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/delay.h>
27	#include <linux/atomic.h>
28	#include <linux/ctype.h>
29	#include <linux/resume_user_mode.h>
30	#include <linux/psi.h>
31	#include <linux/part_stat.h>
32	#include "blk.h"
33	#include "blk-cgroup.h"
34	#include "blk-ioprio.h"
35	#include "blk-throttle.h"
36
37	static void __blkcg_rstat_flush(struct blkcg *blkcg, int cpu);
38
39	/*
40	* blkcg_pol_mutex protects blkcg_policy[] and policy [de]activation.
41	* blkcg_pol_register_mutex nests outside of it and synchronizes entire
42	* policy [un]register operations including cgroup file additions /
43	* removals. Putting cgroup file registration outside blkcg_pol_mutex
44	* allows grabbing it from cgroup callbacks.
45	*/
46	static DEFINE_MUTEX(blkcg_pol_register_mutex);
47	static DEFINE_MUTEX(blkcg_pol_mutex);
48
49	struct blkcg blkcg_root;
50	EXPORT_SYMBOL_GPL(blkcg_root);
51
52	struct cgroup_subsys_state * const blkcg_root_css = &blkcg_root.css;
53	EXPORT_SYMBOL_GPL(blkcg_root_css);
54
55	static struct blkcg_policy *blkcg_policy[BLKCG_MAX_POLS];
56
57	static LIST_HEAD(all_blkcgs); /* protected by blkcg_pol_mutex */
58
59	bool blkcg_debug_stats = false;
60
61	static DEFINE_RAW_SPINLOCK(blkg_stat_lock);
62
63	#define BLKG_DESTROY_BATCH_SIZE 64
64
65	/*
66	* Lockless lists for tracking IO stats update
67	*
68	* New IO stats are stored in the percpu iostat_cpu within blkcg_gq (blkg).
69	* There are multiple blkg's (one for each block device) attached to each
70	* blkcg. The rstat code keeps track of which cpu has IO stats updated,
71	* but it doesn't know which blkg has the updated stats. If there are many
72	* block devices in a system, the cost of iterating all the blkg's to flush
73	* out the IO stats can be high. To reduce such overhead, a set of percpu
74	* lockless lists (lhead) per blkcg are used to track the set of recently
75	* updated iostat_cpu's since the last flush. An iostat_cpu will be put
76	* onto the lockless list on the update side [blk_cgroup_bio_start()] if
77	* not there yet and then removed when being flushed [blkcg_rstat_flush()].
78	* References to blkg are gotten and then put back in the process to
79	* protect against blkg removal.
80	*
81	* Return: 0 if successful or -ENOMEM if allocation fails.
82	*/
83	static int init_blkcg_llists(struct blkcg *blkcg)
84	{
85	int cpu;
86
87	blkcg->lhead = alloc_percpu_gfp(struct llist_head, GFP_KERNEL);
88	if (!blkcg->lhead)
89	return -ENOMEM;
90
91	for_each_possible_cpu(cpu)
92	init_llist_head(per_cpu_ptr(blkcg->lhead, cpu));
93	return 0;
94	}
95
96	/**
97	* blkcg_css - find the current css
98	*
99	* Find the css associated with either the kthread or the current task.
100	* This may return a dying css, so it is up to the caller to use tryget logic
101	* to confirm it is alive and well.
102	*/
103	static struct cgroup_subsys_state *blkcg_css(void)
104	{
105	struct cgroup_subsys_state *css;
106
107	css = kthread_blkcg();
108	if (css)
109	return css;
110	return task_css(current, subsys_id: io_cgrp_id);
111	}
112
113	static bool blkcg_policy_enabled(struct request_queue *q,
114	const struct blkcg_policy *pol)
115	{
116	return pol && test_bit(pol->plid, q->blkcg_pols);
117	}
118
119	static void blkg_free_workfn(struct work_struct *work)
120	{
121	struct blkcg_gq *blkg = container_of(work, struct blkcg_gq,
122	free_work);
123	struct request_queue *q = blkg->q;
124	int i;
125
126	/*
127	* pd_free_fn() can also be called from blkcg_deactivate_policy(),
128	* in order to make sure pd_free_fn() is called in order, the deletion
129	* of the list blkg->q_node is delayed to here from blkg_destroy(), and
130	* blkcg_mutex is used to synchronize blkg_free_workfn() and
131	* blkcg_deactivate_policy().
132	*/
133	mutex_lock(&q->blkcg_mutex);
134	for (i = 0; i < BLKCG_MAX_POLS; i++)
135	if (blkg->pd[i])
136	blkcg_policy[i]->pd_free_fn(blkg->pd[i]);
137	if (blkg->parent)
138	blkg_put(blkg: blkg->parent);
139	spin_lock_irq(lock: &q->queue_lock);
140	list_del_init(entry: &blkg->q_node);
141	spin_unlock_irq(lock: &q->queue_lock);
142	mutex_unlock(lock: &q->blkcg_mutex);
143
144	blk_put_queue(q);
145	free_percpu(pdata: blkg->iostat_cpu);
146	percpu_ref_exit(ref: &blkg->refcnt);
147	kfree(objp: blkg);
148	}
149
150	/**
151	* blkg_free - free a blkg
152	* @blkg: blkg to free
153	*
154	* Free @blkg which may be partially allocated.
155	*/
156	static void blkg_free(struct blkcg_gq *blkg)
157	{
158	if (!blkg)
159	return;
160
161	/*
162	* Both ->pd_free_fn() and request queue's release handler may
163	* sleep, so free us by scheduling one work func
164	*/
165	INIT_WORK(&blkg->free_work, blkg_free_workfn);
166	schedule_work(work: &blkg->free_work);
167	}
168
169	static void __blkg_release(struct rcu_head *rcu)
170	{
171	struct blkcg_gq *blkg = container_of(rcu, struct blkcg_gq, rcu_head);
172	struct blkcg *blkcg = blkg->blkcg;
173	int cpu;
174
175	#ifdef CONFIG_BLK_CGROUP_PUNT_BIO
176	WARN_ON(!bio_list_empty(&blkg->async_bios));
177	#endif
178	/*
179	* Flush all the non-empty percpu lockless lists before releasing
180	* us, given these stat belongs to us.
181	*
182	* blkg_stat_lock is for serializing blkg stat update
183	*/
184	for_each_possible_cpu(cpu)
185	__blkcg_rstat_flush(blkcg, cpu);
186
187	/* release the blkcg and parent blkg refs this blkg has been holding */
188	css_put(css: &blkg->blkcg->css);
189	blkg_free(blkg);
190	}
191
192	/*
193	* A group is RCU protected, but having an rcu lock does not mean that one
194	* can access all the fields of blkg and assume these are valid. For
195	* example, don't try to follow throtl_data and request queue links.
196	*
197	* Having a reference to blkg under an rcu allows accesses to only values
198	* local to groups like group stats and group rate limits.
199	*/
200	static void blkg_release(struct percpu_ref *ref)
201	{
202	struct blkcg_gq *blkg = container_of(ref, struct blkcg_gq, refcnt);
203
204	call_rcu(head: &blkg->rcu_head, func: __blkg_release);
205	}
206
207	#ifdef CONFIG_BLK_CGROUP_PUNT_BIO
208	static struct workqueue_struct *blkcg_punt_bio_wq;
209
210	static void blkg_async_bio_workfn(struct work_struct *work)
211	{
212	struct blkcg_gq *blkg = container_of(work, struct blkcg_gq,
213	async_bio_work);
214	struct bio_list bios = BIO_EMPTY_LIST;
215	struct bio *bio;
216	struct blk_plug plug;
217	bool need_plug = false;
218
219	/* as long as there are pending bios, @blkg can't go away */
220	spin_lock(lock: &blkg->async_bio_lock);
221	bio_list_merge(bl: &bios, bl2: &blkg->async_bios);
222	bio_list_init(bl: &blkg->async_bios);
223	spin_unlock(lock: &blkg->async_bio_lock);
224
225	/* start plug only when bio_list contains at least 2 bios */
226	if (bios.head && bios.head->bi_next) {
227	need_plug = true;
228	blk_start_plug(&plug);
229	}
230	while ((bio = bio_list_pop(bl: &bios)))
231	submit_bio(bio);
232	if (need_plug)
233	blk_finish_plug(&plug);
234	}
235
236	/*
237	* When a shared kthread issues a bio for a cgroup, doing so synchronously can
238	* lead to priority inversions as the kthread can be trapped waiting for that
239	* cgroup. Use this helper instead of submit_bio to punt the actual issuing to
240	* a dedicated per-blkcg work item to avoid such priority inversions.
241	*/
242	void blkcg_punt_bio_submit(struct bio *bio)
243	{
244	struct blkcg_gq *blkg = bio->bi_blkg;
245
246	if (blkg->parent) {
247	spin_lock(lock: &blkg->async_bio_lock);
248	bio_list_add(bl: &blkg->async_bios, bio);
249	spin_unlock(lock: &blkg->async_bio_lock);
250	queue_work(wq: blkcg_punt_bio_wq, work: &blkg->async_bio_work);
251	} else {
252	/* never bounce for the root cgroup */
253	submit_bio(bio);
254	}
255	}
256	EXPORT_SYMBOL_GPL(blkcg_punt_bio_submit);
257
258	static int __init blkcg_punt_bio_init(void)
259	{
260	blkcg_punt_bio_wq = alloc_workqueue(fmt: "blkcg_punt_bio",
261	flags: WQ_MEM_RECLAIM | WQ_FREEZABLE |
262	WQ_UNBOUND | WQ_SYSFS, max_active: 0);
263	if (!blkcg_punt_bio_wq)
264	return -ENOMEM;
265	return 0;
266	}
267	subsys_initcall(blkcg_punt_bio_init);
268	#endif /* CONFIG_BLK_CGROUP_PUNT_BIO */
269
270	/**
271	* bio_blkcg_css - return the blkcg CSS associated with a bio
272	* @bio: target bio
273	*
274	* This returns the CSS for the blkcg associated with a bio, or %NULL if not
275	* associated. Callers are expected to either handle %NULL or know association
276	* has been done prior to calling this.
277	*/
278	struct cgroup_subsys_state *bio_blkcg_css(struct bio *bio)
279	{
280	if (!bio || !bio->bi_blkg)
281	return NULL;
282	return &bio->bi_blkg->blkcg->css;
283	}
284	EXPORT_SYMBOL_GPL(bio_blkcg_css);
285
286	/**
287	* blkcg_parent - get the parent of a blkcg
288	* @blkcg: blkcg of interest
289	*
290	* Return the parent blkcg of @blkcg. Can be called anytime.
