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 */
  80DEFINE_MUTEX(cgroup_mutex);
  81DEFINE_SPINLOCK(css_set_lock);
  82
  83#ifdef CONFIG_PROVE_RCU
  84EXPORT_SYMBOL_GPL(cgroup_mutex);
  85EXPORT_SYMBOL_GPL(css_set_lock);
  86#endif
  87
  88DEFINE_SPINLOCK(trace_cgroup_path_lock);
  89char trace_cgroup_path[TRACE_CGROUP_PATH_LEN];
  90bool 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 */
  96static 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 */
 102static DEFINE_SPINLOCK(cgroup_file_kn_lock);
 103
 104DEFINE_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 */
 117static 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,
 121struct 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,
 128static 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,
 143static 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,
 149static struct static_key_true *cgroup_subsys_on_dfl_key[] = {
 150#include <linux/cgroup_subsys.h>
 151};
 152#undef SUBSYS
 153
 154static DEFINE_PER_CPU(struct cgroup_rstat_cpu, cgrp_dfl_root_rstat_cpu);
 155
 156/*
 157 * The default hierarchy, reserved for the subsystems that are otherwise
 158 * unattached - it never has more than a single cgroup, and all tasks are
 159 * part of that cgroup.
 160 */
 161struct cgroup_root cgrp_dfl_root = { .cgrp.rstat_cpu = &cgrp_dfl_root_rstat_cpu };
 162EXPORT_SYMBOL_GPL(cgrp_dfl_root);
 163
 164/*
 165 * The default hierarchy always exists but is hidden until mounted for the
 166 * first time.  This is for backward compatibility.
 167 */
 168static bool cgrp_dfl_visible;
 169
 170/* some controllers are not supported in the default hierarchy */
 171static u16 cgrp_dfl_inhibit_ss_mask;
 172
 173/* some controllers are implicitly enabled on the default hierarchy */
 174static u16 cgrp_dfl_implicit_ss_mask;
 175
 176/* some controllers can be threaded on the default hierarchy */
 177static u16 cgrp_dfl_threaded_ss_mask;
 178
 179/* The list of hierarchy roots */
 180LIST_HEAD(cgroup_roots);
 181static int cgroup_root_count;
 182
 183/* hierarchy ID allocation and mapping, protected by cgroup_mutex */
 184static DEFINE_IDR(cgroup_hierarchy_idr);
 185
 186/*
 187 * Assign a monotonically increasing serial number to csses.  It guarantees
 188 * cgroups with bigger numbers are newer than those with smaller numbers.
 189 * Also, as csses are always appended to the parent's ->children list, it
 190 * guarantees that sibling csses are always sorted in the ascending serial
 191 * number order on the list.  Protected by cgroup_mutex.
 192 */
 193static u64 css_serial_nr_next = 1;
 194
 195/*
 196 * These bitmasks identify subsystems with specific features to avoid
 197 * having to do iterative checks repeatedly.
 198 */
 199static u16 have_fork_callback __read_mostly;
 200static u16 have_exit_callback __read_mostly;
 201static u16 have_release_callback __read_mostly;
 202static u16 have_canfork_callback __read_mostly;
 203
 204/* cgroup namespace for init task */
 205struct cgroup_namespace init_cgroup_ns = {
 206	.count		= REFCOUNT_INIT(2),
 207	.user_ns	= &init_user_ns,
 208	.ns.ops		= &cgroupns_operations,
 209	.ns.inum	= PROC_CGROUP_INIT_INO,
 210	.root_cset	= &init_css_set,
 211};
 212
 213static struct file_system_type cgroup2_fs_type;
 214static struct cftype cgroup_base_files[];
 215
 216static int cgroup_apply_control(struct cgroup *cgrp);
 217static void cgroup_finalize_control(struct cgroup *cgrp, int ret);
 218static void css_task_iter_skip(struct css_task_iter *it,
 219			       struct task_struct *task);
 220static int cgroup_destroy_locked(struct cgroup *cgrp);
 221static struct cgroup_subsys_state *css_create(struct cgroup *cgrp,
 222					      struct cgroup_subsys *ss);
 223static void css_release(struct percpu_ref *ref);
 224static void kill_css(struct cgroup_subsys_state *css);
 225static int cgroup_addrm_files(struct cgroup_subsys_state *css,
 226			      struct cgroup *cgrp, struct cftype cfts[],
 227			      bool is_add);
 228
 229/**
 230 * cgroup_ssid_enabled - cgroup subsys enabled test by subsys ID
 231 * @ssid: subsys ID of interest
 232 *
 233 * cgroup_subsys_enabled() can only be used with literal subsys names which
 234 * is fine for individual subsystems but unsuitable for cgroup core.  This
 235 * is slower static_key_enabled() based test indexed by @ssid.
