xref: /linux/kernel/cgroup/cgroup.c (revision 4f3c8320c78cdd11c8fdd23c33787407f719322e)
1 /*
2  *  Generic process-grouping system.
3  *
4  *  Based originally on the cpuset system, extracted by Paul Menage
5  *  Copyright (C) 2006 Google, Inc
6  *
7  *  Notifications support
8  *  Copyright (C) 2009 Nokia Corporation
9  *  Author: Kirill A. Shutemov
10  *
11  *  Copyright notices from the original cpuset code:
12  *  --------------------------------------------------
13  *  Copyright (C) 2003 BULL SA.
14  *  Copyright (C) 2004-2006 Silicon Graphics, Inc.
15  *
16  *  Portions derived from Patrick Mochel's sysfs code.
17  *  sysfs is Copyright (c) 2001-3 Patrick Mochel
18  *
19  *  2003-10-10 Written by Simon Derr.
20  *  2003-10-22 Updates by Stephen Hemminger.
21  *  2004 May-July Rework by Paul Jackson.
22  *  ---------------------------------------------------
23  *
24  *  This file is subject to the terms and conditions of the GNU General Public
25  *  License.  See the file COPYING in the main directory of the Linux
26  *  distribution for more details.
27  */
28 
29 #define pr_fmt(fmt) KBUILD_MODNAME ": " fmt
30 
31 #include "cgroup-internal.h"
32 
33 #include <linux/cred.h>
34 #include <linux/errno.h>
35 #include <linux/init_task.h>
36 #include <linux/kernel.h>
37 #include <linux/magic.h>
38 #include <linux/mutex.h>
39 #include <linux/mount.h>
40 #include <linux/pagemap.h>
41 #include <linux/proc_fs.h>
42 #include <linux/rcupdate.h>
43 #include <linux/sched.h>
44 #include <linux/sched/task.h>
45 #include <linux/slab.h>
46 #include <linux/spinlock.h>
47 #include <linux/percpu-rwsem.h>
48 #include <linux/string.h>
49 #include <linux/hashtable.h>
50 #include <linux/idr.h>
51 #include <linux/kthread.h>
52 #include <linux/atomic.h>
53 #include <linux/cpuset.h>
54 #include <linux/proc_ns.h>
55 #include <linux/nsproxy.h>
56 #include <linux/file.h>
57 #include <linux/fs_parser.h>
58 #include <linux/sched/cputime.h>
59 #include <linux/psi.h>
60 #include <net/sock.h>
61 
62 #define CREATE_TRACE_POINTS
63 #include <trace/events/cgroup.h>
64 
65 #define CGROUP_FILE_NAME_MAX		(MAX_CGROUP_TYPE_NAMELEN +	\
66 					 MAX_CFTYPE_NAME + 2)
67 /* let's not notify more than 100 times per second */
68 #define CGROUP_FILE_NOTIFY_MIN_INTV	DIV_ROUND_UP(HZ, 100)
69 
70 /*
71  * cgroup_mutex is the master lock.  Any modification to cgroup or its
72  * hierarchy must be performed while holding it.
73  *
74  * css_set_lock protects task->cgroups pointer, the list of css_set
75  * objects, and the chain of tasks off each css_set.
76  *
77  * These locks are exported if CONFIG_PROVE_RCU so that accessors in
78  * cgroup.h can use them for lockdep annotations.
79  */
80 DEFINE_MUTEX(cgroup_mutex);
81 DEFINE_SPINLOCK(css_set_lock);
82 
83 #ifdef CONFIG_PROVE_RCU
84 EXPORT_SYMBOL_GPL(cgroup_mutex);
85 EXPORT_SYMBOL_GPL(css_set_lock);
86 #endif
87 
88 DEFINE_SPINLOCK(trace_cgroup_path_lock);
89 char trace_cgroup_path[TRACE_CGROUP_PATH_LEN];
90 bool cgroup_debug __read_mostly;
91 
92 /*
93  * Protects cgroup_idr and css_idr so that IDs can be released without
94  * grabbing cgroup_mutex.
95  */
96 static DEFINE_SPINLOCK(cgroup_idr_lock);
97 
98 /*
99  * Protects cgroup_file->kn for !self csses.  It synchronizes notifications
100  * against file removal/re-creation across css hiding.
101  */
102 static DEFINE_SPINLOCK(cgroup_file_kn_lock);
103 
104 DEFINE_PERCPU_RWSEM(cgroup_threadgroup_rwsem);
105 
106 #define cgroup_assert_mutex_or_rcu_locked()				\
107 	RCU_LOCKDEP_WARN(!rcu_read_lock_held() &&			\
108 			   !lockdep_is_held(&cgroup_mutex),		\
109 			   "cgroup_mutex or RCU read lock required");
110 
111 /*
112  * cgroup destruction makes heavy use of work items and there can be a lot
113  * of concurrent destructions.  Use a separate workqueue so that cgroup
114  * destruction work items don't end up filling up max_active of system_wq
115  * which may lead to deadlock.
116  */
117 static struct workqueue_struct *cgroup_destroy_wq;
118 
119 /* generate an array of cgroup subsystem pointers */
120 #define SUBSYS(_x) [_x ## _cgrp_id] = &_x ## _cgrp_subsys,
121 struct cgroup_subsys *cgroup_subsys[] = {
122 #include <linux/cgroup_subsys.h>
123 };
124 #undef SUBSYS
125 
126 /* array of cgroup subsystem names */
127 #define SUBSYS(_x) [_x ## _cgrp_id] = #_x,
128 static const char *cgroup_subsys_name[] = {
129 #include <linux/cgroup_subsys.h>
130 };
131 #undef SUBSYS
132 
133 /* array of static_keys for cgroup_subsys_enabled() and cgroup_subsys_on_dfl() */
134 #define SUBSYS(_x)								\
135 	DEFINE_STATIC_KEY_TRUE(_x ## _cgrp_subsys_enabled_key);			\
136 	DEFINE_STATIC_KEY_TRUE(_x ## _cgrp_subsys_on_dfl_key);			\
137 	EXPORT_SYMBOL_GPL(_x ## _cgrp_subsys_enabled_key);			\
138 	EXPORT_SYMBOL_GPL(_x ## _cgrp_subsys_on_dfl_key);
139 #include <linux/cgroup_subsys.h>
140 #undef SUBSYS
141 
142 #define SUBSYS(_x) [_x ## _cgrp_id] = &_x ## _cgrp_subsys_enabled_key,
143 static struct static_key_true *cgroup_subsys_enabled_key[] = {
144 #include <linux/cgroup_subsys.h>
145 };
146 #undef SUBSYS
147 
148 #define SUBSYS(_x) [_x ## _cgrp_id] = &_x ## _cgrp_subsys_on_dfl_key,
149 static struct static_key_true *cgroup_subsys_on_dfl_key[] = {
150 #include <linux/cgroup_subsys.h>
151 };
152 #undef SUBSYS
153 
154 static DEFINE_PER_CPU(struct cgroup_rstat_cpu, cgrp_dfl_root_rstat_cpu);
155 
156 /* the default hierarchy */
157 struct cgroup_root cgrp_dfl_root = { .cgrp.rstat_cpu = &cgrp_dfl_root_rstat_cpu };
158 EXPORT_SYMBOL_GPL(cgrp_dfl_root);
159 
160 /*
161  * The default hierarchy always exists but is hidden until mounted for the
162  * first time.  This is for backward compatibility.
163  */
164 static bool cgrp_dfl_visible;
165 
166 /* some controllers are not supported in the default hierarchy */
167 static u16 cgrp_dfl_inhibit_ss_mask;
168 
169 /* some controllers are implicitly enabled on the default hierarchy */
170 static u16 cgrp_dfl_implicit_ss_mask;
171 
172 /* some controllers can be threaded on the default hierarchy */
173 static u16 cgrp_dfl_threaded_ss_mask;
174 
175 /* The list of hierarchy roots */
176 LIST_HEAD(cgroup_roots);
177 static int cgroup_root_count;
178 
179 /* hierarchy ID allocation and mapping, protected by cgroup_mutex */
180 static DEFINE_IDR(cgroup_hierarchy_idr);
181 
182 /*
183  * Assign a monotonically increasing serial number to csses.  It guarantees
184  * cgroups with bigger numbers are newer than those with smaller numbers.
185  * Also, as csses are always appended to the parent's ->children list, it
186  * guarantees that sibling csses are always sorted in the ascending serial
187  * number order on the list.  Protected by cgroup_mutex.
188  */
189 static u64 css_serial_nr_next = 1;
190 
191 /*
192  * These bitmasks identify subsystems with specific features to avoid
193  * having to do iterative checks repeatedly.
194  */
195 static u16 have_fork_callback __read_mostly;
196 static u16 have_exit_callback __read_mostly;
197 static u16 have_release_callback __read_mostly;
198 static u16 have_canfork_callback __read_mostly;
199 
200 /* cgroup namespace for init task */
201 struct cgroup_namespace init_cgroup_ns = {
202 	.ns.count	= REFCOUNT_INIT(2),
203 	.user_ns	= &init_user_ns,
204 	.ns.ops		= &cgroupns_operations,
205 	.ns.inum	= PROC_CGROUP_INIT_INO,
206 	.root_cset	= &init_css_set,
207 };
208 
209 static struct file_system_type cgroup2_fs_type;
210 static struct cftype cgroup_base_files[];
211 
212 static int cgroup_apply_control(struct cgroup *cgrp);
213 static void cgroup_finalize_control(struct cgroup *cgrp, int ret);
214 static void css_task_iter_skip(struct css_task_iter *it,
215 			       struct task_struct *task);
216 static int cgroup_destroy_locked(struct cgroup *cgrp);
217 static struct cgroup_subsys_state *css_create(struct cgroup *cgrp,
218 					      struct cgroup_subsys *ss);
219 static void css_release(struct percpu_ref *ref);
220 static void kill_css(struct cgroup_subsys_state *css);
221 static int cgroup_addrm_files(struct cgroup_subsys_state *css,
222 			      struct cgroup *cgrp, struct cftype cfts[],
223 			      bool is_add);
224 
225 /**
226  * cgroup_ssid_enabled - cgroup subsys enabled test by subsys ID
227  * @ssid: subsys ID of interest
228  *
229  * cgroup_subsys_enabled() can only be used with literal subsys names which
230  * is fine for individual subsystems but unsuitable for cgroup core.  This
231  * is slower static_key_enabled() based test indexed by @ssid.
232  */
233 bool cgroup_ssid_enabled(int ssid)
234 {
235 	if (CGROUP_SUBSYS_COUNT == 0)
236 		return false;
237 
238 	return static_key_enabled(cgroup_subsys_enabled_key[ssid]);
239 }
240 
241 /**
242  * cgroup_on_dfl - test whether a cgroup is on the default hierarchy
243  * @cgrp: the cgroup of interest
244  *
245  * The default hierarchy is the v2 interface of cgroup and this function
246  * can be used to test whether a cgroup is on the default hierarchy for
247  * cases where a subsystem should behave differently depending on the
248  * interface version.
249  *
250  * List of changed behaviors:
251  *
252  * - Mount options "noprefix", "xattr", "clone_children", "release_agent"
253  *   and "name" are disallowed.
254  *
255  * - When mounting an existing superblock, mount options should match.
256  *
257  * - Remount is disallowed.
258  *
259  * - rename(2) is disallowed.
260  *
261  * - "tasks" is removed.  Everything should be at process granularity.  Use
262  *   "cgroup.procs" instead.
263  *
264  * - "cgroup.procs" is not sorted.  pids will be unique unless they got
265  *   recycled in-between reads.
266  *
267  * - "release_agent" and "notify_on_release" are removed.  Replacement
268  *   notification mechanism will be implemented.
269  *
270  * - "cgroup.clone_children" is removed.
271  *
272  * - "cgroup.subtree_populated" is available.  Its value is 0 if the cgroup
273  *   and its descendants contain no task; otherwise, 1.  The file also
274  *   generates kernfs notification which can be monitored through poll and
275  *   [di]notify when the value of the file changes.
276  *
277  * - cpuset: tasks will be kept in empty cpusets when hotplug happens and
278  *   take masks of ancestors with non-empty cpus/mems, instead of being
279  *   moved to an ancestor.
280  *
281  * - cpuset: a task can be moved into an empty cpuset, and again it takes
282  *   masks of ancestors.
283  *
284  * - blkcg: blk-throttle becomes properly hierarchical.
285  *
286  * - debug: disallowed on the default hierarchy.
287  */
288 bool cgroup_on_dfl(const struct cgroup *cgrp)
289 {
290 	return cgrp->root == &cgrp_dfl_root;
291 }
292 
293 /* IDR wrappers which synchronize using cgroup_idr_lock */
294 static int cgroup_idr_alloc(struct idr *idr, void *ptr, int start, int end,
295 			    gfp_t gfp_mask)
296 {
297 	int ret;
298 
299 	idr_preload(gfp_mask);
300 	spin_lock_bh(&cgroup_idr_lock);
301 	ret = idr_alloc(idr, ptr, start, end, gfp_mask & ~__GFP_DIRECT_RECLAIM);
302 	spin_unlock_bh(&cgroup_idr_lock);
303 	idr_preload_end();
304 	return ret;
305 }
306 
307 static void *cgroup_idr_replace(struct idr *idr, void *ptr, int id)
308 {
309 	void *ret;
310 
311 	spin_lock_bh(&cgroup_idr_lock);
312 	ret = idr_replace(idr, ptr, id);
313 	spin_unlock_bh(&cgroup_idr_lock);
314 	return ret;
315 }
316 
317 static void cgroup_idr_remove(struct idr *idr, int id)
318 {
319 	spin_lock_bh(&cgroup_idr_lock);
320 	idr_remove(idr, id);
321 	spin_unlock_bh(&cgroup_idr_lock);
322 }
323 
324 static bool cgroup_has_tasks(struct cgroup *cgrp)
325 {
326 	return cgrp->nr_populated_csets;
327 }
328 
329 bool cgroup_is_threaded(struct cgroup *cgrp)
330 {
331 	return cgrp->dom_cgrp != cgrp;
332 }
333 
334 /* can @cgrp host both domain and threaded children? */
335 static bool cgroup_is_mixable(struct cgroup *cgrp)
336 {
337 	/*
338 	 * Root isn't under domain level resource control exempting it from
339 	 * the no-internal-process constraint, so it can serve as a thread
340 	 * root and a parent of resource domains at the same time.
341 	 */
342 	return !cgroup_parent(cgrp);
343 }
344 
345 /* can @cgrp become a thread root? Should always be true for a thread root */
346 static bool cgroup_can_be_thread_root(struct cgroup *cgrp)
347 {
348 	/* mixables don't care */
349 	if (cgroup_is_mixable(cgrp))
350 		return true;
351 
352 	/* domain roots can't be nested under threaded */
353 	if (cgroup_is_threaded(cgrp))
354 		return false;
355 
356 	/* can only have either domain or threaded children */
357 	if (cgrp->nr_populated_domain_children)
358 		return false;
359 
360 	/* and no domain controllers can be enabled */
361 	if (cgrp->subtree_control & ~cgrp_dfl_threaded_ss_mask)
362 		return false;
363 
364 	return true;
365 }
366 
367 /* is @cgrp root of a threaded subtree? */
368 bool cgroup_is_thread_root(struct cgroup *cgrp)
369 {
370 	/* thread root should be a domain */
371 	if (cgroup_is_threaded(cgrp))
372 		return false;
373 
374 	/* a domain w/ threaded children is a thread root */
375 	if (cgrp->nr_threaded_children)
376 		return true;
377 
378 	/*
379 	 * A domain which has tasks and explicit threaded controllers
380 	 * enabled is a thread root.
381 	 */
382 	if (cgroup_has_tasks(cgrp) &&
383 	    (cgrp->subtree_control & cgrp_dfl_threaded_ss_mask))
384 		return true;
385 
386 	return false;
387 }
388 
389 /* a domain which isn't connected to the root w/o brekage can't be used */
390 static bool cgroup_is_valid_domain(struct cgroup *cgrp)
391 {
392 	/* the cgroup itself can be a thread root */
393 	if (cgroup_is_threaded(cgrp))
394 		return false;
395 
396 	/* but the ancestors can't be unless mixable */
397 	while ((cgrp = cgroup_parent(cgrp))) {
398 		if (!cgroup_is_mixable(cgrp) && cgroup_is_thread_root(cgrp))
399 			return false;
400 		if (cgroup_is_threaded(cgrp))
401 			return false;
402 	}
403 
404 	return true;
405 }
406 
407 /* subsystems visibly enabled on a cgroup */
408 static u16 cgroup_control(struct cgroup *cgrp)
409 {
410 	struct cgroup *parent = cgroup_parent(cgrp);
411 	u16 root_ss_mask = cgrp->root->subsys_mask;
412 
413 	if (parent) {
414 		u16 ss_mask = parent->subtree_control;
415 
416 		/* threaded cgroups can only have threaded controllers */
417 		if (cgroup_is_threaded(cgrp))
418 			ss_mask &= cgrp_dfl_threaded_ss_mask;
419 		return ss_mask;
420 	}
421 
422 	if (cgroup_on_dfl(cgrp))
423 		root_ss_mask &= ~(cgrp_dfl_inhibit_ss_mask |
424 				  cgrp_dfl_implicit_ss_mask);
425 	return root_ss_mask;
426 }
427 
428 /* subsystems enabled on a cgroup */
429 static u16 cgroup_ss_mask(struct cgroup *cgrp)
430 {
431 	struct cgroup *parent = cgroup_parent(cgrp);
432 
433 	if (parent) {
434 		u16 ss_mask = parent->subtree_ss_mask;
435 
436 		/* threaded cgroups can only have threaded controllers */
437 		if (cgroup_is_threaded(cgrp))
438 			ss_mask &= cgrp_dfl_threaded_ss_mask;
439 		return ss_mask;
440 	}
441 
442 	return cgrp->root->subsys_mask;
443 }
444 
445 /**
446  * cgroup_css - obtain a cgroup's css for the specified subsystem
447  * @cgrp: the cgroup of interest
448  * @ss: the subsystem of interest (%NULL returns @cgrp->self)
449  *
450  * Return @cgrp's css (cgroup_subsys_state) associated with @ss.  This
451  * function must be called either under cgroup_mutex or rcu_read_lock() and
452  * the caller is responsible for pinning the returned css if it wants to
453  * keep accessing it outside the said locks.  This function may return
454  * %NULL if @cgrp doesn't have @subsys_id enabled.
455  */
456 static struct cgroup_subsys_state *cgroup_css(struct cgroup *cgrp,
457 					      struct cgroup_subsys *ss)
458 {
459 	if (ss)
460 		return rcu_dereference_check(cgrp->subsys[ss->id],
461 					lockdep_is_held(&cgroup_mutex));
462 	else
463 		return &cgrp->self;
464 }
465 
466 /**
467  * cgroup_tryget_css - try to get a cgroup's css for the specified subsystem
468  * @cgrp: the cgroup of interest
469  * @ss: the subsystem of interest
470  *
471  * Find and get @cgrp's css assocaited with @ss.  If the css doesn't exist
472  * or is offline, %NULL is returned.
473  */
474 static struct cgroup_subsys_state *cgroup_tryget_css(struct cgroup *cgrp,
475 						     struct cgroup_subsys *ss)
476 {
477 	struct cgroup_subsys_state *css;
478 
479 	rcu_read_lock();
480 	css = cgroup_css(cgrp, ss);
481 	if (css && !css_tryget_online(css))
482 		css = NULL;
483 	rcu_read_unlock();
484 
485 	return css;
486 }
487 
488 /**
489  * cgroup_e_css_by_mask - obtain a cgroup's effective css for the specified ss
490  * @cgrp: the cgroup of interest
491  * @ss: the subsystem of interest (%NULL returns @cgrp->self)
492  *
493  * Similar to cgroup_css() but returns the effective css, which is defined
494  * as the matching css of the nearest ancestor including self which has @ss
495  * enabled.  If @ss is associated with the hierarchy @cgrp is on, this
496  * function is guaranteed to return non-NULL css.
497  */
498 static struct cgroup_subsys_state *cgroup_e_css_by_mask(struct cgroup *cgrp,
499 							struct cgroup_subsys *ss)
500 {
501 	lockdep_assert_held(&cgroup_mutex);
502 
503 	if (!ss)
504 		return &cgrp->self;
505 
506 	/*
507 	 * This function is used while updating css associations and thus
508 	 * can't test the csses directly.  Test ss_mask.
509 	 */
510 	while (!(cgroup_ss_mask(cgrp) & (1 << ss->id))) {
511 		cgrp = cgroup_parent(cgrp);
512 		if (!cgrp)
513 			return NULL;
514 	}
515 
516 	return cgroup_css(cgrp, ss);
517 }
518 
519 /**
520  * cgroup_e_css - obtain a cgroup's effective css for the specified subsystem
521  * @cgrp: the cgroup of interest
522  * @ss: the subsystem of interest
523  *
524  * Find and get the effective css of @cgrp for @ss.  The effective css is
525  * defined as the matching css of the nearest ancestor including self which
526  * has @ss enabled.  If @ss is not mounted on the hierarchy @cgrp is on,
527  * the root css is returned, so this function always returns a valid css.
528  *
529  * The returned css is not guaranteed to be online, and therefore it is the
530  * callers responsibility to try get a reference for it.
531  */
532 struct cgroup_subsys_state *cgroup_e_css(struct cgroup *cgrp,
533 					 struct cgroup_subsys *ss)
534 {
535 	struct cgroup_subsys_state *css;
536 
537 	do {
538 		css = cgroup_css(cgrp, ss);
539 
540 		if (css)
541 			return css;
542 		cgrp = cgroup_parent(cgrp);
543 	} while (cgrp);
544 
545 	return init_css_set.subsys[ss->id];
546 }
547 
548 /**
549  * cgroup_get_e_css - get a cgroup's effective css for the specified subsystem
550  * @cgrp: the cgroup of interest
551  * @ss: the subsystem of interest
552  *
553  * Find and get the effective css of @cgrp for @ss.  The effective css is
554  * defined as the matching css of the nearest ancestor including self which
555  * has @ss enabled.  If @ss is not mounted on the hierarchy @cgrp is on,
556  * the root css is returned, so this function always returns a valid css.
557  * The returned css must be put using css_put().
558  */
559 struct cgroup_subsys_state *cgroup_get_e_css(struct cgroup *cgrp,
560 					     struct cgroup_subsys *ss)
561 {
562 	struct cgroup_subsys_state *css;
563 
564 	rcu_read_lock();
565 
566 	do {
567 		css = cgroup_css(cgrp, ss);
568 
569 		if (css && css_tryget_online(css))
570 			goto out_unlock;
571 		cgrp = cgroup_parent(cgrp);
572 	} while (cgrp);
573 
574 	css = init_css_set.subsys[ss->id];
575 	css_get(css);
576 out_unlock:
577 	rcu_read_unlock();
578 	return css;
579 }
580 
581 static void cgroup_get_live(struct cgroup *cgrp)
582 {
583 	WARN_ON_ONCE(cgroup_is_dead(cgrp));
584 	css_get(&cgrp->self);
585 }
586 
587 /**
588  * __cgroup_task_count - count the number of tasks in a cgroup. The caller
589  * is responsible for taking the css_set_lock.
590  * @cgrp: the cgroup in question
591  */
592 int __cgroup_task_count(const struct cgroup *cgrp)
593 {
594 	int count = 0;
595 	struct cgrp_cset_link *link;
596 
597 	lockdep_assert_held(&css_set_lock);
598 
599 	list_for_each_entry(link, &cgrp->cset_links, cset_link)
600 		count += link->cset->nr_tasks;
601 
602 	return count;
603 }
604 
605 /**
606  * cgroup_task_count - count the number of tasks in a cgroup.
607  * @cgrp: the cgroup in question
608  */
609 int cgroup_task_count(const struct cgroup *cgrp)
610 {
611 	int count;
612 
613 	spin_lock_irq(&css_set_lock);
614 	count = __cgroup_task_count(cgrp);
615 	spin_unlock_irq(&css_set_lock);
616 
617 	return count;
618 }
619 
620 struct cgroup_subsys_state *of_css(struct kernfs_open_file *of)
621 {
622 	struct cgroup *cgrp = of->kn->parent->priv;
623 	struct cftype *cft = of_cft(of);
624 
625 	/*
626 	 * This is open and unprotected implementation of cgroup_css().
627 	 * seq_css() is only called from a kernfs file operation which has
628 	 * an active reference on the file.  Because all the subsystem
629 	 * files are drained before a css is disassociated with a cgroup,
630 	 * the matching css from the cgroup's subsys table is guaranteed to
631 	 * be and stay valid until the enclosing operation is complete.
632 	 */
633 	if (cft->ss)
634 		return rcu_dereference_raw(cgrp->subsys[cft->ss->id]);
635 	else
636 		return &cgrp->self;
637 }
638 EXPORT_SYMBOL_GPL(of_css);
639 
640 /**
641  * for_each_css - iterate all css's of a cgroup
642  * @css: the iteration cursor
643  * @ssid: the index of the subsystem, CGROUP_SUBSYS_COUNT after reaching the end
644  * @cgrp: the target cgroup to iterate css's of
645  *
646  * Should be called under cgroup_[tree_]mutex.
647  */
648 #define for_each_css(css, ssid, cgrp)					\
649 	for ((ssid) = 0; (ssid) < CGROUP_SUBSYS_COUNT; (ssid)++)	\
650 		if (!((css) = rcu_dereference_check(			\
651 				(cgrp)->subsys[(ssid)],			\
652 				lockdep_is_held(&cgroup_mutex)))) { }	\
653 		else
654 
655 /**
656  * for_each_e_css - iterate all effective css's of a cgroup
657  * @css: the iteration cursor
658  * @ssid: the index of the subsystem, CGROUP_SUBSYS_COUNT after reaching the end
659  * @cgrp: the target cgroup to iterate css's of
660  *
661  * Should be called under cgroup_[tree_]mutex.
662  */
663 #define for_each_e_css(css, ssid, cgrp)					    \
664 	for ((ssid) = 0; (ssid) < CGROUP_SUBSYS_COUNT; (ssid)++)	    \
665 		if (!((css) = cgroup_e_css_by_mask(cgrp,		    \
666 						   cgroup_subsys[(ssid)]))) \
667 			;						    \
668 		else
669 
670 /**
671  * do_each_subsys_mask - filter for_each_subsys with a bitmask
672  * @ss: the iteration cursor
673  * @ssid: the index of @ss, CGROUP_SUBSYS_COUNT after reaching the end
674  * @ss_mask: the bitmask
675  *
676  * The block will only run for cases where the ssid-th bit (1 << ssid) of
677  * @ss_mask is set.
678  */
679 #define do_each_subsys_mask(ss, ssid, ss_mask) do {			\
680 	unsigned long __ss_mask = (ss_mask);				\
681 	if (!CGROUP_SUBSYS_COUNT) { /* to avoid spurious gcc warning */	\
682 		(ssid) = 0;						\
683 		break;							\
684 	}								\
685 	for_each_set_bit(ssid, &__ss_mask, CGROUP_SUBSYS_COUNT) {	\
686 		(ss) = cgroup_subsys[ssid];				\
687 		{
688 
689 #define while_each_subsys_mask()					\
690 		}							\
691 	}								\
692 } while (false)
693 
694 /* iterate over child cgrps, lock should be held throughout iteration */
695 #define cgroup_for_each_live_child(child, cgrp)				\
696 	list_for_each_entry((child), &(cgrp)->self.children, self.sibling) \
697 		if (({ lockdep_assert_held(&cgroup_mutex);		\
698 		       cgroup_is_dead(child); }))			\
699 			;						\
700 		else
701 
702 /* walk live descendants in pre order */
703 #define cgroup_for_each_live_descendant_pre(dsct, d_css, cgrp)		\
704 	css_for_each_descendant_pre((d_css), cgroup_css((cgrp), NULL))	\
705 		if (({ lockdep_assert_held(&cgroup_mutex);		\
706 		       (dsct) = (d_css)->cgroup;			\
707 		       cgroup_is_dead(dsct); }))			\
708 			;						\
709 		else
710 
711 /* walk live descendants in postorder */
712 #define cgroup_for_each_live_descendant_post(dsct, d_css, cgrp)		\
713 	css_for_each_descendant_post((d_css), cgroup_css((cgrp), NULL))	\
714 		if (({ lockdep_assert_held(&cgroup_mutex);		\
715 		       (dsct) = (d_css)->cgroup;			\
716 		       cgroup_is_dead(dsct); }))			\
717 			;						\
718 		else
719 
720 /*
721  * The default css_set - used by init and its children prior to any
722  * hierarchies being mounted. It contains a pointer to the root state
723  * for each subsystem. Also used to anchor the list of css_sets. Not
724  * reference-counted, to improve performance when child cgroups
725  * haven't been created.
726  */
727 struct css_set init_css_set = {
728 	.refcount		= REFCOUNT_INIT(1),
729 	.dom_cset		= &init_css_set,
730 	.tasks			= LIST_HEAD_INIT(init_css_set.tasks),
731 	.mg_tasks		= LIST_HEAD_INIT(init_css_set.mg_tasks),
732 	.dying_tasks		= LIST_HEAD_INIT(init_css_set.dying_tasks),
733 	.task_iters		= LIST_HEAD_INIT(init_css_set.task_iters),
734 	.threaded_csets		= LIST_HEAD_INIT(init_css_set.threaded_csets),
735 	.cgrp_links		= LIST_HEAD_INIT(init_css_set.cgrp_links),
736 	.mg_preload_node	= LIST_HEAD_INIT(init_css_set.mg_preload_node),
737 	.mg_node		= LIST_HEAD_INIT(init_css_set.mg_node),
738 
739 	/*
740 	 * The following field is re-initialized when this cset gets linked
741 	 * in cgroup_init().  However, let's initialize the field
742 	 * statically too so that the default cgroup can be accessed safely
743 	 * early during boot.
744 	 */
745 	.dfl_cgrp		= &cgrp_dfl_root.cgrp,
746 };
747 
748 static int css_set_count	= 1;	/* 1 for init_css_set */
749 
750 static bool css_set_threaded(struct css_set *cset)
751 {
752 	return cset->dom_cset != cset;
753 }
754 
755 /**
756  * css_set_populated - does a css_set contain any tasks?
757  * @cset: target css_set
758  *
759  * css_set_populated() should be the same as !!cset->nr_tasks at steady
760  * state. However, css_set_populated() can be called while a task is being
761  * added to or removed from the linked list before the nr_tasks is
762  * properly updated. Hence, we can't just look at ->nr_tasks here.
763  */
764 static bool css_set_populated(struct css_set *cset)
765 {
766 	lockdep_assert_held(&css_set_lock);
767 
768 	return !list_empty(&cset->tasks) || !list_empty(&cset->mg_tasks);
769 }
770 
771 /**
772  * cgroup_update_populated - update the populated count of a cgroup
773  * @cgrp: the target cgroup
774  * @populated: inc or dec populated count
775  *
776  * One of the css_sets associated with @cgrp is either getting its first
777  * task or losing the last.  Update @cgrp->nr_populated_* accordingly.  The
778  * count is propagated towards root so that a given cgroup's
779  * nr_populated_children is zero iff none of its descendants contain any
780  * tasks.
781  *
782  * @cgrp's interface file "cgroup.populated" is zero if both
783  * @cgrp->nr_populated_csets and @cgrp->nr_populated_children are zero and
784  * 1 otherwise.  When the sum changes from or to zero, userland is notified
785  * that the content of the interface file has changed.  This can be used to
786  * detect when @cgrp and its descendants become populated or empty.
787  */
788 static void cgroup_update_populated(struct cgroup *cgrp, bool populated)
789 {
790 	struct cgroup *child = NULL;
791 	int adj = populated ? 1 : -1;
792 
793 	lockdep_assert_held(&css_set_lock);
794 
795 	do {
796 		bool was_populated = cgroup_is_populated(cgrp);
797 
798 		if (!child) {
799 			cgrp->nr_populated_csets += adj;
800 		} else {
801 			if (cgroup_is_threaded(child))
802 				cgrp->nr_populated_threaded_children += adj;
803 			else
804 				cgrp->nr_populated_domain_children += adj;
805 		}
806 
807 		if (was_populated == cgroup_is_populated(cgrp))
808 			break;
809 
810 		cgroup1_check_for_release(cgrp);
811 		TRACE_CGROUP_PATH(notify_populated, cgrp,
812 				  cgroup_is_populated(cgrp));
813 		cgroup_file_notify(&cgrp->events_file);
814 
815 		child = cgrp;
816 		cgrp = cgroup_parent(cgrp);
817 	} while (cgrp);
818 }
819 
820 /**
821  * css_set_update_populated - update populated state of a css_set
822  * @cset: target css_set
823  * @populated: whether @cset is populated or depopulated
824  *
825  * @cset is either getting the first task or losing the last.  Update the
826  * populated counters of all associated cgroups accordingly.