291	*/
292	static inline struct blkcg *blkcg_parent(struct blkcg *blkcg)
293	{
294	return css_to_blkcg(css: blkcg->css.parent);
295	}
296
297	/**
298	* blkg_alloc - allocate a blkg
299	* @blkcg: block cgroup the new blkg is associated with
300	* @disk: gendisk the new blkg is associated with
301	* @gfp_mask: allocation mask to use
302	*
303	* Allocate a new blkg assocating @blkcg and @q.
304	*/
305	static struct blkcg_gq *blkg_alloc(struct blkcg *blkcg, struct gendisk *disk,
306	gfp_t gfp_mask)
307	{
308	struct blkcg_gq *blkg;
309	int i, cpu;
310
311	/* alloc and init base part */
312	blkg = kzalloc_node(size: sizeof(*blkg), flags: gfp_mask, node: disk->queue->node);
313	if (!blkg)
314	return NULL;
315	if (percpu_ref_init(ref: &blkg->refcnt, release: blkg_release, flags: 0, gfp: gfp_mask))
316	goto out_free_blkg;
317	blkg->iostat_cpu = alloc_percpu_gfp(struct blkg_iostat_set, gfp_mask);
318	if (!blkg->iostat_cpu)
319	goto out_exit_refcnt;
320	if (!blk_get_queue(disk->queue))
321	goto out_free_iostat;
322
323	blkg->q = disk->queue;
324	INIT_LIST_HEAD(list: &blkg->q_node);
325	blkg->blkcg = blkcg;
326	#ifdef CONFIG_BLK_CGROUP_PUNT_BIO
327	spin_lock_init(&blkg->async_bio_lock);
328	bio_list_init(bl: &blkg->async_bios);
329	INIT_WORK(&blkg->async_bio_work, blkg_async_bio_workfn);
330	#endif
331
332	u64_stats_init(syncp: &blkg->iostat.sync);
333	for_each_possible_cpu(cpu) {
334	u64_stats_init(syncp: &per_cpu_ptr(blkg->iostat_cpu, cpu)->sync);
335	per_cpu_ptr(blkg->iostat_cpu, cpu)->blkg = blkg;
336	}
337
338	for (i = 0; i < BLKCG_MAX_POLS; i++) {
339	struct blkcg_policy *pol = blkcg_policy[i];
340	struct blkg_policy_data *pd;
341
342	if (!blkcg_policy_enabled(q: disk->queue, pol))
343	continue;
344
345	/* alloc per-policy data and attach it to blkg */
346	pd = pol->pd_alloc_fn(disk, blkcg, gfp_mask);
347	if (!pd)
348	goto out_free_pds;
349	blkg->pd[i] = pd;
350	pd->blkg = blkg;
351	pd->plid = i;
352	pd->online = false;
353	}
354
355	return blkg;
356
357	out_free_pds:
358	while (--i >= 0)
359	if (blkg->pd[i])
360	blkcg_policy[i]->pd_free_fn(blkg->pd[i]);
361	blk_put_queue(disk->queue);
362	out_free_iostat:
363	free_percpu(pdata: blkg->iostat_cpu);
364	out_exit_refcnt:
365	percpu_ref_exit(ref: &blkg->refcnt);
366	out_free_blkg:
367	kfree(objp: blkg);
368	return NULL;
369	}
370
371	/*
372	* If @new_blkg is %NULL, this function tries to allocate a new one as
373	* necessary using %GFP_NOWAIT. @new_blkg is always consumed on return.
374	*/
375	static struct blkcg_gq *blkg_create(struct blkcg *blkcg, struct gendisk *disk,
376	struct blkcg_gq *new_blkg)
377	{
378	struct blkcg_gq *blkg;
379	int i, ret;
380
381	lockdep_assert_held(&disk->queue->queue_lock);
382
383	/* request_queue is dying, do not create/recreate a blkg */
384	if (blk_queue_dying(disk->queue)) {
385	ret = -ENODEV;
386	goto err_free_blkg;
387	}
388
389	/* blkg holds a reference to blkcg */
390	if (!css_tryget_online(css: &blkcg->css)) {
391	ret = -ENODEV;
392	goto err_free_blkg;
393	}
394
395	/* allocate */
396	if (!new_blkg) {
397	new_blkg = blkg_alloc(blkcg, disk, GFP_NOWAIT | __GFP_NOWARN);
398	if (unlikely(!new_blkg)) {
399	ret = -ENOMEM;
400	goto err_put_css;
401	}
402	}
403	blkg = new_blkg;
404
405	/* link parent */
406	if (blkcg_parent(blkcg)) {
407	blkg->parent = blkg_lookup(blkcg: blkcg_parent(blkcg), q: disk->queue);
408	if (WARN_ON_ONCE(!blkg->parent)) {
409	ret = -ENODEV;
410	goto err_put_css;
411	}
412	blkg_get(blkg: blkg->parent);
413	}
414
415	/* invoke per-policy init */
416	for (i = 0; i < BLKCG_MAX_POLS; i++) {
417	struct blkcg_policy *pol = blkcg_policy[i];
418
419	if (blkg->pd[i] && pol->pd_init_fn)
420	pol->pd_init_fn(blkg->pd[i]);
421	}
422
423	/* insert */
424	spin_lock(lock: &blkcg->lock);
425	ret = radix_tree_insert(&blkcg->blkg_tree, index: disk->queue->id, blkg);
426	if (likely(!ret)) {
427	hlist_add_head_rcu(n: &blkg->blkcg_node, h: &blkcg->blkg_list);
428	list_add(new: &blkg->q_node, head: &disk->queue->blkg_list);
429
430	for (i = 0; i < BLKCG_MAX_POLS; i++) {
431	struct blkcg_policy *pol = blkcg_policy[i];
432
433	if (blkg->pd[i]) {
434	if (pol->pd_online_fn)
435	pol->pd_online_fn(blkg->pd[i]);
436	blkg->pd[i]->online = true;
437	}
438	}
439	}
440	blkg->online = true;
441	spin_unlock(lock: &blkcg->lock);
442
443	if (!ret)
444	return blkg;
445
446	/* @blkg failed fully initialized, use the usual release path */
447	blkg_put(blkg);
448	return ERR_PTR(error: ret);
449
450	err_put_css:
451	css_put(css: &blkcg->css);
452	err_free_blkg:
453	if (new_blkg)
454	blkg_free(blkg: new_blkg);
455	return ERR_PTR(error: ret);
456	}
457
458	/**
459	* blkg_lookup_create - lookup blkg, try to create one if not there
460	* @blkcg: blkcg of interest
461	* @disk: gendisk of interest
462	*
463	* Lookup blkg for the @blkcg - @disk pair. If it doesn't exist, try to
464	* create one. blkg creation is performed recursively from blkcg_root such
465	* that all non-root blkg's have access to the parent blkg. This function
466	* should be called under RCU read lock and takes @disk->queue->queue_lock.
467	*
468	* Returns the blkg or the closest blkg if blkg_create() fails as it walks
469	* down from root.
470	*/
471	static struct blkcg_gq *blkg_lookup_create(struct blkcg *blkcg,
472	struct gendisk *disk)
473	{
474	struct request_queue *q = disk->queue;
475	struct blkcg_gq *blkg;
476	unsigned long flags;
477
478	WARN_ON_ONCE(!rcu_read_lock_held());
479
480	blkg = blkg_lookup(blkcg, q);
481	if (blkg)
482	return blkg;
483
484	spin_lock_irqsave(&q->queue_lock, flags);
485	blkg = blkg_lookup(blkcg, q);
486	if (blkg) {
487	if (blkcg != &blkcg_root &&
488	blkg != rcu_dereference(blkcg->blkg_hint))
489	rcu_assign_pointer(blkcg->blkg_hint, blkg);
490	goto found;
491	}
492
493	/*
494	* Create blkgs walking down from blkcg_root to @blkcg, so that all
495	* non-root blkgs have access to their parents. Returns the closest
496	* blkg to the intended blkg should blkg_create() fail.
497	*/
498	while (true) {
499	struct blkcg *pos = blkcg;
500	struct blkcg *parent = blkcg_parent(blkcg);
501	struct blkcg_gq *ret_blkg = q->root_blkg;
502
503	while (parent) {
504	blkg = blkg_lookup(blkcg: parent, q);
505	if (blkg) {
506	/* remember closest blkg */
507	ret_blkg = blkg;
508	break;
509	}
510	pos = parent;
511	parent = blkcg_parent(blkcg: parent);
512	}
513
514	blkg = blkg_create(blkcg: pos, disk, NULL);
515	if (IS_ERR(ptr: blkg)) {
516	blkg = ret_blkg;
517	break;
518	}
519	if (pos == blkcg)
520	break;
521	}
522
523	found:
524	spin_unlock_irqrestore(lock: &q->queue_lock, flags);
525	return blkg;
526	}
527
528	static void blkg_destroy(struct blkcg_gq *blkg)
529	{
530	struct blkcg *blkcg = blkg->blkcg;
531	int i;
532
533	lockdep_assert_held(&blkg->q->queue_lock);
534	lockdep_assert_held(&blkcg->lock);
535
536	/*
537	* blkg stays on the queue list until blkg_free_workfn(), see details in
538	* blkg_free_workfn(), hence this function can be called from
539	* blkcg_destroy_blkgs() first and again from blkg_destroy_all() before
540	* blkg_free_workfn().
541	*/
542	if (hlist_unhashed(h: &blkg->blkcg_node))
543	return;
544
545	for (i = 0; i < BLKCG_MAX_POLS; i++) {
546	struct blkcg_policy *pol = blkcg_policy[i];
547
548	if (blkg->pd[i] && blkg->pd[i]->online) {
549	blkg->pd[i]->online = false;
550	if (pol->pd_offline_fn)
551	pol->pd_offline_fn(blkg->pd[i]);
552	}
553	}
554
555	blkg->online = false;
556
557	radix_tree_delete(&blkcg->blkg_tree, blkg->q->id);
558	hlist_del_init_rcu(n: &blkg->blkcg_node);
559
560	/*
561	* Both setting lookup hint to and clearing it from @blkg are done
562	* under queue_lock. If it's not pointing to @blkg now, it never
563	* will. Hint assignment itself can race safely.
564	*/
565	if (rcu_access_pointer(blkcg->blkg_hint) == blkg)
566	rcu_assign_pointer(blkcg->blkg_hint, NULL);
567
568	/*
569	* Put the reference taken at the time of creation so that when all
570	* queues are gone, group can be destroyed.