 236 */
 237bool cgroup_ssid_enabled(int ssid)
 238{
 239	if (CGROUP_SUBSYS_COUNT == 0)
 240		return false;
 241
 242	return static_key_enabled(cgroup_subsys_enabled_key[ssid]);
 243}
 244
 245/**
 246 * cgroup_on_dfl - test whether a cgroup is on the default hierarchy
 247 * @cgrp: the cgroup of interest
 248 *
 249 * The default hierarchy is the v2 interface of cgroup and this function
 250 * can be used to test whether a cgroup is on the default hierarchy for
 251 * cases where a subsystem should behave differnetly depending on the
 252 * interface version.
 253 *
 254 * The set of behaviors which change on the default hierarchy are still
 255 * being determined and the mount option is prefixed with __DEVEL__.
 256 *
 257 * List of changed behaviors:
 258 *
 259 * - Mount options "noprefix", "xattr", "clone_children", "release_agent"
 260 *   and "name" are disallowed.
 261 *
 262 * - When mounting an existing superblock, mount options should match.
 263 *
 264 * - Remount is disallowed.
 265 *
 266 * - rename(2) is disallowed.
 267 *
 268 * - "tasks" is removed.  Everything should be at process granularity.  Use
 269 *   "cgroup.procs" instead.
 270 *
 271 * - "cgroup.procs" is not sorted.  pids will be unique unless they got
 272 *   recycled inbetween reads.
 273 *
 274 * - "release_agent" and "notify_on_release" are removed.  Replacement
 275 *   notification mechanism will be implemented.
 276 *
 277 * - "cgroup.clone_children" is removed.
 278 *
 279 * - "cgroup.subtree_populated" is available.  Its value is 0 if the cgroup
 280 *   and its descendants contain no task; otherwise, 1.  The file also
 281 *   generates kernfs notification which can be monitored through poll and
 282 *   [di]notify when the value of the file changes.
 283 *
 284 * - cpuset: tasks will be kept in empty cpusets when hotplug happens and
 285 *   take masks of ancestors with non-empty cpus/mems, instead of being
 286 *   moved to an ancestor.
 287 *
 288 * - cpuset: a task can be moved into an empty cpuset, and again it takes
 289 *   masks of ancestors.
 290 *
 291 * - memcg: use_hierarchy is on by default and the cgroup file for the flag
 292 *   is not created.
 293 *
 294 * - blkcg: blk-throttle becomes properly hierarchical.
 295 *
 296 * - debug: disallowed on the default hierarchy.
 297 */
 298bool cgroup_on_dfl(const struct cgroup *cgrp)
 299{
 300	return cgrp->root == &cgrp_dfl_root;
 301}
 302
 303/* IDR wrappers which synchronize using cgroup_idr_lock */
 304static int cgroup_idr_alloc(struct idr *idr, void *ptr, int start, int end,
 305			    gfp_t gfp_mask)
 306{
 307	int ret;
 308
 309	idr_preload(gfp_mask);
 310	spin_lock_bh(&cgroup_idr_lock);
 311	ret = idr_alloc(idr, ptr, start, end, gfp_mask & ~__GFP_DIRECT_RECLAIM);
 312	spin_unlock_bh(&cgroup_idr_lock);
 313	idr_preload_end();
 314	return ret;
 315}
 316
 317static void *cgroup_idr_replace(struct idr *idr, void *ptr, int id)
 318{
 319	void *ret;
 320
 321	spin_lock_bh(&cgroup_idr_lock);
 322	ret = idr_replace(idr, ptr, id);
 323	spin_unlock_bh(&cgroup_idr_lock);
 324	return ret;
 325}
 326
 327static void cgroup_idr_remove(struct idr *idr, int id)
 328{
 329	spin_lock_bh(&cgroup_idr_lock);
 330	idr_remove(idr, id);
 331	spin_unlock_bh(&cgroup_idr_lock);
 332}
 333
 334static bool cgroup_has_tasks(struct cgroup *cgrp)
 335{
 336	return cgrp->nr_populated_csets;
 337}
 338
 339bool cgroup_is_threaded(struct cgroup *cgrp)
 340{
 341	return cgrp->dom_cgrp != cgrp;
 342}
 343
 344/* can @cgrp host both domain and threaded children? */
 345static bool cgroup_is_mixable(struct cgroup *cgrp)
 346{
 347	/*
 348	 * Root isn't under domain level resource control exempting it from
 349	 * the no-internal-process constraint, so it can serve as a thread
 350	 * root and a parent of resource domains at the same time.