827  */
828 static void css_set_update_populated(struct css_set *cset, bool populated)
829 {
830 	struct cgrp_cset_link *link;
831 
832 	lockdep_assert_held(&css_set_lock);
833 
834 	list_for_each_entry(link, &cset->cgrp_links, cgrp_link)
835 		cgroup_update_populated(link->cgrp, populated);
836 }
837 
838 /*
839  * @task is leaving, advance task iterators which are pointing to it so
840  * that they can resume at the next position.  Advancing an iterator might
841  * remove it from the list, use safe walk.  See css_task_iter_skip() for
842  * details.
843  */
844 static void css_set_skip_task_iters(struct css_set *cset,
845 				    struct task_struct *task)
846 {
847 	struct css_task_iter *it, *pos;
848 
849 	list_for_each_entry_safe(it, pos, &cset->task_iters, iters_node)
850 		css_task_iter_skip(it, task);
851 }
852 
853 /**
854  * css_set_move_task - move a task from one css_set to another
855  * @task: task being moved
856  * @from_cset: css_set @task currently belongs to (may be NULL)
857  * @to_cset: new css_set @task is being moved to (may be NULL)
858  * @use_mg_tasks: move to @to_cset->mg_tasks instead of ->tasks
859  *
860  * Move @task from @from_cset to @to_cset.  If @task didn't belong to any
861  * css_set, @from_cset can be NULL.  If @task is being disassociated
862  * instead of moved, @to_cset can be NULL.
863  *
864  * This function automatically handles populated counter updates and
865  * css_task_iter adjustments but the caller is responsible for managing
866  * @from_cset and @to_cset's reference counts.
867  */
868 static void css_set_move_task(struct task_struct *task,
869 			      struct css_set *from_cset, struct css_set *to_cset,
870 			      bool use_mg_tasks)
871 {
872 	lockdep_assert_held(&css_set_lock);
873 
874 	if (to_cset && !css_set_populated(to_cset))
875 		css_set_update_populated(to_cset, true);
876 
877 	if (from_cset) {
878 		WARN_ON_ONCE(list_empty(&task->cg_list));
879 
880 		css_set_skip_task_iters(from_cset, task);
881 		list_del_init(&task->cg_list);
882 		if (!css_set_populated(from_cset))
883 			css_set_update_populated(from_cset, false);
884 	} else {
885 		WARN_ON_ONCE(!list_empty(&task->cg_list));
886 	}
887 
888 	if (to_cset) {
889 		/*
890 		 * We are synchronized through cgroup_threadgroup_rwsem
891 		 * against PF_EXITING setting such that we can't race
892 		 * against cgroup_exit()/cgroup_free() dropping the css_set.
893 		 */
894 		WARN_ON_ONCE(task->flags & PF_EXITING);
895 
896 		cgroup_move_task(task, to_cset);
897 		list_add_tail(&task->cg_list, use_mg_tasks ? &to_cset->mg_tasks :
898 							     &to_cset->tasks);
899 	}
900 }
901 
902 /*
903  * hash table for cgroup groups. This improves the performance to find
904  * an existing css_set. This hash doesn't (currently) take into
905  * account cgroups in empty hierarchies.
906  */
907 #define CSS_SET_HASH_BITS	7
908 static DEFINE_HASHTABLE(css_set_table, CSS_SET_HASH_BITS);
909 
910 static unsigned long css_set_hash(struct cgroup_subsys_state *css[])
911 {
912 	unsigned long key = 0UL;
913 	struct cgroup_subsys *ss;
914 	int i;
915 
916 	for_each_subsys(ss, i)
917 		key += (unsigned long)css[i];
918 	key = (key >> 16) ^ key;
919 
920 	return key;
921 }
922 
923 void put_css_set_locked(struct css_set *cset)
924 {
925 	struct cgrp_cset_link *link, *tmp_link;
926 	struct cgroup_subsys *ss;
927 	int ssid;
928 
929 	lockdep_assert_held(&css_set_lock);
930 
931 	if (!refcount_dec_and_test(&cset->refcount))
932 		return;
933 
934 	WARN_ON_ONCE(!list_empty(&cset->threaded_csets));
935 
936 	/* This css_set is dead. Unlink it and release cgroup and css refs */
937 	for_each_subsys(ss, ssid) {
938 		list_del(&cset->e_cset_node[ssid]);
939 		css_put(cset->subsys[ssid]);
940 	}
941 	hash_del(&cset->hlist);
942 	css_set_count--;
943 
944 	list_for_each_entry_safe(link, tmp_link, &cset->cgrp_links, cgrp_link) {
945 		list_del(&link->cset_link);
946 		list_del(&link->cgrp_link);
947 		if (cgroup_parent(link->cgrp))
948 			cgroup_put(link->cgrp);
949 		kfree(link);
950 	}
951 
952 	if (css_set_threaded(cset)) {
953 		list_del(&cset->threaded_csets_node);
954 		put_css_set_locked(cset->dom_cset);
955 	}
956 
957 	kfree_rcu(cset, rcu_head);
958 }
959 
960 /**
961  * compare_css_sets - helper function for find_existing_css_set().
962  * @cset: candidate css_set being tested
963  * @old_cset: existing css_set for a task
964  * @new_cgrp: cgroup that's being entered by the task
965  * @template: desired set of css pointers in css_set (pre-calculated)
966  *
967  * Returns true if "cset" matches "old_cset" except for the hierarchy
968  * which "new_cgrp" belongs to, for which it should match "new_cgrp".
969  */
970 static bool compare_css_sets(struct css_set *cset,
971 			     struct css_set *old_cset,
972 			     struct cgroup *new_cgrp,
973 			     struct cgroup_subsys_state *template[])
974 {
975 	struct cgroup *new_dfl_cgrp;
976 	struct list_head *l1, *l2;
977 
978 	/*
979 	 * On the default hierarchy, there can be csets which are
980 	 * associated with the same set of cgroups but different csses.
981 	 * Let's first ensure that csses match.
982 	 */
983 	if (memcmp(template, cset->subsys, sizeof(cset->subsys)))
984 		return false;
985 
986 
987 	/* @cset's domain should match the default cgroup's */
988 	if (cgroup_on_dfl(new_cgrp))
989 		new_dfl_cgrp = new_cgrp;
990 	else
991 		new_dfl_cgrp = old_cset->dfl_cgrp;
992 
993 	if (new_dfl_cgrp->dom_cgrp != cset->dom_cset->dfl_cgrp)
994 		return false;
995 
996 	/*
997 	 * Compare cgroup pointers in order to distinguish between
998 	 * different cgroups in hierarchies.  As different cgroups may
999 	 * share the same effective css, this comparison is always
1000 	 * necessary.
1001 	 */
1002 	l1 = &cset->cgrp_links;
1003 	l2 = &old_cset->cgrp_links;
1004 	while (1) {
1005 		struct cgrp_cset_link *link1, *link2;
1006 		struct cgroup *cgrp1, *cgrp2;
1007 
1008 		l1 = l1->next;
1009 		l2 = l2->next;
1010 		/* See if we reached the end - both lists are equal length. */
1011 		if (l1 == &cset->cgrp_links) {
1012 			BUG_ON(l2 != &old_cset->cgrp_links);
1013 			break;
1014 		} else {
1015 			BUG_ON(l2 == &old_cset->cgrp_links);
1016 		}
1017 		/* Locate the cgroups associated with these links. */
1018 		link1 = list_entry(l1, struct cgrp_cset_link, cgrp_link);
1019 		link2 = list_entry(l2, struct cgrp_cset_link, cgrp_link);
1020 		cgrp1 = link1->cgrp;
1021 		cgrp2 = link2->cgrp;
1022 		/* Hierarchies should be linked in the same order. */
1023 		BUG_ON(cgrp1->root != cgrp2->root);
1024 
1025 		/*
1026 		 * If this hierarchy is the hierarchy of the cgroup
1027 		 * that's changing, then we need to check that this
1028 		 * css_set points to the new cgroup; if it's any other
1029 		 * hierarchy, then this css_set should point to the
1030 		 * same cgroup as the old css_set.
1031 		 */
1032 		if (cgrp1->root == new_cgrp->root) {
1033 			if (cgrp1 != new_cgrp)
1034 				return false;
1035 		} else {
1036 			if (cgrp1 != cgrp2)
1037 				return false;
1038 		}
1039 	}
1040 	return true;
1041 }
1042 
1043 /**
1044  * find_existing_css_set - init css array and find the matching css_set
1045  * @old_cset: the css_set that we're using before the cgroup transition
1046  * @cgrp: the cgroup that we're moving into
1047  * @template: out param for the new set of csses, should be clear on entry
1048  */
1049 static struct css_set *find_existing_css_set(struct css_set *old_cset,
1050 					struct cgroup *cgrp,
1051 					struct cgroup_subsys_state *template[])
1052 {
1053 	struct cgroup_root *root = cgrp->root;
1054 	struct cgroup_subsys *ss;
1055 	struct css_set *cset;
1056 	unsigned long key;
1057 	int i;
1058 
1059 	/*
1060 	 * Build the set of subsystem state objects that we want to see in the
1061 	 * new css_set. While subsystems can change globally, the entries here
1062 	 * won't change, so no need for locking.
1063 	 */
1064 	for_each_subsys(ss, i) {
1065 		if (root->subsys_mask & (1UL << i)) {
1066 			/*
1067 			 * @ss is in this hierarchy, so we want the
1068 			 * effective css from @cgrp.
1069 			 */
1070 			template[i] = cgroup_e_css_by_mask(cgrp, ss);
1071 		} else {
1072 			/*
1073 			 * @ss is not in this hierarchy, so we don't want
1074 			 * to change the css.
1075 			 */
1076 			template[i] = old_cset->subsys[i];
1077 		}
1078 	}
1079 
1080 	key = css_set_hash(template);
1081 	hash_for_each_possible(css_set_table, cset, hlist, key) {
1082 		if (!compare_css_sets(cset, old_cset, cgrp, template))
1083 			continue;
1084 
1085 		/* This css_set matches what we need */
1086 		return cset;
1087 	}
1088 
1089 	/* No existing cgroup group matched */
1090 	return NULL;
1091 }
1092 
1093 static void free_cgrp_cset_links(struct list_head *links_to_free)
1094 {
1095 	struct cgrp_cset_link *link, *tmp_link;
1096 
1097 	list_for_each_entry_safe(link, tmp_link, links_to_free, cset_link) {
1098 		list_del(&link->cset_link);
1099 		kfree(link);
1100 	}
1101 }
1102 
1103 /**
1104  * allocate_cgrp_cset_links - allocate cgrp_cset_links
1105  * @count: the number of links to allocate
1106  * @tmp_links: list_head the allocated links are put on
1107  *
1108  * Allocate @count cgrp_cset_link structures and chain them on @tmp_links
1109  * through ->cset_link.  Returns 0 on success or -errno.
1110  */
1111 static int allocate_cgrp_cset_links(int count, struct list_head *tmp_links)
1112 {
1113 	struct cgrp_cset_link *link;
1114 	int i;
1115 
1116 	INIT_LIST_HEAD(tmp_links);
1117 
1118 	for (i = 0; i < count; i++) {
1119 		link = kzalloc(sizeof(*link), GFP_KERNEL);
1120 		if (!link) {
1121 			free_cgrp_cset_links(tmp_links);
1122 			return -ENOMEM;
1123 		}
1124 		list_add(&link->cset_link, tmp_links);
1125 	}
1126 	return 0;
1127 }
1128 
1129 /**
1130  * link_css_set - a helper function to link a css_set to a cgroup
1131  * @tmp_links: cgrp_cset_link objects allocated by allocate_cgrp_cset_links()
1132  * @cset: the css_set to be linked
1133  * @cgrp: the destination cgroup
1134  */
1135 static void link_css_set(struct list_head *tmp_links, struct css_set *cset,
1136 			 struct cgroup *cgrp)
1137 {
1138 	struct cgrp_cset_link *link;
1139 
1140 	BUG_ON(list_empty(tmp_links));
1141 
1142 	if (cgroup_on_dfl(cgrp))
1143 		cset->dfl_cgrp = cgrp;
1144 
1145 	link = list_first_entry(tmp_links, struct cgrp_cset_link, cset_link);
1146 	link->cset = cset;
1147 	link->cgrp = cgrp;
1148 
1149 	/*
1150 	 * Always add links to the tail of the lists so that the lists are
1151 	 * in chronological order.
1152 	 */
1153 	list_move_tail(&link->cset_link, &cgrp->cset_links);
1154 	list_add_tail(&link->cgrp_link, &cset->cgrp_links);
1155 
1156 	if (cgroup_parent(cgrp))
1157 		cgroup_get_live(cgrp);
1158 }
1159 
1160 /**
1161  * find_css_set - return a new css_set with one cgroup updated
1162  * @old_cset: the baseline css_set
1163  * @cgrp: the cgroup to be updated
1164  *
1165  * Return a new css_set that's equivalent to @old_cset, but with @cgrp
1166  * substituted into the appropriate hierarchy.
1167  */
1168 static struct css_set *find_css_set(struct css_set *old_cset,
1169 				    struct cgroup *cgrp)
1170 {
1171 	struct cgroup_subsys_state *template[CGROUP_SUBSYS_COUNT] = { };
1172 	struct css_set *cset;
1173 	struct list_head tmp_links;
1174 	struct cgrp_cset_link *link;
1175 	struct cgroup_subsys *ss;
1176 	unsigned long key;
1177 	int ssid;
1178 
1179 	lockdep_assert_held(&cgroup_mutex);
1180 
1181 	/* First see if we already have a cgroup group that matches
1182 	 * the desired set */
1183 	spin_lock_irq(&css_set_lock);
1184 	cset = find_existing_css_set(old_cset, cgrp, template);
1185 	if (cset)
1186 		get_css_set(cset);
1187 	spin_unlock_irq(&css_set_lock);
1188 
1189 	if (cset)
1190 		return cset;
1191 
1192 	cset = kzalloc(sizeof(*cset), GFP_KERNEL);
1193 	if (!cset)
1194 		return NULL;
1195 
1196 	/* Allocate all the cgrp_cset_link objects that we'll need */
1197 	if (allocate_cgrp_cset_links(cgroup_root_count, &tmp_links) < 0) {
1198 		kfree(cset);
1199 		return NULL;
1200 	}
1201 
1202 	refcount_set(&cset->refcount, 1);
1203 	cset->dom_cset = cset;
1204 	INIT_LIST_HEAD(&cset->tasks);
1205 	INIT_LIST_HEAD(&cset->mg_tasks);
1206 	INIT_LIST_HEAD(&cset->dying_tasks);
1207 	INIT_LIST_HEAD(&cset->task_iters);
1208 	INIT_LIST_HEAD(&cset->threaded_csets);
1209 	INIT_HLIST_NODE(&cset->hlist);
1210 	INIT_LIST_HEAD(&cset->cgrp_links);
1211 	INIT_LIST_HEAD(&cset->mg_preload_node);
1212 	INIT_LIST_HEAD(&cset->mg_node);
1213 
1214 	/* Copy the set of subsystem state objects generated in
1215 	 * find_existing_css_set() */
1216 	memcpy(cset->subsys, template, sizeof(cset->subsys));
1217 
1218 	spin_lock_irq(&css_set_lock);
1219 	/* Add reference counts and links from the new css_set. */
1220 	list_for_each_entry(link, &old_cset->cgrp_links, cgrp_link) {
1221 		struct cgroup *c = link->cgrp;
1222 
1223 		if (c->root == cgrp->root)
1224 			c = cgrp;
1225 		link_css_set(&tmp_links, cset, c);
1226 	}
1227 
1228 	BUG_ON(!list_empty(&tmp_links));
1229 
1230 	css_set_count++;
1231 
1232 	/* Add @cset to the hash table */
1233 	key = css_set_hash(cset->subsys);
1234 	hash_add(css_set_table, &cset->hlist, key);
1235 
1236 	for_each_subsys(ss, ssid) {
1237 		struct cgroup_subsys_state *css = cset->subsys[ssid];
1238 
1239 		list_add_tail(&cset->e_cset_node[ssid],
1240 			      &css->cgroup->e_csets[ssid]);
1241 		css_get(css);
1242 	}
1243 
1244 	spin_unlock_irq(&css_set_lock);
1245 
1246 	/*
1247 	 * If @cset should be threaded, look up the matching dom_cset and
1248 	 * link them up.  We first fully initialize @cset then look for the
1249 	 * dom_cset.  It's simpler this way and safe as @cset is guaranteed
1250 	 * to stay empty until we return.
1251 	 */
1252 	if (cgroup_is_threaded(cset->dfl_cgrp)) {
1253 		struct css_set *dcset;
1254 
1255 		dcset = find_css_set(cset, cset->dfl_cgrp->dom_cgrp);
1256 		if (!dcset) {
1257 			put_css_set(cset);
1258 			return NULL;
1259 		}
1260 
1261 		spin_lock_irq(&css_set_lock);
1262 		cset->dom_cset = dcset;
1263 		list_add_tail(&cset->threaded_csets_node,
1264 			      &dcset->threaded_csets);
1265 		spin_unlock_irq(&css_set_lock);
1266 	}
1267 
1268 	return cset;
1269 }
1270 
1271 struct cgroup_root *cgroup_root_from_kf(struct kernfs_root *kf_root)
1272 {
1273 	struct cgroup *root_cgrp = kf_root->kn->priv;
1274 
1275 	return root_cgrp->root;
1276 }
1277 
1278 static int cgroup_init_root_id(struct cgroup_root *root)
1279 {
1280 	int id;
1281 
1282 	lockdep_assert_held(&cgroup_mutex);
1283 
1284 	id = idr_alloc_cyclic(&cgroup_hierarchy_idr, root, 0, 0, GFP_KERNEL);
1285 	if (id < 0)
1286 		return id;
1287 
1288 	root->hierarchy_id = id;
1289 	return 0;
1290 }
1291 
1292 static void cgroup_exit_root_id(struct cgroup_root *root)
1293 {
1294 	lockdep_assert_held(&cgroup_mutex);
1295 
1296 	idr_remove(&cgroup_hierarchy_idr, root->hierarchy_id);
1297 }
1298 
1299 void cgroup_free_root(struct cgroup_root *root)
1300 {
1301 	kfree(root);
1302 }
1303 
1304 static void cgroup_destroy_root(struct cgroup_root *root)
1305 {
1306 	struct cgroup *cgrp = &root->cgrp;
1307 	struct cgrp_cset_link *link, *tmp_link;
1308 
1309 	trace_cgroup_destroy_root(root);
1310 
1311 	cgroup_lock_and_drain_offline(&cgrp_dfl_root.cgrp);
1312 
1313 	BUG_ON(atomic_read(&root->nr_cgrps));
1314 	BUG_ON(!list_empty(&cgrp->self.children));
1315 
1316 	/* Rebind all subsystems back to the default hierarchy */
1317 	WARN_ON(rebind_subsystems(&cgrp_dfl_root, root->subsys_mask));
1318 
1319 	/*
1320 	 * Release all the links from cset_links to this hierarchy's
1321 	 * root cgroup
1322 	 */
1323 	spin_lock_irq(&css_set_lock);
1324 
1325 	list_for_each_entry_safe(link, tmp_link, &cgrp->cset_links, cset_link) {
1326 		list_del(&link->cset_link);
1327 		list_del(&link->cgrp_link);
1328 		kfree(link);
1329 	}
1330 
1331 	spin_unlock_irq(&css_set_lock);
1332 
1333 	if (!list_empty(&root->root_list)) {
1334 		list_del(&root->root_list);
1335 		cgroup_root_count--;
1336 	}
1337 
1338 	cgroup_exit_root_id(root);
1339 
1340 	mutex_unlock(&cgroup_mutex);
1341 
1342 	kernfs_destroy_root(root->kf_root);
1343 	cgroup_free_root(root);
1344 }
1345 
1346 /*
1347  * look up cgroup associated with current task's cgroup namespace on the
1348  * specified hierarchy
1349  */
1350 static struct cgroup *
1351 current_cgns_cgroup_from_root(struct cgroup_root *root)
1352 {
1353 	struct cgroup *res = NULL;
1354 	struct css_set *cset;
1355 
1356 	lockdep_assert_held(&css_set_lock);
1357 
1358 	rcu_read_lock();
1359 
1360 	cset = current->nsproxy->cgroup_ns->root_cset;
1361 	if (cset == &init_css_set) {
1362 		res = &root->cgrp;
1363 	} else if (root == &cgrp_dfl_root) {
1364 		res = cset->dfl_cgrp;
1365 	} else {
1366 		struct cgrp_cset_link *link;
1367 
1368 		list_for_each_entry(link, &cset->cgrp_links, cgrp_link) {
1369 			struct cgroup *c = link->cgrp;
1370 
1371 			if (c->root == root) {
1372 				res = c;
1373 				break;
1374 			}
1375 		}
1376 	}
1377 	rcu_read_unlock();
1378 
1379 	BUG_ON(!res);
1380 	return res;
1381 }
1382 
1383 /* look up cgroup associated with given css_set on the specified hierarchy */
1384 static struct cgroup *cset_cgroup_from_root(struct css_set *cset,
1385 					    struct cgroup_root *root)
1386 {
1387 	struct cgroup *res = NULL;
1388 
1389 	lockdep_assert_held(&cgroup_mutex);
1390 	lockdep_assert_held(&css_set_lock);
1391 
1392 	if (cset == &init_css_set) {
1393 		res = &root->cgrp;
1394 	} else if (root == &cgrp_dfl_root) {
1395 		res = cset->dfl_cgrp;
1396 	} else {
1397 		struct cgrp_cset_link *link;
1398 
1399 		list_for_each_entry(link, &cset->cgrp_links, cgrp_link) {
1400 			struct cgroup *c = link->cgrp;
1401 
1402 			if (c->root == root) {
1403 				res = c;
1404 				break;
1405 			}
1406 		}
1407 	}
1408 
1409 	BUG_ON(!res);
1410 	return res;
1411 }
1412 
1413 /*
1414  * Return the cgroup for "task" from the given hierarchy. Must be
1415  * called with cgroup_mutex and css_set_lock held.
1416  */
1417 struct cgroup *task_cgroup_from_root(struct task_struct *task,
1418 				     struct cgroup_root *root)
1419 {
1420 	/*
1421 	 * No need to lock the task - since we hold css_set_lock the
1422 	 * task can't change groups.
1423 	 */
1424 	return cset_cgroup_from_root(task_css_set(task), root);
1425 }
1426 
1427 /*
1428  * A task must hold cgroup_mutex to modify cgroups.
1429  *
1430  * Any task can increment and decrement the count field without lock.
1431  * So in general, code holding cgroup_mutex can't rely on the count
1432  * field not changing.  However, if the count goes to zero, then only
1433  * cgroup_attach_task() can increment it again.  Because a count of zero
1434  * means that no tasks are currently attached, therefore there is no
1435  * way a task attached to that cgroup can fork (the other way to
1436  * increment the count).  So code holding cgroup_mutex can safely
1437  * assume that if the count is zero, it will stay zero. Similarly, if
1438  * a task holds cgroup_mutex on a cgroup with zero count, it
1439  * knows that the cgroup won't be removed, as cgroup_rmdir()
1440  * needs that mutex.
1441  *
1442  * A cgroup can only be deleted if both its 'count' of using tasks
1443  * is zero, and its list of 'children' cgroups is empty.  Since all
1444  * tasks in the system use _some_ cgroup, and since there is always at
1445  * least one task in the system (init, pid == 1), therefore, root cgroup
1446  * always has either children cgroups and/or using tasks.  So we don't
1447  * need a special hack to ensure that root cgroup cannot be deleted.
1448  *
1449  * P.S.  One more locking exception.  RCU is used to guard the
1450  * update of a tasks cgroup pointer by cgroup_attach_task()
1451  */
1452 
1453 static struct kernfs_syscall_ops cgroup_kf_syscall_ops;
1454 
1455 static char *cgroup_file_name(struct cgroup *cgrp, const struct cftype *cft,
1456 			      char *buf)
1457 {
1458 	struct cgroup_subsys *ss = cft->ss;
1459 
1460 	if (cft->ss && !(cft->flags & CFTYPE_NO_PREFIX) &&
1461 	    !(cgrp->root->flags & CGRP_ROOT_NOPREFIX)) {
1462 		const char *dbg = (cft->flags & CFTYPE_DEBUG) ? ".__DEBUG__." : "";
1463 
1464 		snprintf(buf, CGROUP_FILE_NAME_MAX, "%s%s.%s",
1465 			 dbg, cgroup_on_dfl(cgrp) ? ss->name : ss->legacy_name,
1466 			 cft->name);
1467 	} else {
1468 		strscpy(buf, cft->name, CGROUP_FILE_NAME_MAX);
1469 	}
1470 	return buf;
1471 }
1472 
1473 /**
1474  * cgroup_file_mode - deduce file mode of a control file
1475  * @cft: the control file in question
1476  *
1477  * S_IRUGO for read, S_IWUSR for write.
1478  */
1479 static umode_t cgroup_file_mode(const struct cftype *cft)
1480 {
1481 	umode_t mode = 0;
1482 
1483 	if (cft->read_u64 || cft->read_s64 || cft->seq_show)
1484 		mode |= S_IRUGO;
1485 
1486 	if (cft->write_u64 || cft->write_s64 || cft->write) {
1487 		if (cft->flags & CFTYPE_WORLD_WRITABLE)
1488 			mode |= S_IWUGO;
1489 		else
1490 			mode |= S_IWUSR;
1491 	}
1492 
1493 	return mode;
1494 }
1495 
1496 /**
1497  * cgroup_calc_subtree_ss_mask - calculate subtree_ss_mask
1498  * @subtree_control: the new subtree_control mask to consider
1499  * @this_ss_mask: available subsystems
1500  *
1501  * On the default hierarchy, a subsystem may request other subsystems to be
1502  * enabled together through its ->depends_on mask.  In such cases, more
1503  * subsystems than specified in "cgroup.subtree_control" may be enabled.
1504  *
1505  * This function calculates which subsystems need to be enabled if
1506  * @subtree_control is to be applied while restricted to @this_ss_mask.
1507  */
1508 static u16 cgroup_calc_subtree_ss_mask(u16 subtree_control, u16 this_ss_mask)
1509 {
1510 	u16 cur_ss_mask = subtree_control;
1511 	struct cgroup_subsys *ss;
1512 	int ssid;
1513 
1514 	lockdep_assert_held(&cgroup_mutex);
1515 
1516 	cur_ss_mask |= cgrp_dfl_implicit_ss_mask;
1517 
1518 	while (true) {
1519 		u16 new_ss_mask = cur_ss_mask;
1520 
1521 		do_each_subsys_mask(ss, ssid, cur_ss_mask) {
1522 			new_ss_mask |= ss->depends_on;
1523 		} while_each_subsys_mask();
1524 
1525 		/*
1526 		 * Mask out subsystems which aren't available.  This can
1527 		 * happen only if some depended-upon subsystems were bound
1528 		 * to non-default hierarchies.
1529 		 */
1530 		new_ss_mask &= this_ss_mask;
1531 
1532 		if (new_ss_mask == cur_ss_mask)
1533 			break;
1534 		cur_ss_mask = new_ss_mask;
1535 	}
1536 
1537 	return cur_ss_mask;
1538 }
1539 
1540 /**
1541  * cgroup_kn_unlock - unlocking helper for cgroup kernfs methods
1542  * @kn: the kernfs_node being serviced
1543  *
1544  * This helper undoes cgroup_kn_lock_live() and should be invoked before
1545  * the method finishes if locking succeeded.  Note that once this function
1546  * returns the cgroup returned by cgroup_kn_lock_live() may become
1547  * inaccessible any time.  If the caller intends to continue to access the
1548  * cgroup, it should pin it before invoking this function.
1549  */
1550 void cgroup_kn_unlock(struct kernfs_node *kn)
1551 {
1552 	struct cgroup *cgrp;
1553 
1554 	if (kernfs_type(kn) == KERNFS_DIR)
1555 		cgrp = kn->priv;
1556 	else
1557 		cgrp = kn->parent->priv;
1558 
1559 	mutex_unlock(&cgroup_mutex);
1560 
1561 	kernfs_unbreak_active_protection(kn);
1562 	cgroup_put(cgrp);
1563 }
1564 
1565 /**
1566  * cgroup_kn_lock_live - locking helper for cgroup kernfs methods
1567  * @kn: the kernfs_node being serviced
1568  * @drain_offline: perform offline draining on the cgroup
1569  *
1570  * This helper is to be used by a cgroup kernfs method currently servicing
1571  * @kn.  It breaks the active protection, performs cgroup locking and
1572  * verifies that the associated cgroup is alive.  Returns the cgroup if
1573  * alive; otherwise, %NULL.  A successful return should be undone by a
1574  * matching cgroup_kn_unlock() invocation.  If @drain_offline is %true, the
1575  * cgroup is drained of offlining csses before return.
1576  *
1577  * Any cgroup kernfs method implementation which requires locking the
1578  * associated cgroup should use this helper.  It avoids nesting cgroup
1579  * locking under kernfs active protection and allows all kernfs operations
1580  * including self-removal.
1581  */
1582 struct cgroup *cgroup_kn_lock_live(struct kernfs_node *kn, bool drain_offline)
1583 {
1584 	struct cgroup *cgrp;
1585 
1586 	if (kernfs_type(kn) == KERNFS_DIR)
1587 		cgrp = kn->priv;
1588 	else
1589 		cgrp = kn->parent->priv;
1590 
1591 	/*
1592 	 * We're gonna grab cgroup_mutex which nests outside kernfs
1593 	 * active_ref.  cgroup liveliness check alone provides enough
1594 	 * protection against removal.  Ensure @cgrp stays accessible and
1595 	 * break the active_ref protection.
1596 	 */
1597 	if (!cgroup_tryget(cgrp))
1598 		return NULL;
1599 	kernfs_break_active_protection(kn);
1600 
1601 	if (drain_offline)
1602 		cgroup_lock_and_drain_offline(cgrp);
1603 	else
1604 		mutex_lock(&cgroup_mutex);
1605 
1606 	if (!cgroup_is_dead(cgrp))
1607 		return cgrp;
1608 
1609 	cgroup_kn_unlock(kn);
1610 	return NULL;
1611 }
1612 
1613 static void cgroup_rm_file(struct cgroup *cgrp, const struct cftype *cft)
1614 {
1615 	char name[CGROUP_FILE_NAME_MAX];
1616 
1617 	lockdep_assert_held(&cgroup_mutex);
1618 
1619 	if (cft->file_offset) {
1620 		struct cgroup_subsys_state *css = cgroup_css(cgrp, cft->ss);
1621 		struct cgroup_file *cfile = (void *)css + cft->file_offset;
1622 
1623 		spin_lock_irq(&cgroup_file_kn_lock);
1624 		cfile->kn = NULL;
1625 		spin_unlock_irq(&cgroup_file_kn_lock);
1626 
1627 		del_timer_sync(&cfile->notify_timer);
1628 	}
1629 
1630 	kernfs_remove_by_name(cgrp->kn, cgroup_file_name(cgrp, cft, name));
1631 }
1632 
1633 /**
1634  * css_clear_dir - remove subsys files in a cgroup directory
1635  * @css: taget css
1636  */
1637 static void css_clear_dir(struct cgroup_subsys_state *css)
1638 {
1639 	struct cgroup *cgrp = css->cgroup;
1640 	struct cftype *cfts;
1641 
1642 	if (!(css->flags & CSS_VISIBLE))
1643 		return;
1644 
1645 	css->flags &= ~CSS_VISIBLE;
1646 
1647 	if (!css->ss) {
1648 		if (cgroup_on_dfl(cgrp))
1649 			cfts = cgroup_base_files;
1650 		else
1651 			cfts = cgroup1_base_files;
1652 
1653 		cgroup_addrm_files(css, cgrp, cfts, false);
1654 	} else {
1655 		list_for_each_entry(cfts, &css->ss->cfts, node)
1656 			cgroup_addrm_files(css, cgrp, cfts, false);
1657 	}
1658 }
1659 
1660 /**
1661  * css_populate_dir - create subsys files in a cgroup directory
1662  * @css: target css
1663  *
1664  * On failure, no file is added.