571	*/
572	percpu_ref_kill(ref: &blkg->refcnt);
573	}
574
575	static void blkg_destroy_all(struct gendisk *disk)
576	{
577	struct request_queue *q = disk->queue;
578	struct blkcg_gq *blkg, *n;
579	int count = BLKG_DESTROY_BATCH_SIZE;
580
581	restart:
582	spin_lock_irq(lock: &q->queue_lock);
583	list_for_each_entry_safe(blkg, n, &q->blkg_list, q_node) {
584	struct blkcg *blkcg = blkg->blkcg;
585
586	if (hlist_unhashed(h: &blkg->blkcg_node))
587	continue;
588
589	spin_lock(lock: &blkcg->lock);
590	blkg_destroy(blkg);
591	spin_unlock(lock: &blkcg->lock);
592
593	/*
594	* in order to avoid holding the spin lock for too long, release
595	* it when a batch of blkgs are destroyed.
596	*/
597	if (!(--count)) {
598	count = BLKG_DESTROY_BATCH_SIZE;
599	spin_unlock_irq(lock: &q->queue_lock);
600	cond_resched();
601	goto restart;
602	}
603	}
604
605	q->root_blkg = NULL;
606	spin_unlock_irq(lock: &q->queue_lock);
607	}
608
609	static int blkcg_reset_stats(struct cgroup_subsys_state *css,
610	struct cftype *cftype, u64 val)
611	{
612	struct blkcg *blkcg = css_to_blkcg(css);
613	struct blkcg_gq *blkg;
614	int i, cpu;
615
616	mutex_lock(&blkcg_pol_mutex);
617	spin_lock_irq(lock: &blkcg->lock);
618
619	/*
620	* Note that stat reset is racy - it doesn't synchronize against
621	* stat updates. This is a debug feature which shouldn't exist
622	* anyway. If you get hit by a race, retry.
623	*/
624	hlist_for_each_entry(blkg, &blkcg->blkg_list, blkcg_node) {
625	for_each_possible_cpu(cpu) {
626	struct blkg_iostat_set *bis =
627	per_cpu_ptr(blkg->iostat_cpu, cpu);
628	memset(bis, 0, sizeof(*bis));
629
630	/* Re-initialize the cleared blkg_iostat_set */
631	u64_stats_init(syncp: &bis->sync);
632	bis->blkg = blkg;
633	}
634	memset(&blkg->iostat, 0, sizeof(blkg->iostat));
635	u64_stats_init(syncp: &blkg->iostat.sync);
636
637	for (i = 0; i < BLKCG_MAX_POLS; i++) {
638	struct blkcg_policy *pol = blkcg_policy[i];
639
640	if (blkg->pd[i] && pol->pd_reset_stats_fn)
641	pol->pd_reset_stats_fn(blkg->pd[i]);
642	}
643	}
644
645	spin_unlock_irq(lock: &blkcg->lock);
646	mutex_unlock(lock: &blkcg_pol_mutex);
647	return 0;
648	}
649
650	const char *blkg_dev_name(struct blkcg_gq *blkg)
651	{
652	if (!blkg->q->disk)
653	return NULL;
654	return bdi_dev_name(bdi: blkg->q->disk->bdi);
655	}
656
657	/**
658	* blkcg_print_blkgs - helper for printing per-blkg data
659	* @sf: seq_file to print to
660	* @blkcg: blkcg of interest
661	* @prfill: fill function to print out a blkg
662	* @pol: policy in question
663	* @data: data to be passed to @prfill
664	* @show_total: to print out sum of prfill return values or not
665	*
666	* This function invokes @prfill on each blkg of @blkcg if pd for the
667	* policy specified by @pol exists. @prfill is invoked with @sf, the
668	* policy data and @data and the matching queue lock held. If @show_total
669	* is %true, the sum of the return values from @prfill is printed with
670	* "Total" label at the end.
671	*
672	* This is to be used to construct print functions for
673	* cftype->read_seq_string method.
674	*/
675	void blkcg_print_blkgs(struct seq_file *sf, struct blkcg *blkcg,
676	u64 (*prfill)(struct seq_file *,
677	struct blkg_policy_data *, int),
678	const struct blkcg_policy *pol, int data,
679	bool show_total)
680	{
681	struct blkcg_gq *blkg;
682	u64 total = 0;
683
684	rcu_read_lock();
685	hlist_for_each_entry_rcu(blkg, &blkcg->blkg_list, blkcg_node) {
686	spin_lock_irq(lock: &blkg->q->queue_lock);
687	if (blkcg_policy_enabled(q: blkg->q, pol))
688	total += prfill(sf, blkg->pd[pol->plid], data);
689	spin_unlock_irq(lock: &blkg->q->queue_lock);
690	}
691	rcu_read_unlock();
692
693	if (show_total)
694	seq_printf(m: sf, fmt: "Total %llu\n", (unsigned long long)total);
695	}
696	EXPORT_SYMBOL_GPL(blkcg_print_blkgs);
697
698	/**
699	* __blkg_prfill_u64 - prfill helper for a single u64 value
700	* @sf: seq_file to print to
701	* @pd: policy private data of interest
702	* @v: value to print
703	*
704	* Print @v to @sf for the device associated with @pd.
705	*/
706	u64 __blkg_prfill_u64(struct seq_file *sf, struct blkg_policy_data *pd, u64 v)
707	{
708	const char *dname = blkg_dev_name(blkg: pd->blkg);
709
710	if (!dname)
711	return 0;
712
713	seq_printf(m: sf, fmt: "%s %llu\n", dname, (unsigned long long)v);
714	return v;
715	}
716	EXPORT_SYMBOL_GPL(__blkg_prfill_u64);
717
718	/**
719	* blkg_conf_init - initialize a blkg_conf_ctx
720	* @ctx: blkg_conf_ctx to initialize
721	* @input: input string
722	*
723	* Initialize @ctx which can be used to parse blkg config input string @input.
724	* Once initialized, @ctx can be used with blkg_conf_open_bdev() and
725	* blkg_conf_prep(), and must be cleaned up with blkg_conf_exit().
726	*/
727	void blkg_conf_init(struct blkg_conf_ctx *ctx, char *input)
728	{
729	*ctx = (struct blkg_conf_ctx){ .input = input };
730	}
731	EXPORT_SYMBOL_GPL(blkg_conf_init);
732
733	/**
734	* blkg_conf_open_bdev - parse and open bdev for per-blkg config update
735	* @ctx: blkg_conf_ctx initialized with blkg_conf_init()
736	*
737	* Parse the device node prefix part, MAJ:MIN, of per-blkg config update from
738	* @ctx->input and get and store the matching bdev in @ctx->bdev. @ctx->body is
739	* set to point past the device node prefix.
740	*
741	* This function may be called multiple times on @ctx and the extra calls become
742	* NOOPs. blkg_conf_prep() implicitly calls this function. Use this function
743	* explicitly if bdev access is needed without resolving the blkcg / policy part
744	* of @ctx->input. Returns -errno on error.
745	*/
746	int blkg_conf_open_bdev(struct blkg_conf_ctx *ctx)
747	{
748	char *input = ctx->input;
749	unsigned int major, minor;
750	struct block_device *bdev;
751	int key_len;
752
753	if (ctx->bdev)
754	return 0;
755
756	if (sscanf(input, "%u:%u%n", &major, &minor, &key_len) != 2)
757	return -EINVAL;
758
759	input += key_len;
760	if (!isspace(*input))
761	return -EINVAL;
762	input = skip_spaces(input);
763
764	bdev = blkdev_get_no_open(MKDEV(major, minor));
765	if (!bdev)
766	return -ENODEV;
767	if (bdev_is_partition(bdev)) {
768	blkdev_put_no_open(bdev);
769	return -ENODEV;
770	}
771
772	mutex_lock(&bdev->bd_queue->rq_qos_mutex);
773	if (!disk_live(disk: bdev->bd_disk)) {
774	blkdev_put_no_open(bdev);
775	mutex_unlock(lock: &bdev->bd_queue->rq_qos_mutex);
776	return -ENODEV;
777	}
778
779	ctx->body = input;
780	ctx->bdev = bdev;
781	return 0;
782	}
783
784	/**
785	* blkg_conf_prep - parse and prepare for per-blkg config update
786	* @blkcg: target block cgroup
787	* @pol: target policy
788	* @ctx: blkg_conf_ctx initialized with blkg_conf_init()
789	*
790	* Parse per-blkg config update from @ctx->input and initialize @ctx
791	* accordingly. On success, @ctx->body points to the part of @ctx->input
792	* following MAJ:MIN, @ctx->bdev points to the target block device and
793	* @ctx->blkg to the blkg being configured.
794	*
795	* blkg_conf_open_bdev() may be called on @ctx beforehand. On success, this
796	* function returns with queue lock held and must be followed by
797	* blkg_conf_exit().
798	*/
799	int blkg_conf_prep(struct blkcg *blkcg, const struct blkcg_policy *pol,
800	struct blkg_conf_ctx *ctx)
801	__acquires(&bdev->bd_queue->queue_lock)
802	{
803	struct gendisk *disk;
804	struct request_queue *q;
805	struct blkcg_gq *blkg;
806	int ret;
807
808	ret = blkg_conf_open_bdev(ctx);
809	if (ret)
810	return ret;
811
812	disk = ctx->bdev->bd_disk;
813	q = disk->queue;
814
815	/*
816	* blkcg_deactivate_policy() requires queue to be frozen, we can grab
817	* q_usage_counter to prevent concurrent with blkcg_deactivate_policy().
818	*/
819	ret = blk_queue_enter(q, flags: 0);
820	if (ret)
821	goto fail;
822
823	spin_lock_irq(lock: &q->queue_lock);
824
825	if (!blkcg_policy_enabled(q, pol)) {
826	ret = -EOPNOTSUPP;
827	goto fail_unlock;
828	}
829
830	blkg = blkg_lookup(blkcg, q);
831	if (blkg)
832	goto success;
833
834	/*
835	* Create blkgs walking down from blkcg_root to @blkcg, so that all
836	* non-root blkgs have access to their parents.