 351	 */
 352	return !cgroup_parent(cgrp);
 353}
 354
 355/* can @cgrp become a thread root? should always be true for a thread root */
 356static bool cgroup_can_be_thread_root(struct cgroup *cgrp)
 357{
 358	/* mixables don't care */
 359	if (cgroup_is_mixable(cgrp))
 360		return true;
 361
 362	/* domain roots can't be nested under threaded */
 363	if (cgroup_is_threaded(cgrp))
 364		return false;
 365
 366	/* can only have either domain or threaded children */
 367	if (cgrp->nr_populated_domain_children)
 368		return false;
 369
 370	/* and no domain controllers can be enabled */
 371	if (cgrp->subtree_control & ~cgrp_dfl_threaded_ss_mask)
 372		return false;
 373
 374	return true;
 375}
 376
 377/* is @cgrp root of a threaded subtree? */
 378bool cgroup_is_thread_root(struct cgroup *cgrp)
 379{
 380	/* thread root should be a domain */
 381	if (cgroup_is_threaded(cgrp))
 382		return false;
 383
 384	/* a domain w/ threaded children is a thread root */
 385	if (cgrp->nr_threaded_children)
 386		return true;
 387
 388	/*
 389	 * A domain which has tasks and explicit threaded controllers
 390	 * enabled is a thread root.
 391	 */
 392	if (cgroup_has_tasks(cgrp) &&
 393	    (cgrp->subtree_control & cgrp_dfl_threaded_ss_mask))
 394		return true;
 395
 396	return false;
 397}
 398
 399/* a domain which isn't connected to the root w/o brekage can't be used */
 400static bool cgroup_is_valid_domain(struct cgroup *cgrp)
 401{
 402	/* the cgroup itself can be a thread root */
 403	if (cgroup_is_threaded(cgrp))
 404		return false;
 405
 406	/* but the ancestors can't be unless mixable */
 407	while ((cgrp = cgroup_parent(cgrp))) {
 408		if (!cgroup_is_mixable(cgrp) && cgroup_is_thread_root(cgrp))
 409			return false;
 410		if (cgroup_is_threaded(cgrp))
 411			return false;
 412	}
 413
 414	return true;
 415}
 416
 417/* subsystems visibly enabled on a cgroup */
 418static u16 cgroup_control(struct cgroup *cgrp)
 419{
 420	struct cgroup *parent = cgroup_parent(cgrp);
 421	u16 root_ss_mask = cgrp->root->subsys_mask;
 422
 423	if (parent) {
 424		u16 ss_mask = parent->subtree_control;
 425
 426		/* threaded cgroups can only have threaded controllers */
 427		if (cgroup_is_threaded(cgrp))
 428			ss_mask &= cgrp_dfl_threaded_ss_mask;
 429		return ss_mask;
 430	}
 431
 432	if (cgroup_on_dfl(cgrp))
 433		root_ss_mask &= ~(cgrp_dfl_inhibit_ss_mask |
 434				  cgrp_dfl_implicit_ss_mask);
 435	return root_ss_mask;
 436}
 437
 438/* subsystems enabled on a cgroup */
 439static u16 cgroup_ss_mask(struct cgroup *cgrp)
 440{
 441	struct cgroup *parent = cgroup_parent(cgrp);
 442
 443	if (parent) {
 444		u16 ss_mask = parent->subtree_ss_mask;
 445
 446		/* threaded cgroups can only have threaded controllers */
 447		if (cgroup_is_threaded(cgrp))
 448			ss_mask &= cgrp_dfl_threaded_ss_mask;
 449		return ss_mask;
 450	}
 451
 452	return cgrp->root->subsys_mask;
 453}
 454
 455/**
 456 * cgroup_css - obtain a cgroup's css for the specified subsystem
 457 * @cgrp: the cgroup of interest
 458 * @ss: the subsystem of interest (%NULL returns @cgrp->self)
 459 *
 460 * Return @cgrp's css (cgroup_subsys_state) associated with @ss.  This
 461 * function must be called either under cgroup_mutex or rcu_read_lock() and
 462 * the caller is responsible for pinning the returned css if it wants to
 463 * keep accessing it outside the said locks.  This function may return
 464 * %NULL if @cgrp doesn't have @subsys_id enabled.
 465 */
 466static struct cgroup_subsys_state *cgroup_css(struct cgroup *cgrp,
 467					      struct cgroup_subsys *ss)
 468{
 469	if (ss)
 470		return rcu_dereference_check(cgrp->subsys[ss->id],
 471					lockdep_is_held(&cgroup_mutex));
 472	else
 473		return &cgrp->self;
 474}
 475
 476/**
 477 * cgroup_tryget_css - try to get a cgroup's css for the specified subsystem
 478 * @cgrp: the cgroup of interest
 479 * @ss: the subsystem of interest
 480 *
 481 * Find and get @cgrp's css assocaited with @ss.  If the css doesn't exist
 482 * or is offline, %NULL is returned.
 483 */
 484static struct cgroup_subsys_state *cgroup_tryget_css(struct cgroup *cgrp,
 485						     struct cgroup_subsys *ss)
 486{
 487	struct cgroup_subsys_state *css;
 488
 489	rcu_read_lock();
 490	css = cgroup_css(cgrp, ss);
 491	if (css && !css_tryget_online(css))
 492		css = NULL;
 493	rcu_read_unlock();
 494
 495	return css;
 496}
 497
 498/**
 499 * cgroup_e_css_by_mask - obtain a cgroup's effective css for the specified ss
 500 * @cgrp: the cgroup of interest
 501 * @ss: the subsystem of interest (%NULL returns @cgrp->self)
 502 *
 503 * Similar to cgroup_css() but returns the effective css, which is defined
 504 * as the matching css of the nearest ancestor including self which has @ss
 505 * enabled.  If @ss is associated with the hierarchy @cgrp is on, this
 506 * function is guaranteed to return non-NULL css.