1665  */
1666 static int css_populate_dir(struct cgroup_subsys_state *css)
1667 {
1668 	struct cgroup *cgrp = css->cgroup;
1669 	struct cftype *cfts, *failed_cfts;
1670 	int ret;
1671 
1672 	if ((css->flags & CSS_VISIBLE) || !cgrp->kn)
1673 		return 0;
1674 
1675 	if (!css->ss) {
1676 		if (cgroup_on_dfl(cgrp))
1677 			cfts = cgroup_base_files;
1678 		else
1679 			cfts = cgroup1_base_files;
1680 
1681 		ret = cgroup_addrm_files(&cgrp->self, cgrp, cfts, true);
1682 		if (ret < 0)
1683 			return ret;
1684 	} else {
1685 		list_for_each_entry(cfts, &css->ss->cfts, node) {
1686 			ret = cgroup_addrm_files(css, cgrp, cfts, true);
1687 			if (ret < 0) {
1688 				failed_cfts = cfts;
1689 				goto err;
1690 			}
1691 		}
1692 	}
1693 
1694 	css->flags |= CSS_VISIBLE;
1695 
1696 	return 0;
1697 err:
1698 	list_for_each_entry(cfts, &css->ss->cfts, node) {
1699 		if (cfts == failed_cfts)
1700 			break;
1701 		cgroup_addrm_files(css, cgrp, cfts, false);
1702 	}
1703 	return ret;
1704 }
1705 
1706 int rebind_subsystems(struct cgroup_root *dst_root, u16 ss_mask)
1707 {
1708 	struct cgroup *dcgrp = &dst_root->cgrp;
1709 	struct cgroup_subsys *ss;
1710 	int ssid, i, ret;
1711 
1712 	lockdep_assert_held(&cgroup_mutex);
1713 
1714 	do_each_subsys_mask(ss, ssid, ss_mask) {
1715 		/*
1716 		 * If @ss has non-root csses attached to it, can't move.
1717 		 * If @ss is an implicit controller, it is exempt from this
1718 		 * rule and can be stolen.
1719 		 */
1720 		if (css_next_child(NULL, cgroup_css(&ss->root->cgrp, ss)) &&
1721 		    !ss->implicit_on_dfl)
1722 			return -EBUSY;
1723 
1724 		/* can't move between two non-dummy roots either */
1725 		if (ss->root != &cgrp_dfl_root && dst_root != &cgrp_dfl_root)
1726 			return -EBUSY;
1727 	} while_each_subsys_mask();
1728 
1729 	do_each_subsys_mask(ss, ssid, ss_mask) {
1730 		struct cgroup_root *src_root = ss->root;
1731 		struct cgroup *scgrp = &src_root->cgrp;
1732 		struct cgroup_subsys_state *css = cgroup_css(scgrp, ss);
1733 		struct css_set *cset;
1734 
1735 		WARN_ON(!css || cgroup_css(dcgrp, ss));
1736 
1737 		/* disable from the source */
1738 		src_root->subsys_mask &= ~(1 << ssid);
1739 		WARN_ON(cgroup_apply_control(scgrp));
1740 		cgroup_finalize_control(scgrp, 0);
1741 
1742 		/* rebind */
1743 		RCU_INIT_POINTER(scgrp->subsys[ssid], NULL);
1744 		rcu_assign_pointer(dcgrp->subsys[ssid], css);
1745 		ss->root = dst_root;
1746 		css->cgroup = dcgrp;
1747 
1748 		spin_lock_irq(&css_set_lock);
1749 		hash_for_each(css_set_table, i, cset, hlist)
1750 			list_move_tail(&cset->e_cset_node[ss->id],
1751 				       &dcgrp->e_csets[ss->id]);
1752 		spin_unlock_irq(&css_set_lock);
1753 
1754 		/* default hierarchy doesn't enable controllers by default */
1755 		dst_root->subsys_mask |= 1 << ssid;
1756 		if (dst_root == &cgrp_dfl_root) {
1757 			static_branch_enable(cgroup_subsys_on_dfl_key[ssid]);
1758 		} else {
1759 			dcgrp->subtree_control |= 1 << ssid;
1760 			static_branch_disable(cgroup_subsys_on_dfl_key[ssid]);
1761 		}
1762 
1763 		ret = cgroup_apply_control(dcgrp);
1764 		if (ret)
1765 			pr_warn("partial failure to rebind %s controller (err=%d)\n",
1766 				ss->name, ret);
1767 
1768 		if (ss->bind)
1769 			ss->bind(css);
1770 	} while_each_subsys_mask();
1771 
1772 	kernfs_activate(dcgrp->kn);
1773 	return 0;
1774 }
1775 
1776 int cgroup_show_path(struct seq_file *sf, struct kernfs_node *kf_node,
1777 		     struct kernfs_root *kf_root)
1778 {
1779 	int len = 0;
1780 	char *buf = NULL;
1781 	struct cgroup_root *kf_cgroot = cgroup_root_from_kf(kf_root);
1782 	struct cgroup *ns_cgroup;
1783 
1784 	buf = kmalloc(PATH_MAX, GFP_KERNEL);
1785 	if (!buf)
1786 		return -ENOMEM;
1787 
1788 	spin_lock_irq(&css_set_lock);
1789 	ns_cgroup = current_cgns_cgroup_from_root(kf_cgroot);
1790 	len = kernfs_path_from_node(kf_node, ns_cgroup->kn, buf, PATH_MAX);
1791 	spin_unlock_irq(&css_set_lock);
1792 
1793 	if (len >= PATH_MAX)
1794 		len = -ERANGE;
1795 	else if (len > 0) {
1796 		seq_escape(sf, buf, " \t\n\\");
1797 		len = 0;
1798 	}
1799 	kfree(buf);
1800 	return len;
1801 }
1802 
1803 enum cgroup2_param {
1804 	Opt_nsdelegate,
1805 	Opt_memory_localevents,
1806 	Opt_memory_recursiveprot,
1807 	nr__cgroup2_params
1808 };
1809 
1810 static const struct fs_parameter_spec cgroup2_fs_parameters[] = {
1811 	fsparam_flag("nsdelegate",		Opt_nsdelegate),
1812 	fsparam_flag("memory_localevents",	Opt_memory_localevents),
1813 	fsparam_flag("memory_recursiveprot",	Opt_memory_recursiveprot),
1814 	{}
1815 };
1816 
1817 static int cgroup2_parse_param(struct fs_context *fc, struct fs_parameter *param)
1818 {
1819 	struct cgroup_fs_context *ctx = cgroup_fc2context(fc);
1820 	struct fs_parse_result result;
1821 	int opt;
1822 
1823 	opt = fs_parse(fc, cgroup2_fs_parameters, param, &result);
1824 	if (opt < 0)
1825 		return opt;
1826 
1827 	switch (opt) {
1828 	case Opt_nsdelegate:
1829 		ctx->flags |= CGRP_ROOT_NS_DELEGATE;
1830 		return 0;
1831 	case Opt_memory_localevents:
1832 		ctx->flags |= CGRP_ROOT_MEMORY_LOCAL_EVENTS;
1833 		return 0;
1834 	case Opt_memory_recursiveprot:
1835 		ctx->flags |= CGRP_ROOT_MEMORY_RECURSIVE_PROT;
1836 		return 0;
1837 	}
1838 	return -EINVAL;
1839 }
1840 
1841 static void apply_cgroup_root_flags(unsigned int root_flags)
1842 {
1843 	if (current->nsproxy->cgroup_ns == &init_cgroup_ns) {
1844 		if (root_flags & CGRP_ROOT_NS_DELEGATE)
1845 			cgrp_dfl_root.flags |= CGRP_ROOT_NS_DELEGATE;
1846 		else
1847 			cgrp_dfl_root.flags &= ~CGRP_ROOT_NS_DELEGATE;
1848 
1849 		if (root_flags & CGRP_ROOT_MEMORY_LOCAL_EVENTS)
1850 			cgrp_dfl_root.flags |= CGRP_ROOT_MEMORY_LOCAL_EVENTS;
1851 		else
1852 			cgrp_dfl_root.flags &= ~CGRP_ROOT_MEMORY_LOCAL_EVENTS;
1853 
1854 		if (root_flags & CGRP_ROOT_MEMORY_RECURSIVE_PROT)
1855 			cgrp_dfl_root.flags |= CGRP_ROOT_MEMORY_RECURSIVE_PROT;
1856 		else
1857 			cgrp_dfl_root.flags &= ~CGRP_ROOT_MEMORY_RECURSIVE_PROT;
1858 	}
1859 }
1860 
1861 static int cgroup_show_options(struct seq_file *seq, struct kernfs_root *kf_root)
1862 {
1863 	if (cgrp_dfl_root.flags & CGRP_ROOT_NS_DELEGATE)
1864 		seq_puts(seq, ",nsdelegate");
1865 	if (cgrp_dfl_root.flags & CGRP_ROOT_MEMORY_LOCAL_EVENTS)
1866 		seq_puts(seq, ",memory_localevents");
1867 	if (cgrp_dfl_root.flags & CGRP_ROOT_MEMORY_RECURSIVE_PROT)
1868 		seq_puts(seq, ",memory_recursiveprot");
1869 	return 0;
1870 }
1871 
1872 static int cgroup_reconfigure(struct fs_context *fc)
1873 {
1874 	struct cgroup_fs_context *ctx = cgroup_fc2context(fc);
1875 
1876 	apply_cgroup_root_flags(ctx->flags);
1877 	return 0;
1878 }
1879 
1880 static void init_cgroup_housekeeping(struct cgroup *cgrp)
1881 {
1882 	struct cgroup_subsys *ss;
1883 	int ssid;
1884 
1885 	INIT_LIST_HEAD(&cgrp->self.sibling);
1886 	INIT_LIST_HEAD(&cgrp->self.children);
1887 	INIT_LIST_HEAD(&cgrp->cset_links);
1888 	INIT_LIST_HEAD(&cgrp->pidlists);
1889 	mutex_init(&cgrp->pidlist_mutex);
1890 	cgrp->self.cgroup = cgrp;
1891 	cgrp->self.flags |= CSS_ONLINE;
1892 	cgrp->dom_cgrp = cgrp;
1893 	cgrp->max_descendants = INT_MAX;
1894 	cgrp->max_depth = INT_MAX;
1895 	INIT_LIST_HEAD(&cgrp->rstat_css_list);
1896 	prev_cputime_init(&cgrp->prev_cputime);
1897 
1898 	for_each_subsys(ss, ssid)
1899 		INIT_LIST_HEAD(&cgrp->e_csets[ssid]);
1900 
1901 	init_waitqueue_head(&cgrp->offline_waitq);
1902 	INIT_WORK(&cgrp->release_agent_work, cgroup1_release_agent);
1903 }
1904 
1905 void init_cgroup_root(struct cgroup_fs_context *ctx)
1906 {
1907 	struct cgroup_root *root = ctx->root;
1908 	struct cgroup *cgrp = &root->cgrp;
1909 
1910 	INIT_LIST_HEAD(&root->root_list);
1911 	atomic_set(&root->nr_cgrps, 1);
1912 	cgrp->root = root;
1913 	init_cgroup_housekeeping(cgrp);
1914 
1915 	root->flags = ctx->flags;
1916 	if (ctx->release_agent)
1917 		strscpy(root->release_agent_path, ctx->release_agent, PATH_MAX);
1918 	if (ctx->name)
1919 		strscpy(root->name, ctx->name, MAX_CGROUP_ROOT_NAMELEN);
1920 	if (ctx->cpuset_clone_children)
1921 		set_bit(CGRP_CPUSET_CLONE_CHILDREN, &root->cgrp.flags);
1922 }
1923 
1924 int cgroup_setup_root(struct cgroup_root *root, u16 ss_mask)
1925 {
1926 	LIST_HEAD(tmp_links);
1927 	struct cgroup *root_cgrp = &root->cgrp;
1928 	struct kernfs_syscall_ops *kf_sops;
1929 	struct css_set *cset;
1930 	int i, ret;
1931 
1932 	lockdep_assert_held(&cgroup_mutex);
1933 
1934 	ret = percpu_ref_init(&root_cgrp->self.refcnt, css_release,
1935 			      0, GFP_KERNEL);
1936 	if (ret)
1937 		goto out;
1938 
1939 	/*
1940 	 * We're accessing css_set_count without locking css_set_lock here,
1941 	 * but that's OK - it can only be increased by someone holding
1942 	 * cgroup_lock, and that's us.  Later rebinding may disable
1943 	 * controllers on the default hierarchy and thus create new csets,
1944 	 * which can't be more than the existing ones.  Allocate 2x.
1945 	 */
1946 	ret = allocate_cgrp_cset_links(2 * css_set_count, &tmp_links);
1947 	if (ret)
1948 		goto cancel_ref;
1949 
1950 	ret = cgroup_init_root_id(root);
1951 	if (ret)
1952 		goto cancel_ref;
1953 
1954 	kf_sops = root == &cgrp_dfl_root ?
1955 		&cgroup_kf_syscall_ops : &cgroup1_kf_syscall_ops;
1956 
1957 	root->kf_root = kernfs_create_root(kf_sops,
1958 					   KERNFS_ROOT_CREATE_DEACTIVATED |
1959 					   KERNFS_ROOT_SUPPORT_EXPORTOP |
1960 					   KERNFS_ROOT_SUPPORT_USER_XATTR,
1961 					   root_cgrp);
1962 	if (IS_ERR(root->kf_root)) {
1963 		ret = PTR_ERR(root->kf_root);
1964 		goto exit_root_id;
1965 	}
1966 	root_cgrp->kn = root->kf_root->kn;
1967 	WARN_ON_ONCE(cgroup_ino(root_cgrp) != 1);
1968 	root_cgrp->ancestor_ids[0] = cgroup_id(root_cgrp);
1969 
1970 	ret = css_populate_dir(&root_cgrp->self);
1971 	if (ret)
1972 		goto destroy_root;
1973 
1974 	ret = rebind_subsystems(root, ss_mask);
1975 	if (ret)
1976 		goto destroy_root;
1977 
1978 	ret = cgroup_bpf_inherit(root_cgrp);
1979 	WARN_ON_ONCE(ret);
1980 
1981 	trace_cgroup_setup_root(root);
1982 
1983 	/*
1984 	 * There must be no failure case after here, since rebinding takes
1985 	 * care of subsystems' refcounts, which are explicitly dropped in
1986 	 * the failure exit path.
1987 	 */
1988 	list_add(&root->root_list, &cgroup_roots);
1989 	cgroup_root_count++;
1990 
1991 	/*
1992 	 * Link the root cgroup in this hierarchy into all the css_set
1993 	 * objects.
1994 	 */
1995 	spin_lock_irq(&css_set_lock);
1996 	hash_for_each(css_set_table, i, cset, hlist) {
1997 		link_css_set(&tmp_links, cset, root_cgrp);
1998 		if (css_set_populated(cset))
1999 			cgroup_update_populated(root_cgrp, true);
2000 	}
2001 	spin_unlock_irq(&css_set_lock);
2002 
2003 	BUG_ON(!list_empty(&root_cgrp->self.children));
2004 	BUG_ON(atomic_read(&root->nr_cgrps) != 1);
2005 
2006 	ret = 0;
2007 	goto out;
2008 
2009 destroy_root:
2010 	kernfs_destroy_root(root->kf_root);
2011 	root->kf_root = NULL;
2012 exit_root_id:
2013 	cgroup_exit_root_id(root);
2014 cancel_ref:
2015 	percpu_ref_exit(&root_cgrp->self.refcnt);
2016 out:
2017 	free_cgrp_cset_links(&tmp_links);
2018 	return ret;
2019 }
2020 
2021 int cgroup_do_get_tree(struct fs_context *fc)
2022 {
2023 	struct cgroup_fs_context *ctx = cgroup_fc2context(fc);
2024 	int ret;
2025 
2026 	ctx->kfc.root = ctx->root->kf_root;
2027 	if (fc->fs_type == &cgroup2_fs_type)
2028 		ctx->kfc.magic = CGROUP2_SUPER_MAGIC;
2029 	else
2030 		ctx->kfc.magic = CGROUP_SUPER_MAGIC;
2031 	ret = kernfs_get_tree(fc);
2032 
2033 	/*
2034 	 * In non-init cgroup namespace, instead of root cgroup's dentry,
2035 	 * we return the dentry corresponding to the cgroupns->root_cgrp.
2036 	 */
2037 	if (!ret && ctx->ns != &init_cgroup_ns) {
2038 		struct dentry *nsdentry;
2039 		struct super_block *sb = fc->root->d_sb;
2040 		struct cgroup *cgrp;
2041 
2042 		mutex_lock(&cgroup_mutex);
2043 		spin_lock_irq(&css_set_lock);
2044 
2045 		cgrp = cset_cgroup_from_root(ctx->ns->root_cset, ctx->root);
2046 
2047 		spin_unlock_irq(&css_set_lock);
2048 		mutex_unlock(&cgroup_mutex);
2049 
2050 		nsdentry = kernfs_node_dentry(cgrp->kn, sb);
2051 		dput(fc->root);
2052 		if (IS_ERR(nsdentry)) {
2053 			deactivate_locked_super(sb);
2054 			ret = PTR_ERR(nsdentry);
2055 			nsdentry = NULL;
2056 		}
2057 		fc->root = nsdentry;
2058 	}
2059 
2060 	if (!ctx->kfc.new_sb_created)
2061 		cgroup_put(&ctx->root->cgrp);
2062 
2063 	return ret;
2064 }
2065 
2066 /*
2067  * Destroy a cgroup filesystem context.
2068  */
2069 static void cgroup_fs_context_free(struct fs_context *fc)
2070 {
2071 	struct cgroup_fs_context *ctx = cgroup_fc2context(fc);
2072 
2073 	kfree(ctx->name);
2074 	kfree(ctx->release_agent);
2075 	put_cgroup_ns(ctx->ns);
2076 	kernfs_free_fs_context(fc);
2077 	kfree(ctx);
2078 }
2079 
2080 static int cgroup_get_tree(struct fs_context *fc)
2081 {
2082 	struct cgroup_fs_context *ctx = cgroup_fc2context(fc);
2083 	int ret;
2084 
2085 	cgrp_dfl_visible = true;
2086 	cgroup_get_live(&cgrp_dfl_root.cgrp);
2087 	ctx->root = &cgrp_dfl_root;
2088 
2089 	ret = cgroup_do_get_tree(fc);
2090 	if (!ret)
2091 		apply_cgroup_root_flags(ctx->flags);
2092 	return ret;
2093 }
2094 
2095 static const struct fs_context_operations cgroup_fs_context_ops = {
2096 	.free		= cgroup_fs_context_free,
2097 	.parse_param	= cgroup2_parse_param,
2098 	.get_tree	= cgroup_get_tree,
2099 	.reconfigure	= cgroup_reconfigure,
2100 };
2101 
2102 static const struct fs_context_operations cgroup1_fs_context_ops = {
2103 	.free		= cgroup_fs_context_free,
2104 	.parse_param	= cgroup1_parse_param,
2105 	.get_tree	= cgroup1_get_tree,
2106 	.reconfigure	= cgroup1_reconfigure,
2107 };
2108 
2109 /*
2110  * Initialise the cgroup filesystem creation/reconfiguration context.  Notably,
2111  * we select the namespace we're going to use.
2112  */
2113 static int cgroup_init_fs_context(struct fs_context *fc)
2114 {
2115 	struct cgroup_fs_context *ctx;
2116 
2117 	ctx = kzalloc(sizeof(struct cgroup_fs_context), GFP_KERNEL);
2118 	if (!ctx)
2119 		return -ENOMEM;
2120 
2121 	ctx->ns = current->nsproxy->cgroup_ns;
2122 	get_cgroup_ns(ctx->ns);
2123 	fc->fs_private = &ctx->kfc;
2124 	if (fc->fs_type == &cgroup2_fs_type)
2125 		fc->ops = &cgroup_fs_context_ops;
2126 	else
2127 		fc->ops = &cgroup1_fs_context_ops;
2128 	put_user_ns(fc->user_ns);
2129 	fc->user_ns = get_user_ns(ctx->ns->user_ns);
2130 	fc->global = true;
2131 	return 0;
2132 }
2133 
2134 static void cgroup_kill_sb(struct super_block *sb)
2135 {
2136 	struct kernfs_root *kf_root = kernfs_root_from_sb(sb);
2137 	struct cgroup_root *root = cgroup_root_from_kf(kf_root);
2138 
2139 	/*
2140 	 * If @root doesn't have any children, start killing it.
2141 	 * This prevents new mounts by disabling percpu_ref_tryget_live().
2142 	 * cgroup_mount() may wait for @root's release.
2143 	 *
2144 	 * And don't kill the default root.
2145 	 */
2146 	if (list_empty(&root->cgrp.self.children) && root != &cgrp_dfl_root &&
2147 	    !percpu_ref_is_dying(&root->cgrp.self.refcnt))
2148 		percpu_ref_kill(&root->cgrp.self.refcnt);
2149 	cgroup_put(&root->cgrp);
2150 	kernfs_kill_sb(sb);
2151 }
2152 
2153 struct file_system_type cgroup_fs_type = {
2154 	.name			= "cgroup",
2155 	.init_fs_context	= cgroup_init_fs_context,
2156 	.parameters		= cgroup1_fs_parameters,
2157 	.kill_sb		= cgroup_kill_sb,
2158 	.fs_flags		= FS_USERNS_MOUNT,
2159 };
2160 
2161 static struct file_system_type cgroup2_fs_type = {
2162 	.name			= "cgroup2",
2163 	.init_fs_context	= cgroup_init_fs_context,
2164 	.parameters		= cgroup2_fs_parameters,
2165 	.kill_sb		= cgroup_kill_sb,
2166 	.fs_flags		= FS_USERNS_MOUNT,
2167 };
2168 
2169 #ifdef CONFIG_CPUSETS
2170 static const struct fs_context_operations cpuset_fs_context_ops = {
2171 	.get_tree	= cgroup1_get_tree,
2172 	.free		= cgroup_fs_context_free,
2173 };
2174 
2175 /*
2176  * This is ugly, but preserves the userspace API for existing cpuset
2177  * users. If someone tries to mount the "cpuset" filesystem, we
2178  * silently switch it to mount "cgroup" instead
2179  */
2180 static int cpuset_init_fs_context(struct fs_context *fc)
2181 {
2182 	char *agent = kstrdup("/sbin/cpuset_release_agent", GFP_USER);
2183 	struct cgroup_fs_context *ctx;
2184 	int err;
2185 
2186 	err = cgroup_init_fs_context(fc);
2187 	if (err) {
2188 		kfree(agent);
2189 		return err;
2190 	}
2191 
2192 	fc->ops = &cpuset_fs_context_ops;
2193 
2194 	ctx = cgroup_fc2context(fc);
2195 	ctx->subsys_mask = 1 << cpuset_cgrp_id;
2196 	ctx->flags |= CGRP_ROOT_NOPREFIX;
2197 	ctx->release_agent = agent;
2198 
2199 	get_filesystem(&cgroup_fs_type);
2200 	put_filesystem(fc->fs_type);
2201 	fc->fs_type = &cgroup_fs_type;
2202 
2203 	return 0;
2204 }
2205 
2206 static struct file_system_type cpuset_fs_type = {
2207 	.name			= "cpuset",
2208 	.init_fs_context	= cpuset_init_fs_context,
2209 	.fs_flags		= FS_USERNS_MOUNT,
2210 };
2211 #endif
2212 
2213 int cgroup_path_ns_locked(struct cgroup *cgrp, char *buf, size_t buflen,
2214 			  struct cgroup_namespace *ns)
2215 {
2216 	struct cgroup *root = cset_cgroup_from_root(ns->root_cset, cgrp->root);
2217 
2218 	return kernfs_path_from_node(cgrp->kn, root->kn, buf, buflen);
2219 }
2220 
2221 int cgroup_path_ns(struct cgroup *cgrp, char *buf, size_t buflen,
2222 		   struct cgroup_namespace *ns)
2223 {
2224 	int ret;
2225 
2226 	mutex_lock(&cgroup_mutex);
2227 	spin_lock_irq(&css_set_lock);
2228 
2229 	ret = cgroup_path_ns_locked(cgrp, buf, buflen, ns);
2230 
2231 	spin_unlock_irq(&css_set_lock);
2232 	mutex_unlock(&cgroup_mutex);
2233 
2234 	return ret;
2235 }
2236 EXPORT_SYMBOL_GPL(cgroup_path_ns);
2237 
2238 /**
2239  * task_cgroup_path - cgroup path of a task in the first cgroup hierarchy
2240  * @task: target task
2241  * @buf: the buffer to write the path into
2242  * @buflen: the length of the buffer
2243  *
2244  * Determine @task's cgroup on the first (the one with the lowest non-zero
2245  * hierarchy_id) cgroup hierarchy and copy its path into @buf.  This
2246  * function grabs cgroup_mutex and shouldn't be used inside locks used by
2247  * cgroup controller callbacks.
2248  *
2249  * Return value is the same as kernfs_path().
2250  */
2251 int task_cgroup_path(struct task_struct *task, char *buf, size_t buflen)
2252 {
2253 	struct cgroup_root *root;
2254 	struct cgroup *cgrp;
2255 	int hierarchy_id = 1;
2256 	int ret;
2257 
2258 	mutex_lock(&cgroup_mutex);
2259 	spin_lock_irq(&css_set_lock);
2260 
2261 	root = idr_get_next(&cgroup_hierarchy_idr, &hierarchy_id);
2262 
2263 	if (root) {
2264 		cgrp = task_cgroup_from_root(task, root);
2265 		ret = cgroup_path_ns_locked(cgrp, buf, buflen, &init_cgroup_ns);
2266 	} else {
2267 		/* if no hierarchy exists, everyone is in "/" */
2268 		ret = strlcpy(buf, "/", buflen);
2269 	}
2270 
2271 	spin_unlock_irq(&css_set_lock);
2272 	mutex_unlock(&cgroup_mutex);
2273 	return ret;
2274 }
2275 EXPORT_SYMBOL_GPL(task_cgroup_path);
2276 
2277 /**
2278  * cgroup_migrate_add_task - add a migration target task to a migration context
2279  * @task: target task
2280  * @mgctx: target migration context
2281  *
2282  * Add @task, which is a migration target, to @mgctx->tset.  This function
2283  * becomes noop if @task doesn't need to be migrated.  @task's css_set
2284  * should have been added as a migration source and @task->cg_list will be
2285  * moved from the css_set's tasks list to mg_tasks one.
2286  */
2287 static void cgroup_migrate_add_task(struct task_struct *task,
2288 				    struct cgroup_mgctx *mgctx)
2289 {
2290 	struct css_set *cset;
2291 
2292 	lockdep_assert_held(&css_set_lock);
2293 
2294 	/* @task either already exited or can't exit until the end */
2295 	if (task->flags & PF_EXITING)
2296 		return;
2297 
2298 	/* cgroup_threadgroup_rwsem protects racing against forks */
2299 	WARN_ON_ONCE(list_empty(&task->cg_list));
2300 
2301 	cset = task_css_set(task);
2302 	if (!cset->mg_src_cgrp)
2303 		return;
2304 
2305 	mgctx->tset.nr_tasks++;
2306 
2307 	list_move_tail(&task->cg_list, &cset->mg_tasks);
2308 	if (list_empty(&cset->mg_node))
2309 		list_add_tail(&cset->mg_node,
2310 			      &mgctx->tset.src_csets);
2311 	if (list_empty(&cset->mg_dst_cset->mg_node))
2312 		list_add_tail(&cset->mg_dst_cset->mg_node,
2313 			      &mgctx->tset.dst_csets);
2314 }
2315 
2316 /**
2317  * cgroup_taskset_first - reset taskset and return the first task
2318  * @tset: taskset of interest
2319  * @dst_cssp: output variable for the destination css
2320  *
2321  * @tset iteration is initialized and the first task is returned.
2322  */
2323 struct task_struct *cgroup_taskset_first(struct cgroup_taskset *tset,
2324 					 struct cgroup_subsys_state **dst_cssp)
2325 {
2326 	tset->cur_cset = list_first_entry(tset->csets, struct css_set, mg_node);
2327 	tset->cur_task = NULL;
2328 
2329 	return cgroup_taskset_next(tset, dst_cssp);
2330 }
2331 
2332 /**
2333  * cgroup_taskset_next - iterate to the next task in taskset
2334  * @tset: taskset of interest
2335  * @dst_cssp: output variable for the destination css
2336  *
2337  * Return the next task in @tset.  Iteration must have been initialized
2338  * with cgroup_taskset_first().
2339  */
2340 struct task_struct *cgroup_taskset_next(struct cgroup_taskset *tset,
2341 					struct cgroup_subsys_state **dst_cssp)
2342 {
2343 	struct css_set *cset = tset->cur_cset;
2344 	struct task_struct *task = tset->cur_task;
2345 
2346 	while (&cset->mg_node != tset->csets) {
2347 		if (!task)
2348 			task = list_first_entry(&cset->mg_tasks,
2349 						struct task_struct, cg_list);
2350 		else
2351 			task = list_next_entry(task, cg_list);
2352 
2353 		if (&task->cg_list != &cset->mg_tasks) {
2354 			tset->cur_cset = cset;
2355 			tset->cur_task = task;
2356 
2357 			/*
2358 			 * This function may be called both before and
2359 			 * after cgroup_taskset_migrate().  The two cases
2360 			 * can be distinguished by looking at whether @cset
2361 			 * has its ->mg_dst_cset set.
2362 			 */
2363 			if (cset->mg_dst_cset)
2364 				*dst_cssp = cset->mg_dst_cset->subsys[tset->ssid];
2365 			else
2366 				*dst_cssp = cset->subsys[tset->ssid];
2367 
2368 			return task;
2369 		}
2370 
2371 		cset = list_next_entry(cset, mg_node);
2372 		task = NULL;
2373 	}
2374 
2375 	return NULL;
2376 }
2377 
2378 /**
2379  * cgroup_taskset_migrate - migrate a taskset
2380  * @mgctx: migration context
2381  *
2382  * Migrate tasks in @mgctx as setup by migration preparation functions.
2383  * This function fails iff one of the ->can_attach callbacks fails and
2384  * guarantees that either all or none of the tasks in @mgctx are migrated.
2385  * @mgctx is consumed regardless of success.
2386  */
2387 static int cgroup_migrate_execute(struct cgroup_mgctx *mgctx)
2388 {
2389 	struct cgroup_taskset *tset = &mgctx->tset;
2390 	struct cgroup_subsys *ss;
2391 	struct task_struct *task, *tmp_task;
2392 	struct css_set *cset, *tmp_cset;
2393 	int ssid, failed_ssid, ret;
2394 
2395 	/* check that we can legitimately attach to the cgroup */
2396 	if (tset->nr_tasks) {
2397 		do_each_subsys_mask(ss, ssid, mgctx->ss_mask) {
2398 			if (ss->can_attach) {
2399 				tset->ssid = ssid;
2400 				ret = ss->can_attach(tset);
2401 				if (ret) {
2402 					failed_ssid = ssid;
2403 					goto out_cancel_attach;
2404 				}
2405 			}
2406 		} while_each_subsys_mask();
2407 	}
2408 
2409 	/*
2410 	 * Now that we're guaranteed success, proceed to move all tasks to
2411 	 * the new cgroup.  There are no failure cases after here, so this
2412 	 * is the commit point.
2413 	 */
2414 	spin_lock_irq(&css_set_lock);
2415 	list_for_each_entry(cset, &tset->src_csets, mg_node) {
2416 		list_for_each_entry_safe(task, tmp_task, &cset->mg_tasks, cg_list) {
2417 			struct css_set *from_cset = task_css_set(task);
2418 			struct css_set *to_cset = cset->mg_dst_cset;
2419 
2420 			get_css_set(to_cset);
2421 			to_cset->nr_tasks++;
2422 			css_set_move_task(task, from_cset, to_cset, true);
2423 			from_cset->nr_tasks--;
2424 			/*
2425 			 * If the source or destination cgroup is frozen,
2426 			 * the task might require to change its state.
2427 			 */
2428 			cgroup_freezer_migrate_task(task, from_cset->dfl_cgrp,
2429 						    to_cset->dfl_cgrp);
2430 			put_css_set_locked(from_cset);
2431 
2432 		}
2433 	}
2434 	spin_unlock_irq(&css_set_lock);
2435 
2436 	/*
2437 	 * Migration is committed, all target tasks are now on dst_csets.