837	*/
838	while (true) {
839	struct blkcg *pos = blkcg;
840	struct blkcg *parent;
841	struct blkcg_gq *new_blkg;
842
843	parent = blkcg_parent(blkcg);
844	while (parent && !blkg_lookup(blkcg: parent, q)) {
845	pos = parent;
846	parent = blkcg_parent(blkcg: parent);
847	}
848
849	/* Drop locks to do new blkg allocation with GFP_KERNEL. */
850	spin_unlock_irq(lock: &q->queue_lock);
851
852	new_blkg = blkg_alloc(blkcg: pos, disk, GFP_KERNEL);
853	if (unlikely(!new_blkg)) {
854	ret = -ENOMEM;
855	goto fail_exit_queue;
856	}
857
858	if (radix_tree_preload(GFP_KERNEL)) {
859	blkg_free(blkg: new_blkg);
860	ret = -ENOMEM;
861	goto fail_exit_queue;
862	}
863
864	spin_lock_irq(lock: &q->queue_lock);
865
866	if (!blkcg_policy_enabled(q, pol)) {
867	blkg_free(blkg: new_blkg);
868	ret = -EOPNOTSUPP;
869	goto fail_preloaded;
870	}
871
872	blkg = blkg_lookup(blkcg: pos, q);
873	if (blkg) {
874	blkg_free(blkg: new_blkg);
875	} else {
876	blkg = blkg_create(blkcg: pos, disk, new_blkg);
877	if (IS_ERR(ptr: blkg)) {
878	ret = PTR_ERR(ptr: blkg);
879	goto fail_preloaded;
880	}
881	}
882
883	radix_tree_preload_end();
884
885	if (pos == blkcg)
886	goto success;
887	}
888	success:
889	blk_queue_exit(q);
890	ctx->blkg = blkg;
891	return 0;
892
893	fail_preloaded:
894	radix_tree_preload_end();
895	fail_unlock:
896	spin_unlock_irq(lock: &q->queue_lock);
897	fail_exit_queue:
898	blk_queue_exit(q);
899	fail:
900	/*
901	* If queue was bypassing, we should retry. Do so after a
902	* short msleep(). It isn't strictly necessary but queue
903	* can be bypassing for some time and it's always nice to
904	* avoid busy looping.
905	*/
906	if (ret == -EBUSY) {
907	msleep(msecs: 10);
908	ret = restart_syscall();
909	}
910	return ret;
911	}
912	EXPORT_SYMBOL_GPL(blkg_conf_prep);
913
914	/**
915	* blkg_conf_exit - clean up per-blkg config update
916	* @ctx: blkg_conf_ctx initialized with blkg_conf_init()
917	*
918	* Clean up after per-blkg config update. This function must be called on all
919	* blkg_conf_ctx's initialized with blkg_conf_init().
920	*/
921	void blkg_conf_exit(struct blkg_conf_ctx *ctx)
922	__releases(&ctx->bdev->bd_queue->queue_lock)
923	__releases(&ctx->bdev->bd_queue->rq_qos_mutex)
924	{
925	if (ctx->blkg) {
926	spin_unlock_irq(lock: &bdev_get_queue(bdev: ctx->bdev)->queue_lock);
927	ctx->blkg = NULL;
928	}
929
930	if (ctx->bdev) {
931	mutex_unlock(lock: &ctx->bdev->bd_queue->rq_qos_mutex);
932	blkdev_put_no_open(bdev: ctx->bdev);
933	ctx->body = NULL;
934	ctx->bdev = NULL;
935	}
936	}
937	EXPORT_SYMBOL_GPL(blkg_conf_exit);
938
939	static void blkg_iostat_set(struct blkg_iostat *dst, struct blkg_iostat *src)
940	{
941	int i;
942
943	for (i = 0; i < BLKG_IOSTAT_NR; i++) {
944	dst->bytes[i] = src->bytes[i];
945	dst->ios[i] = src->ios[i];
946	}
947	}
948
949	static void blkg_iostat_add(struct blkg_iostat *dst, struct blkg_iostat *src)
950	{
951	int i;
952
953	for (i = 0; i < BLKG_IOSTAT_NR; i++) {
954	dst->bytes[i] += src->bytes[i];
955	dst->ios[i] += src->ios[i];
956	}
957	}
958
959	static void blkg_iostat_sub(struct blkg_iostat *dst, struct blkg_iostat *src)
960	{
961	int i;
962
963	for (i = 0; i < BLKG_IOSTAT_NR; i++) {
964	dst->bytes[i] -= src->bytes[i];
965	dst->ios[i] -= src->ios[i];
966	}
967	}
968
969	static void blkcg_iostat_update(struct blkcg_gq *blkg, struct blkg_iostat *cur,
970	struct blkg_iostat *last)
971	{
972	struct blkg_iostat delta;
973	unsigned long flags;
974
975	/* propagate percpu delta to global */
976	flags = u64_stats_update_begin_irqsave(syncp: &blkg->iostat.sync);
977	blkg_iostat_set(dst: &delta, src: cur);
978	blkg_iostat_sub(dst: &delta, src: last);
979	blkg_iostat_add(dst: &blkg->iostat.cur, src: &delta);
980	blkg_iostat_add(dst: last, src: &delta);
981	u64_stats_update_end_irqrestore(syncp: &blkg->iostat.sync, flags);
982	}
983
984	static void __blkcg_rstat_flush(struct blkcg *blkcg, int cpu)
985	{
986	struct llist_head *lhead = per_cpu_ptr(blkcg->lhead, cpu);
987	struct llist_node *lnode;
988	struct blkg_iostat_set *bisc, *next_bisc;
989	unsigned long flags;
990
991	rcu_read_lock();
992
993	lnode = llist_del_all(head: lhead);
994	if (!lnode)
995	goto out;
996
997	/*
998	* For covering concurrent parent blkg update from blkg_release().
999	*
1000	* When flushing from cgroup, cgroup_rstat_lock is always held, so
1001	* this lock won't cause contention most of time.
1002	*/
1003	raw_spin_lock_irqsave(&blkg_stat_lock, flags);
1004
1005	/*
1006	* Iterate only the iostat_cpu's queued in the lockless list.
1007	*/
1008	llist_for_each_entry_safe(bisc, next_bisc, lnode, lnode) {
1009	struct blkcg_gq *blkg = bisc->blkg;
1010	struct blkcg_gq *parent = blkg->parent;
1011	struct blkg_iostat cur;
1012	unsigned int seq;
1013
1014	WRITE_ONCE(bisc->lqueued, false);
1015
1016	/* fetch the current per-cpu values */
1017	do {
1018	seq = u64_stats_fetch_begin(syncp: &bisc->sync);
1019	blkg_iostat_set(dst: &cur, src: &bisc->cur);
1020	} while (u64_stats_fetch_retry(syncp: &bisc->sync, start: seq));
1021
1022	blkcg_iostat_update(blkg, cur: &cur, last: &bisc->last);
1023
1024	/* propagate global delta to parent (unless that's root) */
1025	if (parent && parent->parent)
1026	blkcg_iostat_update(blkg: parent, cur: &blkg->iostat.cur,
1027	last: &blkg->iostat.last);
1028	}
1029	raw_spin_unlock_irqrestore(&blkg_stat_lock, flags);
1030	out:
1031	rcu_read_unlock();
1032	}
1033
1034	static void blkcg_rstat_flush(struct cgroup_subsys_state *css, int cpu)
1035	{
1036	/* Root-level stats are sourced from system-wide IO stats */
1037	if (cgroup_parent(cgrp: css->cgroup))
1038	__blkcg_rstat_flush(blkcg: css_to_blkcg(css), cpu);
1039	}
1040
1041	/*
1042	* We source root cgroup stats from the system-wide stats to avoid
1043	* tracking the same information twice and incurring overhead when no
1044	* cgroups are defined. For that reason, cgroup_rstat_flush in
1045	* blkcg_print_stat does not actually fill out the iostat in the root
1046	* cgroup's blkcg_gq.
1047	*
1048	* However, we would like to re-use the printing code between the root and
1049	* non-root cgroups to the extent possible. For that reason, we simulate
1050	* flushing the root cgroup's stats by explicitly filling in the iostat
1051	* with disk level statistics.