 507 */
 508static struct cgroup_subsys_state *cgroup_e_css_by_mask(struct cgroup *cgrp,
 509							struct cgroup_subsys *ss)
 510{
 511	lockdep_assert_held(&cgroup_mutex);
 512
 513	if (!ss)
 514		return &cgrp->self;
 515
 516	/*
 517	 * This function is used while updating css associations and thus
 518	 * can't test the csses directly.  Test ss_mask.
 519	 */
 520	while (!(cgroup_ss_mask(cgrp) & (1 << ss->id))) {
 521		cgrp = cgroup_parent(cgrp);
 522		if (!cgrp)
 523			return NULL;
 524	}
 525
 526	return cgroup_css(cgrp, ss);
 527}
 528
 529/**
 530 * cgroup_e_css - obtain a cgroup's effective css for the specified subsystem
 531 * @cgrp: the cgroup of interest
 532 * @ss: the subsystem of interest
 533 *
 534 * Find and get the effective css of @cgrp for @ss.  The effective css is
 535 * defined as the matching css of the nearest ancestor including self which
 536 * has @ss enabled.  If @ss is not mounted on the hierarchy @cgrp is on,
 537 * the root css is returned, so this function always returns a valid css.
 538 *
 539 * The returned css is not guaranteed to be online, and therefore it is the
 540 * callers responsiblity to tryget a reference for it.
 541 */
 542struct cgroup_subsys_state *cgroup_e_css(struct cgroup *cgrp,
 543					 struct cgroup_subsys *ss)
 544{
 545	struct cgroup_subsys_state *css;
 546
 547	do {
 548		css = cgroup_css(cgrp, ss);
 549
 550		if (css)
 551			return css;
 552		cgrp = cgroup_parent(cgrp);
 553	} while (cgrp);
 554
 555	return init_css_set.subsys[ss->id];
 556}
 557
 558/**
 559 * cgroup_get_e_css - get a cgroup's effective css for the specified subsystem
 560 * @cgrp: the cgroup of interest
 561 * @ss: the subsystem of interest
 562 *
 563 * Find and get the effective css of @cgrp for @ss.  The effective css is
 564 * defined as the matching css of the nearest ancestor including self which
 565 * has @ss enabled.  If @ss is not mounted on the hierarchy @cgrp is on,
 566 * the root css is returned, so this function always returns a valid css.
 567 * The returned css must be put using css_put().
 568 */
 569struct cgroup_subsys_state *cgroup_get_e_css(struct cgroup *cgrp,
 570					     struct cgroup_subsys *ss)
 571{
 572	struct cgroup_subsys_state *css;
 573
 574	rcu_read_lock();
 575
 576	do {
 577		css = cgroup_css(cgrp, ss);
 578
 579		if (css && css_tryget_online(css))
 580			goto out_unlock;
 581		cgrp = cgroup_parent(cgrp);
 582	} while (cgrp);
 583
 584	css = init_css_set.subsys[ss->id];
 585	css_get(css);
 586out_unlock:
 587	rcu_read_unlock();
 588	return css;
 589}
 590
 591static void cgroup_get_live(struct cgroup *cgrp)
 592{
 593	WARN_ON_ONCE(cgroup_is_dead(cgrp));
 594	css_get(&cgrp->self);
 595}
 596
 597/**
 598 * __cgroup_task_count - count the number of tasks in a cgroup. The caller
 599 * is responsible for taking the css_set_lock.
 600 * @cgrp: the cgroup in question
 601 */
 602int __cgroup_task_count(const struct cgroup *cgrp)
 603{
 604	int count = 0;
 605	struct cgrp_cset_link *link;
 606
 607	lockdep_assert_held(&css_set_lock);
 608
 609	list_for_each_entry(link, &cgrp->cset_links, cset_link)
 610		count += link->cset->nr_tasks;
 611
 612	return count;
 613}
 614
 615/**
 616 * cgroup_task_count - count the number of tasks in a cgroup.
 617 * @cgrp: the cgroup in question
 618 */
 619int cgroup_task_count(const struct cgroup *cgrp)
 620{
 621	int count;
 622
 623	spin_lock_irq(&css_set_lock);
 624	count = __cgroup_task_count(cgrp);
 625	spin_unlock_irq(&css_set_lock);
 626
 627	return count;
 628}
 629
 630struct cgroup_subsys_state *of_css(struct kernfs_open_file *of)
 631{
 632	struct cgroup *cgrp = of->kn->parent->priv;
 633	struct cftype *cft = of_cft(of);
 634
 635	/*
 636	 * This is open and unprotected implementation of cgroup_css().
