: do we charge this to memory delay for PSI
1748  *
1749  * This is called by the IO controller when we know there's delay accumulated
1750  * for the blkg for this task.  We do not pass the blkg because there are places
1751  * we call this that may not have that information, the swapping code for
1752  * instance will only have a request_queue at that point.  This set's the
1753  * notify_resume for the task to check and see if it requires throttling before
1754  * returning to user space.
1755  *
1756  * We will only schedule once per syscall.  You can call this over and over
1757  * again and it will only do the check once upon return to user space, and only
1758  * throttle once.  If the task needs to be throttled again it'll need to be
1759  * re-set at the next time we see the task.
1760  */
1761 void blkcg_schedule_throttle(struct request_queue *q, bool use_memdelay)
1762 {
1763         if (unlikely(current->flags & PF_KTHREAD))
1764                 return;
1765
1766         if (current->throttle_queue != q) {
1767                 if (!blk_get_queue(q))
1768                         return;
1769
1770                 if (current->throttle_queue)
1771                         blk_put_queue(current->throttle_queue);
1772                 current->throttle_queue = q;
1773         }
1774
1775         if (use_memdelay)
1776                 current->use_memdelay = use_memdelay;
1777         set_notify_resume(current);
1778 }
1779
1780 /**
1781  * blkcg_add_delay - add delay to this blkg
1782  * @blkg: blkg of interest
1783  * @now: the current time in nanoseconds
1784  * @delta: how many nanoseconds of delay to add
1785  *
1786  * Charge @delta to the blkg's current delay accumulation.  This is used to
1787  * throttle tasks if an IO controller thinks we need more throttling.
1788  */
1789 void blkcg_add_delay(struct blkcg_gq *blkg, u64 now, u64 delta)
1790 {
1791         if (WARN_ON_ONCE(atomic_read(&blkg->use_delay) < 0))
1792                 return;
1793         blkcg_scale_delay(blkg, now);
1794         atomic64_add(delta, &blkg->delay_nsec);
1795 }
1796
1797 /**
1798  * blkg_tryget_closest - try and get a blkg ref on the closet blkg
1799  * @bio: target bio
1800  * @css: target css
1801  *
1802  * As the failure mode here is to walk up the blkg tree, this ensure that the
1803  * blkg->parent pointers are always valid.  This returns the blkg that it ended
1804  * up taking a reference on or %NULL if no reference was taken.
1805  */
1806 static inline struct blkcg_gq *blkg_tryget_closest(struct bio *bio,
1807                 struct cgroup_subsys_state *css)
1808 {
1809         struct blkcg_gq *blkg, *ret_blkg = NULL;
1810
1811         rcu_read_lock();
1812         blkg = blkg_lookup_create(css_to_blkcg(css),
1813                                   bio->bi_bdev->bd_disk->queue);
1814         while (blkg) {
1815                 if (blkg_tryget(blkg)) {
1816                         ret_blkg = blkg;
1817                         break;
1818                 }
1819                 blkg = blkg->parent;
1820         }
1821         rcu_read_unlock();
1822
1823         return ret_blkg;
1824 }
1825
1826 /**
1827  * bio_associate_blkg_from_css - associate a bio with a specified css
1828  * @bio: target bio
1829  * @css: target css
1830  *
1831  * Associate @bio with the blkg found by combining the css's blkg and the
1832  * request_queue of the @bio.  An association failure is handled by walking up
1833  * the blkg tree.  Therefore, the blkg associated can be anything between @blkg
1834  * and q->root_blkg.  This situation only happens when a cgroup is dying and
1835  * then the remaining bios will spill to the closest alive blkg.
1836  *
1837  * A reference will be taken on the blkg and will be released when @bio is
1838  * freed.