1052	*/
1053	static void blkcg_fill_root_iostats(void)
1054	{
1055	struct class_dev_iter iter;
1056	struct device *dev;
1057
1058	class_dev_iter_init(iter: &iter, class: &block_class, NULL, type: &disk_type);
1059	while ((dev = class_dev_iter_next(iter: &iter))) {
1060	struct block_device *bdev = dev_to_bdev(dev);
1061	struct blkcg_gq *blkg = bdev->bd_disk->queue->root_blkg;
1062	struct blkg_iostat tmp;
1063	int cpu;
1064	unsigned long flags;
1065
1066	memset(&tmp, 0, sizeof(tmp));
1067	for_each_possible_cpu(cpu) {
1068	struct disk_stats *cpu_dkstats;
1069
1070	cpu_dkstats = per_cpu_ptr(bdev->bd_stats, cpu);
1071	tmp.ios[BLKG_IOSTAT_READ] +=
1072	cpu_dkstats->ios[STAT_READ];
1073	tmp.ios[BLKG_IOSTAT_WRITE] +=
1074	cpu_dkstats->ios[STAT_WRITE];
1075	tmp.ios[BLKG_IOSTAT_DISCARD] +=
1076	cpu_dkstats->ios[STAT_DISCARD];
1077	// convert sectors to bytes
1078	tmp.bytes[BLKG_IOSTAT_READ] +=
1079	cpu_dkstats->sectors[STAT_READ] << 9;
1080	tmp.bytes[BLKG_IOSTAT_WRITE] +=
1081	cpu_dkstats->sectors[STAT_WRITE] << 9;
1082	tmp.bytes[BLKG_IOSTAT_DISCARD] +=
1083	cpu_dkstats->sectors[STAT_DISCARD] << 9;
1084	}
1085
1086	flags = u64_stats_update_begin_irqsave(syncp: &blkg->iostat.sync);
1087	blkg_iostat_set(dst: &blkg->iostat.cur, src: &tmp);
1088	u64_stats_update_end_irqrestore(syncp: &blkg->iostat.sync, flags);
1089	}
1090	}
1091
1092	static void blkcg_print_one_stat(struct blkcg_gq *blkg, struct seq_file *s)
1093	{
1094	struct blkg_iostat_set *bis = &blkg->iostat;
1095	u64 rbytes, wbytes, rios, wios, dbytes, dios;
1096	const char *dname;
1097	unsigned seq;
1098	int i;
1099
1100	if (!blkg->online)
1101	return;
1102
1103	dname = blkg_dev_name(blkg);
1104	if (!dname)
1105	return;
1106
1107	seq_printf(m: s, fmt: "%s ", dname);
1108
1109	do {
1110	seq = u64_stats_fetch_begin(syncp: &bis->sync);
1111
1112	rbytes = bis->cur.bytes[BLKG_IOSTAT_READ];
1113	wbytes = bis->cur.bytes[BLKG_IOSTAT_WRITE];
1114	dbytes = bis->cur.bytes[BLKG_IOSTAT_DISCARD];
1115	rios = bis->cur.ios[BLKG_IOSTAT_READ];
1116	wios = bis->cur.ios[BLKG_IOSTAT_WRITE];
1117	dios = bis->cur.ios[BLKG_IOSTAT_DISCARD];
1118	} while (u64_stats_fetch_retry(syncp: &bis->sync, start: seq));
1119
1120	if (rbytes || wbytes || rios || wios) {
1121	seq_printf(m: s, fmt: "rbytes=%llu wbytes=%llu rios=%llu wios=%llu dbytes=%llu dios=%llu",
1122	rbytes, wbytes, rios, wios,
1123	dbytes, dios);
1124	}
1125
1126	if (blkcg_debug_stats && atomic_read(v: &blkg->use_delay)) {
1127	seq_printf(m: s, fmt: " use_delay=%d delay_nsec=%llu",
1128	atomic_read(v: &blkg->use_delay),
1129	atomic64_read(v: &blkg->delay_nsec));
1130	}
1131
1132	for (i = 0; i < BLKCG_MAX_POLS; i++) {
1133	struct blkcg_policy *pol = blkcg_policy[i];
1134
1135	if (!blkg->pd[i] || !pol->pd_stat_fn)
1136	continue;
1137
1138	pol->pd_stat_fn(blkg->pd[i], s);
1139	}
1140
1141	seq_puts(m: s, s: "\n");
1142	}
1143
1144	static int blkcg_print_stat(struct seq_file *sf, void *v)
1145	{
1146	struct blkcg *blkcg = css_to_blkcg(css: seq_css(seq: sf));
1147	struct blkcg_gq *blkg;
1148
1149	if (!seq_css(seq: sf)->parent)
1150	blkcg_fill_root_iostats();
1151	else
1152	cgroup_rstat_flush(cgrp: blkcg->css.cgroup);
1153
1154	rcu_read_lock();
1155	hlist_for_each_entry_rcu(blkg, &blkcg->blkg_list, blkcg_node) {
1156	spin_lock_irq(lock: &blkg->q->queue_lock);
1157	blkcg_print_one_stat(blkg, s: sf);
1158	spin_unlock_irq(lock: &blkg->q->queue_lock);
1159	}
1160	rcu_read_unlock();
1161	return 0;
1162	}
1163
1164	static struct cftype blkcg_files[] = {
1165	{
1166	.name = "stat",
1167	.seq_show = blkcg_print_stat,
1168	},
1169	{ } /* terminate */
1170	};
1171
1172	static struct cftype blkcg_legacy_files[] = {
1173	{
1174	.name = "reset_stats",
1175	.write_u64 = blkcg_reset_stats,
1176	},
1177	{ } /* terminate */
1178	};
1179
1180	#ifdef CONFIG_CGROUP_WRITEBACK
1181	struct list_head *blkcg_get_cgwb_list(struct cgroup_subsys_state *css)
1182	{
1183	return &css_to_blkcg(css)->cgwb_list;
1184	}
1185	#endif
1186
1187	/*
1188	* blkcg destruction is a three-stage process.
1189	*
1190	* 1. Destruction starts. The blkcg_css_offline() callback is invoked
1191	* which offlines writeback. Here we tie the next stage of blkg destruction
1192	* to the completion of writeback associated with the blkcg. This lets us
1193	* avoid punting potentially large amounts of outstanding writeback to root
1194	* while maintaining any ongoing policies. The next stage is triggered when
1195	* the nr_cgwbs count goes to zero.
1196	*
1197	* 2. When the nr_cgwbs count goes to zero, blkcg_destroy_blkgs() is called
1198	* and handles the destruction of blkgs. Here the css reference held by
1199	* the blkg is put back eventually allowing blkcg_css_free() to be called.
1200	* This work may occur in cgwb_release_workfn() on the cgwb_release
1201	* workqueue. Any submitted ios that fail to get the blkg ref will be
1202	* punted to the root_blkg.
1203	*
1204	* 3. Once the blkcg ref count goes to zero, blkcg_css_free() is called.
1205	* This finally frees the blkcg.
1206	*/
1207
1208	/**
1209	* blkcg_destroy_blkgs - responsible for shooting down blkgs
1210	* @blkcg: blkcg of interest
1211	*
1212	* blkgs should be removed while holding both q and blkcg locks. As blkcg lock
1213	* is nested inside q lock, this function performs reverse double lock dancing.
1214	* Destroying the blkgs releases the reference held on the blkcg's css allowing
1215	* blkcg_css_free to eventually be called.
1216	*
1217	* This is the blkcg counterpart of ioc_release_fn().
1218	*/
1219	static void blkcg_destroy_blkgs(struct blkcg *blkcg)
1220	{
1221	might_sleep();
1222
1223	spin_lock_irq(lock: &blkcg->lock);
1224
1225	while (!hlist_empty(h: &blkcg->blkg_list)) {
1226	struct blkcg_gq *blkg = hlist_entry(blkcg->blkg_list.first,
1227	struct blkcg_gq, blkcg_node);
1228	struct request_queue *q = blkg->q;
1229
1230	if (need_resched() || !spin_trylock(lock: &q->queue_lock)) {
1231	/*
1232	* Given that the system can accumulate a huge number
1233	* of blkgs in pathological cases, check to see if we
1234	* need to rescheduling to avoid softlockup.
1235	*/
1236	spin_unlock_irq(lock: &blkcg->lock);
1237	cond_resched();
1238	spin_lock_irq(lock: &blkcg->lock);
1239	continue;
1240	}
1241
1242	blkg_destroy(blkg);
1243	spin_unlock(lock: &q->queue_lock);
1244	}
1245
1246	spin_unlock_irq(lock: &blkcg->lock);
1247	}
1248
1249	/**
1250	* blkcg_pin_online - pin online state
1251	* @blkcg_css: blkcg of interest
1252	*
1253	* While pinned, a blkcg is kept online. This is primarily used to
1254	* impedance-match blkg and cgwb lifetimes so that blkg doesn't go offline
1255	* while an associated cgwb is still active.
1256	*/
1257	void blkcg_pin_online(struct cgroup_subsys_state *blkcg_css)
1258	{
1259	refcount_inc(r: &css_to_blkcg(css: blkcg_css)->online_pin);
1260	}
1261
1262	/**
1263	* blkcg_unpin_online - unpin online state
1264	* @blkcg_css: blkcg of interest
1265	*
1266	* This is primarily used to impedance-match blkg and cgwb lifetimes so
1267	* that blkg doesn't go offline while an associated cgwb is still active.
1268	* When this count goes to zero, all active cgwbs have finished so the
1269	* blkcg can continue destruction by calling blkcg_destroy_blkgs().
1270	*/
1271	void blkcg_unpin_online(struct cgroup_subsys_state *blkcg_css)
1272	{
1273	struct blkcg *blkcg = css_to_blkcg(css: blkcg_css);
1274
1275	do {
1276	if (!refcount_dec_and_test(r: &blkcg->online_pin))
1277	break;
1278	blkcg_destroy_blkgs(blkcg);
1279	blkcg = blkcg_parent(blkcg);
1280	} while (blkcg);
1281	}
1282
1283	/**
1284	* blkcg_css_offline - cgroup css_offline callback
1285	* @css: css of interest
1286	*
1287	* This function is called when @css is about to go away. Here the cgwbs are
1288	* offlined first and only once writeback associated with the blkcg has
1289	* finished do we start step 2 (see above).
1290	*/
1291	static void blkcg_css_offline(struct cgroup_subsys_state *css)
1292	{
1293	/* this prevents anyone from attaching or migrating to this blkcg */
1294	wb_blkcg_offline(css);
1295
1296	/* put the base online pin allowing step 2 to be triggered */
1297	blkcg_unpin_online(blkcg_css: css);
1298	}
1299
1300	static void blkcg_css_free(struct cgroup_subsys_state *css)
1301	{
1302	struct blkcg *blkcg = css_to_blkcg(css);
1303	int i;
1304
1305	mutex_lock(&blkcg_pol_mutex);
1306
1307	list_del(entry: &blkcg->all_blkcgs_node);
1308
1309	for (i = 0; i < BLKCG_MAX_POLS; i++)
1310	if (blkcg->cpd[i])
1311	blkcg_policy[i]->cpd_free_fn(blkcg->cpd[i]);
1312
1313	mutex_unlock(lock: &blkcg_pol_mutex);
1314
1315	free_percpu(pdata: blkcg->lhead);
1316	kfree(objp: blkcg);
1317	}
1318
1319	static struct cgroup_subsys_state *
1320	blkcg_css_alloc(struct cgroup_subsys_state *parent_css)
1321	{
1322	struct blkcg *blkcg;
1323	int i;
1324
1325	mutex_lock(&blkcg_pol_mutex);
1326
1327	if (!parent_css) {
1328	blkcg = &blkcg_root;
1329	} else {
1330	blkcg = kzalloc(size: sizeof(*blkcg), GFP_KERNEL);
1331	if (!blkcg)
1332	goto unlock;
1333	}
1334
1335	if (init_blkcg_llists(blkcg))
1336	goto free_blkcg;
1337
1338	for (i = 0; i < BLKCG_MAX_POLS ; i++) {
1339	struct blkcg_policy *pol = blkcg_policy[i];
1340	struct blkcg_policy_data *cpd;
1341
1342	/*
1343	* If the policy hasn't been attached yet, wait for it
1344	* to be attached before doing anything else. Otherwise,
1345	* check if the policy requires any specific per-cgroup
1346	* data: if it does, allocate and initialize it.