 637	 * seq_css() is only called from a kernfs file operation which has
 638	 * an active reference on the file.  Because all the subsystem
 639	 * files are drained before a css is disassociated with a cgroup,
 640	 * the matching css from the cgroup's subsys table is guaranteed to
 641	 * be and stay valid until the enclosing operation is complete.
 642	 */
 643	if (cft->ss)
 644		return rcu_dereference_raw(cgrp->subsys[cft->ss->id]);
 645	else
 646		return &cgrp->self;
 647}
 648EXPORT_SYMBOL_GPL(of_css);
 649
 650/**
 651 * for_each_css - iterate all css's of a cgroup
 652 * @css: the iteration cursor
 653 * @ssid: the index of the subsystem, CGROUP_SUBSYS_COUNT after reaching the end
 654 * @cgrp: the target cgroup to iterate css's of
 655 *
 656 * Should be called under cgroup_[tree_]mutex.
 657 */
 658#define for_each_css(css, ssid, cgrp)					\
 659	for ((ssid) = 0; (ssid) < CGROUP_SUBSYS_COUNT; (ssid)++)	\
 660		if (!((css) = rcu_dereference_check(			\
 661				(cgrp)->subsys[(ssid)],			\
 662				lockdep_is_held(&cgroup_mutex)))) { }	\
 663		else
 664
 665/**
 666 * for_each_e_css - iterate all effective css's of a cgroup
 667 * @css: the iteration cursor
 668 * @ssid: the index of the subsystem, CGROUP_SUBSYS_COUNT after reaching the end
 669 * @cgrp: the target cgroup to iterate css's of
 670 *
 671 * Should be called under cgroup_[tree_]mutex.
 672 */
 673#define for_each_e_css(css, ssid, cgrp)					    \
 674	for ((ssid) = 0; (ssid) < CGROUP_SUBSYS_COUNT; (ssid)++)	    \
 675		if (!((css) = cgroup_e_css_by_mask(cgrp,		    \
 676						   cgroup_subsys[(ssid)]))) \
 677			;						    \
 678		else
 679
 680/**
 681 * do_each_subsys_mask - filter for_each_subsys with a bitmask
 682 * @ss: the iteration cursor
 683 * @ssid: the index of @ss, CGROUP_SUBSYS_COUNT after reaching the end
 684 * @ss_mask: the bitmask
 685 *
 686 * The block will only run for cases where the ssid-th bit (1 << ssid) of
 687 * @ss_mask is set.
 688 */
 689#define do_each_subsys_mask(ss, ssid, ss_mask) do {			\
 690	unsigned long __ss_mask = (ss_mask);				\
 691	if (!CGROUP_SUBSYS_COUNT) { /* to avoid spurious gcc warning */	\
 692		(ssid) = 0;						\
 693		break;							\
 694	}								\
 695	for_each_set_bit(ssid, &__ss_mask, CGROUP_SUBSYS_COUNT) {	\
 696		(ss) = cgroup_subsys[ssid];				\
 697		{
 698
 699#define while_each_subsys_mask()					\
 700		}							\
 701	}								\
 702} while (false)
 703
 704/* iterate over child cgrps, lock should be held throughout iteration */
 705#define cgroup_for_each_live_child(child, cgrp)				\
 706	list_for_each_entry((child), &(cgrp)->self.children, self.sibling) \
 707		if (({ lockdep_assert_held(&cgroup_mutex);		\
 708		       cgroup_is_dead(child); }))			\
 709			;						\
 710		else
 711
 712/* walk live descendants in preorder */
 713#define cgroup_for_each_live_descendant_pre(dsct, d_css, cgrp)		\
 714	css_for_each_descendant_pre((d_css), cgroup_css((cgrp), NULL))	\
 715		if (({ lockdep_assert_held(&cgroup_mutex);		\
 716		       (dsct) = (d_css)->cgroup;			\
 717		       cgroup_is_dead(dsct); }))			\
 718			;						\
 719		else
 720
 721/* walk live descendants in postorder */
 722#define cgroup_for_each_live_descendant_post(dsct, d_css, cgrp)		\
 723	css_for_each_descendant_post((d_css), cgroup_css((cgrp), NULL))	\
 724		if (({ lockdep_assert_held(&cgroup_mutex);		\
 725		       (dsct) = (d_css)->cgroup;			\
 726		       cgroup_is_dead(dsct); }))			\
 727			;						\
 728		else
 729
 730/*
 731 * The default css_set - used by init and its children prior to any
 732 * hierarchies being mounted. It contains a pointer to the root state
 733 * for each subsystem. Also used to anchor the list of css_sets. Not
 734 * reference-counted, to improve performance when child cgroups
 735 * haven't been created.