2438 	 * Nothing is sensitive to fork() after this point.  Notify
2439 	 * controllers that migration is complete.
2440 	 */
2441 	tset->csets = &tset->dst_csets;
2442 
2443 	if (tset->nr_tasks) {
2444 		do_each_subsys_mask(ss, ssid, mgctx->ss_mask) {
2445 			if (ss->attach) {
2446 				tset->ssid = ssid;
2447 				ss->attach(tset);
2448 			}
2449 		} while_each_subsys_mask();
2450 	}
2451 
2452 	ret = 0;
2453 	goto out_release_tset;
2454 
2455 out_cancel_attach:
2456 	if (tset->nr_tasks) {
2457 		do_each_subsys_mask(ss, ssid, mgctx->ss_mask) {
2458 			if (ssid == failed_ssid)
2459 				break;
2460 			if (ss->cancel_attach) {
2461 				tset->ssid = ssid;
2462 				ss->cancel_attach(tset);
2463 			}
2464 		} while_each_subsys_mask();
2465 	}
2466 out_release_tset:
2467 	spin_lock_irq(&css_set_lock);
2468 	list_splice_init(&tset->dst_csets, &tset->src_csets);
2469 	list_for_each_entry_safe(cset, tmp_cset, &tset->src_csets, mg_node) {
2470 		list_splice_tail_init(&cset->mg_tasks, &cset->tasks);
2471 		list_del_init(&cset->mg_node);
2472 	}
2473 	spin_unlock_irq(&css_set_lock);
2474 
2475 	/*
2476 	 * Re-initialize the cgroup_taskset structure in case it is reused
2477 	 * again in another cgroup_migrate_add_task()/cgroup_migrate_execute()
2478 	 * iteration.
2479 	 */
2480 	tset->nr_tasks = 0;
2481 	tset->csets    = &tset->src_csets;
2482 	return ret;
2483 }
2484 
2485 /**
2486  * cgroup_migrate_vet_dst - verify whether a cgroup can be migration destination
2487  * @dst_cgrp: destination cgroup to test
2488  *
2489  * On the default hierarchy, except for the mixable, (possible) thread root
2490  * and threaded cgroups, subtree_control must be zero for migration
2491  * destination cgroups with tasks so that child cgroups don't compete
2492  * against tasks.
2493  */
2494 int cgroup_migrate_vet_dst(struct cgroup *dst_cgrp)
2495 {
2496 	/* v1 doesn't have any restriction */
2497 	if (!cgroup_on_dfl(dst_cgrp))
2498 		return 0;
2499 
2500 	/* verify @dst_cgrp can host resources */
2501 	if (!cgroup_is_valid_domain(dst_cgrp->dom_cgrp))
2502 		return -EOPNOTSUPP;
2503 
2504 	/* mixables don't care */
2505 	if (cgroup_is_mixable(dst_cgrp))
2506 		return 0;
2507 
2508 	/*
2509 	 * If @dst_cgrp is already or can become a thread root or is
2510 	 * threaded, it doesn't matter.
2511 	 */
2512 	if (cgroup_can_be_thread_root(dst_cgrp) || cgroup_is_threaded(dst_cgrp))
2513 		return 0;
2514 
2515 	/* apply no-internal-process constraint */
2516 	if (dst_cgrp->subtree_control)
2517 		return -EBUSY;
2518 
2519 	return 0;
2520 }
2521 
2522 /**
2523  * cgroup_migrate_finish - cleanup after attach
2524  * @mgctx: migration context
2525  *
2526  * Undo cgroup_migrate_add_src() and cgroup_migrate_prepare_dst().  See
2527  * those functions for details.
2528  */
2529 void cgroup_migrate_finish(struct cgroup_mgctx *mgctx)
2530 {
2531 	LIST_HEAD(preloaded);
2532 	struct css_set *cset, *tmp_cset;
2533 
2534 	lockdep_assert_held(&cgroup_mutex);
2535 
2536 	spin_lock_irq(&css_set_lock);
2537 
2538 	list_splice_tail_init(&mgctx->preloaded_src_csets, &preloaded);
2539 	list_splice_tail_init(&mgctx->preloaded_dst_csets, &preloaded);
2540 
2541 	list_for_each_entry_safe(cset, tmp_cset, &preloaded, mg_preload_node) {
2542 		cset->mg_src_cgrp = NULL;
2543 		cset->mg_dst_cgrp = NULL;
2544 		cset->mg_dst_cset = NULL;
2545 		list_del_init(&cset->mg_preload_node);
2546 		put_css_set_locked(cset);
2547 	}
2548 
2549 	spin_unlock_irq(&css_set_lock);
2550 }
2551 
2552 /**
2553  * cgroup_migrate_add_src - add a migration source css_set
2554  * @src_cset: the source css_set to add
2555  * @dst_cgrp: the destination cgroup
2556  * @mgctx: migration context
2557  *
2558  * Tasks belonging to @src_cset are about to be migrated to @dst_cgrp.  Pin
2559  * @src_cset and add it to @mgctx->src_csets, which should later be cleaned
2560  * up by cgroup_migrate_finish().
2561  *
2562  * This function may be called without holding cgroup_threadgroup_rwsem
2563  * even if the target is a process.  Threads may be created and destroyed
2564  * but as long as cgroup_mutex is not dropped, no new css_set can be put
2565  * into play and the preloaded css_sets are guaranteed to cover all
2566  * migrations.
2567  */
2568 void cgroup_migrate_add_src(struct css_set *src_cset,
2569 			    struct cgroup *dst_cgrp,
2570 			    struct cgroup_mgctx *mgctx)
2571 {
2572 	struct cgroup *src_cgrp;
2573 
2574 	lockdep_assert_held(&cgroup_mutex);
2575 	lockdep_assert_held(&css_set_lock);
2576 
2577 	/*
2578 	 * If ->dead, @src_set is associated with one or more dead cgroups
2579 	 * and doesn't contain any migratable tasks.  Ignore it early so
2580 	 * that the rest of migration path doesn't get confused by it.
2581 	 */
2582 	if (src_cset->dead)
2583 		return;
2584 
2585 	src_cgrp = cset_cgroup_from_root(src_cset, dst_cgrp->root);
2586 
2587 	if (!list_empty(&src_cset->mg_preload_node))
2588 		return;
2589 
2590 	WARN_ON(src_cset->mg_src_cgrp);
2591 	WARN_ON(src_cset->mg_dst_cgrp);
2592 	WARN_ON(!list_empty(&src_cset->mg_tasks));
2593 	WARN_ON(!list_empty(&src_cset->mg_node));
2594 
2595 	src_cset->mg_src_cgrp = src_cgrp;
2596 	src_cset->mg_dst_cgrp = dst_cgrp;
2597 	get_css_set(src_cset);
2598 	list_add_tail(&src_cset->mg_preload_node, &mgctx->preloaded_src_csets);
2599 }
2600 
2601 /**
2602  * cgroup_migrate_prepare_dst - prepare destination css_sets for migration
2603  * @mgctx: migration context
2604  *
2605  * Tasks are about to be moved and all the source css_sets have been
2606  * preloaded to @mgctx->preloaded_src_csets.  This function looks up and
2607  * pins all destination css_sets, links each to its source, and append them
2608  * to @mgctx->preloaded_dst_csets.
2609  *
2610  * This function must be called after cgroup_migrate_add_src() has been
2611  * called on each migration source css_set.  After migration is performed
2612  * using cgroup_migrate(), cgroup_migrate_finish() must be called on
2613  * @mgctx.
2614  */
2615 int cgroup_migrate_prepare_dst(struct cgroup_mgctx *mgctx)
2616 {
2617 	struct css_set *src_cset, *tmp_cset;
2618 
2619 	lockdep_assert_held(&cgroup_mutex);
2620 
2621 	/* look up the dst cset for each src cset and link it to src */
2622 	list_for_each_entry_safe(src_cset, tmp_cset, &mgctx->preloaded_src_csets,
2623 				 mg_preload_node) {
2624 		struct css_set *dst_cset;
2625 		struct cgroup_subsys *ss;
2626 		int ssid;
2627 
2628 		dst_cset = find_css_set(src_cset, src_cset->mg_dst_cgrp);
2629 		if (!dst_cset)
2630 			return -ENOMEM;
2631 
2632 		WARN_ON_ONCE(src_cset->mg_dst_cset || dst_cset->mg_dst_cset);
2633 
2634 		/*
2635 		 * If src cset equals dst, it's noop.  Drop the src.
2636 		 * cgroup_migrate() will skip the cset too.  Note that we
2637 		 * can't handle src == dst as some nodes are used by both.
2638 		 */
2639 		if (src_cset == dst_cset) {
2640 			src_cset->mg_src_cgrp = NULL;
2641 			src_cset->mg_dst_cgrp = NULL;
2642 			list_del_init(&src_cset->mg_preload_node);
2643 			put_css_set(src_cset);
2644 			put_css_set(dst_cset);
2645 			continue;
2646 		}
2647 
2648 		src_cset->mg_dst_cset = dst_cset;
2649 
2650 		if (list_empty(&dst_cset->mg_preload_node))
2651 			list_add_tail(&dst_cset->mg_preload_node,
2652 				      &mgctx->preloaded_dst_csets);
2653 		else
2654 			put_css_set(dst_cset);
2655 
2656 		for_each_subsys(ss, ssid)
2657 			if (src_cset->subsys[ssid] != dst_cset->subsys[ssid])
2658 				mgctx->ss_mask |= 1 << ssid;
2659 	}
2660 
2661 	return 0;
2662 }
2663 
2664 /**
2665  * cgroup_migrate - migrate a process or task to a cgroup
2666  * @leader: the leader of the process or the task to migrate
2667  * @threadgroup: whether @leader points to the whole process or a single task
2668  * @mgctx: migration context
2669  *
2670  * Migrate a process or task denoted by @leader.  If migrating a process,
2671  * the caller must be holding cgroup_threadgroup_rwsem.  The caller is also
2672  * responsible for invoking cgroup_migrate_add_src() and
2673  * cgroup_migrate_prepare_dst() on the targets before invoking this
2674  * function and following up with cgroup_migrate_finish().
2675  *
2676  * As long as a controller's ->can_attach() doesn't fail, this function is
2677  * guaranteed to succeed.  This means that, excluding ->can_attach()
2678  * failure, when migrating multiple targets, the success or failure can be
2679  * decided for all targets by invoking group_migrate_prepare_dst() before
2680  * actually starting migrating.
2681  */
2682 int cgroup_migrate(struct task_struct *leader, bool threadgroup,
2683 		   struct cgroup_mgctx *mgctx)
2684 {
2685 	struct task_struct *task;
2686 
2687 	/*
2688 	 * Prevent freeing of tasks while we take a snapshot. Tasks that are
2689 	 * already PF_EXITING could be freed from underneath us unless we
2690 	 * take an rcu_read_lock.
2691 	 */
2692 	spin_lock_irq(&css_set_lock);
2693 	rcu_read_lock();
2694 	task = leader;
2695 	do {
2696 		cgroup_migrate_add_task(task, mgctx);
2697 		if (!threadgroup)
2698 			break;
2699 	} while_each_thread(leader, task);
2700 	rcu_read_unlock();
2701 	spin_unlock_irq(&css_set_lock);
2702 
2703 	return cgroup_migrate_execute(mgctx);
2704 }
2705 
2706 /**
2707  * cgroup_attach_task - attach a task or a whole threadgroup to a cgroup
2708  * @dst_cgrp: the cgroup to attach to
2709  * @leader: the task or the leader of the threadgroup to be attached
2710  * @threadgroup: attach the whole threadgroup?
2711  *
2712  * Call holding cgroup_mutex and cgroup_threadgroup_rwsem.
2713  */
2714 int cgroup_attach_task(struct cgroup *dst_cgrp, struct task_struct *leader,
2715 		       bool threadgroup)
2716 {
2717 	DEFINE_CGROUP_MGCTX(mgctx);
2718 	struct task_struct *task;
2719 	int ret = 0;
2720 
2721 	/* look up all src csets */
2722 	spin_lock_irq(&css_set_lock);
2723 	rcu_read_lock();
2724 	task = leader;
2725 	do {
2726 		cgroup_migrate_add_src(task_css_set(task), dst_cgrp, &mgctx);
2727 		if (!threadgroup)
2728 			break;
2729 	} while_each_thread(leader, task);
2730 	rcu_read_unlock();
2731 	spin_unlock_irq(&css_set_lock);
2732 
2733 	/* prepare dst csets and commit */
2734 	ret = cgroup_migrate_prepare_dst(&mgctx);
2735 	if (!ret)
2736 		ret = cgroup_migrate(leader, threadgroup, &mgctx);
2737 
2738 	cgroup_migrate_finish(&mgctx);
2739 
2740 	if (!ret)
2741 		TRACE_CGROUP_PATH(attach_task, dst_cgrp, leader, threadgroup);
2742 
2743 	return ret;
2744 }
2745 
2746 struct task_struct *cgroup_procs_write_start(char *buf, bool threadgroup,
2747 					     bool *locked)
2748 	__acquires(&cgroup_threadgroup_rwsem)
2749 {
2750 	struct task_struct *tsk;
2751 	pid_t pid;
2752 
2753 	if (kstrtoint(strstrip(buf), 0, &pid) || pid < 0)
2754 		return ERR_PTR(-EINVAL);
2755 
2756 	/*
2757 	 * If we migrate a single thread, we don't care about threadgroup
2758 	 * stability. If the thread is `current`, it won't exit(2) under our
2759 	 * hands or change PID through exec(2). We exclude
2760 	 * cgroup_update_dfl_csses and other cgroup_{proc,thread}s_write
2761 	 * callers by cgroup_mutex.
2762 	 * Therefore, we can skip the global lock.
2763 	 */
2764 	lockdep_assert_held(&cgroup_mutex);
2765 	if (pid || threadgroup) {
2766 		percpu_down_write(&cgroup_threadgroup_rwsem);
2767 		*locked = true;
2768 	} else {
2769 		*locked = false;
2770 	}
2771 
2772 	rcu_read_lock();
2773 	if (pid) {
2774 		tsk = find_task_by_vpid(pid);
2775 		if (!tsk) {
2776 			tsk = ERR_PTR(-ESRCH);
2777 			goto out_unlock_threadgroup;
2778 		}
2779 	} else {
2780 		tsk = current;
2781 	}
2782 
2783 	if (threadgroup)
2784 		tsk = tsk->group_leader;
2785 
2786 	/*
2787 	 * kthreads may acquire PF_NO_SETAFFINITY during initialization.
2788 	 * If userland migrates such a kthread to a non-root cgroup, it can
2789 	 * become trapped in a cpuset, or RT kthread may be born in a
2790 	 * cgroup with no rt_runtime allocated.  Just say no.
2791 	 */
2792 	if (tsk->no_cgroup_migration || (tsk->flags & PF_NO_SETAFFINITY)) {
2793 		tsk = ERR_PTR(-EINVAL);
2794 		goto out_unlock_threadgroup;
2795 	}
2796 
2797 	get_task_struct(tsk);
2798 	goto out_unlock_rcu;
2799 
2800 out_unlock_threadgroup:
2801 	if (*locked) {
2802 		percpu_up_write(&cgroup_threadgroup_rwsem);
2803 		*locked = false;
2804 	}
2805 out_unlock_rcu:
2806 	rcu_read_unlock();
2807 	return tsk;
2808 }
2809 
2810 void cgroup_procs_write_finish(struct task_struct *task, bool locked)
2811 	__releases(&cgroup_threadgroup_rwsem)
2812 {
2813 	struct cgroup_subsys *ss;
2814 	int ssid;
2815 
2816 	/* release reference from cgroup_procs_write_start() */
2817 	put_task_struct(task);
2818 
2819 	if (locked)
2820 		percpu_up_write(&cgroup_threadgroup_rwsem);
2821 	for_each_subsys(ss, ssid)
2822 		if (ss->post_attach)
2823 			ss->post_attach();
2824 }
2825 
2826 static void cgroup_print_ss_mask(struct seq_file *seq, u16 ss_mask)
2827 {
2828 	struct cgroup_subsys *ss;
2829 	bool printed = false;
2830 	int ssid;
2831 
2832 	do_each_subsys_mask(ss, ssid, ss_mask) {
2833 		if (printed)
2834 			seq_putc(seq, ' ');
2835 		seq_puts(seq, ss->name);
2836 		printed = true;
2837 	} while_each_subsys_mask();
2838 	if (printed)
2839 		seq_putc(seq, '\n');
2840 }
2841 
2842 /* show controllers which are enabled from the parent */
2843 static int cgroup_controllers_show(struct seq_file *seq, void *v)
2844 {
2845 	struct cgroup *cgrp = seq_css(seq)->cgroup;
2846 
2847 	cgroup_print_ss_mask(seq, cgroup_control(cgrp));
2848 	return 0;
2849 }
2850 
2851 /* show controllers which are enabled for a given cgroup's children */
2852 static int cgroup_subtree_control_show(struct seq_file *seq, void *v)
2853 {
2854 	struct cgroup *cgrp = seq_css(seq)->cgroup;
2855 
2856 	cgroup_print_ss_mask(seq, cgrp->subtree_control);
2857 	return 0;
2858 }
2859 
2860 /**
2861  * cgroup_update_dfl_csses - update css assoc of a subtree in default hierarchy
2862  * @cgrp: root of the subtree to update csses for
2863  *
2864  * @cgrp's control masks have changed and its subtree's css associations
2865  * need to be updated accordingly.  This function looks up all css_sets
2866  * which are attached to the subtree, creates the matching updated css_sets
2867  * and migrates the tasks to the new ones.
2868  */
2869 static int cgroup_update_dfl_csses(struct cgroup *cgrp)
2870 {
2871 	DEFINE_CGROUP_MGCTX(mgctx);
2872 	struct cgroup_subsys_state *d_css;
2873 	struct cgroup *dsct;
2874 	struct css_set *src_cset;
2875 	int ret;
2876 
2877 	lockdep_assert_held(&cgroup_mutex);
2878 
2879 	percpu_down_write(&cgroup_threadgroup_rwsem);
2880 
2881 	/* look up all csses currently attached to @cgrp's subtree */
2882 	spin_lock_irq(&css_set_lock);
2883 	cgroup_for_each_live_descendant_pre(dsct, d_css, cgrp) {
2884 		struct cgrp_cset_link *link;
2885 
2886 		list_for_each_entry(link, &dsct->cset_links, cset_link)
2887 			cgroup_migrate_add_src(link->cset, dsct, &mgctx);
2888 	}
2889 	spin_unlock_irq(&css_set_lock);
2890 
2891 	/* NULL dst indicates self on default hierarchy */
2892 	ret = cgroup_migrate_prepare_dst(&mgctx);
2893 	if (ret)
2894 		goto out_finish;
2895 
2896 	spin_lock_irq(&css_set_lock);
2897 	list_for_each_entry(src_cset, &mgctx.preloaded_src_csets, mg_preload_node) {
2898 		struct task_struct *task, *ntask;
2899 
2900 		/* all tasks in src_csets need to be migrated */
2901 		list_for_each_entry_safe(task, ntask, &src_cset->tasks, cg_list)
2902 			cgroup_migrate_add_task(task, &mgctx);
2903 	}
2904 	spin_unlock_irq(&css_set_lock);
2905 
2906 	ret = cgroup_migrate_execute(&mgctx);
2907 out_finish:
2908 	cgroup_migrate_finish(&mgctx);
2909 	percpu_up_write(&cgroup_threadgroup_rwsem);
2910 	return ret;
2911 }
2912 
2913 /**
2914  * cgroup_lock_and_drain_offline - lock cgroup_mutex and drain offlined csses
2915  * @cgrp: root of the target subtree
2916  *
2917  * Because css offlining is asynchronous, userland may try to re-enable a
2918  * controller while the previous css is still around.  This function grabs
2919  * cgroup_mutex and drains the previous css instances of @cgrp's subtree.
2920  */
2921 void cgroup_lock_and_drain_offline(struct cgroup *cgrp)
2922 	__acquires(&cgroup_mutex)
2923 {
2924 	struct cgroup *dsct;
2925 	struct cgroup_subsys_state *d_css;
2926 	struct cgroup_subsys *ss;
2927 	int ssid;
2928 
2929 restart:
2930 	mutex_lock(&cgroup_mutex);
2931 
2932 	cgroup_for_each_live_descendant_post(dsct, d_css, cgrp) {
2933 		for_each_subsys(ss, ssid) {
2934 			struct cgroup_subsys_state *css = cgroup_css(dsct, ss);
2935 			DEFINE_WAIT(wait);
2936 
2937 			if (!css || !percpu_ref_is_dying(&css->refcnt))
2938 				continue;
2939 
2940 			cgroup_get_live(dsct);
2941 			prepare_to_wait(&dsct->offline_waitq, &wait,
2942 					TASK_UNINTERRUPTIBLE);
2943 
2944 			mutex_unlock(&cgroup_mutex);
2945 			schedule();
2946 			finish_wait(&dsct->offline_waitq, &wait);
2947 
2948 			cgroup_put(dsct);
2949 			goto restart;
2950 		}
2951 	}
2952 }
2953 
2954 /**
2955  * cgroup_save_control - save control masks and dom_cgrp of a subtree
2956  * @cgrp: root of the target subtree
2957  *
2958  * Save ->subtree_control, ->subtree_ss_mask and ->dom_cgrp to the
2959  * respective old_ prefixed fields for @cgrp's subtree including @cgrp
2960  * itself.
2961  */
2962 static void cgroup_save_control(struct cgroup *cgrp)
2963 {
2964 	struct cgroup *dsct;
2965 	struct cgroup_subsys_state *d_css;
2966 
2967 	cgroup_for_each_live_descendant_pre(dsct, d_css, cgrp) {
2968 		dsct->old_subtree_control = dsct->subtree_control;
2969 		dsct->old_subtree_ss_mask = dsct->subtree_ss_mask;
2970 		dsct->old_dom_cgrp = dsct->dom_cgrp;
2971 	}
2972 }
2973 
2974 /**
2975  * cgroup_propagate_control - refresh control masks of a subtree
2976  * @cgrp: root of the target subtree
2977  *
2978  * For @cgrp and its subtree, ensure ->subtree_ss_mask matches
2979  * ->subtree_control and propagate controller availability through the
2980  * subtree so that descendants don't have unavailable controllers enabled.
2981  */
2982 static void cgroup_propagate_control(struct cgroup *cgrp)
2983 {
2984 	struct cgroup *dsct;
2985 	struct cgroup_subsys_state *d_css;
2986 
2987 	cgroup_for_each_live_descendant_pre(dsct, d_css, cgrp) {
2988 		dsct->subtree_control &= cgroup_control(dsct);
2989 		dsct->subtree_ss_mask =
2990 			cgroup_calc_subtree_ss_mask(dsct->subtree_control,
2991 						    cgroup_ss_mask(dsct));
2992 	}
2993 }
2994 
2995 /**
2996  * cgroup_restore_control - restore control masks and dom_cgrp of a subtree
2997  * @cgrp: root of the target subtree
2998  *
2999  * Restore ->subtree_control, ->subtree_ss_mask and ->dom_cgrp from the
3000  * respective old_ prefixed fields for @cgrp's subtree including @cgrp
3001  * itself.
3002  */
3003 static void cgroup_restore_control(struct cgroup *cgrp)
3004 {
3005 	struct cgroup *dsct;
3006 	struct cgroup_subsys_state *d_css;
3007 
3008 	cgroup_for_each_live_descendant_post(dsct, d_css, cgrp) {
3009 		dsct->subtree_control = dsct->old_subtree_control;
3010 		dsct->subtree_ss_mask = dsct->old_subtree_ss_mask;
3011 		dsct->dom_cgrp = dsct->old_dom_cgrp;
3012 	}
3013 }
3014 
3015 static bool css_visible(struct cgroup_subsys_state *css)
3016 {
3017 	struct cgroup_subsys *ss = css->ss;
3018 	struct cgroup *cgrp = css->cgroup;
3019 
3020 	if (cgroup_control(cgrp) & (1 << ss->id))
3021 		return true;
3022 	if (!(cgroup_ss_mask(cgrp) & (1 << ss->id)))
3023 		return false;
3024 	return cgroup_on_dfl(cgrp) && ss->implicit_on_dfl;
3025 }
3026 
3027 /**
3028  * cgroup_apply_control_enable - enable or show csses according to control
3029  * @cgrp: root of the target subtree
3030  *
3031  * Walk @cgrp's subtree and create new csses or make the existing ones
3032  * visible.  A css is created invisible if it's being implicitly enabled
3033  * through dependency.  An invisible css is made visible when the userland
3034  * explicitly enables it.
3035  *
3036  * Returns 0 on success, -errno on failure.  On failure, csses which have
3037  * been processed already aren't cleaned up.  The caller is responsible for
3038  * cleaning up with cgroup_apply_control_disable().
3039  */
3040 static int cgroup_apply_control_enable(struct cgroup *cgrp)
3041 {
3042 	struct cgroup *dsct;
3043 	struct cgroup_subsys_state *d_css;
3044 	struct cgroup_subsys *ss;
3045 	int ssid, ret;
3046 
3047 	cgroup_for_each_live_descendant_pre(dsct, d_css, cgrp) {
3048 		for_each_subsys(ss, ssid) {
3049 			struct cgroup_subsys_state *css = cgroup_css(dsct, ss);
3050 
3051 			if (!(cgroup_ss_mask(dsct) & (1 << ss->id)))
3052 				continue;
3053 
3054 			if (!css) {
3055 				css = css_create(dsct, ss);
3056 				if (IS_ERR(css))
3057 					return PTR_ERR(css);
3058 			}
3059 
3060 			WARN_ON_ONCE(percpu_ref_is_dying(&css->refcnt));
3061 
3062 			if (css_visible(css)) {
3063 				ret = css_populate_dir(css);
3064 				if (ret)
3065 					return ret;
3066 			}
3067 		}
3068 	}
3069 
3070 	return 0;
3071 }
3072 
3073 /**
3074  * cgroup_apply_control_disable - kill or hide csses according to control
3075  * @cgrp: root of the target subtree
3076  *
3077  * Walk @cgrp's subtree and kill and hide csses so that they match
3078  * cgroup_ss_mask() and cgroup_visible_mask().
3079  *
3080  * A css is hidden when the userland requests it to be disabled while other
3081  * subsystems are still depending on it.  The css must not actively control
3082  * resources and be in the vanilla state if it's made visible again later.
3083  * Controllers which may be depended upon should provide ->css_reset() for
3084  * this purpose.
3085  */
3086 static void cgroup_apply_control_disable(struct cgroup *cgrp)
3087 {
3088 	struct cgroup *dsct;
3089 	struct cgroup_subsys_state *d_css;
3090 	struct cgroup_subsys *ss;
3091 	int ssid;
3092 
3093 	cgroup_for_each_live_descendant_post(dsct, d_css, cgrp) {
3094 		for_each_subsys(ss, ssid) {
3095 			struct cgroup_subsys_state *css = cgroup_css(dsct, ss);
3096 
3097 			if (!css)
3098 				continue;
3099 
3100 			WARN_ON_ONCE(percpu_ref_is_dying(&css->refcnt));
3101 
3102 			if (css->parent &&
3103 			    !(cgroup_ss_mask(dsct) & (1 << ss->id))) {
3104 				kill_css(css);
3105 			} else if (!css_visible(css)) {
3106 				css_clear_dir(css);
3107 				if (ss->css_reset)
3108 					ss->css_reset(css);
3109 			}
3110 		}
3111 	}
3112 }
3113 
3114 /**
3115  * cgroup_apply_control - apply control mask updates to the subtree
3116  * @cgrp: root of the target subtree
3117  *
3118  * subsystems can be enabled and disabled in a subtree using the following
3119  * steps.
3120  *
3121  * 1. Call cgroup_save_control() to stash the current state.
3122  * 2. Update ->subtree_control masks in the subtree as desired.
3123  * 3. Call cgroup_apply_control() to apply the changes.
3124  * 4. Optionally perform other related operations.
3125  * 5. Call cgroup_finalize_control() to finish up.
3126  *
3127  * This function implements step 3 and propagates the mask changes
3128  * throughout @cgrp's subtree, updates csses accordingly and perform
3129  * process migrations.
3130  */
3131 static int cgroup_apply_control(struct cgroup *cgrp)
3132 {
3133 	int ret;
3134 
3135 	cgroup_propagate_control(cgrp);
3136 
3137 	ret = cgroup_apply_control_enable(cgrp);
3138 	if (ret)
3139 		return ret;
3140 
3141 	/*
3142 	 * At this point, cgroup_e_css_by_mask() results reflect the new csses
3143 	 * making the following cgroup_update_dfl_csses() properly update
3144 	 * css associations of all tasks in the subtree.
3145 	 */
3146 	ret = cgroup_update_dfl_csses(cgrp);
3147 	if (ret)
3148 		return ret;
3149 
3150 	return 0;
3151 }
3152 
3153 /**
3154  * cgroup_finalize_control - finalize control mask update
3155  * @cgrp: root of the target subtree
3156  * @ret: the result of the update
3157  *
3158  * Finalize control mask update.  See cgroup_apply_control() for more info.
3159  */
3160 static void cgroup_finalize_control(struct cgroup *cgrp, int ret)
3161 {
3162 	if (ret) {
3163 		cgroup_restore_control(cgrp);
3164 		cgroup_propagate_control(cgrp);
3165 	}
3166 
3167 	cgroup_apply_control_disable(cgrp);
3168 }
3169 
3170 static int cgroup_vet_subtree_control_enable(struct cgroup *cgrp, u16 enable)
3171 {
3172 	u16 domain_enable = enable & ~cgrp_dfl_threaded_ss_mask;
3173 
3174 	/* if nothing is getting enabled, nothing to worry about */
3175 	if (!enable)
3176 		return 0;
3177 
3178 	/* can @cgrp host any resources? */
3179 	if (!cgroup_is_valid_domain(cgrp->dom_cgrp))
3180 		return -EOPNOTSUPP;
3181 
3182 	/* mixables don't care */
3183 	if (cgroup_is_mixable(cgrp))
3184 		return 0;
3185 
3186 	if (domain_enable) {
3187 		/* can't enable domain controllers inside a thread subtree */
3188 		if (cgroup_is_thread_root(cgrp) || cgroup_is_threaded(cgrp))
3189 			return -EOPNOTSUPP;
3190 	} else {
3191 		/*
3192 		 * Threaded controllers can handle internal competitions
3193 		 * and are always allowed inside a (prospective) thread
3194 		 * subtree.
3195 		 */
3196 		if (cgroup_can_be_thread_root(cgrp) || cgroup_is_threaded(cgrp))
3197 			return 0;
3198 	}
3199 
3200 	/*
3201 	 * Controllers can't be enabled for a cgroup with tasks to avoid
3202 	 * child cgroups competing against tasks.
3203 	 */
3204 	if (cgroup_has_tasks(cgrp))
3205 		return -EBUSY;
3206 
3207 	return 0;
3208 }
3209 
3210 /* change the enabled child controllers for a cgroup in the default hierarchy */
3211 static ssize_t cgroup_subtree_control_write(struct kernfs_open_file *of,
3212 					    char *buf, size_t nbytes,
3213 					    loff_t off)
3214 {
3215 	u16 enable = 0, disable = 0;
3216 	struct cgroup *cgrp, *child;
3217 	struct cgroup_subsys *ss;
3218 	char *tok;
3219 	int ssid, ret;
3220 
3221 	/*
3222 	 * Parse input - space separated list of subsystem names prefixed
3223 	 * with either + or -.