1347	*/
1348	if (!pol || !pol->cpd_alloc_fn)
1349	continue;
1350
1351	cpd = pol->cpd_alloc_fn(GFP_KERNEL);
1352	if (!cpd)
1353	goto free_pd_blkcg;
1354
1355	blkcg->cpd[i] = cpd;
1356	cpd->blkcg = blkcg;
1357	cpd->plid = i;
1358	}
1359
1360	spin_lock_init(&blkcg->lock);
1361	refcount_set(r: &blkcg->online_pin, n: 1);
1362	INIT_RADIX_TREE(&blkcg->blkg_tree, GFP_NOWAIT | __GFP_NOWARN);
1363	INIT_HLIST_HEAD(&blkcg->blkg_list);
1364	#ifdef CONFIG_CGROUP_WRITEBACK
1365	INIT_LIST_HEAD(list: &blkcg->cgwb_list);
1366	#endif
1367	list_add_tail(new: &blkcg->all_blkcgs_node, head: &all_blkcgs);
1368
1369	mutex_unlock(lock: &blkcg_pol_mutex);
1370	return &blkcg->css;
1371
1372	free_pd_blkcg:
1373	for (i--; i >= 0; i--)
1374	if (blkcg->cpd[i])
1375	blkcg_policy[i]->cpd_free_fn(blkcg->cpd[i]);
1376	free_percpu(pdata: blkcg->lhead);
1377	free_blkcg:
1378	if (blkcg != &blkcg_root)
1379	kfree(objp: blkcg);
1380	unlock:
1381	mutex_unlock(lock: &blkcg_pol_mutex);
1382	return ERR_PTR(error: -ENOMEM);
1383	}
1384
1385	static int blkcg_css_online(struct cgroup_subsys_state *css)
1386	{
1387	struct blkcg *parent = blkcg_parent(blkcg: css_to_blkcg(css));
1388
1389	/*
1390	* blkcg_pin_online() is used to delay blkcg offline so that blkgs
1391	* don't go offline while cgwbs are still active on them. Pin the
1392	* parent so that offline always happens towards the root.
1393	*/
1394	if (parent)
1395	blkcg_pin_online(blkcg_css: &parent->css);
1396	return 0;
1397	}
1398
1399	int blkcg_init_disk(struct gendisk *disk)
1400	{
1401	struct request_queue *q = disk->queue;
1402	struct blkcg_gq *new_blkg, *blkg;
1403	bool preloaded;
1404	int ret;
1405
1406	INIT_LIST_HEAD(list: &q->blkg_list);
1407	mutex_init(&q->blkcg_mutex);
1408
1409	new_blkg = blkg_alloc(blkcg: &blkcg_root, disk, GFP_KERNEL);
1410	if (!new_blkg)
1411	return -ENOMEM;
1412
1413	preloaded = !radix_tree_preload(GFP_KERNEL);
1414
1415	/* Make sure the root blkg exists. */
1416	/* spin_lock_irq can serve as RCU read-side critical section. */
1417	spin_lock_irq(lock: &q->queue_lock);
1418	blkg = blkg_create(blkcg: &blkcg_root, disk, new_blkg);
1419	if (IS_ERR(ptr: blkg))
1420	goto err_unlock;
1421	q->root_blkg = blkg;
1422	spin_unlock_irq(lock: &q->queue_lock);
1423
1424	if (preloaded)
1425	radix_tree_preload_end();
1426
1427	ret = blk_ioprio_init(disk);
1428	if (ret)
1429	goto err_destroy_all;
1430
1431	ret = blk_throtl_init(disk);
1432	if (ret)
1433	goto err_ioprio_exit;
1434
1435	return 0;
1436
1437	err_ioprio_exit:
1438	blk_ioprio_exit(disk);
1439	err_destroy_all:
1440	blkg_destroy_all(disk);
1441	return ret;
1442	err_unlock:
1443	spin_unlock_irq(lock: &q->queue_lock);
1444	if (preloaded)
1445	radix_tree_preload_end();
1446	return PTR_ERR(ptr: blkg);
1447	}
1448
1449	void blkcg_exit_disk(struct gendisk *disk)
1450	{
1451	blkg_destroy_all(disk);
1452	blk_throtl_exit(disk);
1453	}
1454
1455	static void blkcg_exit(struct task_struct *tsk)
1456	{
1457	if (tsk->throttle_disk)
1458	put_disk(disk: tsk->throttle_disk);
1459	tsk->throttle_disk = NULL;
1460	}
1461
1462	struct cgroup_subsys io_cgrp_subsys = {
1463	.css_alloc = blkcg_css_alloc,
1464	.css_online = blkcg_css_online,
1465	.css_offline = blkcg_css_offline,
1466	.css_free = blkcg_css_free,
1467	.css_rstat_flush = blkcg_rstat_flush,
1468	.dfl_cftypes = blkcg_files,
1469	.legacy_cftypes = blkcg_legacy_files,
1470	.legacy_name = "blkio",
1471	.exit = blkcg_exit,
1472	#ifdef CONFIG_MEMCG
1473	/*
1474	* This ensures that, if available, memcg is automatically enabled
1475	* together on the default hierarchy so that the owner cgroup can
1476	* be retrieved from writeback pages.
1477	*/
1478	.depends_on = 1 << memory_cgrp_id,
1479	#endif
1480	};
1481	EXPORT_SYMBOL_GPL(io_cgrp_subsys);
1482
1483	/**
1484	* blkcg_activate_policy - activate a blkcg policy on a gendisk
1485	* @disk: gendisk of interest
1486	* @pol: blkcg policy to activate
1487	*
1488	* Activate @pol on @disk. Requires %GFP_KERNEL context. @disk goes through
1489	* bypass mode to populate its blkgs with policy_data for @pol.
1490	*
1491	* Activation happens with @disk bypassed, so nobody would be accessing blkgs
1492	* from IO path. Update of each blkg is protected by both queue and blkcg
1493	* locks so that holding either lock and testing blkcg_policy_enabled() is
1494	* always enough for dereferencing policy data.
1495	*
1496	* The caller is responsible for synchronizing [de]activations and policy
1497	* [un]registerations. Returns 0 on success, -errno on failure.
1498	*/
1499	int blkcg_activate_policy(struct gendisk *disk, const struct blkcg_policy *pol)
1500	{
1501	struct request_queue *q = disk->queue;
1502	struct blkg_policy_data *pd_prealloc = NULL;
1503	struct blkcg_gq *blkg, *pinned_blkg = NULL;
1504	int ret;
1505
1506	if (blkcg_policy_enabled(q, pol))
1507	return 0;
1508
1509	if (queue_is_mq(q))
1510	blk_mq_freeze_queue(q);
1511	retry:
1512	spin_lock_irq(lock: &q->queue_lock);
1513
1514	/* blkg_list is pushed at the head, reverse walk to initialize parents first */
1515	list_for_each_entry_reverse(blkg, &q->blkg_list, q_node) {
1516	struct blkg_policy_data *pd;
1517
1518	if (blkg->pd[pol->plid])
1519	continue;
1520
1521	/* If prealloc matches, use it; otherwise try GFP_NOWAIT */
1522	if (blkg == pinned_blkg) {
1523	pd = pd_prealloc;
1524	pd_prealloc = NULL;
1525	} else {
1526	pd = pol->pd_alloc_fn(disk, blkg->blkcg,
1527	GFP_NOWAIT | __GFP_NOWARN);
1528	}
1529
1530	if (!pd) {
1531	/*
1532	* GFP_NOWAIT failed. Free the existing one and
1533	* prealloc for @blkg w/ GFP_KERNEL.
1534	*/
1535	if (pinned_blkg)
1536	blkg_put(blkg: pinned_blkg);
1537	blkg_get(blkg);
1538	pinned_blkg = blkg;
1539
1540	spin_unlock_irq(lock: &q->queue_lock);
1541
1542	if (pd_prealloc)
1543	pol->pd_free_fn(pd_prealloc);
1544	pd_prealloc = pol->pd_alloc_fn(disk, blkg->blkcg,
1545	GFP_KERNEL);
1546	if (pd_prealloc)
1547	goto retry;
1548	else
1549	goto enomem;
1550	}
1551
1552	spin_lock(lock: &blkg->blkcg->lock);
1553
1554	pd->blkg = blkg;
1555	pd->plid = pol->plid;
1556	blkg->pd[pol->plid] = pd;
1557
1558	if (pol->pd_init_fn)
1559	pol->pd_init_fn(pd);
1560
1561	if (pol->pd_online_fn)
1562	pol->pd_online_fn(pd);
1563	pd->online = true;
1564
1565	spin_unlock(lock: &blkg->blkcg->lock);
1566	}
1567
1568	__set_bit(pol->plid, q->blkcg_pols);
1569	ret = 0;
1570
1571	spin_unlock_irq(lock: &q->queue_lock);
1572	out:
1573	if (queue_is_mq(q))
1574	blk_mq_unfreeze_queue(q);
1575	if (pinned_blkg)
1576	blkg_put(blkg: pinned_blkg);
1577	if (pd_prealloc)
1578	pol->pd_free_fn(pd_prealloc);
1579	return ret;
1580
1581	enomem:
1582	/* alloc failed, take down everything */
1583	spin_lock_irq(lock: &q->queue_lock);
1584	list_for_each_entry(blkg, &q->blkg_list, q_node) {
1585	struct blkcg *blkcg = blkg->blkcg;
1586	struct blkg_policy_data *pd;
1587
1588	spin_lock(lock: &blkcg->lock);
1589	pd = blkg->pd[pol->plid];
1590	if (pd) {
1591	if (pd->online && pol->pd_offline_fn)
1592	pol->pd_offline_fn(pd);
1593	pd->online = false;
1594	pol->pd_free_fn(pd);
1595	blkg->pd[pol->plid] = NULL;
1596	}
1597	spin_unlock(lock: &blkcg->lock);
1598	}
1599	spin_unlock_irq(lock: &q->queue_lock);
1600	ret = -ENOMEM;
1601	goto out;
1602	}
1603	EXPORT_SYMBOL_GPL(blkcg_activate_policy);
1604
1605	/**
1606	* blkcg_deactivate_policy - deactivate a blkcg policy on a gendisk
1607	* @disk: gendisk of interest
1608	* @pol: blkcg policy to deactivate
1609	*
1610	* Deactivate @pol on @disk. Follows the same synchronization rules as
1611	* blkcg_activate_policy().