 736 */
 737struct css_set init_css_set = {
 738	.refcount		= REFCOUNT_INIT(1),
 739	.dom_cset		= &init_css_set,
 740	.tasks			= LIST_HEAD_INIT(init_css_set.tasks),
 741	.mg_tasks		= LIST_HEAD_INIT(init_css_set.mg_tasks),
 742	.dying_tasks		= LIST_HEAD_INIT(init_css_set.dying_tasks),
 743	.task_iters		= LIST_HEAD_INIT(init_css_set.task_iters),
 744	.threaded_csets		= LIST_HEAD_INIT(init_css_set.threaded_csets),
 745	.cgrp_links		= LIST_HEAD_INIT(init_css_set.cgrp_links),
 746	.mg_preload_node	= LIST_HEAD_INIT(init_css_set.mg_preload_node),
 747	.mg_node		= LIST_HEAD_INIT(init_css_set.mg_node),
 748
 749	/*
 750	 * The following field is re-initialized when this cset gets linked
 751	 * in cgroup_init().  However, let's initialize the field
 752	 * statically too so that the default cgroup can be accessed safely
 753	 * early during boot.
 754	 */
 755	.dfl_cgrp		= &cgrp_dfl_root.cgrp,
 756};
 757
 758static int css_set_count	= 1;	/* 1 for init_css_set */
 759
 760static bool css_set_threaded(struct css_set *cset)
 761{
 762	return cset->dom_cset != cset;
 763}
 764
 765/**
 766 * css_set_populated - does a css_set contain any tasks?
 767 * @cset: target css_set
 768 *
 769 * css_set_populated() should be the same as !!cset->nr_tasks at steady
 770 * state. However, css_set_populated() can be called while a task is being
 771 * added to or removed from the linked list before the nr_tasks is
 772 * properly updated. Hence, we can't just look at ->nr_tasks here.
 773 */
 774static bool css_set_populated(struct css_set *cset)
 775{
 776	lockdep_assert_held(&css_set_lock);
 777
 778	return !list_empty(&cset->tasks) || !list_empty(&cset->mg_tasks);
 779}
 780
 781/**
 782 * cgroup_update_populated - update the populated count of a cgroup
 783 * @cgrp: the target cgroup
 784 * @populated: inc or dec populated count
 785 *
 786 * One of the css_sets associated with @cgrp is either getting its first
 787 * task or losing the last.  Update @cgrp->nr_populated_* accordingly.  The
 788 * count is propagated towards root so that a given cgroup's
 789 * nr_populated_children is zero iff none of its descendants contain any
 790 * tasks.
 791 *
 792 * @cgrp's interface file "cgroup.populated" is zero if both
 793 * @cgrp->nr_populated_csets and @cgrp->nr_populated_children are zero and
 794 * 1 otherwise.  When the sum changes from or to zero, userland is notified
 795 * that the content of the interface file has changed.  This can be used to
 796 * detect when @cgrp and its descendants become populated or empty.
 797 */
 798static void cgroup_update_populated(struct cgroup *cgrp, bool populated)
 799{
 800	struct cgroup *child = NULL;
 801	int adj = populated ? 1 : -1;
 802
 803	lockdep_assert_held(&css_set_lock);
 804
 805	do {
 806		bool was_populated = cgroup_is_populated(cgrp);
 807
 808		if (!child) {
 809			cgrp->nr_populated_csets += adj;
 810		} else {
 811			if (cgroup_is_threaded(child))
 812				cgrp->nr_populated_threaded_children += adj;
 813			else
 814				cgrp->nr_populated_domain_children += adj;
 815		}
 816
 817		if (was_populated == cgroup_is_populated(cgrp))
 818			break;
 819
 820		cgroup1_check_for_release(cgrp);
 821		TRACE_CGROUP_PATH(notify_populated, cgrp,
 822				  cgroup_is_populated(cgrp));
 823		cgroup_file_notify(&cgrp->events_file);
 824
 825		child = cgrp;
 826		cgrp = cgroup_parent(cgrp);
 827	} while (cgrp);
 828}
 829
 830/**
 831 * css_set_update_populated - update populated state of a css_set
 832 * @cset: target css_set
 833 * @populated: whether @cset is populated or depopulated
 834 *
 835 * @cset is either getting the first task or losing the last.  Update the
 836 * populated counters of all associated cgroups accordingly.
 837 */
 838static void css_set_update_populated(struct css_set *cset, bool populated)
 839{
 840	struct cgrp_cset_link *link;
 841
 842	lockdep_assert_held(&css_set_lock);
 843
 844	list_for_each_entry(link, &cset->cgrp_links, cgrp_link)
 845		cgroup_update_populated(link->cgrp, populated);
 846}
 847
 848/*
 849 * @task is leaving, advance task iterators which are pointing to it so
 850 * that they can resume at the next position.  Advancing an iterator might
 851 * remove it from the list, use safe walk.  See css_task_iter_skip() for
 852 * details.