1839  */
1840 void bio_associate_blkg_from_css(struct bio *bio,
1841                                  struct cgroup_subsys_state *css)
1842 {
1843         if (bio->bi_blkg)
1844                 blkg_put(bio->bi_blkg);
1845
1846         if (css && css->parent) {
1847                 bio->bi_blkg = blkg_tryget_closest(bio, css);
1848         } else {
1849                 blkg_get(bio->bi_bdev->bd_disk->queue->root_blkg);
1850                 bio->bi_blkg = bio->bi_bdev->bd_disk->queue->root_blkg;
1851         }
1852 }
1853 EXPORT_SYMBOL_GPL(bio_associate_blkg_from_css);
1854
1855 /**
1856  * bio_associate_blkg - associate a bio with a blkg
1857  * @bio: target bio
1858  *
1859  * Associate @bio with the blkg found from the bio's css and request_queue.
1860  * If one is not found, bio_lookup_blkg() creates the blkg.  If a blkg is
1861  * already associated, the css is reused and association redone as the
1862  * request_queue may have changed.
1863  */
1864 void bio_associate_blkg(struct bio *bio)
1865 {
1866         struct cgroup_subsys_state *css;
1867
1868         rcu_read_lock();
1869
1870         if (bio->bi_blkg)
1871                 css = &bio_blkcg(bio)->css;
1872         else
1873                 css = blkcg_css();
1874
1875         bio_associate_blkg_from_css(bio, css);
1876
1877         rcu_read_unlock();
1878 }
1879 EXPORT_SYMBOL_GPL(bio_associate_blkg);
1880
1881 /**
1882  * bio_clone_blkg_association - clone blkg association from src to dst bio
1883  * @dst: destination bio
1884  * @src: source bio
1885  */
1886 void bio_clone_blkg_association(struct bio *dst, struct bio *src)
1887 {
1888         if (src->bi_blkg) {
1889                 if (dst->bi_blkg)
1890                         blkg_put(dst->bi_blkg);
1891                 blkg_get(src->bi_blkg);
1892                 dst->bi_blkg = src->bi_blkg;
1893         }
1894 }
1895 EXPORT_SYMBOL_GPL(bio_clone_blkg_association);
1896
1897 static int blk_cgroup_io_type(struct bio *bio)
1898 {
1899         if (op_is_discard(bio->bi_opf))
1900                 return BLKG_IOSTAT_DISCARD;
1901         if (op_is_write(bio->bi_opf))
1902                 return BLKG_IOSTAT_WRITE;
1903         return BLKG_IOSTAT_READ;
1904 }
1905
1906 void blk_cgroup_bio_start(struct bio *bio)
1907 {
1908         int rwd = blk_cgroup_io_type(bio), cpu;
1909         struct blkg_iostat_set *bis;
1910
1911         cpu = get_cpu();
1912         bis = per_cpu_ptr(bio->bi_blkg->iostat_cpu, cpu);
1913         u64_stats_update_begin(&bis->sync);
1914
1915         /*
1916          * If the bio is flagged with BIO_CGROUP_ACCT it means this is a split
1917          * bio and we would have already accounted for the size of the bio.
1918          */
1919         if (!bio_flagged(bio, BIO_CGROUP_ACCT)) {
1920                 bio_set_flag(bio, BIO_CGROUP_ACCT);
1921                 bis->cur.bytes[rwd] += bio->bi_iter.bi_size;
1922         }
1923         bis->cur.ios[rwd]++;
1924
1925         u64_stats_update_end(&bis->sync);
1926         if (cgroup_subsys_on_dfl(io_cgrp_subsys))
1927                 cgroup_rstat_updated(bio->bi_blkg->blkcg->css.cgroup, cpu);
1928         put_cpu();
1929 }
1930
1931 static int __init blkcg_init(void)
1932 {
1933         blkcg_punt_bio_wq = alloc_workqueue("blkcg_punt_bio",
1934                                             WQ_MEM_RECLAIM | WQ_FREEZABLE |
1935                                             WQ_UNBOUND | WQ_SYSFS, 0);
1936         if (!blkcg_punt_bio_wq)
1937                 return -ENOMEM;
1938         return 0;
1939 }
1940 subsys_initcall(blkcg_init);
1941
1942 module_param(blkcg_debug_stats, bool, 0644);
1943 MODULE_PARM_DESC(blkcg_debug_stats, "True if you want debug stats, false if not");