1612	*/
1613	void blkcg_deactivate_policy(struct gendisk *disk,
1614	const struct blkcg_policy *pol)
1615	{
1616	struct request_queue *q = disk->queue;
1617	struct blkcg_gq *blkg;
1618
1619	if (!blkcg_policy_enabled(q, pol))
1620	return;
1621
1622	if (queue_is_mq(q))
1623	blk_mq_freeze_queue(q);
1624
1625	mutex_lock(&q->blkcg_mutex);
1626	spin_lock_irq(lock: &q->queue_lock);
1627
1628	__clear_bit(pol->plid, q->blkcg_pols);
1629
1630	list_for_each_entry(blkg, &q->blkg_list, q_node) {
1631	struct blkcg *blkcg = blkg->blkcg;
1632
1633	spin_lock(lock: &blkcg->lock);
1634	if (blkg->pd[pol->plid]) {
1635	if (blkg->pd[pol->plid]->online && pol->pd_offline_fn)
1636	pol->pd_offline_fn(blkg->pd[pol->plid]);
1637	pol->pd_free_fn(blkg->pd[pol->plid]);
1638	blkg->pd[pol->plid] = NULL;
1639	}
1640	spin_unlock(lock: &blkcg->lock);
1641	}
1642
1643	spin_unlock_irq(lock: &q->queue_lock);
1644	mutex_unlock(lock: &q->blkcg_mutex);
1645
1646	if (queue_is_mq(q))
1647	blk_mq_unfreeze_queue(q);
1648	}
1649	EXPORT_SYMBOL_GPL(blkcg_deactivate_policy);
1650
1651	static void blkcg_free_all_cpd(struct blkcg_policy *pol)
1652	{
1653	struct blkcg *blkcg;
1654
1655	list_for_each_entry(blkcg, &all_blkcgs, all_blkcgs_node) {
1656	if (blkcg->cpd[pol->plid]) {
1657	pol->cpd_free_fn(blkcg->cpd[pol->plid]);
1658	blkcg->cpd[pol->plid] = NULL;
1659	}
1660	}
1661	}
1662
1663	/**
1664	* blkcg_policy_register - register a blkcg policy
1665	* @pol: blkcg policy to register
1666	*
1667	* Register @pol with blkcg core. Might sleep and @pol may be modified on
1668	* successful registration. Returns 0 on success and -errno on failure.
1669	*/
1670	int blkcg_policy_register(struct blkcg_policy *pol)
1671	{
1672	struct blkcg *blkcg;
1673	int i, ret;
1674
1675	mutex_lock(&blkcg_pol_register_mutex);
1676	mutex_lock(&blkcg_pol_mutex);
1677
1678	/* find an empty slot */
1679	ret = -ENOSPC;
1680	for (i = 0; i < BLKCG_MAX_POLS; i++)
1681	if (!blkcg_policy[i])
1682	break;
1683	if (i >= BLKCG_MAX_POLS) {
1684	pr_warn("blkcg_policy_register: BLKCG_MAX_POLS too small\n");
1685	goto err_unlock;
1686	}
1687
1688	/* Make sure cpd/pd_alloc_fn and cpd/pd_free_fn in pairs */
1689	if ((!pol->cpd_alloc_fn ^ !pol->cpd_free_fn) ||
1690	(!pol->pd_alloc_fn ^ !pol->pd_free_fn))
1691	goto err_unlock;
1692
1693	/* register @pol */
1694	pol->plid = i;
1695	blkcg_policy[pol->plid] = pol;
1696
1697	/* allocate and install cpd's */
1698	if (pol->cpd_alloc_fn) {
1699	list_for_each_entry(blkcg, &all_blkcgs, all_blkcgs_node) {
1700	struct blkcg_policy_data *cpd;
1701
1702	cpd = pol->cpd_alloc_fn(GFP_KERNEL);
1703	if (!cpd)
1704	goto err_free_cpds;
1705
1706	blkcg->cpd[pol->plid] = cpd;
1707	cpd->blkcg = blkcg;
1708	cpd->plid = pol->plid;
1709	}
1710	}
1711
1712	mutex_unlock(lock: &blkcg_pol_mutex);
1713
1714	/* everything is in place, add intf files for the new policy */
1715	if (pol->dfl_cftypes)
1716	WARN_ON(cgroup_add_dfl_cftypes(&io_cgrp_subsys,
1717	pol->dfl_cftypes));
1718	if (pol->legacy_cftypes)
1719	WARN_ON(cgroup_add_legacy_cftypes(&io_cgrp_subsys,
1720	pol->legacy_cftypes));
1721	mutex_unlock(lock: &blkcg_pol_register_mutex);
1722	return 0;
1723
1724	err_free_cpds:
1725	if (pol->cpd_free_fn)
1726	blkcg_free_all_cpd(pol);
1727
1728	blkcg_policy[pol->plid] = NULL;
1729	err_unlock:
1730	mutex_unlock(lock: &blkcg_pol_mutex);
1731	mutex_unlock(lock: &blkcg_pol_register_mutex);
1732	return ret;
1733	}
1734	EXPORT_SYMBOL_GPL(blkcg_policy_register);
1735
1736	/**
1737	* blkcg_policy_unregister - unregister a blkcg policy
1738	* @pol: blkcg policy to unregister
1739	*
1740	* Undo blkcg_policy_register(@pol). Might sleep.
1741	*/
1742	void blkcg_policy_unregister(struct blkcg_policy *pol)
1743	{
1744	mutex_lock(&blkcg_pol_register_mutex);
1745
1746	if (WARN_ON(blkcg_policy[pol->plid] != pol))
1747	goto out_unlock;
1748
1749	/* kill the intf files first */
1750	if (pol->dfl_cftypes)
1751	cgroup_rm_cftypes(cfts: pol->dfl_cftypes);
1752	if (pol->legacy_cftypes)
1753	cgroup_rm_cftypes(cfts: pol->legacy_cftypes);
1754
1755	/* remove cpds and unregister */
1756	mutex_lock(&blkcg_pol_mutex);
1757
1758	if (pol->cpd_free_fn)
1759	blkcg_free_all_cpd(pol);
1760
1761	blkcg_policy[pol->plid] = NULL;
1762
1763	mutex_unlock(lock: &blkcg_pol_mutex);
1764	out_unlock:
1765	mutex_unlock(lock: &blkcg_pol_register_mutex);
1766	}
1767	EXPORT_SYMBOL_GPL(blkcg_policy_unregister);
1768
1769	/*
1770	* Scale the accumulated delay based on how long it has been since we updated
1771	* the delay. We only call this when we are adding delay, in case it's been a
1772	* while since we added delay, and when we are checking to see if we need to
1773	* delay a task, to account for any delays that may have occurred.
1774	*/
1775	static void blkcg_scale_delay(struct blkcg_gq *blkg, u64 now)
1776	{
1777	u64 old = atomic64_read(v: &blkg->delay_start);
1778
1779	/* negative use_delay means no scaling, see blkcg_set_delay() */
1780	if (atomic_read(v: &blkg->use_delay) < 0)
1781	return;
1782
1783	/*
1784	* We only want to scale down every second. The idea here is that we
1785	* want to delay people for min(delay_nsec, NSEC_PER_SEC) in a certain
1786	* time window. We only want to throttle tasks for recent delay that
1787	* has occurred, in 1 second time windows since that's the maximum
1788	* things can be throttled. We save the current delay window in
1789	* blkg->last_delay so we know what amount is still left to be charged
1790	* to the blkg from this point onward. blkg->last_use keeps track of
1791	* the use_delay counter. The idea is if we're unthrottling the blkg we
1792	* are ok with whatever is happening now, and we can take away more of
1793	* the accumulated delay as we've already throttled enough that
1794	* everybody is happy with their IO latencies.
1795	*/
1796	if (time_before64(old + NSEC_PER_SEC, now) &&
1797	atomic64_try_cmpxchg(v: &blkg->delay_start, old: &old, new: now)) {
1798	u64 cur = atomic64_read(v: &blkg->delay_nsec);
1799	u64 sub = min_t(u64, blkg->last_delay, now - old);
1800	int cur_use = atomic_read(v: &blkg->use_delay);
1801
1802	/*
1803	* We've been unthrottled, subtract a larger chunk of our
1804	* accumulated delay.
1805	*/
1806	if (cur_use < blkg->last_use)
1807	sub = max_t(u64, sub, blkg->last_delay >> 1);
1808
1809	/*
1810	* This shouldn't happen, but handle it anyway. Our delay_nsec
1811	* should only ever be growing except here where we subtract out
1812	* min(last_delay, 1 second), but lord knows bugs happen and I'd
1813	* rather not end up with negative numbers.
1814	*/
1815	if (unlikely(cur < sub)) {
1816	atomic64_set(v: &blkg->delay_nsec, i: 0);
1817	blkg->last_delay = 0;
1818	} else {
1819	atomic64_sub(i: sub, v: &blkg->delay_nsec);
1820	blkg->last_delay = cur - sub;
1821	}
1822	blkg->last_use = cur_use;
1823	}
1824	}
1825
1826	/*
1827	* This is called when we want to actually walk up the hierarchy and check to
1828	* see if we need to throttle, and then actually throttle if there is some
1829	* accumulated delay. This should only be called upon return to user space so
1830	* we're not holding some lock that would induce a priority inversion.
1831	*/
1832	static void blkcg_maybe_throttle_blkg(struct blkcg_gq *blkg, bool use_memdelay)
1833	{
1834	unsigned long pflags;
1835	bool clamp;
1836	u64 now = ktime_to_ns(kt: ktime_get());
1837	u64 exp;
1838	u64 delay_nsec = 0;
1839	int tok;
1840
1841	while (blkg->parent) {
1842	int use_delay = atomic_read(v: &blkg->use_delay);
1843
1844	if (use_delay) {
1845	u64 this_delay;
1846
1847	blkcg_scale_delay(blkg, now);
1848	this_delay = atomic64_read(v: &blkg->delay_nsec);
1849	if (this_delay > delay_nsec) {
1850	delay_nsec = this_delay;
1851	clamp = use_delay > 0;
1852	}
1853	}
1854	blkg = blkg->parent;
1855	}
1856
1857	if (!delay_nsec)
1858	return;
1859
1860	/*
1861	* Let's not sleep for all eternity if we've amassed a huge delay.
1862	* Swapping or metadata IO can accumulate 10's of seconds worth of
1863	* delay, and we want userspace to be able to do _something_ so cap the
1864	* delays at 0.25s. If there's 10's of seconds worth of delay then the
1865	* tasks will be delayed for 0.25 second for every syscall. If
1866	* blkcg_set_delay() was used as indicated by negative use_delay, the
1867	* caller is responsible for regulating the range.