 853 */
 854static void css_set_skip_task_iters(struct css_set *cset,
 855				    struct task_struct *task)
 856{
 857	struct css_task_iter *it, *pos;
 858
 859	list_for_each_entry_safe(it, pos, &cset->task_iters, iters_node)
 860		css_task_iter_skip(it, task);
 861}
 862
 863/**
 864 * css_set_move_task - move a task from one css_set to another
 865 * @task: task being moved
 866 * @from_cset: css_set @task currently belongs to (may be NULL)
 867 * @to_cset: new css_set @task is being moved to (may be NULL)
 868 * @use_mg_tasks: move to @to_cset->mg_tasks instead of ->tasks
 869 *
 870 * Move @task from @from_cset to @to_cset.  If @task didn't belong to any
 871 * css_set, @from_cset can be NULL.  If @task is being disassociated
 872 * instead of moved, @to_cset can be NULL.
 873 *
 874 * This function automatically handles populated counter updates and
 875 * css_task_iter adjustments but the caller is responsible for managing
 876 * @from_cset and @to_cset's reference counts.
 877 */
 878static void css_set_move_task(struct task_struct *task,
 879			      struct css_set *from_cset, struct css_set *to_cset,
 880			      bool use_mg_tasks)
 881{
 882	lockdep_assert_held(&css_set_lock);
 883
 884	if (to_cset && !css_set_populated(to_cset))
 885		css_set_update_populated(to_cset, true);
 886
 887	if (from_cset) {
 
 
 888		WARN_ON_ONCE(list_empty(&task->cg_list));
 889
 890		css_set_skip_task_iters(from_cset, task);
 
 
 
 
 
 
 
 
 
 
 
 891		list_del_init(&task->cg_list);
 892		if (!css_set_populated(from_cset))
 893			css_set_update_populated(from_cset, false);
 894	} else {
 895		WARN_ON_ONCE(!list_empty(&task->cg_list));
 896	}
 897
 898	if (to_cset) {
 899		/*
 900		 * We are synchronized through cgroup_threadgroup_rwsem
 901		 * against PF_EXITING setting such that we can't race
 902		 * against cgroup_exit() changing the css_set to
 903		 * init_css_set and dropping the old one.
 904		 */
 905		WARN_ON_ONCE(task->flags & PF_EXITING);
 906
 907		cgroup_move_task(task, to_cset);
 908		list_add_tail(&task->cg_list, use_mg_tasks ? &to_cset->mg_tasks :
 909							     &to_cset->tasks);
 910	}
 911}
 912
 913/*
 914 * hash table for cgroup groups. This improves the performance to find
 915 * an existing css_set. This hash doesn't (currently) take into
 916 * account cgroups in empty hierarchies.
 917 */
 918#define CSS_SET_HASH_BITS	7
 919static DEFINE_HASHTABLE(css_set_table, CSS_SET_HASH_BITS);
 920
 921static unsigned long css_set_hash(struct cgroup_subsys_state *css[])
 922{
 923	unsigned long key = 0UL;
 924	struct cgroup_subsys *ss;
 925	int i;
 926
 927	for_each_subsys(ss, i)
 928		key += (unsigned long)css[i];
 929	key = (key >> 16) ^ key;
 930
 931	return key;
 932}
 933
 934void put_css_set_locked(struct css_set *cset)
 935{
 936	struct cgrp_cset_link *link, *tmp_link;
 937	struct cgroup_subsys *ss;
 938	int ssid;
 939
 940	lockdep_assert_held(&css_set_lock);
 941
 942	if (!refcount_dec_and_test(&cset->refcount))
 943		return;
 944
 945	WARN_ON_ONCE(!list_empty(&cset->threaded_csets));
 946
 947	/* This css_set is dead. unlink it and release cgroup and css refs */
 948	for_each_subsys(ss, ssid) {
 949		list_del(&cset->e_cset_node[ssid]);
 950		css_put(cset->subsys[ssid]);
 951	}
 952	hash_del(&cset->hlist);
 953	css_set_count--;
 954
 955	list_for_each_entry_safe(link, tmp_link, &cset->cgrp_links, cgrp_link) {
 956		list_del(&link->cset_link);
 957		list_del(&link->cgrp_link);
 958		if (cgroup_parent(link->cgrp))
 959			cgroup_put(link->cgrp);
 960		kfree(link);
 961	}
 962
 963	if (css_set_threaded(cset)) {
 964		list_del(&cset->threaded_csets_node);
 965		put_css_set_locked(cset->dom_cset);
 966	}
 967
 968	kfree_rcu(cset, rcu_head);
 969}
 970
 971/**
 972 * compare_css_sets - helper function for find_existing_css_set().
 973 * @cset: candidate css_set being tested
 974 * @old_cset: existing css_set for a task
 975 * @new_cgrp: cgroup that's being entered by the task
 976 * @template: desired set of css pointers in css_set (pre-calculated)
 977 *
 978 * Returns true if "cset" matches "old_cset" except for the hierarchy
 979 * which "new_cgrp" belongs to, for which it should match "new_cgrp".
 980 */
 981static bool compare_css_sets(struct css_set *cset,
 982			     struct css_set *old_cset,
 983			     struct cgroup *new_cgrp,
 984			     struct cgroup_subsys_state *template[])
 985{
 986	struct cgroup *new_dfl_cgrp;
 987	struct list_head *l1, *l2;
 988
 989	/*
 990	 * On the default hierarchy, there can be csets which are
 991	 * associated with the same set of cgroups but different csses.