3224 	 */
3225 	buf = strstrip(buf);
3226 	while ((tok = strsep(&buf, " "))) {
3227 		if (tok[0] == '\0')
3228 			continue;
3229 		do_each_subsys_mask(ss, ssid, ~cgrp_dfl_inhibit_ss_mask) {
3230 			if (!cgroup_ssid_enabled(ssid) ||
3231 			    strcmp(tok + 1, ss->name))
3232 				continue;
3233 
3234 			if (*tok == '+') {
3235 				enable |= 1 << ssid;
3236 				disable &= ~(1 << ssid);
3237 			} else if (*tok == '-') {
3238 				disable |= 1 << ssid;
3239 				enable &= ~(1 << ssid);
3240 			} else {
3241 				return -EINVAL;
3242 			}
3243 			break;
3244 		} while_each_subsys_mask();
3245 		if (ssid == CGROUP_SUBSYS_COUNT)
3246 			return -EINVAL;
3247 	}
3248 
3249 	cgrp = cgroup_kn_lock_live(of->kn, true);
3250 	if (!cgrp)
3251 		return -ENODEV;
3252 
3253 	for_each_subsys(ss, ssid) {
3254 		if (enable & (1 << ssid)) {
3255 			if (cgrp->subtree_control & (1 << ssid)) {
3256 				enable &= ~(1 << ssid);
3257 				continue;
3258 			}
3259 
3260 			if (!(cgroup_control(cgrp) & (1 << ssid))) {
3261 				ret = -ENOENT;
3262 				goto out_unlock;
3263 			}
3264 		} else if (disable & (1 << ssid)) {
3265 			if (!(cgrp->subtree_control & (1 << ssid))) {
3266 				disable &= ~(1 << ssid);
3267 				continue;
3268 			}
3269 
3270 			/* a child has it enabled? */
3271 			cgroup_for_each_live_child(child, cgrp) {
3272 				if (child->subtree_control & (1 << ssid)) {
3273 					ret = -EBUSY;
3274 					goto out_unlock;
3275 				}
3276 			}
3277 		}
3278 	}
3279 
3280 	if (!enable && !disable) {
3281 		ret = 0;
3282 		goto out_unlock;
3283 	}
3284 
3285 	ret = cgroup_vet_subtree_control_enable(cgrp, enable);
3286 	if (ret)
3287 		goto out_unlock;
3288 
3289 	/* save and update control masks and prepare csses */
3290 	cgroup_save_control(cgrp);
3291 
3292 	cgrp->subtree_control |= enable;
3293 	cgrp->subtree_control &= ~disable;
3294 
3295 	ret = cgroup_apply_control(cgrp);
3296 	cgroup_finalize_control(cgrp, ret);
3297 	if (ret)
3298 		goto out_unlock;
3299 
3300 	kernfs_activate(cgrp->kn);
3301 out_unlock:
3302 	cgroup_kn_unlock(of->kn);
3303 	return ret ?: nbytes;
3304 }
3305 
3306 /**
3307  * cgroup_enable_threaded - make @cgrp threaded
3308  * @cgrp: the target cgroup
3309  *
3310  * Called when "threaded" is written to the cgroup.type interface file and
3311  * tries to make @cgrp threaded and join the parent's resource domain.
3312  * This function is never called on the root cgroup as cgroup.type doesn't
3313  * exist on it.
3314  */
3315 static int cgroup_enable_threaded(struct cgroup *cgrp)
3316 {
3317 	struct cgroup *parent = cgroup_parent(cgrp);
3318 	struct cgroup *dom_cgrp = parent->dom_cgrp;
3319 	struct cgroup *dsct;
3320 	struct cgroup_subsys_state *d_css;
3321 	int ret;
3322 
3323 	lockdep_assert_held(&cgroup_mutex);
3324 
3325 	/* noop if already threaded */
3326 	if (cgroup_is_threaded(cgrp))
3327 		return 0;
3328 
3329 	/*
3330 	 * If @cgroup is populated or has domain controllers enabled, it
3331 	 * can't be switched.  While the below cgroup_can_be_thread_root()
3332 	 * test can catch the same conditions, that's only when @parent is
3333 	 * not mixable, so let's check it explicitly.
3334 	 */
3335 	if (cgroup_is_populated(cgrp) ||
3336 	    cgrp->subtree_control & ~cgrp_dfl_threaded_ss_mask)
3337 		return -EOPNOTSUPP;
3338 
3339 	/* we're joining the parent's domain, ensure its validity */
3340 	if (!cgroup_is_valid_domain(dom_cgrp) ||
3341 	    !cgroup_can_be_thread_root(dom_cgrp))
3342 		return -EOPNOTSUPP;
3343 
3344 	/*
3345 	 * The following shouldn't cause actual migrations and should
3346 	 * always succeed.
3347 	 */
3348 	cgroup_save_control(cgrp);
3349 
3350 	cgroup_for_each_live_descendant_pre(dsct, d_css, cgrp)
3351 		if (dsct == cgrp || cgroup_is_threaded(dsct))
3352 			dsct->dom_cgrp = dom_cgrp;
3353 
3354 	ret = cgroup_apply_control(cgrp);
3355 	if (!ret)
3356 		parent->nr_threaded_children++;
3357 
3358 	cgroup_finalize_control(cgrp, ret);
3359 	return ret;
3360 }
3361 
3362 static int cgroup_type_show(struct seq_file *seq, void *v)
3363 {
3364 	struct cgroup *cgrp = seq_css(seq)->cgroup;
3365 
3366 	if (cgroup_is_threaded(cgrp))
3367 		seq_puts(seq, "threaded\n");
3368 	else if (!cgroup_is_valid_domain(cgrp))
3369 		seq_puts(seq, "domain invalid\n");
3370 	else if (cgroup_is_thread_root(cgrp))
3371 		seq_puts(seq, "domain threaded\n");
3372 	else
3373 		seq_puts(seq, "domain\n");
3374 
3375 	return 0;
3376 }
3377 
3378 static ssize_t cgroup_type_write(struct kernfs_open_file *of, char *buf,
3379 				 size_t nbytes, loff_t off)
3380 {
3381 	struct cgroup *cgrp;
3382 	int ret;
3383 
3384 	/* only switching to threaded mode is supported */
3385 	if (strcmp(strstrip(buf), "threaded"))
3386 		return -EINVAL;
3387 
3388 	/* drain dying csses before we re-apply (threaded) subtree control */
3389 	cgrp = cgroup_kn_lock_live(of->kn, true);
3390 	if (!cgrp)
3391 		return -ENOENT;
3392 
3393 	/* threaded can only be enabled */
3394 	ret = cgroup_enable_threaded(cgrp);
3395 
3396 	cgroup_kn_unlock(of->kn);
3397 	return ret ?: nbytes;
3398 }
3399 
3400 static int cgroup_max_descendants_show(struct seq_file *seq, void *v)
3401 {
3402 	struct cgroup *cgrp = seq_css(seq)->cgroup;
3403 	int descendants = READ_ONCE(cgrp->max_descendants);
3404 
3405 	if (descendants == INT_MAX)
3406 		seq_puts(seq, "max\n");
3407 	else
3408 		seq_printf(seq, "%d\n", descendants);
3409 
3410 	return 0;
3411 }
3412 
3413 static ssize_t cgroup_max_descendants_write(struct kernfs_open_file *of,
3414 					   char *buf, size_t nbytes, loff_t off)
3415 {
3416 	struct cgroup *cgrp;
3417 	int descendants;
3418 	ssize_t ret;
3419 
3420 	buf = strstrip(buf);
3421 	if (!strcmp(buf, "max")) {
3422 		descendants = INT_MAX;
3423 	} else {
3424 		ret = kstrtoint(buf, 0, &descendants);
3425 		if (ret)
3426 			return ret;
3427 	}
3428 
3429 	if (descendants < 0)
3430 		return -ERANGE;
3431 
3432 	cgrp = cgroup_kn_lock_live(of->kn, false);
3433 	if (!cgrp)
3434 		return -ENOENT;
3435 
3436 	cgrp->max_descendants = descendants;
3437 
3438 	cgroup_kn_unlock(of->kn);
3439 
3440 	return nbytes;
3441 }
3442 
3443 static int cgroup_max_depth_show(struct seq_file *seq, void *v)
3444 {
3445 	struct cgroup *cgrp = seq_css(seq)->cgroup;
3446 	int depth = READ_ONCE(cgrp->max_depth);
3447 
3448 	if (depth == INT_MAX)
3449 		seq_puts(seq, "max\n");
3450 	else
3451 		seq_printf(seq, "%d\n", depth);
3452 
3453 	return 0;
3454 }
3455 
3456 static ssize_t cgroup_max_depth_write(struct kernfs_open_file *of,
3457 				      char *buf, size_t nbytes, loff_t off)
3458 {
3459 	struct cgroup *cgrp;
3460 	ssize_t ret;
3461 	int depth;
3462 
3463 	buf = strstrip(buf);
3464 	if (!strcmp(buf, "max")) {
3465 		depth = INT_MAX;
3466 	} else {
3467 		ret = kstrtoint(buf, 0, &depth);
3468 		if (ret)
3469 			return ret;
3470 	}
3471 
3472 	if (depth < 0)
3473 		return -ERANGE;
3474 
3475 	cgrp = cgroup_kn_lock_live(of->kn, false);
3476 	if (!cgrp)
3477 		return -ENOENT;
3478 
3479 	cgrp->max_depth = depth;
3480 
3481 	cgroup_kn_unlock(of->kn);
3482 
3483 	return nbytes;
3484 }
3485 
3486 static int cgroup_events_show(struct seq_file *seq, void *v)
3487 {
3488 	struct cgroup *cgrp = seq_css(seq)->cgroup;
3489 
3490 	seq_printf(seq, "populated %d\n", cgroup_is_populated(cgrp));
3491 	seq_printf(seq, "frozen %d\n", test_bit(CGRP_FROZEN, &cgrp->flags));
3492 
3493 	return 0;
3494 }
3495 
3496 static int cgroup_stat_show(struct seq_file *seq, void *v)
3497 {
3498 	struct cgroup *cgroup = seq_css(seq)->cgroup;
3499 
3500 	seq_printf(seq, "nr_descendants %d\n",
3501 		   cgroup->nr_descendants);
3502 	seq_printf(seq, "nr_dying_descendants %d\n",
3503 		   cgroup->nr_dying_descendants);
3504 
3505 	return 0;
3506 }
3507 
3508 static int __maybe_unused cgroup_extra_stat_show(struct seq_file *seq,
3509 						 struct cgroup *cgrp, int ssid)
3510 {
3511 	struct cgroup_subsys *ss = cgroup_subsys[ssid];
3512 	struct cgroup_subsys_state *css;
3513 	int ret;
3514 
3515 	if (!ss->css_extra_stat_show)
3516 		return 0;
3517 
3518 	css = cgroup_tryget_css(cgrp, ss);
3519 	if (!css)
3520 		return 0;
3521 
3522 	ret = ss->css_extra_stat_show(seq, css);
3523 	css_put(css);
3524 	return ret;
3525 }
3526 
3527 static int cpu_stat_show(struct seq_file *seq, void *v)
3528 {
3529 	struct cgroup __maybe_unused *cgrp = seq_css(seq)->cgroup;
3530 	int ret = 0;
3531 
3532 	cgroup_base_stat_cputime_show(seq);
3533 #ifdef CONFIG_CGROUP_SCHED
3534 	ret = cgroup_extra_stat_show(seq, cgrp, cpu_cgrp_id);
3535 #endif
3536 	return ret;
3537 }
3538 
3539 #ifdef CONFIG_PSI
3540 static int cgroup_io_pressure_show(struct seq_file *seq, void *v)
3541 {
3542 	struct cgroup *cgrp = seq_css(seq)->cgroup;
3543 	struct psi_group *psi = cgroup_ino(cgrp) == 1 ? &psi_system : &cgrp->psi;
3544 
3545 	return psi_show(seq, psi, PSI_IO);
3546 }
3547 static int cgroup_memory_pressure_show(struct seq_file *seq, void *v)
3548 {
3549 	struct cgroup *cgrp = seq_css(seq)->cgroup;
3550 	struct psi_group *psi = cgroup_ino(cgrp) == 1 ? &psi_system : &cgrp->psi;
3551 
3552 	return psi_show(seq, psi, PSI_MEM);
3553 }
3554 static int cgroup_cpu_pressure_show(struct seq_file *seq, void *v)
3555 {
3556 	struct cgroup *cgrp = seq_css(seq)->cgroup;
3557 	struct psi_group *psi = cgroup_ino(cgrp) == 1 ? &psi_system : &cgrp->psi;
3558 
3559 	return psi_show(seq, psi, PSI_CPU);
3560 }
3561 
3562 static ssize_t cgroup_pressure_write(struct kernfs_open_file *of, char *buf,
3563 					  size_t nbytes, enum psi_res res)
3564 {
3565 	struct psi_trigger *new;
3566 	struct cgroup *cgrp;
3567 
3568 	cgrp = cgroup_kn_lock_live(of->kn, false);
3569 	if (!cgrp)
3570 		return -ENODEV;
3571 
3572 	cgroup_get(cgrp);
3573 	cgroup_kn_unlock(of->kn);
3574 
3575 	new = psi_trigger_create(&cgrp->psi, buf, nbytes, res);
3576 	if (IS_ERR(new)) {
3577 		cgroup_put(cgrp);
3578 		return PTR_ERR(new);
3579 	}
3580 
3581 	psi_trigger_replace(&of->priv, new);
3582 
3583 	cgroup_put(cgrp);
3584 
3585 	return nbytes;
3586 }
3587 
3588 static ssize_t cgroup_io_pressure_write(struct kernfs_open_file *of,
3589 					  char *buf, size_t nbytes,
3590 					  loff_t off)
3591 {
3592 	return cgroup_pressure_write(of, buf, nbytes, PSI_IO);
3593 }
3594 
3595 static ssize_t cgroup_memory_pressure_write(struct kernfs_open_file *of,
3596 					  char *buf, size_t nbytes,
3597 					  loff_t off)
3598 {
3599 	return cgroup_pressure_write(of, buf, nbytes, PSI_MEM);
3600 }
3601 
3602 static ssize_t cgroup_cpu_pressure_write(struct kernfs_open_file *of,
3603 					  char *buf, size_t nbytes,
3604 					  loff_t off)
3605 {
3606 	return cgroup_pressure_write(of, buf, nbytes, PSI_CPU);
3607 }
3608 
3609 static __poll_t cgroup_pressure_poll(struct kernfs_open_file *of,
3610 					  poll_table *pt)
3611 {
3612 	return psi_trigger_poll(&of->priv, of->file, pt);
3613 }
3614 
3615 static void cgroup_pressure_release(struct kernfs_open_file *of)
3616 {
3617 	psi_trigger_replace(&of->priv, NULL);
3618 }
3619 #endif /* CONFIG_PSI */
3620 
3621 static int cgroup_freeze_show(struct seq_file *seq, void *v)
3622 {
3623 	struct cgroup *cgrp = seq_css(seq)->cgroup;
3624 
3625 	seq_printf(seq, "%d\n", cgrp->freezer.freeze);
3626 
3627 	return 0;
3628 }
3629 
3630 static ssize_t cgroup_freeze_write(struct kernfs_open_file *of,
3631 				   char *buf, size_t nbytes, loff_t off)
3632 {
3633 	struct cgroup *cgrp;
3634 	ssize_t ret;
3635 	int freeze;
3636 
3637 	ret = kstrtoint(strstrip(buf), 0, &freeze);
3638 	if (ret)
3639 		return ret;
3640 
3641 	if (freeze < 0 || freeze > 1)
3642 		return -ERANGE;
3643 
3644 	cgrp = cgroup_kn_lock_live(of->kn, false);
3645 	if (!cgrp)
3646 		return -ENOENT;
3647 
3648 	cgroup_freeze(cgrp, freeze);
3649 
3650 	cgroup_kn_unlock(of->kn);
3651 
3652 	return nbytes;
3653 }
3654 
3655 static int cgroup_file_open(struct kernfs_open_file *of)
3656 {
3657 	struct cftype *cft = of_cft(of);
3658 
3659 	if (cft->open)
3660 		return cft->open(of);
3661 	return 0;
3662 }
3663 
3664 static void cgroup_file_release(struct kernfs_open_file *of)
3665 {
3666 	struct cftype *cft = of_cft(of);
3667 
3668 	if (cft->release)
3669 		cft->release(of);
3670 }
3671 
3672 static ssize_t cgroup_file_write(struct kernfs_open_file *of, char *buf,
3673 				 size_t nbytes, loff_t off)
3674 {
3675 	struct cgroup_namespace *ns = current->nsproxy->cgroup_ns;
3676 	struct cgroup *cgrp = of->kn->parent->priv;
3677 	struct cftype *cft = of_cft(of);
3678 	struct cgroup_subsys_state *css;
3679 	int ret;
3680 
3681 	if (!nbytes)
3682 		return 0;
3683 
3684 	/*
3685 	 * If namespaces are delegation boundaries, disallow writes to
3686 	 * files in an non-init namespace root from inside the namespace
3687 	 * except for the files explicitly marked delegatable -
3688 	 * cgroup.procs and cgroup.subtree_control.
3689 	 */
3690 	if ((cgrp->root->flags & CGRP_ROOT_NS_DELEGATE) &&
3691 	    !(cft->flags & CFTYPE_NS_DELEGATABLE) &&
3692 	    ns != &init_cgroup_ns && ns->root_cset->dfl_cgrp == cgrp)
3693 		return -EPERM;
3694 
3695 	if (cft->write)
3696 		return cft->write(of, buf, nbytes, off);
3697 
3698 	/*
3699 	 * kernfs guarantees that a file isn't deleted with operations in
3700 	 * flight, which means that the matching css is and stays alive and
3701 	 * doesn't need to be pinned.  The RCU locking is not necessary
3702 	 * either.  It's just for the convenience of using cgroup_css().
3703 	 */
3704 	rcu_read_lock();
3705 	css = cgroup_css(cgrp, cft->ss);
3706 	rcu_read_unlock();
3707 
3708 	if (cft->write_u64) {
3709 		unsigned long long v;
3710 		ret = kstrtoull(buf, 0, &v);
3711 		if (!ret)
3712 			ret = cft->write_u64(css, cft, v);
3713 	} else if (cft->write_s64) {
3714 		long long v;
3715 		ret = kstrtoll(buf, 0, &v);
3716 		if (!ret)
3717 			ret = cft->write_s64(css, cft, v);
3718 	} else {
3719 		ret = -EINVAL;
3720 	}
3721 
3722 	return ret ?: nbytes;
3723 }
3724 
3725 static __poll_t cgroup_file_poll(struct kernfs_open_file *of, poll_table *pt)
3726 {
3727 	struct cftype *cft = of_cft(of);
3728 
3729 	if (cft->poll)
3730 		return cft->poll(of, pt);
3731 
3732 	return kernfs_generic_poll(of, pt);
3733 }
3734 
3735 static void *cgroup_seqfile_start(struct seq_file *seq, loff_t *ppos)
3736 {
3737 	return seq_cft(seq)->seq_start(seq, ppos);
3738 }
3739 
3740 static void *cgroup_seqfile_next(struct seq_file *seq, void *v, loff_t *ppos)
3741 {
3742 	return seq_cft(seq)->seq_next(seq, v, ppos);
3743 }
3744 
3745 static void cgroup_seqfile_stop(struct seq_file *seq, void *v)
3746 {
3747 	if (seq_cft(seq)->seq_stop)
3748 		seq_cft(seq)->seq_stop(seq, v);
3749 }
3750 
3751 static int cgroup_seqfile_show(struct seq_file *m, void *arg)
3752 {
3753 	struct cftype *cft = seq_cft(m);
3754 	struct cgroup_subsys_state *css = seq_css(m);
3755 
3756 	if (cft->seq_show)
3757 		return cft->seq_show(m, arg);
3758 
3759 	if (cft->read_u64)
3760 		seq_printf(m, "%llu\n", cft->read_u64(css, cft));
3761 	else if (cft->read_s64)
3762 		seq_printf(m, "%lld\n", cft->read_s64(css, cft));
3763 	else
3764 		return -EINVAL;
3765 	return 0;
3766 }
3767 
3768 static struct kernfs_ops cgroup_kf_single_ops = {
3769 	.atomic_write_len	= PAGE_SIZE,
3770 	.open			= cgroup_file_open,
3771 	.release		= cgroup_file_release,
3772 	.write			= cgroup_file_write,
3773 	.poll			= cgroup_file_poll,
3774 	.seq_show		= cgroup_seqfile_show,
3775 };
3776 
3777 static struct kernfs_ops cgroup_kf_ops = {
3778 	.atomic_write_len	= PAGE_SIZE,
3779 	.open			= cgroup_file_open,
3780 	.release		= cgroup_file_release,
3781 	.write			= cgroup_file_write,
3782 	.poll			= cgroup_file_poll,
3783 	.seq_start		= cgroup_seqfile_start,
3784 	.seq_next		= cgroup_seqfile_next,
3785 	.seq_stop		= cgroup_seqfile_stop,
3786 	.seq_show		= cgroup_seqfile_show,
3787 };
3788 
3789 /* set uid and gid of cgroup dirs and files to that of the creator */
3790 static int cgroup_kn_set_ugid(struct kernfs_node *kn)
3791 {
3792 	struct iattr iattr = { .ia_valid = ATTR_UID | ATTR_GID,
3793 			       .ia_uid = current_fsuid(),
3794 			       .ia_gid = current_fsgid(), };
3795 
3796 	if (uid_eq(iattr.ia_uid, GLOBAL_ROOT_UID) &&
3797 	    gid_eq(iattr.ia_gid, GLOBAL_ROOT_GID))
3798 		return 0;
3799 
3800 	return kernfs_setattr(kn, &iattr);
3801 }
3802 
3803 static void cgroup_file_notify_timer(struct timer_list *timer)
3804 {
3805 	cgroup_file_notify(container_of(timer, struct cgroup_file,
3806 					notify_timer));
3807 }
3808 
3809 static int cgroup_add_file(struct cgroup_subsys_state *css, struct cgroup *cgrp,
3810 			   struct cftype *cft)
3811 {
3812 	char name[CGROUP_FILE_NAME_MAX];
3813 	struct kernfs_node *kn;
3814 	struct lock_class_key *key = NULL;
3815 	int ret;
3816 
3817 #ifdef CONFIG_DEBUG_LOCK_ALLOC
3818 	key = &cft->lockdep_key;
3819 #endif
3820 	kn = __kernfs_create_file(cgrp->kn, cgroup_file_name(cgrp, cft, name),
3821 				  cgroup_file_mode(cft),
3822 				  GLOBAL_ROOT_UID, GLOBAL_ROOT_GID,
3823 				  0, cft->kf_ops, cft,
3824 				  NULL, key);
3825 	if (IS_ERR(kn))
3826 		return PTR_ERR(kn);
3827 
3828 	ret = cgroup_kn_set_ugid(kn);
3829 	if (ret) {
3830 		kernfs_remove(kn);
3831 		return ret;
3832 	}
3833 
3834 	if (cft->file_offset) {
3835 		struct cgroup_file *cfile = (void *)css + cft->file_offset;
3836 
3837 		timer_setup(&cfile->notify_timer, cgroup_file_notify_timer, 0);
3838 
3839 		spin_lock_irq(&cgroup_file_kn_lock);
3840 		cfile->kn = kn;
3841 		spin_unlock_irq(&cgroup_file_kn_lock);
3842 	}
3843 
3844 	return 0;
3845 }
3846 
3847 /**
3848  * cgroup_addrm_files - add or remove files to a cgroup directory
3849  * @css: the target css
3850  * @cgrp: the target cgroup (usually css->cgroup)
3851  * @cfts: array of cftypes to be added
3852  * @is_add: whether to add or remove
3853  *
3854  * Depending on @is_add, add or remove files defined by @cfts on @cgrp.
3855  * For removals, this function never fails.
3856  */
3857 static int cgroup_addrm_files(struct cgroup_subsys_state *css,
3858 			      struct cgroup *cgrp, struct cftype cfts[],
3859 			      bool is_add)
3860 {
3861 	struct cftype *cft, *cft_end = NULL;
3862 	int ret = 0;
3863 
3864 	lockdep_assert_held(&cgroup_mutex);
3865 
3866 restart:
3867 	for (cft = cfts; cft != cft_end && cft->name[0] != '\0'; cft++) {
3868 		/* does cft->flags tell us to skip this file on @cgrp? */
3869 		if ((cft->flags & __CFTYPE_ONLY_ON_DFL) && !cgroup_on_dfl(cgrp))
3870 			continue;
3871 		if ((cft->flags & __CFTYPE_NOT_ON_DFL) && cgroup_on_dfl(cgrp))
3872 			continue;
3873 		if ((cft->flags & CFTYPE_NOT_ON_ROOT) && !cgroup_parent(cgrp))
3874 			continue;
3875 		if ((cft->flags & CFTYPE_ONLY_ON_ROOT) && cgroup_parent(cgrp))
3876 			continue;
3877 		if ((cft->flags & CFTYPE_DEBUG) && !cgroup_debug)
3878 			continue;
3879 		if (is_add) {
3880 			ret = cgroup_add_file(css, cgrp, cft);
3881 			if (ret) {
3882 				pr_warn("%s: failed to add %s, err=%d\n",
3883 					__func__, cft->name, ret);
3884 				cft_end = cft;
3885 				is_add = false;
3886 				goto restart;
3887 			}
3888 		} else {
3889 			cgroup_rm_file(cgrp, cft);
3890 		}
3891 	}
3892 	return ret;
3893 }
3894 
3895 static int cgroup_apply_cftypes(struct cftype *cfts, bool is_add)
3896 {
3897 	struct cgroup_subsys *ss = cfts[0].ss;
3898 	struct cgroup *root = &ss->root->cgrp;
3899 	struct cgroup_subsys_state *css;
3900 	int ret = 0;
3901 
3902 	lockdep_assert_held(&cgroup_mutex);
3903 
3904 	/* add/rm files for all cgroups created before */
3905 	css_for_each_descendant_pre(css, cgroup_css(root, ss)) {
3906 		struct cgroup *cgrp = css->cgroup;
3907 
3908 		if (!(css->flags & CSS_VISIBLE))
3909 			continue;
3910 
3911 		ret = cgroup_addrm_files(css, cgrp, cfts, is_add);
3912 		if (ret)
3913 			break;
3914 	}
3915 
3916 	if (is_add && !ret)
3917 		kernfs_activate(root->kn);
3918 	return ret;
3919 }
3920 
3921 static void cgroup_exit_cftypes(struct cftype *cfts)
3922 {
3923 	struct cftype *cft;
3924 
3925 	for (cft = cfts; cft->name[0] != '\0'; cft++) {
3926 		/* free copy for custom atomic_write_len, see init_cftypes() */
3927 		if (cft->max_write_len && cft->max_write_len != PAGE_SIZE)
3928 			kfree(cft->kf_ops);
3929 		cft->kf_ops = NULL;
3930 		cft->ss = NULL;
3931 
3932 		/* revert flags set by cgroup core while adding @cfts */
3933 		cft->flags &= ~(__CFTYPE_ONLY_ON_DFL | __CFTYPE_NOT_ON_DFL);
3934 	}
3935 }
3936 
3937 static int cgroup_init_cftypes(struct cgroup_subsys *ss, struct cftype *cfts)
3938 {
3939 	struct cftype *cft;
3940 
3941 	for (cft = cfts; cft->name[0] != '\0'; cft++) {
3942 		struct kernfs_ops *kf_ops;
3943 
3944 		WARN_ON(cft->ss || cft->kf_ops);
3945 
3946 		if (cft->seq_start)
3947 			kf_ops = &cgroup_kf_ops;
3948 		else
3949 			kf_ops = &cgroup_kf_single_ops;
3950 
3951 		/*
3952 		 * Ugh... if @cft wants a custom max_write_len, we need to
3953 		 * make a copy of kf_ops to set its atomic_write_len.
3954 		 */
3955 		if (cft->max_write_len && cft->max_write_len != PAGE_SIZE) {
3956 			kf_ops = kmemdup(kf_ops, sizeof(*kf_ops), GFP_KERNEL);
3957 			if (!kf_ops) {
3958 				cgroup_exit_cftypes(cfts);
3959 				return -ENOMEM;
3960 			}
3961 			kf_ops->atomic_write_len = cft->max_write_len;
3962 		}
3963 
3964 		cft->kf_ops = kf_ops;
3965 		cft->ss = ss;
3966 	}
3967 
3968 	return 0;
3969 }
3970 
3971 static int cgroup_rm_cftypes_locked(struct cftype *cfts)
3972 {
3973 	lockdep_assert_held(&cgroup_mutex);
3974 
3975 	if (!cfts || !cfts[0].ss)
3976 		return -ENOENT;
3977 
3978 	list_del(&cfts->node);
3979 	cgroup_apply_cftypes(cfts, false);
3980 	cgroup_exit_cftypes(cfts);
3981 	return 0;
3982 }
3983 
3984 /**
3985  * cgroup_rm_cftypes - remove an array of cftypes from a subsystem
3986  * @cfts: zero-length name terminated array of cftypes
3987  *
3988  * Unregister @cfts.  Files described by @cfts are removed from all
3989  * existing cgroups and all future cgroups won't have them either.  This
3990  * function can be called anytime whether @cfts' subsys is attached or not.
3991  *
3992  * Returns 0 on successful unregistration, -ENOENT if @cfts is not
3993  * registered.
3994  */
3995 int cgroup_rm_cftypes(struct cftype *cfts)
3996 {
3997 	int ret;
3998 
3999 	mutex_lock(&cgroup_mutex);
4000 	ret = cgroup_rm_cftypes_locked(cfts);
4001 	mutex_unlock(&cgroup_mutex);
4002 	return ret;
4003 }
4004 
4005 /**
4006  * cgroup_add_cftypes - add an array of cftypes to a subsystem
4007  * @ss: target cgroup subsystem
4008  * @cfts: zero-length name terminated array of cftypes
4009  *
4010  * Register @cfts to @ss.  Files described by @cfts are created for all
4011  * existing cgroups to which @ss is attached and all future cgroups will
4012  * have them too.  This function can be called anytime whether @ss is
4013  * attached or not.
4014  *
4015  * Returns 0 on successful registration, -errno on failure.  Note that this
4016  * function currently returns 0 as long as @cfts registration is successful
4017  * even if some file creation attempts on existing cgroups fail.
4018  */
4019 static int cgroup_add_cftypes(struct cgroup_subsys *ss, struct cftype *cfts)
4020 {
4021 	int ret;
4022 
4023 	if (!cgroup_ssid_enabled(ss->id))
4024 		return 0;
4025 
4026 	if (!cfts || cfts[0].name[0] == '\0')
4027 		return 0;
4028 
4029 	ret = cgroup_init_cftypes(ss, cfts);
4030 	if (ret)
4031 		return ret;
4032 
4033 	mutex_lock(&cgroup_mutex);
4034 
4035 	list_add_tail(&cfts->node, &ss->cfts);
4036 	ret = cgroup_apply_cftypes(cfts, true);
4037 	if (ret)
4038 		cgroup_rm_cftypes_locked(cfts);
4039 
4040 	mutex_unlock(&cgroup_mutex);
4041 	return ret;
4042 }
4043 
4044 /**
4045  * cgroup_add_dfl_cftypes - add an array of cftypes for default hierarchy
4046  * @ss: target cgroup subsystem
4047  * @cfts: zero-length name terminated array of cftypes
4048  *
4049  * Similar to cgroup_add_cftypes() but the added files are only used for
4050  * the default hierarchy.
4051  */
4052 int cgroup_add_dfl_cftypes(struct cgroup_subsys *ss, struct cftype *cfts)
4053 {
4054 	struct cftype *cft;
4055 
4056 	for (cft = cfts; cft && cft->name[0] != '\0'; cft++)
4057 		cft->flags |= __CFTYPE_ONLY_ON_DFL;
4058 	return cgroup_add_cftypes(ss, cfts);
4059 }
4060 
4061 /**
4062  * cgroup_add_legacy_cftypes - add an array of cftypes for legacy hierarchies
4063  * @ss: target cgroup subsystem
4064  * @cfts: zero-length name terminated array of cftypes
4065  *
4066  * Similar to cgroup_add_cftypes() but the added files are only used for
4067  * the legacy hierarchies.
4068  */
4069 int cgroup_add_legacy_cftypes(struct cgroup_subsys *ss, struct cftype *cfts)
4070 {
4071 	struct cftype *cft;
4072 
4073 	for (cft = cfts; cft && cft->name[0] != '\0'; cft++)
4074 		cft->flags |= __CFTYPE_NOT_ON_DFL;
4075 	return cgroup_add_cftypes(ss, cfts);
4076 }
4077 
4078 /**
4079  * cgroup_file_notify - generate a file modified event for a cgroup_file
4080  * @cfile: target cgroup_file
4081  *
4082  * @cfile must have been obtained by setting cftype->file_offset.