1868	*/
1869	if (clamp)
1870	delay_nsec = min_t(u64, delay_nsec, 250 * NSEC_PER_MSEC);
1871
1872	if (use_memdelay)
1873	psi_memstall_enter(flags: &pflags);
1874
1875	exp = ktime_add_ns(now, delay_nsec);
1876	tok = io_schedule_prepare();
1877	do {
1878	__set_current_state(TASK_KILLABLE);
1879	if (!schedule_hrtimeout(expires: &exp, mode: HRTIMER_MODE_ABS))
1880	break;
1881	} while (!fatal_signal_pending(current));
1882	io_schedule_finish(token: tok);
1883
1884	if (use_memdelay)
1885	psi_memstall_leave(flags: &pflags);
1886	}
1887
1888	/**
1889	* blkcg_maybe_throttle_current - throttle the current task if it has been marked
1890	*
1891	* This is only called if we've been marked with set_notify_resume(). Obviously
1892	* we can be set_notify_resume() for reasons other than blkcg throttling, so we
1893	* check to see if current->throttle_disk is set and if not this doesn't do
1894	* anything. This should only ever be called by the resume code, it's not meant
1895	* to be called by people willy-nilly as it will actually do the work to
1896	* throttle the task if it is setup for throttling.
1897	*/
1898	void blkcg_maybe_throttle_current(void)
1899	{
1900	struct gendisk *disk = current->throttle_disk;
1901	struct blkcg *blkcg;
1902	struct blkcg_gq *blkg;
1903	bool use_memdelay = current->use_memdelay;
1904
1905	if (!disk)
1906	return;
1907
1908	current->throttle_disk = NULL;
1909	current->use_memdelay = false;
1910
1911	rcu_read_lock();
1912	blkcg = css_to_blkcg(css: blkcg_css());
1913	if (!blkcg)
1914	goto out;
1915	blkg = blkg_lookup(blkcg, q: disk->queue);
1916	if (!blkg)
1917	goto out;
1918	if (!blkg_tryget(blkg))
1919	goto out;
1920	rcu_read_unlock();
1921
1922	blkcg_maybe_throttle_blkg(blkg, use_memdelay);
1923	blkg_put(blkg);
1924	put_disk(disk);
1925	return;
1926	out:
1927	rcu_read_unlock();
1928	}
1929
1930	/**
1931	* blkcg_schedule_throttle - this task needs to check for throttling
1932	* @disk: disk to throttle
1933	* @use_memdelay: do we charge this to memory delay for PSI
1934	*
1935	* This is called by the IO controller when we know there's delay accumulated
1936	* for the blkg for this task. We do not pass the blkg because there are places
1937	* we call this that may not have that information, the swapping code for
1938	* instance will only have a block_device at that point. This set's the
1939	* notify_resume for the task to check and see if it requires throttling before
1940	* returning to user space.
1941	*
1942	* We will only schedule once per syscall. You can call this over and over
1943	* again and it will only do the check once upon return to user space, and only
1944	* throttle once. If the task needs to be throttled again it'll need to be
1945	* re-set at the next time we see the task.
1946	*/
1947	void blkcg_schedule_throttle(struct gendisk *disk, bool use_memdelay)
1948	{
1949	if (unlikely(current->flags & PF_KTHREAD))
1950	return;
1951
1952	if (current->throttle_disk != disk) {
1953	if (test_bit(GD_DEAD, &disk->state))
1954	return;
1955	get_device(disk_to_dev(disk));
1956
1957	if (current->throttle_disk)
1958	put_disk(current->throttle_disk);
1959	current->throttle_disk = disk;
1960	}
1961
1962	if (use_memdelay)
1963	current->use_memdelay = use_memdelay;
1964	set_notify_resume(current);
1965	}
1966
1967	/**
1968	* blkcg_add_delay - add delay to this blkg
1969	* @blkg: blkg of interest
1970	* @now: the current time in nanoseconds
1971	* @delta: how many nanoseconds of delay to add
1972	*
1973	* Charge @delta to the blkg's current delay accumulation. This is used to
1974	* throttle tasks if an IO controller thinks we need more throttling.
1975	*/
1976	void blkcg_add_delay(struct blkcg_gq *blkg, u64 now, u64 delta)
1977	{
1978	if (WARN_ON_ONCE(atomic_read(&blkg->use_delay) < 0))
1979	return;
1980	blkcg_scale_delay(blkg, now);
1981	atomic64_add(i: delta, v: &blkg->delay_nsec);
1982	}
1983
1984	/**
1985	* blkg_tryget_closest - try and get a blkg ref on the closet blkg
1986	* @bio: target bio
1987	* @css: target css
1988	*
1989	* As the failure mode here is to walk up the blkg tree, this ensure that the
1990	* blkg->parent pointers are always valid. This returns the blkg that it ended
1991	* up taking a reference on or %NULL if no reference was taken.
1992	*/
1993	static inline struct blkcg_gq *blkg_tryget_closest(struct bio *bio,
1994	struct cgroup_subsys_state *css)
1995	{
1996	struct blkcg_gq *blkg, *ret_blkg = NULL;
1997
1998	rcu_read_lock();
1999	blkg = blkg_lookup_create(blkcg: css_to_blkcg(css), disk: bio->bi_bdev->bd_disk);
2000	while (blkg) {
2001	if (blkg_tryget(blkg)) {
2002	ret_blkg = blkg;
2003	break;
2004	}
2005	blkg = blkg->parent;
2006	}
2007	rcu_read_unlock();
2008
2009	return ret_blkg;
2010	}
2011
2012	/**
2013	* bio_associate_blkg_from_css - associate a bio with a specified css
2014	* @bio: target bio
2015	* @css: target css
2016	*
2017	* Associate @bio with the blkg found by combining the css's blkg and the
2018	* request_queue of the @bio. An association failure is handled by walking up
2019	* the blkg tree. Therefore, the blkg associated can be anything between @blkg
2020	* and q->root_blkg. This situation only happens when a cgroup is dying and
2021	* then the remaining bios will spill to the closest alive blkg.
2022	*
2023	* A reference will be taken on the blkg and will be released when @bio is
2024	* freed.
2025	*/
2026	void bio_associate_blkg_from_css(struct bio *bio,
2027	struct cgroup_subsys_state *css)
2028	{
2029	if (bio->bi_blkg)
2030	blkg_put(blkg: bio->bi_blkg);
2031
2032	if (css && css->parent) {
2033	bio->bi_blkg = blkg_tryget_closest(bio, css);
2034	} else {
2035	blkg_get(blkg: bdev_get_queue(bdev: bio->bi_bdev)->root_blkg);
2036	bio->bi_blkg = bdev_get_queue(bdev: bio->bi_bdev)->root_blkg;
2037	}
2038	}
2039	EXPORT_SYMBOL_GPL(bio_associate_blkg_from_css);
2040
2041	/**
2042	* bio_associate_blkg - associate a bio with a blkg
2043	* @bio: target bio
2044	*
2045	* Associate @bio with the blkg found from the bio's css and request_queue.
2046	* If one is not found, bio_lookup_blkg() creates the blkg. If a blkg is
2047	* already associated, the css is reused and association redone as the
2048	* request_queue may have changed.
2049	*/
2050	void bio_associate_blkg(struct bio *bio)
2051	{
2052	struct cgroup_subsys_state *css;
2053
2054	rcu_read_lock();
2055
2056	if (bio->bi_blkg)
2057	css = bio_blkcg_css(bio);
2058	else
2059	css = blkcg_css();
2060
2061	bio_associate_blkg_from_css(bio, css);
2062
2063	rcu_read_unlock();
2064	}
2065	EXPORT_SYMBOL_GPL(bio_associate_blkg);
2066
2067	/**
2068	* bio_clone_blkg_association - clone blkg association from src to dst bio
2069	* @dst: destination bio
2070	* @src: source bio
2071	*/
2072	void bio_clone_blkg_association(struct bio *dst, struct bio *src)
2073	{
2074	if (src->bi_blkg)
2075	bio_associate_blkg_from_css(dst, bio_blkcg_css(src));
2076	}
2077	EXPORT_SYMBOL_GPL(bio_clone_blkg_association);
2078
2079	static int blk_cgroup_io_type(struct bio *bio)
2080	{
2081	if (op_is_discard(op: bio->bi_opf))
2082	return BLKG_IOSTAT_DISCARD;
2083	if (op_is_write(op: bio->bi_opf))
2084	return BLKG_IOSTAT_WRITE;
2085	return BLKG_IOSTAT_READ;
2086	}
2087
2088	void blk_cgroup_bio_start(struct bio *bio)
2089	{
2090	struct blkcg *blkcg = bio->bi_blkg->blkcg;
2091	int rwd = blk_cgroup_io_type(bio), cpu;
2092	struct blkg_iostat_set *bis;
2093	unsigned long flags;
2094
2095	if (!cgroup_subsys_on_dfl(io_cgrp_subsys))
2096	return;
2097
2098	/* Root-level stats are sourced from system-wide IO stats */
2099	if (!cgroup_parent(cgrp: blkcg->css.cgroup))
2100	return;
2101
2102	cpu = get_cpu();
2103	bis = per_cpu_ptr(bio->bi_blkg->iostat_cpu, cpu);
2104	flags = u64_stats_update_begin_irqsave(syncp: &bis->sync);
2105
2106	/*
2107	* If the bio is flagged with BIO_CGROUP_ACCT it means this is a split
2108	* bio and we would have already accounted for the size of the bio.
2109	*/
2110	if (!bio_flagged(bio, bit: BIO_CGROUP_ACCT)) {
2111	bio_set_flag(bio, bit: BIO_CGROUP_ACCT);
2112	bis->cur.bytes[rwd] += bio->bi_iter.bi_size;
2113	}
2114	bis->cur.ios[rwd]++;
2115
2116	/*
2117	* If the iostat_cpu isn't in a lockless list, put it into the
2118	* list to indicate that a stat update is pending.
2119	*/
2120	if (!READ_ONCE(bis->lqueued)) {
2121	struct llist_head *lhead = this_cpu_ptr(blkcg->lhead);
2122
2123	llist_add(new: &bis->lnode, head: lhead);
2124	WRITE_ONCE(bis->lqueued, true);
2125	}
2126
2127	u64_stats_update_end_irqrestore(syncp: &bis->sync, flags);
2128	cgroup_rstat_updated(cgrp: blkcg->css.cgroup, cpu);
2129	put_cpu();
2130	}
2131
2132	bool blk_cgroup_congested(void)
2133	{
2134	struct cgroup_subsys_state *css;
2135	bool ret = false;
2136
2137	rcu_read_lock();
2138	for (css = blkcg_css(); css; css = css->parent) {
2139	if (atomic_read(v: &css->cgroup->congestion_count)) {
2140	ret = true;
2141	break;
2142	}
2143	}
2144	rcu_read_unlock();
2145	return ret;
2146	}
2147
2148	module_param(blkcg_debug_stats, bool, 0644);
2149	MODULE_PARM_DESC(blkcg_debug_stats, "True if you want debug stats, false if not");
2150