4083  */
4084 void cgroup_file_notify(struct cgroup_file *cfile)
4085 {
4086 	unsigned long flags;
4087 
4088 	spin_lock_irqsave(&cgroup_file_kn_lock, flags);
4089 	if (cfile->kn) {
4090 		unsigned long last = cfile->notified_at;
4091 		unsigned long next = last + CGROUP_FILE_NOTIFY_MIN_INTV;
4092 
4093 		if (time_in_range(jiffies, last, next)) {
4094 			timer_reduce(&cfile->notify_timer, next);
4095 		} else {
4096 			kernfs_notify(cfile->kn);
4097 			cfile->notified_at = jiffies;
4098 		}
4099 	}
4100 	spin_unlock_irqrestore(&cgroup_file_kn_lock, flags);
4101 }
4102 
4103 /**
4104  * css_next_child - find the next child of a given css
4105  * @pos: the current position (%NULL to initiate traversal)
4106  * @parent: css whose children to walk
4107  *
4108  * This function returns the next child of @parent and should be called
4109  * under either cgroup_mutex or RCU read lock.  The only requirement is
4110  * that @parent and @pos are accessible.  The next sibling is guaranteed to
4111  * be returned regardless of their states.
4112  *
4113  * If a subsystem synchronizes ->css_online() and the start of iteration, a
4114  * css which finished ->css_online() is guaranteed to be visible in the
4115  * future iterations and will stay visible until the last reference is put.
4116  * A css which hasn't finished ->css_online() or already finished
4117  * ->css_offline() may show up during traversal.  It's each subsystem's
4118  * responsibility to synchronize against on/offlining.
4119  */
4120 struct cgroup_subsys_state *css_next_child(struct cgroup_subsys_state *pos,
4121 					   struct cgroup_subsys_state *parent)
4122 {
4123 	struct cgroup_subsys_state *next;
4124 
4125 	cgroup_assert_mutex_or_rcu_locked();
4126 
4127 	/*
4128 	 * @pos could already have been unlinked from the sibling list.
4129 	 * Once a cgroup is removed, its ->sibling.next is no longer
4130 	 * updated when its next sibling changes.  CSS_RELEASED is set when
4131 	 * @pos is taken off list, at which time its next pointer is valid,
4132 	 * and, as releases are serialized, the one pointed to by the next
4133 	 * pointer is guaranteed to not have started release yet.  This
4134 	 * implies that if we observe !CSS_RELEASED on @pos in this RCU
4135 	 * critical section, the one pointed to by its next pointer is
4136 	 * guaranteed to not have finished its RCU grace period even if we
4137 	 * have dropped rcu_read_lock() in-between iterations.
4138 	 *
4139 	 * If @pos has CSS_RELEASED set, its next pointer can't be
4140 	 * dereferenced; however, as each css is given a monotonically
4141 	 * increasing unique serial number and always appended to the
4142 	 * sibling list, the next one can be found by walking the parent's
4143 	 * children until the first css with higher serial number than
4144 	 * @pos's.  While this path can be slower, it happens iff iteration
4145 	 * races against release and the race window is very small.
4146 	 */
4147 	if (!pos) {
4148 		next = list_entry_rcu(parent->children.next, struct cgroup_subsys_state, sibling);
4149 	} else if (likely(!(pos->flags & CSS_RELEASED))) {
4150 		next = list_entry_rcu(pos->sibling.next, struct cgroup_subsys_state, sibling);
4151 	} else {
4152 		list_for_each_entry_rcu(next, &parent->children, sibling,
4153 					lockdep_is_held(&cgroup_mutex))
4154 			if (next->serial_nr > pos->serial_nr)
4155 				break;
4156 	}
4157 
4158 	/*
4159 	 * @next, if not pointing to the head, can be dereferenced and is
4160 	 * the next sibling.
4161 	 */
4162 	if (&next->sibling != &parent->children)
4163 		return next;
4164 	return NULL;
4165 }
4166 
4167 /**
4168  * css_next_descendant_pre - find the next descendant for pre-order walk
4169  * @pos: the current position (%NULL to initiate traversal)
4170  * @root: css whose descendants to walk
4171  *
4172  * To be used by css_for_each_descendant_pre().  Find the next descendant
4173  * to visit for pre-order traversal of @root's descendants.  @root is
4174  * included in the iteration and the first node to be visited.
4175  *
4176  * While this function requires cgroup_mutex or RCU read locking, it
4177  * doesn't require the whole traversal to be contained in a single critical
4178  * section.  This function will return the correct next descendant as long
4179  * as both @pos and @root are accessible and @pos is a descendant of @root.
4180  *
4181  * If a subsystem synchronizes ->css_online() and the start of iteration, a
4182  * css which finished ->css_online() is guaranteed to be visible in the
4183  * future iterations and will stay visible until the last reference is put.
4184  * A css which hasn't finished ->css_online() or already finished
4185  * ->css_offline() may show up during traversal.  It's each subsystem's
4186  * responsibility to synchronize against on/offlining.
4187  */
4188 struct cgroup_subsys_state *
4189 css_next_descendant_pre(struct cgroup_subsys_state *pos,
4190 			struct cgroup_subsys_state *root)
4191 {
4192 	struct cgroup_subsys_state *next;
4193 
4194 	cgroup_assert_mutex_or_rcu_locked();
4195 
4196 	/* if first iteration, visit @root */
4197 	if (!pos)
4198 		return root;
4199 
4200 	/* visit the first child if exists */
4201 	next = css_next_child(NULL, pos);
4202 	if (next)
4203 		return next;
4204 
4205 	/* no child, visit my or the closest ancestor's next sibling */
4206 	while (pos != root) {
4207 		next = css_next_child(pos, pos->parent);
4208 		if (next)
4209 			return next;
4210 		pos = pos->parent;
4211 	}
4212 
4213 	return NULL;
4214 }
4215 EXPORT_SYMBOL_GPL(css_next_descendant_pre);
4216 
4217 /**
4218  * css_rightmost_descendant - return the rightmost descendant of a css
4219  * @pos: css of interest
4220  *
4221  * Return the rightmost descendant of @pos.  If there's no descendant, @pos
4222  * is returned.  This can be used during pre-order traversal to skip
4223  * subtree of @pos.
4224  *
4225  * While this function requires cgroup_mutex or RCU read locking, it
4226  * doesn't require the whole traversal to be contained in a single critical
4227  * section.  This function will return the correct rightmost descendant as
4228  * long as @pos is accessible.
4229  */
4230 struct cgroup_subsys_state *
4231 css_rightmost_descendant(struct cgroup_subsys_state *pos)
4232 {
4233 	struct cgroup_subsys_state *last, *tmp;
4234 
4235 	cgroup_assert_mutex_or_rcu_locked();
4236 
4237 	do {
4238 		last = pos;
4239 		/* ->prev isn't RCU safe, walk ->next till the end */
4240 		pos = NULL;
4241 		css_for_each_child(tmp, last)
4242 			pos = tmp;
4243 	} while (pos);
4244 
4245 	return last;
4246 }
4247 
4248 static struct cgroup_subsys_state *
4249 css_leftmost_descendant(struct cgroup_subsys_state *pos)
4250 {
4251 	struct cgroup_subsys_state *last;
4252 
4253 	do {
4254 		last = pos;
4255 		pos = css_next_child(NULL, pos);
4256 	} while (pos);
4257 
4258 	return last;
4259 }
4260 
4261 /**
4262  * css_next_descendant_post - find the next descendant for post-order walk
4263  * @pos: the current position (%NULL to initiate traversal)
4264  * @root: css whose descendants to walk
4265  *
4266  * To be used by css_for_each_descendant_post().  Find the next descendant
4267  * to visit for post-order traversal of @root's descendants.  @root is
4268  * included in the iteration and the last node to be visited.
4269  *
4270  * While this function requires cgroup_mutex or RCU read locking, it
4271  * doesn't require the whole traversal to be contained in a single critical
4272  * section.  This function will return the correct next descendant as long
4273  * as both @pos and @cgroup are accessible and @pos is a descendant of
4274  * @cgroup.
4275  *
4276  * If a subsystem synchronizes ->css_online() and the start of iteration, a
4277  * css which finished ->css_online() is guaranteed to be visible in the
4278  * future iterations and will stay visible until the last reference is put.
4279  * A css which hasn't finished ->css_online() or already finished
4280  * ->css_offline() may show up during traversal.  It's each subsystem's
4281  * responsibility to synchronize against on/offlining.
4282  */
4283 struct cgroup_subsys_state *
4284 css_next_descendant_post(struct cgroup_subsys_state *pos,
4285 			 struct cgroup_subsys_state *root)
4286 {
4287 	struct cgroup_subsys_state *next;
4288 
4289 	cgroup_assert_mutex_or_rcu_locked();
4290 
4291 	/* if first iteration, visit leftmost descendant which may be @root */
4292 	if (!pos)
4293 		return css_leftmost_descendant(root);
4294 
4295 	/* if we visited @root, we're done */
4296 	if (pos == root)
4297 		return NULL;
4298 
4299 	/* if there's an unvisited sibling, visit its leftmost descendant */
4300 	next = css_next_child(pos, pos->parent);
4301 	if (next)
4302 		return css_leftmost_descendant(next);
4303 
4304 	/* no sibling left, visit parent */
4305 	return pos->parent;
4306 }
4307 
4308 /**
4309  * css_has_online_children - does a css have online children
4310  * @css: the target css
4311  *
4312  * Returns %true if @css has any online children; otherwise, %false.  This
4313  * function can be called from any context but the caller is responsible
4314  * for synchronizing against on/offlining as necessary.
4315  */
4316 bool css_has_online_children(struct cgroup_subsys_state *css)
4317 {
4318 	struct cgroup_subsys_state *child;
4319 	bool ret = false;
4320 
4321 	rcu_read_lock();
4322 	css_for_each_child(child, css) {
4323 		if (child->flags & CSS_ONLINE) {
4324 			ret = true;
4325 			break;
4326 		}
4327 	}
4328 	rcu_read_unlock();
4329 	return ret;
4330 }
4331 
4332 static struct css_set *css_task_iter_next_css_set(struct css_task_iter *it)
4333 {
4334 	struct list_head *l;
4335 	struct cgrp_cset_link *link;
4336 	struct css_set *cset;
4337 
4338 	lockdep_assert_held(&css_set_lock);
4339 
4340 	/* find the next threaded cset */
4341 	if (it->tcset_pos) {
4342 		l = it->tcset_pos->next;
4343 
4344 		if (l != it->tcset_head) {
4345 			it->tcset_pos = l;
4346 			return container_of(l, struct css_set,
4347 					    threaded_csets_node);
4348 		}
4349 
4350 		it->tcset_pos = NULL;
4351 	}
4352 
4353 	/* find the next cset */
4354 	l = it->cset_pos;
4355 	l = l->next;
4356 	if (l == it->cset_head) {
4357 		it->cset_pos = NULL;
4358 		return NULL;
4359 	}
4360 
4361 	if (it->ss) {
4362 		cset = container_of(l, struct css_set, e_cset_node[it->ss->id]);
4363 	} else {
4364 		link = list_entry(l, struct cgrp_cset_link, cset_link);
4365 		cset = link->cset;
4366 	}
4367 
4368 	it->cset_pos = l;
4369 
4370 	/* initialize threaded css_set walking */
4371 	if (it->flags & CSS_TASK_ITER_THREADED) {
4372 		if (it->cur_dcset)
4373 			put_css_set_locked(it->cur_dcset);
4374 		it->cur_dcset = cset;
4375 		get_css_set(cset);
4376 
4377 		it->tcset_head = &cset->threaded_csets;
4378 		it->tcset_pos = &cset->threaded_csets;
4379 	}
4380 
4381 	return cset;
4382 }
4383 
4384 /**
4385  * css_task_iter_advance_css_set - advance a task iterator to the next css_set
4386  * @it: the iterator to advance
4387  *
4388  * Advance @it to the next css_set to walk.
4389  */
4390 static void css_task_iter_advance_css_set(struct css_task_iter *it)
4391 {
4392 	struct css_set *cset;
4393 
4394 	lockdep_assert_held(&css_set_lock);
4395 
4396 	/* Advance to the next non-empty css_set and find first non-empty tasks list*/
4397 	while ((cset = css_task_iter_next_css_set(it))) {
4398 		if (!list_empty(&cset->tasks)) {
4399 			it->cur_tasks_head = &cset->tasks;
4400 			break;
4401 		} else if (!list_empty(&cset->mg_tasks)) {
4402 			it->cur_tasks_head = &cset->mg_tasks;
4403 			break;
4404 		} else if (!list_empty(&cset->dying_tasks)) {
4405 			it->cur_tasks_head = &cset->dying_tasks;
4406 			break;
4407 		}
4408 	}
4409 	if (!cset) {
4410 		it->task_pos = NULL;
4411 		return;
4412 	}
4413 	it->task_pos = it->cur_tasks_head->next;
4414 
4415 	/*
4416 	 * We don't keep css_sets locked across iteration steps and thus
4417 	 * need to take steps to ensure that iteration can be resumed after
4418 	 * the lock is re-acquired.  Iteration is performed at two levels -
4419 	 * css_sets and tasks in them.
4420 	 *
4421 	 * Once created, a css_set never leaves its cgroup lists, so a
4422 	 * pinned css_set is guaranteed to stay put and we can resume
4423 	 * iteration afterwards.
4424 	 *
4425 	 * Tasks may leave @cset across iteration steps.  This is resolved
4426 	 * by registering each iterator with the css_set currently being
4427 	 * walked and making css_set_move_task() advance iterators whose
4428 	 * next task is leaving.
4429 	 */
4430 	if (it->cur_cset) {
4431 		list_del(&it->iters_node);
4432 		put_css_set_locked(it->cur_cset);
4433 	}
4434 	get_css_set(cset);
4435 	it->cur_cset = cset;
4436 	list_add(&it->iters_node, &cset->task_iters);
4437 }
4438 
4439 static void css_task_iter_skip(struct css_task_iter *it,
4440 			       struct task_struct *task)
4441 {
4442 	lockdep_assert_held(&css_set_lock);
4443 
4444 	if (it->task_pos == &task->cg_list) {
4445 		it->task_pos = it->task_pos->next;
4446 		it->flags |= CSS_TASK_ITER_SKIPPED;
4447 	}
4448 }
4449 
4450 static void css_task_iter_advance(struct css_task_iter *it)
4451 {
4452 	struct task_struct *task;
4453 
4454 	lockdep_assert_held(&css_set_lock);
4455 repeat:
4456 	if (it->task_pos) {
4457 		/*
4458 		 * Advance iterator to find next entry. We go through cset
4459 		 * tasks, mg_tasks and dying_tasks, when consumed we move onto
4460 		 * the next cset.
4461 		 */
4462 		if (it->flags & CSS_TASK_ITER_SKIPPED)
4463 			it->flags &= ~CSS_TASK_ITER_SKIPPED;
4464 		else
4465 			it->task_pos = it->task_pos->next;
4466 
4467 		if (it->task_pos == &it->cur_cset->tasks) {
4468 			it->cur_tasks_head = &it->cur_cset->mg_tasks;
4469 			it->task_pos = it->cur_tasks_head->next;
4470 		}
4471 		if (it->task_pos == &it->cur_cset->mg_tasks) {
4472 			it->cur_tasks_head = &it->cur_cset->dying_tasks;
4473 			it->task_pos = it->cur_tasks_head->next;
4474 		}
4475 		if (it->task_pos == &it->cur_cset->dying_tasks)
4476 			css_task_iter_advance_css_set(it);
4477 	} else {
4478 		/* called from start, proceed to the first cset */
4479 		css_task_iter_advance_css_set(it);
4480 	}
4481 
4482 	if (!it->task_pos)
4483 		return;
4484 
4485 	task = list_entry(it->task_pos, struct task_struct, cg_list);
4486 
4487 	if (it->flags & CSS_TASK_ITER_PROCS) {
4488 		/* if PROCS, skip over tasks which aren't group leaders */
4489 		if (!thread_group_leader(task))
4490 			goto repeat;
4491 
4492 		/* and dying leaders w/o live member threads */
4493 		if (it->cur_tasks_head == &it->cur_cset->dying_tasks &&
4494 		    !atomic_read(&task->signal->live))
4495 			goto repeat;
4496 	} else {
4497 		/* skip all dying ones */
4498 		if (it->cur_tasks_head == &it->cur_cset->dying_tasks)
4499 			goto repeat;
4500 	}
4501 }
4502 
4503 /**
4504  * css_task_iter_start - initiate task iteration
4505  * @css: the css to walk tasks of
4506  * @flags: CSS_TASK_ITER_* flags
4507  * @it: the task iterator to use
4508  *
4509  * Initiate iteration through the tasks of @css.  The caller can call
4510  * css_task_iter_next() to walk through the tasks until the function
4511  * returns NULL.  On completion of iteration, css_task_iter_end() must be
4512  * called.
4513  */
4514 void css_task_iter_start(struct cgroup_subsys_state *css, unsigned int flags,
4515 			 struct css_task_iter *it)
4516 {
4517 	memset(it, 0, sizeof(*it));
4518 
4519 	spin_lock_irq(&css_set_lock);
4520 
4521 	it->ss = css->ss;
4522 	it->flags = flags;
4523 
4524 	if (it->ss)
4525 		it->cset_pos = &css->cgroup->e_csets[css->ss->id];
4526 	else
4527 		it->cset_pos = &css->cgroup->cset_links;
4528 
4529 	it->cset_head = it->cset_pos;
4530 
4531 	css_task_iter_advance(it);
4532 
4533 	spin_unlock_irq(&css_set_lock);
4534 }
4535 
4536 /**
4537  * css_task_iter_next - return the next task for the iterator
4538  * @it: the task iterator being iterated
4539  *
4540  * The "next" function for task iteration.  @it should have been
4541  * initialized via css_task_iter_start().  Returns NULL when the iteration
4542  * reaches the end.
4543  */
4544 struct task_struct *css_task_iter_next(struct css_task_iter *it)
4545 {
4546 	if (it->cur_task) {
4547 		put_task_struct(it->cur_task);
4548 		it->cur_task = NULL;
4549 	}
4550 
4551 	spin_lock_irq(&css_set_lock);
4552 
4553 	/* @it may be half-advanced by skips, finish advancing */
4554 	if (it->flags & CSS_TASK_ITER_SKIPPED)
4555 		css_task_iter_advance(it);
4556 
4557 	if (it->task_pos) {
4558 		it->cur_task = list_entry(it->task_pos, struct task_struct,
4559 					  cg_list);
4560 		get_task_struct(it->cur_task);
4561 		css_task_iter_advance(it);
4562 	}
4563 
4564 	spin_unlock_irq(&css_set_lock);
4565 
4566 	return it->cur_task;
4567 }
4568 
4569 /**
4570  * css_task_iter_end - finish task iteration
4571  * @it: the task iterator to finish
4572  *
4573  * Finish task iteration started by css_task_iter_start().
4574  */
4575 void css_task_iter_end(struct css_task_iter *it)
4576 {
4577 	if (it->cur_cset) {
4578 		spin_lock_irq(&css_set_lock);
4579 		list_del(&it->iters_node);
4580 		put_css_set_locked(it->cur_cset);
4581 		spin_unlock_irq(&css_set_lock);
4582 	}
4583 
4584 	if (it->cur_dcset)
4585 		put_css_set(it->cur_dcset);
4586 
4587 	if (it->cur_task)
4588 		put_task_struct(it->cur_task);
4589 }
4590 
4591 static void cgroup_procs_release(struct kernfs_open_file *of)
4592 {
4593 	if (of->priv) {
4594 		css_task_iter_end(of->priv);
4595 		kfree(of->priv);
4596 	}
4597 }
4598 
4599 static void *cgroup_procs_next(struct seq_file *s, void *v, loff_t *pos)
4600 {
4601 	struct kernfs_open_file *of = s->private;
4602 	struct css_task_iter *it = of->priv;
4603 
4604 	if (pos)
4605 		(*pos)++;
4606 
4607 	return css_task_iter_next(it);
4608 }
4609 
4610 static void *__cgroup_procs_start(struct seq_file *s, loff_t *pos,
4611 				  unsigned int iter_flags)
4612 {
4613 	struct kernfs_open_file *of = s->private;
4614 	struct cgroup *cgrp = seq_css(s)->cgroup;
4615 	struct css_task_iter *it = of->priv;
4616 
4617 	/*
4618 	 * When a seq_file is seeked, it's always traversed sequentially
4619 	 * from position 0, so we can simply keep iterating on !0 *pos.
4620 	 */
4621 	if (!it) {
4622 		if (WARN_ON_ONCE((*pos)))
4623 			return ERR_PTR(-EINVAL);
4624 
4625 		it = kzalloc(sizeof(*it), GFP_KERNEL);
4626 		if (!it)
4627 			return ERR_PTR(-ENOMEM);
4628 		of->priv = it;
4629 		css_task_iter_start(&cgrp->self, iter_flags, it);
4630 	} else if (!(*pos)) {
4631 		css_task_iter_end(it);
4632 		css_task_iter_start(&cgrp->self, iter_flags, it);
4633 	} else
4634 		return it->cur_task;
4635 
4636 	return cgroup_procs_next(s, NULL, NULL);
4637 }
4638 
4639 static void *cgroup_procs_start(struct seq_file *s, loff_t *pos)
4640 {
4641 	struct cgroup *cgrp = seq_css(s)->cgroup;
4642 
4643 	/*
4644 	 * All processes of a threaded subtree belong to the domain cgroup
4645 	 * of the subtree.  Only threads can be distributed across the
4646 	 * subtree.  Reject reads on cgroup.procs in the subtree proper.
4647 	 * They're always empty anyway.
4648 	 */
4649 	if (cgroup_is_threaded(cgrp))
4650 		return ERR_PTR(-EOPNOTSUPP);
4651 
4652 	return __cgroup_procs_start(s, pos, CSS_TASK_ITER_PROCS |
4653 					    CSS_TASK_ITER_THREADED);
4654 }
4655 
4656 static int cgroup_procs_show(struct seq_file *s, void *v)
4657 {
4658 	seq_printf(s, "%d\n", task_pid_vnr(v));
4659 	return 0;
4660 }
4661 
4662 static int cgroup_may_write(const struct cgroup *cgrp, struct super_block *sb)
4663 {
4664 	int ret;
4665 	struct inode *inode;
4666 
4667 	lockdep_assert_held(&cgroup_mutex);
4668 
4669 	inode = kernfs_get_inode(sb, cgrp->procs_file.kn);
4670 	if (!inode)
4671 		return -ENOMEM;
4672 
4673 	ret = inode_permission(inode, MAY_WRITE);
4674 	iput(inode);
4675 	return ret;
4676 }
4677 
4678 static int cgroup_procs_write_permission(struct cgroup *src_cgrp,
4679 					 struct cgroup *dst_cgrp,
4680 					 struct super_block *sb)
4681 {
4682 	struct cgroup_namespace *ns = current->nsproxy->cgroup_ns;
4683 	struct cgroup *com_cgrp = src_cgrp;
4684 	int ret;
4685 
4686 	lockdep_assert_held(&cgroup_mutex);
4687 
4688 	/* find the common ancestor */
4689 	while (!cgroup_is_descendant(dst_cgrp, com_cgrp))
4690 		com_cgrp = cgroup_parent(com_cgrp);
4691 
4692 	/* %current should be authorized to migrate to the common ancestor */
4693 	ret = cgroup_may_write(com_cgrp, sb);
4694 	if (ret)
4695 		return ret;
4696 
4697 	/*
4698 	 * If namespaces are delegation boundaries, %current must be able
4699 	 * to see both source and destination cgroups from its namespace.
4700 	 */
4701 	if ((cgrp_dfl_root.flags & CGRP_ROOT_NS_DELEGATE) &&
4702 	    (!cgroup_is_descendant(src_cgrp, ns->root_cset->dfl_cgrp) ||
4703 	     !cgroup_is_descendant(dst_cgrp, ns->root_cset->dfl_cgrp)))
4704 		return -ENOENT;
4705 
4706 	return 0;
4707 }
4708 
4709 static int cgroup_attach_permissions(struct cgroup *src_cgrp,
4710 				     struct cgroup *dst_cgrp,
4711 				     struct super_block *sb, bool threadgroup)
4712 {
4713 	int ret = 0;
4714 
4715 	ret = cgroup_procs_write_permission(src_cgrp, dst_cgrp, sb);
4716 	if (ret)
4717 		return ret;
4718 
4719 	ret = cgroup_migrate_vet_dst(dst_cgrp);
4720 	if (ret)
4721 		return ret;
4722 
4723 	if (!threadgroup && (src_cgrp->dom_cgrp != dst_cgrp->dom_cgrp))
4724 		ret = -EOPNOTSUPP;
4725 
4726 	return ret;
4727 }
4728 
4729 static ssize_t cgroup_procs_write(struct kernfs_open_file *of,
4730 				  char *buf, size_t nbytes, loff_t off)
4731 {
4732 	struct cgroup *src_cgrp, *dst_cgrp;
4733 	struct task_struct *task;
4734 	ssize_t ret;
4735 	bool locked;
4736 
4737 	dst_cgrp = cgroup_kn_lock_live(of->kn, false);
4738 	if (!dst_cgrp)
4739 		return -ENODEV;
4740 
4741 	task = cgroup_procs_write_start(buf, true, &locked);
4742 	ret = PTR_ERR_OR_ZERO(task);
4743 	if (ret)
4744 		goto out_unlock;
4745 
4746 	/* find the source cgroup */
4747 	spin_lock_irq(&css_set_lock);
4748 	src_cgrp = task_cgroup_from_root(task, &cgrp_dfl_root);
4749 	spin_unlock_irq(&css_set_lock);
4750 
4751 	ret = cgroup_attach_permissions(src_cgrp, dst_cgrp,
4752 					of->file->f_path.dentry->d_sb, true);
4753 	if (ret)
4754 		goto out_finish;
4755 
4756 	ret = cgroup_attach_task(dst_cgrp, task, true);
4757 
4758 out_finish:
4759 	cgroup_procs_write_finish(task, locked);
4760 out_unlock:
4761 	cgroup_kn_unlock(of->kn);
4762 
4763 	return ret ?: nbytes;
4764 }
4765 
4766 static void *cgroup_threads_start(struct seq_file *s, loff_t *pos)
4767 {
4768 	return __cgroup_procs_start(s, pos, 0);
4769 }
4770 
4771 static ssize_t cgroup_threads_write(struct kernfs_open_file *of,
4772 				    char *buf, size_t nbytes, loff_t off)
4773 {
4774 	struct cgroup *src_cgrp, *dst_cgrp;
4775 	struct task_struct *task;
4776 	ssize_t ret;
4777 	bool locked;
4778 
4779 	buf = strstrip(buf);
4780 
4781 	dst_cgrp = cgroup_kn_lock_live(of->kn, false);
4782 	if (!dst_cgrp)
4783 		return -ENODEV;
4784 
4785 	task = cgroup_procs_write_start(buf, false, &locked);
4786 	ret = PTR_ERR_OR_ZERO(task);
4787 	if (ret)
4788 		goto out_unlock;
4789 
4790 	/* find the source cgroup */
4791 	spin_lock_irq(&css_set_lock);
4792 	src_cgrp = task_cgroup_from_root(task, &cgrp_dfl_root);
4793 	spin_unlock_irq(&css_set_lock);
4794 
4795 	/* thread migrations follow the cgroup.procs delegation rule */
4796 	ret = cgroup_attach_permissions(src_cgrp, dst_cgrp,
4797 					of->file->f_path.dentry->d_sb, false);
4798 	if (ret)
4799 		goto out_finish;
4800 
4801 	ret = cgroup_attach_task(dst_cgrp, task, false);
4802 
4803 out_finish:
4804 	cgroup_procs_write_finish(task, locked);
4805 out_unlock:
4806 	cgroup_kn_unlock(of->kn);
4807 
4808 	return ret ?: nbytes;
4809 }
4810 
4811 /* cgroup core interface files for the default hierarchy */
4812 static struct cftype cgroup_base_files[] = {
4813 	{
4814 		.name = "cgroup.type",
4815 		.flags = CFTYPE_NOT_ON_ROOT,
4816 		.seq_show = cgroup_type_show,
4817 		.write = cgroup_type_write,
4818 	},
4819 	{
4820 		.name = "cgroup.procs",
4821 		.flags = CFTYPE_NS_DELEGATABLE,
4822 		.file_offset = offsetof(struct cgroup, procs_file),
4823 		.release = cgroup_procs_release,
4824 		.seq_start = cgroup_procs_start,
4825 		.seq_next = cgroup_procs_next,
4826 		.seq_show = cgroup_procs_show,
4827 		.write = cgroup_procs_write,
4828 	},
4829 	{
4830 		.name = "cgroup.threads",
4831 		.flags = CFTYPE_NS_DELEGATABLE,
4832 		.release = cgroup_procs_release,
4833 		.seq_start = cgroup_threads_start,
4834 		.seq_next = cgroup_procs_next,
4835 		.seq_show = cgroup_procs_show,
4836 		.write = cgroup_threads_write,
4837 	},
4838 	{
4839 		.name = "cgroup.controllers",
4840 		.seq_show = cgroup_controllers_show,
4841 	},
4842 	{
4843 		.name = "cgroup.subtree_control",
4844 		.flags = CFTYPE_NS_DELEGATABLE,
4845 		.seq_show = cgroup_subtree_control_show,
4846 		.write = cgroup_subtree_control_write,
4847 	},
4848 	{
4849 		.name = "cgroup.events",
4850 		.flags = CFTYPE_NOT_ON_ROOT,
4851 		.file_offset = offsetof(struct cgroup, events_file),
4852 		.seq_show = cgroup_events_show,
4853 	},
4854 	{
4855 		.name = "cgroup.max.descendants",
4856 		.seq_show = cgroup_max_descendants_show,
4857 		.write = cgroup_max_descendants_write,
4858 	},
4859 	{
4860 		.name = "cgroup.max.depth",
4861 		.seq_show = cgroup_max_depth_show,
4862 		.write = cgroup_max_depth_write,
4863 	},
4864 	{
4865 		.name = "cgroup.stat",
4866 		.seq_show = cgroup_stat_show,
4867 	},
4868 	{
4869 		.name = "cgroup.freeze",
4870 		.flags = CFTYPE_NOT_ON_ROOT,
4871 		.seq_show = cgroup_freeze_show,
4872 		.write = cgroup_freeze_write,
4873 	},
4874 	{
4875 		.name = "cpu.stat",
4876 		.seq_show = cpu_stat_show,
4877 	},
4878 #ifdef CONFIG_PSI
4879 	{
4880 		.name = "io.pressure",
4881 		.seq_show = cgroup_io_pressure_show,
4882 		.write = cgroup_io_pressure_write,
4883 		.poll = cgroup_pressure_poll,
4884 		.release = cgroup_pressure_release,
4885 	},
4886 	{
4887 		.name = "memory.pressure",
4888 		.seq_show = cgroup_memory_pressure_show,
4889 		.write = cgroup_memory_pressure_write,
4890 		.poll = cgroup_pressure_poll,
4891 		.release = cgroup_pressure_release,
4892 	},
4893 	{
4894 		.name = "cpu.pressure",
4895 		.seq_show = cgroup_cpu_pressure_show,
4896 		.write = cgroup_cpu_pressure_write,
4897 		.poll = cgroup_pressure_poll,
4898 		.release = cgroup_pressure_release,
4899 	},
4900 #endif /* CONFIG_PSI */
4901 	{ }	/* terminate */
4902 };
4903 
4904 /*
4905  * css destruction is four-stage process.
4906  *
4907  * 1. Destruction starts.  Killing of the percpu_ref is initiated.
4908  *    Implemented in kill_css().
4909  *
4910  * 2. When the percpu_ref is confirmed to be visible as killed on all CPUs
4911  *    and thus css_tryget_online() is guaranteed to fail, the css can be
4912  *    offlined by invoking offline_css().  After offlining, the base ref is
4913  *    put.  Implemented in css_killed_work_fn().
4914  *
4915  * 3. When the percpu_ref reaches zero, the only possible remaining
4916  *    accessors are inside RCU read sections.  css_release() schedules the
4917  *    RCU callback.
4918  *
4919  * 4. After the grace period, the css can be freed.  Implemented in
4920  *    css_free_work_fn().
4921  *
4922  * It is actually hairier because both step 2 and 4 require process context
4923  * and thus involve punting to css->destroy_work adding two additional
4924  * steps to the already complex sequence.
4925  */
4926 static void css_free_rwork_fn(struct work_struct *work)
4927 {
4928 	struct cgroup_subsys_state *css = container_of(to_rcu_work(work),
4929 				struct cgroup_subsys_state, destroy_rwork);
4930 	struct cgroup_subsys *ss = css->ss;
4931 	struct cgroup *cgrp = css->cgroup;
4932 
4933 	percpu_ref_exit(&css->refcnt);
4934 
4935 	if (ss) {
4936 		/* css free path */
4937 		struct cgroup_subsys_state *parent = css->parent;
4938 		int id = css->id;
4939 
4940 		ss->css_free(css);
4941 		cgroup_idr_remove(&ss->css_idr, id);
4942 		cgroup_put(cgrp);
4943 
4944 		if (parent)
4945 			css_put(parent);
4946 	} else {
4947 		/* cgroup free path */
4948 		atomic_dec(&cgrp->root->nr_cgrps);
4949 		cgroup1_pidlist_destroy_all(cgrp);
4950 		cancel_work_sync(&cgrp->release_agent_work);
4951 
4952 		if (cgroup_parent(cgrp)) {
4953 			/*
4954 			 * We get a ref to the parent, and put the ref when
4955 			 * this cgroup is being freed, so it's guaranteed
4956 			 * that the parent won't be destroyed before its
4957 			 * children.
4958 			 */
4959 			cgroup_put(cgroup_parent(cgrp));
4960 			kernfs_put(cgrp->kn);
4961 			psi_cgroup_free(cgrp);
4962 			if (cgroup_on_dfl(cgrp))
4963 				cgroup_rstat_exit(cgrp);
4964 			kfree(cgrp);
4965 		} else {
4966 			/*
4967 			 * This is root cgroup's refcnt reaching zero,
4968 			 * which indicates that the root should be
4969 			 * released.
4970 			 */
4971 			cgroup_destroy_root(cgrp->root);
4972 		}
4973 	}
4974 }
4975 
4976 static void css_release_work_fn(struct work_struct *work)
4977 {
4978 	struct cgroup_subsys_state *css =
4979 		container_of(work, struct cgroup_subsys_state, destroy_work);
4980 	struct cgroup_subsys *ss = css->ss;
4981 	struct cgroup *cgrp = css->cgroup;
4982 
4983 	mutex_lock(&cgroup_mutex);
4984 
4985 	css->flags |= CSS_RELEASED;
4986 	list_del_rcu(&css->sibling);
4987 
4988 	if (ss) {
4989 		/* css release path */
4990 		if (!list_empty(&css->rstat_css_node)) {
4991 			cgroup_rstat_flush(cgrp);
4992 			list_del_rcu(&css->rstat_css_node);
4993 		}
4994 
4995 		cgroup_idr_replace(&ss->css_idr, NULL, css->id);
4996 		if (ss->css_released)
4997 			ss->css_released(css);
4998 	} else {
4999 		struct cgroup *tcgrp;
5000 
5001 		/* cgroup release path */
5002 		TRACE_CGROUP_PATH(release, cgrp);
5003 
5004 		if (cgroup_on_dfl(cgrp))
5005 			cgroup_rstat_flush(cgrp);
5006 
5007 		spin_lock_irq(&css_set_lock);
5008 		for (tcgrp = cgroup_parent(cgrp); tcgrp;
5009 		     tcgrp = cgroup_parent(tcgrp))
5010 			tcgrp->nr_dying_descendants--;
5011 		spin_unlock_irq(&css_set_lock);
5012 
5013 		/*
5014 		 * There are two control paths which try to determine
5015 		 * cgroup from dentry without going through kernfs -
5016 		 * cgroupstats_build() and css_tryget_online_from_dir().
5017 		 * Those are supported by RCU protecting clearing of
5018 		 * cgrp->kn->priv backpointer.
5019 		 */
5020 		if (cgrp->kn)
5021 			RCU_INIT_POINTER(*(void __rcu __force **)&cgrp->kn->priv,
5022 					 NULL);
5023 	}
5024 
5025 	mutex_unlock(&cgroup_mutex);
5026 
5027 	INIT_RCU_WORK(&css->destroy_rwork, css_free_rwork_fn);
5028 	queue_rcu_work(cgroup_destroy_wq, &css->destroy_rwork);
5029 }
5030 
5031 static void css_release(struct percpu_ref *ref)
5032 {
5033 	struct cgroup_subsys_state *css =
5034 		container_of(ref, struct cgroup_subsys_state, refcnt);
5035 
5036 	INIT_WORK(&css->destroy_work, css_release_work_fn);
5037 	queue_work(cgroup_destroy_wq, &css->destroy_work);
5038 }
5039 
5040 static void init_and_link_css(struct cgroup_subsys_state *css,
5041 			      struct cgroup_subsys *ss, struct cgroup *cgrp)
5042 {
5043 	lockdep_assert_held(&cgroup_mutex);
5044 
5045 	cgroup_get_live(cgrp);
5046 
5047 	memset(css, 0, sizeof(*css));
5048 	css->cgroup = cgrp;
5049 	css->ss = ss;
5050 	css->id = -1;
5051 	INIT_LIST_HEAD(&css->sibling);
5052 	INIT_LIST_HEAD(&css->children);
5053 	INIT_LIST_HEAD(&css->rstat_css_node);
5054 	css->serial_nr = css_serial_nr_next++;
5055 	atomic_set(&css->online_cnt, 0);
5056 
5057 	if (cgroup_parent(cgrp)) {
5058 		css->parent = cgroup_css(cgroup_parent(cgrp), ss);
5059 		css_get(css->parent);
5060 	}
5061 
5062 	if (cgroup_on_dfl(cgrp) && ss->css_rstat_flush)
5063 		list_add_rcu(&css->rstat_css_node, &cgrp->rstat_css_list);
5064 
5065 	BUG_ON(cgroup_css(cgrp, ss));
5066 }
5067 
5068 /* invoke ->css_online() on a new CSS and mark it online if successful */
5069 static int online_css(struct cgroup_subsys_state *css)
5070 {
5071 	struct cgroup_subsys *ss = css->ss;
5072 	int ret = 0;
5073 
5074 	lockdep_assert_held(&cgroup_mutex);
5075 
5076 	if (ss->css_online)
5077 		ret = ss->css_online(css);
5078 	if (!ret) {
5079 		css->flags |= CSS_ONLINE;
5080 		rcu_assign_pointer(css->cgroup->subsys[ss->id], css);
5081 
5082 		atomic_inc(&css->online_cnt);
5083 		if (css->parent)
5084 			atomic_inc(&css->parent->online_cnt);
5085 	}
5086 	return ret;
5087 }
5088 
5089 /* if the CSS is online, invoke ->css_offline() on it and mark it offline */
5090 static void offline_css(struct cgroup_subsys_state *css)
5091 {
5092 	struct cgroup_subsys *ss = css->ss;
5093 
5094 	lockdep_assert_held(&cgroup_mutex);
5095 
5096 	if (!(css->flags & CSS_ONLINE))
5097 		return;
5098 
5099 	if (ss->css_offline)
5100 		ss->css_offline(css);
5101 
5102 	css->flags &= ~CSS_ONLINE;
5103 	RCU_INIT_POINTER(css->cgroup->subsys[ss->id], NULL);
5104 
5105 	wake_up_all(&css->cgroup->offline_waitq);
5106 }
5107 
5108 /**
5109  * css_create - create a cgroup_subsys_state
5110  * @cgrp: the cgroup new css will be associated with
5111  * @ss: the subsys of new css
5112  *
5113  * Create a new css associated with @cgrp - @ss pair.  On success, the new
5114  * css is online and installed in @cgrp.  This function doesn't create the
5115  * interface files.  Returns 0 on success, -errno on failure.
5116  */
5117 static struct cgroup_subsys_state *css_create(struct cgroup *cgrp,
5118 					      struct cgroup_subsys *ss)
5119 {
5120 	struct cgroup *parent = cgroup_parent(cgrp);
5121 	struct cgroup_subsys_state *parent_css = cgroup_css(parent, ss);
5122 	struct cgroup_subsys_state *css;
5123 	int err;
5124 
5125 	lockdep_assert_held(&cgroup_mutex);
5126 
5127 	css = ss->css_alloc(parent_css);
5128 	if (!css)
5129 		css = ERR_PTR(-ENOMEM);
5130 	if (IS_ERR(css))
5131 		return css;
5132 
5133 	init_and_link_css(css, ss, cgrp);
5134 
5135 	err = percpu_ref_init(&css->refcnt, css_release, 0, GFP_KERNEL);
5136 	if (err)
5137 		goto err_free_css;
5138 
5139 	err = cgroup_idr_alloc(&ss->css_idr, NULL, 2, 0, GFP_KERNEL);
5140 	if (err < 0)
5141 		goto err_free_css;
5142 	css->id = err;
5143 
5144 	/* @css is ready to be brought online now, make it visible */
5145 	list_add_tail_rcu(&css->sibling, &parent_css->children);
5146 	cgroup_idr_replace(&ss->css_idr, css, css->id);
5147 
5148 	err = online_css(css);
5149 	if (err)
5150 		goto err_list_del;
5151 
5152 	return css;
5153 
5154 err_list_del:
5155 	list_del_rcu(&css->sibling);
5156 err_free_css:
5157 	list_del_rcu(&css->rstat_css_node);
5158 	INIT_RCU_WORK(&css->destroy_rwork, css_free_rwork_fn);
5159 	queue_rcu_work(cgroup_destroy_wq, &css->destroy_rwork);
5160 	return ERR_PTR(err);
5161 }
5162 
5163 /*
5164  * The returned cgroup is fully initialized including its control mask, but
5165  * it isn't associated with its kernfs_node and doesn't have the control
5166  * mask applied.
5167  */
5168 static struct cgroup *cgroup_create(struct cgroup *parent, const char *name,
5169 				    umode_t mode)
5170 {
5171 	struct cgroup_root *root = parent->root;
5172 	struct cgroup *cgrp, *tcgrp;
5173 	struct kernfs_node *kn;
5174 	int level = parent->level + 1;
5175 	int ret;
5176 
5177 	/* allocate the cgroup and its ID, 0 is reserved for the root */
5178 	cgrp = kzalloc(struct_size(cgrp, ancestor_ids, (level + 1)),
5179 		       GFP_KERNEL);
5180 	if (!cgrp)
5181 		return ERR_PTR(-ENOMEM);
5182 
5183 	ret = percpu_ref_init(&cgrp->self.refcnt, css_release, 0, GFP_KERNEL);
5184 	if (ret)
5185 		goto out_free_cgrp;
5186 
5187 	if (cgroup_on_dfl(parent)) {
5188 		ret = cgroup_rstat_init(cgrp);
5189 		if (ret)
5190 			goto out_cancel_ref;
5191 	}
5192 
5193 	/* create the directory */
5194 	kn = kernfs_create_dir(parent->kn, name, mode, cgrp);
5195 	if (IS_ERR(kn)) {
5196 		ret = PTR_ERR(kn);
5197 		goto out_stat_exit;
5198 	}
5199 	cgrp->kn = kn;
5200 
5201 	init_cgroup_housekeeping(cgrp);
5202 
5203 	cgrp->self.parent = &parent->self;
5204 	cgrp->root = root;
5205 	cgrp->level = level;
5206 
5207 	ret = psi_cgroup_alloc(cgrp);
5208 	if (ret)
5209 		goto out_kernfs_remove;
5210 
5211 	ret = cgroup_bpf_inherit(cgrp);
5212 	if (ret)
5213 		goto out_psi_free;
5214 
5215 	/*
5216 	 * New cgroup inherits effective freeze counter, and
5217 	 * if the parent has to be frozen, the child has too.
5218 	 */
5219 	cgrp->freezer.e_freeze = parent->freezer.e_freeze;
5220 	if (cgrp->freezer.e_freeze) {
5221 		/*
5222 		 * Set the CGRP_FREEZE flag, so when a process will be
5223 		 * attached to the child cgroup, it will become frozen.
5224 		 * At this point the new cgroup is unpopulated, so we can
5225 		 * consider it frozen immediately.
5226 		 */
5227 		set_bit(CGRP_FREEZE, &cgrp->flags);
5228 		set_bit(CGRP_FROZEN, &cgrp->flags);
5229 	}
5230 
5231 	spin_lock_irq(&css_set_lock);
5232 	for (tcgrp = cgrp; tcgrp; tcgrp = cgroup_parent(tcgrp)) {
5233 		cgrp->ancestor_ids[tcgrp->level] = cgroup_id(tcgrp);
5234 
5235 		if (tcgrp != cgrp) {
5236 			tcgrp->nr_descendants++;
5237 
5238 			/*
5239 			 * If the new cgroup is frozen, all ancestor cgroups
5240 			 * get a new frozen descendant, but their state can't
5241 			 * change because of this.
5242 			 */
5243 			if (cgrp->freezer.e_freeze)
5244 				tcgrp->freezer.nr_frozen_descendants++;
5245 		}
5246 	}
5247 	spin_unlock_irq(&css_set_lock);
5248 
5249 	if (notify_on_release(parent))
5250 		set_bit(CGRP_NOTIFY_ON_RELEASE, &cgrp->flags);
5251 
5252 	if (test_bit(CGRP_CPUSET_CLONE_CHILDREN, &parent->flags))
5253 		set_bit(CGRP_CPUSET_CLONE_CHILDREN, &cgrp->flags);
5254 
5255 	cgrp->self.serial_nr = css_serial_nr_next++;
5256 
5257 	/* allocation complete, commit to creation */
5258 	list_add_tail_rcu(&cgrp->self.sibling, &cgroup_parent(cgrp)->self.children);
5259 	atomic_inc(&root->nr_cgrps);
5260 	cgroup_get_live(parent);
5261 
5262 	/*
5263 	 * On the default hierarchy, a child doesn't automatically inherit
5264 	 * subtree_control from the parent.  Each is configured manually.
5265 	 */
5266 	if (!cgroup_on_dfl(cgrp))
5267 		cgrp->subtree_control = cgroup_control(cgrp);
5268 
5269 	cgroup_propagate_control(cgrp);
5270 
5271 	return cgrp;
5272 
5273 out_psi_free:
5274 	psi_cgroup_free(cgrp);
5275 out_kernfs_remove:
5276 	kernfs_remove(cgrp->kn);
5277 out_stat_exit:
5278 	if (cgroup_on_dfl(parent))
5279 		cgroup_rstat_exit(cgrp);
5280 out_cancel_ref:
5281 	percpu_ref_exit(&cgrp->self.refcnt);
5282 out_free_cgrp:
5283 	kfree(cgrp);
5284 	return ERR_PTR(ret);
5285 }
5286 
5287 static bool cgroup_check_hierarchy_limits(struct cgroup *parent)
5288 {
5289 	struct cgroup *cgroup;
5290 	int ret = false;
5291 	int level = 1;
5292 
5293 	lockdep_assert_held(&cgroup_mutex);
5294 
5295 	for (cgroup = parent; cgroup; cgroup = cgroup_parent(cgroup)) {
5296 		if (cgroup->nr_descendants >= cgroup->max_descendants)
5297 			goto fail;
5298 
5299 		if (level > cgroup->max_depth)
5300 			goto fail;
5301 
5302 		level++;
5303 	}
5304 
5305 	ret = true;
5306 fail:
5307 	return ret;
5308 }
5309 
5310 int cgroup_mkdir(struct kernfs_node *parent_kn, const char *name, umode_t mode)
5311 {
5312 	struct cgroup *parent, *cgrp;
5313 	int ret;
5314 
5315 	/* do not accept '\n' to prevent making /proc/<pid>/cgroup unparsable */
5316 	if (strchr(name, '\n'))
5317 		return -EINVAL;
5318 
5319 	parent = cgroup_kn_lock_live(parent_kn, false);
5320 	if (!parent)
5321 		return -ENODEV;
5322 
5323 	if (!cgroup_check_hierarchy_limits(parent)) {
5324 		ret = -EAGAIN;
5325 		goto out_unlock;
5326 	}
5327 
5328 	cgrp = cgroup_create(parent, name, mode);
5329 	if (IS_ERR(cgrp)) {
5330 		ret = PTR_ERR(cgrp);
5331 		goto out_unlock;
5332 	}
5333 
5334 	/*
5335 	 * This extra ref will be put in cgroup_free_fn() and guarantees
5336 	 * that @cgrp->kn is always accessible.
5337 	 */
5338 	kernfs_get(cgrp->kn);
5339 
5340 	ret = cgroup_kn_set_ugid(cgrp->kn);
5341 	if (ret)
5342 		goto out_destroy;
5343 
5344 	ret = css_populate_dir(&cgrp->self);
5345 	if (ret)
5346 		goto out_destroy;
5347 
5348 	ret = cgroup_apply_control_enable(cgrp);
5349 	if (ret)
5350 		goto out_destroy;
5351 
5352 	TRACE_CGROUP_PATH(mkdir, cgrp);
5353 
5354 	/* let's create and online css's */
5355 	kernfs_activate(cgrp->kn);
5356 
5357 	ret = 0;
5358 	goto out_unlock;
5359 
5360 out_destroy:
5361 	cgroup_destroy_locked(cgrp);
5362 out_unlock:
5363 	cgroup_kn_unlock(parent_kn);
5364 	return ret;
5365 }
5366 
5367 /*
5368  * This is called when the refcnt of a css is confirmed to be killed.
5369  * css_tryget_online() is now guaranteed to fail.  Tell the subsystem to
5370  * initate destruction and put the css ref from kill_css().
5371  */
5372 static void css_killed_work_fn(struct work_struct *work)
5373 {
5374 	struct cgroup_subsys_state *css =
5375 		container_of(work, struct cgroup_subsys_state, destroy_work);
5376 
5377 	mutex_lock(&cgroup_mutex);
5378 
5379 	do {
5380 		offline_css(css);
5381 		css_put(css);
5382 		/* @css can't go away while we're holding cgroup_mutex */
5383 		css = css->parent;
5384 	} while (css && atomic_dec_and_test(&css->online_cnt));
5385 
5386 	mutex_unlock(&cgroup_mutex);
5387 }
5388 
5389 /* css kill confirmation processing requires process context, bounce */
5390 static void css_killed_ref_fn(struct percpu_ref *ref)
5391 {
5392 	struct cgroup_subsys_state *css =
5393 		container_of(ref, struct cgroup_subsys_state, refcnt);
5394 
5395 	if (atomic_dec_and_test(&css->online_cnt)) {
5396 		INIT_WORK(&css->destroy_work, css_killed_work_fn);
5397 		queue_work(cgroup_destroy_wq, &css->destroy_work);
5398 	}
5399 }
5400 
5401 /**
5402  * kill_css - destroy a css
5403  * @css: css to destroy
5404  *
5405  * This function initiates destruction of @css by removing cgroup interface
5406  * files and putting its base reference.  ->css_offline() will be invoked
5407  * asynchronously once css_tryget_online() is guaranteed to fail and when
5408  * the reference count reaches zero, @css will be released.
5409  */
5410 static void kill_css(struct cgroup_subsys_state *css)
5411 {
5412 	lockdep_assert_held(&cgroup_mutex);
5413 
5414 	if (css->flags & CSS_DYING)
5415 		return;
5416 
5417 	css->flags |= CSS_DYING;
5418 
5419 	/*
5420 	 * This must happen before css is disassociated with its cgroup.
5421 	 * See seq_css() for details.
5422 	 */
5423 	css_clear_dir(css);
5424 
5425 	/*
5426 	 * Killing would put the base ref, but we need to keep it alive
5427 	 * until after ->css_offline().
5428 	 */
5429 	css_get(css);
5430 
5431 	/*
5432 	 * cgroup core guarantees that, by the time ->css_offline() is
5433 	 * invoked, no new css reference will be given out via
5434 	 * css_tryget_online().  We can't simply call percpu_ref_kill() and
5435 	 * proceed to offlining css's because percpu_ref_kill() doesn't
5436 	 * guarantee that the ref is seen as killed on all CPUs on return.
5437 	 *
5438 	 * Use percpu_ref_kill_and_confirm() to get notifications as each
5439 	 * css is confirmed to be seen as killed on all CPUs.
5440 	 */
5441 	percpu_ref_kill_and_confirm(&css->refcnt, css_killed_ref_fn);
5442 }
5443 
5444 /**
5445  * cgroup_destroy_locked - the first stage of cgroup destruction
5446  * @cgrp: cgroup to be destroyed
5447  *
5448  * css's make use of percpu refcnts whose killing latency shouldn't be
5449  * exposed to userland and are RCU protected.  Also, cgroup core needs to
5450  * guarantee that css_tryget_online() won't succeed by the time
5451  * ->css_offline() is invoked.  To satisfy all the requirements,
5452  * destruction is implemented in the following two steps.
5453  *
5454  * s1. Verify @cgrp can be destroyed and mark it dying.  Remove all
5455  *     userland visible parts and start killing the percpu refcnts of
5456  *     css's.  Set up so that the next stage will be kicked off once all
5457  *     the percpu refcnts are confirmed to be killed.
5458  *
5459  * s2. Invoke ->css_offline(), mark the cgroup dead and proceed with the
5460  *     rest of destruction.  Once all cgroup references are gone, the
5461  *     cgroup is RCU-freed.
5462  *
5463  * This function implements s1.  After this step, @cgrp is gone as far as
5464  * the userland is concerned and a new cgroup with the same name may be
5465  * created.  As cgroup doesn't care about the names internally, this
5466  * doesn't cause any problem.
5467  */
5468 static int cgroup_destroy_locked(struct cgroup *cgrp)
5469 	__releases(&cgroup_mutex) __acquires(&cgroup_mutex)
5470 {
5471 	struct cgroup *tcgrp, *parent = cgroup_parent(cgrp);
5472 	struct cgroup_subsys_state *css;
5473 	struct cgrp_cset_link *link;
5474 	int ssid;
5475 
5476 	lockdep_assert_held(&cgroup_mutex);
5477 
5478 	/*
5479 	 * Only migration can raise populated from zero and we're already
5480 	 * holding cgroup_mutex.
5481 	 */
5482 	if (cgroup_is_populated(cgrp))
5483 		return -EBUSY;
5484 
5485 	/*
5486 	 * Make sure there's no live children.  We can't test emptiness of
5487 	 * ->self.children as dead children linger on it while being
5488 	 * drained; otherwise, "rmdir parent/child parent" may fail.
5489 	 */
5490 	if (css_has_online_children(&cgrp->self))
5491 		return -EBUSY;
5492 
5493 	/*
5494 	 * Mark @cgrp and the associated csets dead.  The former prevents
5495 	 * further task migration and child creation by disabling
5496 	 * cgroup_lock_live_group().  The latter makes the csets ignored by
5497 	 * the migration path.
5498 	 */
5499 	cgrp->self.flags &= ~CSS_ONLINE;
5500 
5501 	spin_lock_irq(&css_set_lock);
5502 	list_for_each_entry(link, &cgrp->cset_links, cset_link)
5503 		link->cset->dead = true;
5504 	spin_unlock_irq(&css_set_lock);
5505 
5506 	/* initiate massacre of all css's */
5507 	for_each_css(css, ssid, cgrp)
5508 		kill_css(css);
5509 
5510 	/* clear and remove @cgrp dir, @cgrp has an extra ref on its kn */
5511 	css_clear_dir(&cgrp->self);
5512 	kernfs_remove(cgrp->kn);
5513 
5514 	if (parent && cgroup_is_threaded(cgrp))
5515 		parent->nr_threaded_children--;
5516 
5517 	spin_lock_irq(&css_set_lock);
5518 	for (tcgrp = cgroup_parent(cgrp); tcgrp; tcgrp = cgroup_parent(tcgrp)) {
5519 		tcgrp->nr_descendants--;
5520 		tcgrp->nr_dying_descendants++;
5521 		/*
5522 		 * If the dying cgroup is frozen, decrease frozen descendants
5523 		 * counters of ancestor cgroups.
5524 		 */
5525 		if (test_bit(CGRP_FROZEN, &cgrp->flags))
5526 			tcgrp->freezer.nr_frozen_descendants--;
5527 	}
5528 	spin_unlock_irq(&css_set_lock);
5529 
5530 	cgroup1_check_for_release(parent);
5531 
5532 	cgroup_bpf_offline(cgrp);
5533 
5534 	/* put the base reference */
5535 	percpu_ref_kill(&cgrp->self.refcnt);
5536 
5537 	return 0;
5538 };
5539 
5540 int cgroup_rmdir(struct kernfs_node *kn)
5541 {
5542 	struct cgroup *cgrp;
5543 	int ret = 0;
5544 
5545 	cgrp = cgroup_kn_lock_live(kn, false);
5546 	if (!cgrp)
5547 		return 0;
5548 
5549 	ret = cgroup_destroy_locked(cgrp);
5550 	if (!ret)
5551 		TRACE_CGROUP_PATH(rmdir, cgrp);
5552 
5553 	cgroup_kn_unlock(kn);
5554 	return ret;
5555 }
5556 
5557 static struct kernfs_syscall_ops cgroup_kf_syscall_ops = {
5558 	.show_options		= cgroup_show_options,
5559 	.mkdir			= cgroup_mkdir,
5560 	.rmdir			= cgroup_rmdir,
5561 	.show_path		= cgroup_show_path,
5562 };
5563 
5564 static void __init cgroup_init_subsys(struct cgroup_subsys *ss, bool early)
5565 {
5566 	struct cgroup_subsys_state *css;
5567 
5568 	pr_debug("Initializing cgroup subsys %s\n", ss->name);
5569 
5570 	mutex_lock(&cgroup_mutex);
5571 
5572 	idr_init(&ss->css_idr);
5573 	INIT_LIST_HEAD(&ss->cfts);
5574 
5575 	/* Create the root cgroup state for this subsystem */
5576 	ss->root = &cgrp_dfl_root;
5577 	css = ss->css_alloc(cgroup_css(&cgrp_dfl_root.cgrp, ss));
5578 	/* We don't handle early failures gracefully */
5579 	BUG_ON(IS_ERR(css));
5580 	init_and_link_css(css, ss, &cgrp_dfl_root.cgrp);
5581 
5582 	/*
5583 	 * Root csses are never destroyed and we can't initialize
5584 	 * percpu_ref during early init.  Disable refcnting.
5585 	 */
5586 	css->flags |= CSS_NO_REF;
5587 
5588 	if (early) {
5589 		/* allocation can't be done safely during early init */
5590 		css->id = 1;
5591 	} else {
5592 		css->id = cgroup_idr_alloc(&ss->css_idr, css, 1, 2, GFP_KERNEL);
5593 		BUG_ON(css->id < 0);
5594 	}
5595 
5596 	/* Update the init_css_set to contain a subsys
5597 	 * pointer to this state - since the subsystem is
5598 	 * newly registered, all tasks and hence the
5599 	 * init_css_set is in the subsystem's root cgroup. */
5600 	init_css_set.subsys[ss->id] = css;
5601 
5602 	have_fork_callback |= (bool)ss->fork << ss->id;
5603 	have_exit_callback |= (bool)ss->exit << ss->id;
5604 	have_release_callback |= (bool)ss->release << ss->id;
5605 	have_canfork_callback |= (bool)ss->can_fork << ss->id;
5606 
5607 	/* At system boot, before all subsystems have been
5608 	 * registered, no tasks have been forked, so we don't
5609 	 * need to invoke fork callbacks here. */
5610 	BUG_ON(!list_empty(&init_task.tasks));
5611 
5612 	BUG_ON(online_css(css));
5613 
5614 	mutex_unlock(&cgroup_mutex);
5615 }
5616 
5617 /**
5618  * cgroup_init_early - cgroup initialization at system boot
5619  *
5620  * Initialize cgroups at system boot, and initialize any
5621  * subsystems that request early init.
5622  */
5623 int __init cgroup_init_early(void)
5624 {
5625 	static struct cgroup_fs_context __initdata ctx;
5626 	struct cgroup_subsys *ss;
5627 	int i;
5628 
5629 	ctx.root = &cgrp_dfl_root;
5630 	init_cgroup_root(&ctx);
5631 	cgrp_dfl_root.cgrp.self.flags |= CSS_NO_REF;
5632 
5633 	RCU_INIT_POINTER(init_task.cgroups, &init_css_set);
5634 
5635 	for_each_subsys(ss, i) {
5636 		WARN(!ss->css_alloc || !ss->css_free || ss->name || ss->id,
5637 		     "invalid cgroup_subsys %d:%s css_alloc=%p css_free=%p id:name=%d:%s\n",
5638 		     i, cgroup_subsys_name[i], ss->css_alloc, ss->css_free,
5639 		     ss->id, ss->name);
5640 		WARN(strlen(cgroup_subsys_name[i]) > MAX_CGROUP_TYPE_NAMELEN,
5641 		     "cgroup_subsys_name %s too long\n", cgroup_subsys_name[i]);
5642 
5643 		ss->id = i;
5644 		ss->name = cgroup_subsys_name[i];
5645 		if (!ss->legacy_name)
5646 			ss->legacy_name = cgroup_subsys_name[i];
5647 
5648 		if (ss->early_init)
5649 			cgroup_init_subsys(ss, true);
5650 	}
5651 	return 0;
5652 }
5653 
5654 static u16 cgroup_disable_mask __initdata;
5655 
5656 /**
5657  * cgroup_init - cgroup initialization
5658  *
5659  * Register cgroup filesystem and /proc file, and initialize
5660  * any subsystems that didn't request early init.
5661  */
5662 int __init cgroup_init(void)
5663 {
5664 	struct cgroup_subsys *ss;
5665 	int ssid;
5666 
5667 	BUILD_BUG_ON(CGROUP_SUBSYS_COUNT > 16);
5668 	BUG_ON(cgroup_init_cftypes(NULL, cgroup_base_files));
5669 	BUG_ON(cgroup_init_cftypes(NULL, cgroup1_base_files));
5670 
5671 	cgroup_rstat_boot();
5672 
5673 	/*
5674 	 * The latency of the synchronize_rcu() is too high for cgroups,
5675 	 * avoid it at the cost of forcing all readers into the slow path.
5676 	 */
5677 	rcu_sync_enter_start(&cgroup_threadgroup_rwsem.rss);
5678 
5679 	get_user_ns(init_cgroup_ns.user_ns);
5680 
5681 	mutex_lock(&cgroup_mutex);
5682 
5683 	/*
5684 	 * Add init_css_set to the hash table so that dfl_root can link to
5685 	 * it during init.
5686 	 */
5687 	hash_add(css_set_table, &init_css_set.hlist,
5688 		 css_set_hash(init_css_set.subsys));
5689 
5690 	BUG_ON(cgroup_setup_root(&cgrp_dfl_root, 0));
5691 
5692 	mutex_unlock(&cgroup_mutex);
5693 
5694 	for_each_subsys(ss, ssid) {
5695 		if (ss->early_init) {
5696 			struct cgroup_subsys_state *css =
5697 				init_css_set.subsys[ss->id];
5698 
5699 			css->id = cgroup_idr_alloc(&ss->css_idr, css, 1, 2,
5700 						   GFP_KERNEL);
5701 			BUG_ON(css->id < 0);
5702 		} else {
5703 			cgroup_init_subsys(ss, false);
5704 		}
5705 
5706 		list_add_tail(&init_css_set.e_cset_node[ssid],
5707 			      &cgrp_dfl_root.cgrp.e_csets[ssid]);
5708 
5709 		/*
5710 		 * Setting dfl_root subsys_mask needs to consider the
5711 		 * disabled flag and cftype registration needs kmalloc,
5712 		 * both of which aren't available during early_init.
5713 		 */
5714 		if (cgroup_disable_mask & (1 << ssid)) {
5715 			static_branch_disable(cgroup_subsys_enabled_key[ssid]);
5716 			printk(KERN_INFO "Disabling %s control group subsystem\n",
5717 			       ss->name);
5718 			continue;
5719 		}
5720 
5721 		if (cgroup1_ssid_disabled(ssid))
5722 			printk(KERN_INFO "Disabling %s control group subsystem in v1 mounts\n",
5723 			       ss->name);
5724 
5725 		cgrp_dfl_root.subsys_mask |= 1 << ss->id;
5726 
5727 		/* implicit controllers must be threaded too */
5728 		WARN_ON(ss->implicit_on_dfl && !ss->threaded);
5729 
5730 		if (ss->implicit_on_dfl)
5731 			cgrp_dfl_implicit_ss_mask |= 1 << ss->id;
5732 		else if (!ss->dfl_cftypes)
5733 			cgrp_dfl_inhibit_ss_mask |= 1 << ss->id;
5734 
5735 		if (ss->threaded)
5736 			cgrp_dfl_threaded_ss_mask |= 1 << ss->id;
5737 
5738 		if (ss->dfl_cftypes == ss->legacy_cftypes) {
5739 			WARN_ON(cgroup_add_cftypes(ss, ss->dfl_cftypes));
5740 		} else {
5741 			WARN_ON(cgroup_add_dfl_cftypes(ss, ss->dfl_cftypes));
5742 			WARN_ON(cgroup_add_legacy_cftypes(ss, ss->legacy_cftypes));
5743 		}
5744 
5745 		if (ss->bind)
5746 			ss->bind(init_css_set.subsys[ssid]);
5747 
5748 		mutex_lock(&cgroup_mutex);
5749 		css_populate_dir(init_css_set.subsys[ssid]);
5750 		mutex_unlock(&cgroup_mutex);
5751 	}
5752 
5753 	/* init_css_set.subsys[] has been updated, re-hash */
5754 	hash_del(&init_css_set.hlist);
5755 	hash_add(css_set_table, &init_css_set.hlist,
5756 		 css_set_hash(init_css_set.subsys));
5757 
5758 	WARN_ON(sysfs_create_mount_point(fs_kobj, "cgroup"));
5759 	WARN_ON(register_filesystem(&cgroup_fs_type));
5760 	WARN_ON(register_filesystem(&cgroup2_fs_type));
5761 	WARN_ON(!proc_create_single("cgroups", 0, NULL, proc_cgroupstats_show));
5762 #ifdef CONFIG_CPUSETS
5763 	WARN_ON(register_filesystem(&cpuset_fs_type));
5764 #endif
5765 
5766 	return 0;
5767 }
5768 
5769 static int __init cgroup_wq_init(void)
5770 {
5771 	/*
5772 	 * There isn't much point in executing destruction path in
5773 	 * parallel.  Good chunk is serialized with cgroup_mutex anyway.
5774 	 * Use 1 for @max_active.
5775 	 *
5776 	 * We would prefer to do this in cgroup_init() above, but that
5777 	 * is called before init_workqueues(): so leave this until after.
5778 	 */
5779 	cgroup_destroy_wq = alloc_workqueue("cgroup_destroy", 0, 1);
5780 	BUG_ON(!cgroup_destroy_wq);
5781 	return 0;
5782 }
5783 core_initcall(cgroup_wq_init);
5784 
5785 void cgroup_path_from_kernfs_id(u64 id, char *buf, size_t buflen)
5786 {
5787 	struct kernfs_node *kn;
5788 
5789 	kn = kernfs_find_and_get_node_by_id(cgrp_dfl_root.kf_root, id);
5790 	if (!kn)
5791 		return;
5792 	kernfs_path(kn, buf, buflen);
5793 	kernfs_put(kn);
5794 }
5795 
5796 /*
5797  * proc_cgroup_show()
5798  *  - Print task's cgroup paths into seq_file, one line for each hierarchy
5799  *  - Used for /proc/<pid>/cgroup.
5800  */
5801 int proc_cgroup_show(struct seq_file *m, struct pid_namespace *ns,
5802 		     struct pid *pid, struct task_struct *tsk)
5803 {
5804 	char *buf;
5805 	int retval;
5806 	struct cgroup_root *root;
5807 
5808 	retval = -ENOMEM;
5809 	buf = kmalloc(PATH_MAX, GFP_KERNEL);
5810 	if (!buf)
5811 		goto out;
5812 
5813 	mutex_lock(&cgroup_mutex);
5814 	spin_lock_irq(&css_set_lock);
5815 
5816 	for_each_root(root) {
5817 		struct cgroup_subsys *ss;
5818 		struct cgroup *cgrp;
5819 		int ssid, count = 0;
5820 
5821 		if (root == &cgrp_dfl_root && !cgrp_dfl_visible)
5822 			continue;
5823 
5824 		seq_printf(m, "%d:", root->hierarchy_id);
5825 		if (root != &cgrp_dfl_root)
5826 			for_each_subsys(ss, ssid)
5827 				if (root->subsys_mask & (1 << ssid))
5828 					seq_printf(m, "%s%s", count++ ? "," : "",
5829 						   ss->legacy_name);
5830 		if (strlen(root->name))
5831 			seq_printf(m, "%sname=%s", count ? "," : "",
5832 				   root->name);
5833 		seq_putc(m, ':');
5834 
5835 		cgrp = task_cgroup_from_root(tsk, root);
5836 
5837 		/*
5838 		 * On traditional hierarchies, all zombie tasks show up as
5839 		 * belonging to the root cgroup.  On the default hierarchy,
5840 		 * while a zombie doesn't show up in "cgroup.procs" and
5841 		 * thus can't be migrated, its /proc/PID/cgroup keeps
5842 		 * reporting the cgroup it belonged to before exiting.  If
5843 		 * the cgroup is removed before the zombie is reaped,
5844 		 * " (deleted)" is appended to the cgroup path.
5845 		 */
5846 		if (cgroup_on_dfl(cgrp) || !(tsk->flags & PF_EXITING)) {
5847 			retval = cgroup_path_ns_locked(cgrp, buf, PATH_MAX,
5848 						current->nsproxy->cgroup_ns);
5849 			if (retval >= PATH_MAX)
5850 				retval = -ENAMETOOLONG;
5851 			if (retval < 0)
5852 				goto out_unlock;
5853 
5854 			seq_puts(m, buf);
5855 		} else {
5856 			seq_puts(m, "/");
5857 		}
5858 
5859 		if (cgroup_on_dfl(cgrp) && cgroup_is_dead(cgrp))
5860 			seq_puts(m, " (deleted)\n");
5861 		else
5862 			seq_putc(m, '\n');
5863 	}
5864 
5865 	retval = 0;
5866 out_unlock:
5867 	spin_unlock_irq(&css_set_lock);
5868 	mutex_unlock(&cgroup_mutex);
5869 	kfree(buf);
5870 out:
5871 	return retval;
5872 }
5873 
5874 /**
5875  * cgroup_fork - initialize cgroup related fields during copy_process()
5876  * @child: pointer to task_struct of forking parent process.
5877  *
5878  * A task is associated with the init_css_set until cgroup_post_fork()
5879  * attaches it to the target css_set.
5880  */
5881 void cgroup_fork(struct task_struct *child)
5882 {
5883 	RCU_INIT_POINTER(child->cgroups, &init_css_set);
5884 	INIT_LIST_HEAD(&child->cg_list);
5885 }
5886 
5887 static struct cgroup *cgroup_get_from_file(struct file *f)
5888 {
5889 	struct cgroup_subsys_state *css;
5890 	struct cgroup *cgrp;
5891 
5892 	css = css_tryget_online_from_dir(f->f_path.dentry, NULL);
5893 	if (IS_ERR(css))
5894 		return ERR_CAST(css);
5895 
5896 	cgrp = css->cgroup;
5897 	if (!cgroup_on_dfl(cgrp)) {
5898 		cgroup_put(cgrp);
5899 		return ERR_PTR(-EBADF);
5900 	}
5901 
5902 	return cgrp;
5903 }
5904 
5905 /**
5906  * cgroup_css_set_fork - find or create a css_set for a child process
5907  * @kargs: the arguments passed to create the child process
5908  *
5909  * This functions finds or creates a new css_set which the child
5910  * process will be attached to in cgroup_post_fork(). By default,
5911  * the child process will be given the same css_set as its parent.
5912  *
5913  * If CLONE_INTO_CGROUP is specified this function will try to find an
5914  * existing css_set which includes the requested cgroup and if not create
5915  * a new css_set that the child will be attached to later. If this function
5916  * succeeds it will hold cgroup_threadgroup_rwsem on return. If
5917  * CLONE_INTO_CGROUP is requested this function will grab cgroup mutex
5918  * before grabbing cgroup_threadgroup_rwsem and will hold a reference
5919  * to the target cgroup.
5920  */
5921 static int cgroup_css_set_fork(struct kernel_clone_args *kargs)
5922 	__acquires(&cgroup_mutex) __acquires(&cgroup_threadgroup_rwsem)
5923 {
5924 	int ret;
5925 	struct cgroup *dst_cgrp = NULL;
5926 	struct css_set *cset;
5927 	struct super_block *sb;
5928 	struct file *f;
5929 
5930 	if (kargs->flags & CLONE_INTO_CGROUP)
5931 		mutex_lock(&cgroup_mutex);
5932 
5933 	cgroup_threadgroup_change_begin(current);
5934 
5935 	spin_lock_irq(&css_set_lock);
5936 	cset = task_css_set(current);
5937 	get_css_set(cset);
5938 	spin_unlock_irq(&css_set_lock);
5939 
5940 	if (!(kargs->flags & CLONE_INTO_CGROUP)) {
5941 		kargs->cset = cset;
5942 		return 0;
5943 	}
5944 
5945 	f = fget_raw(kargs->cgroup);
5946 	if (!f) {
5947 		ret = -EBADF;
5948 		goto err;
5949 	}
5950 	sb = f->f_path.dentry->d_sb;
5951 
5952 	dst_cgrp = cgroup_get_from_file(f);
5953 	if (IS_ERR(dst_cgrp)) {
5954 		ret = PTR_ERR(dst_cgrp);
5955 		dst_cgrp = NULL;
5956 		goto err;
5957 	}
5958 
5959 	if (cgroup_is_dead(dst_cgrp)) {
5960 		ret = -ENODEV;
5961 		goto err;
5962 	}
5963 
5964 	/*
5965 	 * Verify that we the target cgroup is writable for us. This is
5966 	 * usually done by the vfs layer but since we're not going through
5967 	 * the vfs layer here we need to do it "manually".
5968 	 */
5969 	ret = cgroup_may_write(dst_cgrp, sb);
5970 	if (ret)
5971 		goto err;
5972 
5973 	ret = cgroup_attach_permissions(cset->dfl_cgrp, dst_cgrp, sb,
5974 					!(kargs->flags & CLONE_THREAD));
5975 	if (ret)
5976 		goto err;
5977 
5978 	kargs->cset = find_css_set(cset, dst_cgrp);
5979 	if (!kargs->cset) {
5980 		ret = -ENOMEM;
5981 		goto err;
5982 	}
5983 
5984 	put_css_set(cset);
5985 	fput(f);
5986 	kargs->cgrp = dst_cgrp;
5987 	return ret;
5988 
5989 err:
5990 	cgroup_threadgroup_change_end(current);
5991 	mutex_unlock(&cgroup_mutex);
5992 	if (f)
5993 		fput(f);
5994 	if (dst_cgrp)
5995 		cgroup_put(dst_cgrp);
5996 	put_css_set(cset);
5997 	if (kargs->cset)
5998 		put_css_set(kargs->cset);
5999 	return ret;
6000 }
6001 
6002 /**
6003  * cgroup_css_set_put_fork - drop references we took during fork
6004  * @kargs: the arguments passed to create the child process
6005  *
6006  * Drop references to the prepared css_set and target cgroup if
6007  * CLONE_INTO_CGROUP was requested.
6008  */
6009 static void cgroup_css_set_put_fork(struct kernel_clone_args *kargs)
6010 	__releases(&cgroup_threadgroup_rwsem) __releases(&cgroup_mutex)
6011 {
6012 	cgroup_threadgroup_change_end(current);
6013 
6014 	if (kargs->flags & CLONE_INTO_CGROUP) {
6015 		struct cgroup *cgrp = kargs->cgrp;
6016 		struct css_set *cset = kargs->cset;
6017 
6018 		mutex_unlock(&cgroup_mutex);
6019 
6020 		if (cset) {
6021 			put_css_set(cset);
6022 			kargs->cset = NULL;
6023 		}
6024 
6025 		if (cgrp) {
6026 			cgroup_put(cgrp);
6027 			kargs->cgrp = NULL;
6028 		}
6029 	}
6030 }
6031 
6032 /**
6033  * cgroup_can_fork - called on a new task before the process is exposed
6034  * @child: the child process
6035  *
6036  * This prepares a new css_set for the child process which the child will
6037  * be attached to in cgroup_post_fork().
6038  * This calls the subsystem can_fork() callbacks. If the cgroup_can_fork()
6039  * callback returns an error, the fork aborts with that error code. This
6040  * allows for a cgroup subsystem to conditionally allow or deny new forks.
6041  */
6042 int cgroup_can_fork(struct task_struct *child, struct kernel_clone_args *kargs)
6043 {
6044 	struct cgroup_subsys *ss;
6045 	int i, j, ret;
6046 
6047 	ret = cgroup_css_set_fork(kargs);
6048 	if (ret)
6049 		return ret;
6050 
6051 	do_each_subsys_mask(ss, i, have_canfork_callback) {
6052 		ret = ss->can_fork(child, kargs->cset);
6053 		if (ret)
6054 			goto out_revert;
6055 	} while_each_subsys_mask();
6056 
6057 	return 0;
6058 
6059 out_revert:
6060 	for_each_subsys(ss, j) {
6061 		if (j >= i)
6062 			break;
6063 		if (ss->cancel_fork)
6064 			ss->cancel_fork(child, kargs->cset);
6065 	}
6066 
6067 	cgroup_css_set_put_fork(kargs);
6068 
6069 	return ret;
6070 }
6071 
6072 /**
6073  * cgroup_cancel_fork - called if a fork failed after cgroup_can_fork()
6074  * @child: the child process
6075  * @kargs: the arguments passed to create the child process
6076  *
6077  * This calls the cancel_fork() callbacks if a fork failed *after*
6078  * cgroup_can_fork() succeded and cleans up references we took to
6079  * prepare a new css_set for the child process in cgroup_can_fork().
6080  */
6081 void cgroup_cancel_fork(struct task_struct *child,
6082 			struct kernel_clone_args *kargs)
6083 {
6084 	struct cgroup_subsys *ss;
6085 	int i;
6086 
6087 	for_each_subsys(ss, i)
6088 		if (ss->cancel_fork)
6089 			ss->cancel_fork(child, kargs->cset);
6090 
6091 	cgroup_css_set_put_fork(kargs);
6092 }
6093 
6094 /**
6095  * cgroup_post_fork - finalize cgroup setup for the child process
6096  * @child: the child process
6097  *
6098  * Attach the child process to its css_set calling the subsystem fork()
6099  * callbacks.
6100  */
6101 void cgroup_post_fork(struct task_struct *child,
6102 		      struct kernel_clone_args *kargs)
6103 	__releases(&cgroup_threadgroup_rwsem) __releases(&cgroup_mutex)
6104 {
6105 	struct cgroup_subsys *ss;
6106 	struct css_set *cset;
6107 	int i;
6108 
6109 	cset = kargs->cset;
6110 	kargs->cset = NULL;
6111 
6112 	spin_lock_irq(&css_set_lock);
6113 
6114 	/* init tasks are special, only link regular threads */
6115 	if (likely(child->pid)) {
6116 		WARN_ON_ONCE(!list_empty(&child->cg_list));
6117 		cset->nr_tasks++;
6118 		css_set_move_task(child, NULL, cset, false);
6119 	} else {
6120 		put_css_set(cset);
6121 		cset = NULL;
6122 	}
6123 
6124 	/*
6125 	 * If the cgroup has to be frozen, the new task has too.  Let's set
6126 	 * the JOBCTL_TRAP_FREEZE jobctl bit to get the task into the
6127 	 * frozen state.
6128 	 */
6129 	if (unlikely(cgroup_task_freeze(child))) {
6130 		spin_lock(&child->sighand->siglock);
6131 		WARN_ON_ONCE(child->frozen);
6132 		child->jobctl |= JOBCTL_TRAP_FREEZE;
6133 		spin_unlock(&child->sighand->siglock);
6134 
6135 		/*
6136 		 * Calling cgroup_update_frozen() isn't required here,
6137 		 * because it will be called anyway a bit later from
6138 		 * do_freezer_trap(). So we avoid cgroup's transient switch
6139 		 * from the frozen state and back.
6140 		 */
6141 	}
6142 
6143 	spin_unlock_irq(&css_set_lock);
6144 
6145 	/*
6146 	 * Call ss->fork().  This must happen after @child is linked on
6147 	 * css_set; otherwise, @child might change state between ->fork()
6148 	 * and addition to css_set.
6149 	 */
6150 	do_each_subsys_mask(ss, i, have_fork_callback) {
6151 		ss->fork(child);
6152 	} while_each_subsys_mask();
6153 
6154 	/* Make the new cset the root_cset of the new cgroup namespace. */
6155 	if (kargs->flags & CLONE_NEWCGROUP) {
6156 		struct css_set *rcset = child->nsproxy->cgroup_ns->root_cset;
6157 
6158 		get_css_set(cset);
6159 		child->nsproxy->cgroup_ns->root_cset = cset;
6160 		put_css_set(rcset);
6161 	}
6162 
6163 	cgroup_css_set_put_fork(kargs);
6164 }
6165 
6166 /**
6167  * cgroup_exit - detach cgroup from exiting task
6168  * @tsk: pointer to task_struct of exiting process
6169  *
6170  * Description: Detach cgroup from @tsk.
6171  *
6172  */
6173 void cgroup_exit(struct task_struct *tsk)
6174 {
6175 	struct cgroup_subsys *ss;
6176 	struct css_set *cset;
6177 	int i;
6178 
6179 	spin_lock_irq(&css_set_lock);
6180 
6181 	WARN_ON_ONCE(list_empty(&tsk->cg_list));
6182 	cset = task_css_set(tsk);
6183 	css_set_move_task(tsk, cset, NULL, false);
6184 	list_add_tail(&tsk->cg_list, &cset->dying_tasks);
6185 	cset->nr_tasks--;
6186 
6187 	WARN_ON_ONCE(cgroup_task_frozen(tsk));
6188 	if (unlikely(cgroup_task_freeze(tsk)))
6189 		cgroup_update_frozen(task_dfl_cgroup(tsk));
6190 
6191 	spin_unlock_irq(&css_set_lock);
6192 
6193 	/* see cgroup_post_fork() for details */
6194 	do_each_subsys_mask(ss, i, have_exit_callback) {
6195 		ss->exit(tsk);
6196 	} while_each_subsys_mask();
6197 }
6198 
6199 void cgroup_release(struct task_struct *task)
6200 {
6201 	struct cgroup_subsys *ss;
6202 	int ssid;
6203 
6204 	do_each_subsys_mask(ss, ssid, have_release_callback) {
6205 		ss->release(task);
6206 	} while_each_subsys_mask();
6207 
6208 	spin_lock_irq(&css_set_lock);
6209 	css_set_skip_task_iters(task_css_set(task), task);
6210 	list_del_init(&task->cg_list);
6211 	spin_unlock_irq(&css_set_lock);
6212 }
6213 
6214 void cgroup_free(struct task_struct *task)
6215 {
6216 	struct css_set *cset = task_css_set(task);
6217 	put_css_set(cset);
6218 }
6219 
6220 static int __init cgroup_disable(char *str)
6221 {
6222 	struct cgroup_subsys *ss;
6223 	char *token;
6224 	int i;
6225 
6226 	while ((token = strsep(&str, ",")) != NULL) {
6227 		if (!*token)
6228 			continue;
6229 
6230 		for_each_subsys(ss, i) {
6231 			if (strcmp(token, ss->name) &&
6232 			    strcmp(token, ss->legacy_name))
6233 				continue;
6234 			cgroup_disable_mask |= 1 << i;
6235 		}
6236 	}
6237 	return 1;
6238 }
6239 __setup("cgroup_disable=", cgroup_disable);
6240 
6241 void __init __weak enable_debug_cgroup(void) { }
6242 
6243 static int __init enable_cgroup_debug(char *str)
6244 {
6245 	cgroup_debug = true;
6246 	enable_debug_cgroup();
6247 	return 1;
6248 }
6249 __setup("cgroup_debug", enable_cgroup_debug);
6250 
6251 /**
6252  * css_tryget_online_from_dir - get corresponding css from a cgroup dentry
6253  * @dentry: directory dentry of interest
6254  * @ss: subsystem of interest
6255  *
6256  * If @dentry is a directory for a cgroup which has @ss enabled on it, try
6257  * to get the corresponding css and return it.  If such css doesn't exist
6258  * or can't be pinned, an ERR_PTR value is returned.
6259  */
6260 struct cgroup_subsys_state *css_tryget_online_from_dir(struct dentry *dentry,
6261 						       struct cgroup_subsys *ss)
6262 {
6263 	struct kernfs_node *kn = kernfs_node_from_dentry(dentry);
6264 	struct file_system_type *s_type = dentry->d_sb->s_type;
6265 	struct cgroup_subsys_state *css = NULL;
6266 	struct cgroup *cgrp;
6267 
6268 	/* is @dentry a cgroup dir? */
6269 	if ((s_type != &cgroup_fs_type && s_type != &cgroup2_fs_type) ||
6270 	    !kn || kernfs_type(kn) != KERNFS_DIR)
6271 		return ERR_PTR(-EBADF);
6272 
6273 	rcu_read_lock();
6274 
6275 	/*
6276 	 * This path doesn't originate from kernfs and @kn could already
6277 	 * have been or be removed at any point.  @kn->priv is RCU
6278 	 * protected for this access.  See css_release_work_fn() for details.
6279 	 */
6280 	cgrp = rcu_dereference(*(void __rcu __force **)&kn->priv);
6281 	if (cgrp)
6282 		css = cgroup_css(cgrp, ss);
6283 
6284 	if (!css || !css_tryget_online(css))
6285 		css = ERR_PTR(-ENOENT);
6286 
6287 	rcu_read_unlock();
6288 	return css;
6289 }
6290 
6291 /**
6292  * css_from_id - lookup css by id
6293  * @id: the cgroup id
6294  * @ss: cgroup subsys to be looked into
6295  *
6296  * Returns the css if there's valid one with @id, otherwise returns NULL.
6297  * Should be called under rcu_read_lock().
6298  */
6299 struct cgroup_subsys_state *css_from_id(int id, struct cgroup_subsys *ss)
6300 {
6301 	WARN_ON_ONCE(!rcu_read_lock_held());
6302 	return idr_find(&ss->css_idr, id);
6303 }
6304 
6305 /**
6306  * cgroup_get_from_path - lookup and get a cgroup from its default hierarchy path
6307  * @path: path on the default hierarchy
6308  *
6309  * Find the cgroup at @path on the default hierarchy, increment its
6310  * reference count and return it.  Returns pointer to the found cgroup on
6311  * success, ERR_PTR(-ENOENT) if @path doesn't exist and ERR_PTR(-ENOTDIR)
6312  * if @path points to a non-directory.
6313  */
6314 struct cgroup *cgroup_get_from_path(const char *path)
6315 {
6316 	struct kernfs_node *kn;
6317 	struct cgroup *cgrp;
6318 
6319 	mutex_lock(&cgroup_mutex);
6320 
6321 	kn = kernfs_walk_and_get(cgrp_dfl_root.cgrp.kn, path);
6322 	if (kn) {
6323 		if (kernfs_type(kn) == KERNFS_DIR) {
6324 			cgrp = kn->priv;
6325 			cgroup_get_live(cgrp);
6326 		} else {
6327 			cgrp = ERR_PTR(-ENOTDIR);
6328 		}
6329 		kernfs_put(kn);
6330 	} else {
6331 		cgrp = ERR_PTR(-ENOENT);
6332 	}
6333 
6334 	mutex_unlock(&cgroup_mutex);
6335 	return cgrp;
6336 }
6337 EXPORT_SYMBOL_GPL(cgroup_get_from_path);
6338 
6339 /**
6340  * cgroup_get_from_fd - get a cgroup pointer from a fd
6341  * @fd: fd obtained by open(cgroup2_dir)
6342  *
6343  * Find the cgroup from a fd which should be obtained
6344  * by opening a cgroup directory.  Returns a pointer to the
6345  * cgroup on success. ERR_PTR is returned if the cgroup
6346  * cannot be found.
6347  */
6348 struct cgroup *cgroup_get_from_fd(int fd)
6349 {
6350 	struct cgroup *cgrp;
6351 	struct file *f;
6352 
6353 	f = fget_raw(fd);
6354 	if (!f)
6355 		return ERR_PTR(-EBADF);
6356 
6357 	cgrp = cgroup_get_from_file(f);
6358 	fput(f);
6359 	return cgrp;
6360 }
6361 EXPORT_SYMBOL_GPL(cgroup_get_from_fd);
6362 
6363 static u64 power_of_ten(int power)
6364 {
6365 	u64 v = 1;
6366 	while (power--)
6367 		v *= 10;
6368 	return v;
6369 }
6370 
6371 /**
6372  * cgroup_parse_float - parse a floating number
6373  * @input: input string
6374  * @dec_shift: number of decimal digits to shift
6375  * @v: output
6376  *
6377  * Parse a decimal floating point number in @input and store the result in
6378  * @v with decimal point right shifted @dec_shift times.  For example, if
6379  * @input is "12.3456" and @dec_shift is 3, *@v will be set to 12345.
6380  * Returns 0 on success, -errno otherwise.
6381  *
6382  * There's nothing cgroup specific about this function except that it's
6383  * currently the only user.
6384  */
6385 int cgroup_parse_float(const char *input, unsigned dec_shift, s64 *v)
6386 {
6387 	s64 whole, frac = 0;
6388 	int fstart = 0, fend = 0, flen;
6389 
6390 	if (!sscanf(input, "%lld.%n%lld%n", &whole, &fstart, &frac, &fend))
6391 		return -EINVAL;
6392 	if (frac < 0)
6393 		return -EINVAL;
6394 
6395 	flen = fend > fstart ? fend - fstart : 0;
6396 	if (flen < dec_shift)
6397 		frac *= power_of_ten(dec_shift - flen);
6398 	else
6399 		frac = DIV_ROUND_CLOSEST_ULL(frac, power_of_ten(flen - dec_shift));
6400 
6401 	*v = whole * power_of_ten(dec_shift) + frac;
6402 	return 0;
6403 }
6404 
6405 /*
6406  * sock->sk_cgrp_data handling.  For more info, see sock_cgroup_data
6407  * definition in cgroup-defs.h.
6408  */
6409 #ifdef CONFIG_SOCK_CGROUP_DATA
6410 
6411 #if defined(CONFIG_CGROUP_NET_PRIO) || defined(CONFIG_CGROUP_NET_CLASSID)
6412 
6413 DEFINE_SPINLOCK(cgroup_sk_update_lock);
6414 static bool cgroup_sk_alloc_disabled __read_mostly;
6415 
6416 void cgroup_sk_alloc_disable(void)
6417 {
6418 	if (cgroup_sk_alloc_disabled)
6419 		return;
6420 	pr_info("cgroup: disabling cgroup2 socket matching due to net_prio or net_cls activation\n");
6421 	cgroup_sk_alloc_disabled = true;
6422 }
6423 
6424 #else
6425 
6426 #define cgroup_sk_alloc_disabled	false
6427 
6428 #endif
6429 
6430 void cgroup_sk_alloc(struct sock_cgroup_data *skcd)
6431 {
6432 	if (cgroup_sk_alloc_disabled) {
6433 		skcd->no_refcnt = 1;
6434 		return;
6435 	}
6436 
6437 	/* Don't associate the sock with unrelated interrupted task's cgroup. */
6438 	if (in_interrupt())
6439 		return;
6440 
6441 	rcu_read_lock();
6442 
6443 	while (true) {
6444 		struct css_set *cset;
6445 
6446 		cset = task_css_set(current);
6447 		if (likely(cgroup_tryget(cset->dfl_cgrp))) {
6448 			skcd->val = (unsigned long)cset->dfl_cgrp;
6449 			cgroup_bpf_get(cset->dfl_cgrp);
6450 			break;
6451 		}
6452 		cpu_relax();
6453 	}
6454 
6455 	rcu_read_unlock();
6456 }
6457 
6458 void cgroup_sk_clone(struct sock_cgroup_data *skcd)
6459 {
6460 	if (skcd->val) {
6461 		if (skcd->no_refcnt)
6462 			return;
6463 		/*
6464 		 * We might be cloning a socket which is left in an empty
6465 		 * cgroup and the cgroup might have already been rmdir'd.
6466 		 * Don't use cgroup_get_live().
6467 		 */
6468 		cgroup_get(sock_cgroup_ptr(skcd));
6469 		cgroup_bpf_get(sock_cgroup_ptr(skcd));
6470 	}
6471 }
6472 
6473 void cgroup_sk_free(struct sock_cgroup_data *skcd)
6474 {
6475 	struct cgroup *cgrp = sock_cgroup_ptr(skcd);
6476 
6477 	if (skcd->no_refcnt)
6478 		return;
6479 	cgroup_bpf_put(cgrp);
6480 	cgroup_put(cgrp);
6481 }
6482 
6483 #endif	/* CONFIG_SOCK_CGROUP_DATA */
6484 
6485 #ifdef CONFIG_CGROUP_BPF
6486 int cgroup_bpf_attach(struct cgroup *cgrp,
6487 		      struct bpf_prog *prog, struct bpf_prog *replace_prog,
6488 		      struct bpf_cgroup_link *link,
6489 		      enum bpf_attach_type type,
6490 		      u32 flags)
6491 {
6492 	int ret;
6493 
6494 	mutex_lock(&cgroup_mutex);
6495 	ret = __cgroup_bpf_attach(cgrp, prog, replace_prog, link, type, flags);
6496 	mutex_unlock(&cgroup_mutex);
6497 	return ret;
6498 }
6499 
6500 int cgroup_bpf_detach(struct cgroup *cgrp, struct bpf_prog *prog,
6501 		      enum bpf_attach_type type)
6502 {
6503 	int ret;
6504 
6505 	mutex_lock(&cgroup_mutex);
6506 	ret = __cgroup_bpf_detach(cgrp, prog, NULL, type);
6507 	mutex_unlock(&cgroup_mutex);
6508 	return ret;
6509 }
6510 
6511 int cgroup_bpf_query(struct cgroup *cgrp, const union bpf_attr *attr,
6512 		     union bpf_attr __user *uattr)
6513 {
6514 	int ret;
6515 
6516 	mutex_lock(&cgroup_mutex);
6517 	ret = __cgroup_bpf_query(cgrp, attr, uattr);
6518 	mutex_unlock(&cgroup_mutex);
6519 	return ret;
6520 }
6521 #endif /* CONFIG_CGROUP_BPF */
6522 
6523 #ifdef CONFIG_SYSFS
6524 static ssize_t show_delegatable_files(struct cftype *files, char *buf,
6525 				      ssize_t size, const char *prefix)
6526 {
6527 	struct cftype *cft;
6528 	ssize_t ret = 0;
6529 
6530 	for (cft = files; cft && cft->name[0] != '\0'; cft++) {
6531 		if (!(cft->flags & CFTYPE_NS_DELEGATABLE))
6532 			continue;
6533 
6534 		if (prefix)
6535 			ret += snprintf(buf + ret, size - ret, "%s.", prefix);
6536 
6537 		ret += snprintf(buf + ret, size - ret, "%s\n", cft->name);
6538 
6539 		if (WARN_ON(ret >= size))
6540 			break;
6541 	}
6542 
6543 	return ret;
6544 }
6545 
6546 static ssize_t delegate_show(struct kobject *kobj, struct kobj_attribute *attr,
6547 			      char *buf)
6548 {
6549 	struct cgroup_subsys *ss;
6550 	int ssid;
6551 	ssize_t ret = 0;
6552 
6553 	ret = show_delegatable_files(cgroup_base_files, buf, PAGE_SIZE - ret,
6554 				     NULL);
6555 
6556 	for_each_subsys(ss, ssid)
6557 		ret += show_delegatable_files(ss->dfl_cftypes, buf + ret,
6558 					      PAGE_SIZE - ret,
6559 					      cgroup_subsys_name[ssid]);
6560 
6561 	return ret;
6562 }
6563 static struct kobj_attribute cgroup_delegate_attr = __ATTR_RO(delegate);
6564 
6565 static ssize_t features_show(struct kobject *kobj, struct kobj_attribute *attr,
6566 			     char *buf)
6567 {
6568 	return snprintf(buf, PAGE_SIZE,
6569 			"nsdelegate\n"
6570 			"memory_localevents\n"
6571 			"memory_recursiveprot\n");
6572 }
6573 static struct kobj_attribute cgroup_features_attr = __ATTR_RO(features);
6574 
6575 static struct attribute *cgroup_sysfs_attrs[] = {
6576 	&cgroup_delegate_attr.attr,
6577 	&cgroup_features_attr.attr,
6578 	NULL,
6579 };
6580 
6581 static const struct attribute_group cgroup_sysfs_attr_group = {
6582 	.attrs = cgroup_sysfs_attrs,
6583 	.name = "cgroup",
6584 };
6585 
6586 static int __init cgroup_sysfs_init(void)
6587 {
6588 	return sysfs_create_group(kernel_kobj, &cgroup_sysfs_attr_group);
6589 }
6590 subsys_initcall(cgroup_sysfs_init);
6591 
6592 #endif /* CONFIG_SYSFS */
6593