 992	 * Let's first ensure that csses match.
 993	 */
 994	if (memcmp(template, cset->subsys, sizeof(cset->subsys)))
 995		return false;
 996
 997
 998	/* @cset's domain should match the default cgroup's */
 999	if (cgroup_on_dfl(new_cgrp))
1000		new_dfl_cgrp = new_cgrp;
1001	else
1002		new_dfl_cgrp = old_cset->dfl_cgrp;
1003
1004	if (new_dfl_cgrp->dom_cgrp != cset->dom_cset->dfl_cgrp)
1005		return false;
1006
1007	/*
1008	 * Compare cgroup pointers in order to distinguish between
1009	 * different cgroups in hierarchies.  As different cgroups may
1010	 * share the same effective css, this comparison is always
1011	 * necessary.
1012	 */
1013	l1 = &cset->cgrp_links;
1014	l2 = &old_cset->cgrp_links;
1015	while (1) {
1016		struct cgrp_cset_link *link1, *link2;
1017		struct cgroup *cgrp1, *cgrp2;
1018
1019		l1 = l1->next;
1020		l2 = l2->next;
1021		/* See if we reached the end - both lists are equal length. */
1022		if (l1 == &cset->cgrp_links) {
1023			BUG_ON(l2 != &old_cset->cgrp_links);
1024			break;
1025		} else {
1026			BUG_ON(l2 == &old_cset->cgrp_links);
1027		}
1028		/* Locate the cgroups associated with these links. */
1029		link1 = list_entry(l1, struct cgrp_cset_link, cgrp_link);
1030		link2 = list_entry(l2, struct cgrp_cset_link, cgrp_link);
1031		cgrp1 = link1->cgrp;
1032		cgrp2 = link2->cgrp;
1033		/* Hierarchies should be linked in the same order. */
1034		BUG_ON(cgrp1->root != cgrp2->root);
1035
1036		/*
1037		 * If this hierarchy is the hierarchy of the cgroup
1038		 * that's changing, then we need to check that this
1039		 * css_set points to the new cgroup; if it's any other
1040		 * hierarchy, then this css_set should point to the
1041		 * same cgroup as the old css_set.
1042		 */
1043		if (cgrp1->root == new_cgrp->root) {
1044			if (cgrp1 != new_cgrp)
1045				return false;
1046		} else {
1047			if (cgrp1 != cgrp2)
1048				return false;
1049		}
1050	}
1051	return true;
1052}
1053
1054/**
1055 * find_existing_css_set - init css array and find the matching css_set
1056 * @old_cset: the css_set that we're using before the cgroup transition
1057 * @cgrp: the cgroup that we're moving into
1058 * @template: out param for the new set of csses, should be clear on entry
1059 */
1060static struct css_set *find_existing_css_set(struct css_set *old_cset,
1061					struct cgroup *cgrp,
1062					struct cgroup_subsys_state *template[])
1063{
1064	struct cgroup_root *root = cgrp->root;
1065	struct cgroup_subsys *ss;
1066	struct css_set *cset;
1067	unsigned long key;
1068	int i;
1069
1070	/*
1071	 * Build the set of subsystem state objects that we want to see in the
1072	 * new css_set. while subsystems can change globally, the entries here
1073	 * won't change, so no need for locking.
1074	 */
1075	for_each_subsys(ss, i) {
1076		if (root->subsys_mask & (1UL << i)) {
1077			/*
1078			 * @ss is in this hierarchy, so we want the
1079			 * effective css from @cgrp.
1080			 */
1081			template[i] = cgroup_e_css_by_mask(cgrp, ss);
1082		} else {
1083			/*
1084			 * @ss is not in this hierarchy, so we don't want
1085			 * to change the css.
1086			 */
1087			template[i] = old_cset->subsys[i];
1088		}
1089	}
1090
1091	key = css_set_hash(template);
1092	hash_for_each_possible(css_set_table, cset, hlist, key) {
1093		if (!compare_css_sets(cset, old_cset, cgrp, template))
1094			continue;
1095
1096		/* This css_set matches what we need */
1097		return cset;
1098	}
1099
1100	/* No existing cgroup group matched */
1101	return NULL;
1102}
1103
1104static void free_cgrp_cset_links(struct list_head *links_to_free)
1105{
1106	struct cgrp_cset_link *link, *tmp_link;
1107
1108	list_for_each_entry_safe(link, tmp_link, links_to_free, cset_link) {
1109		list_del(&link->cset_link);
1110		kfree(link);
1111	}
1112}
1113
1114/**
1115 * allocate_cgrp_cset_links - allocate cgrp_cset_links
1116 * @count: the number of links to allocate
1117 * @tmp_links: list_head the allocated links are put on
1118 *
1119 * Allocate @count cgrp_cset_link structures and chain them on @tmp_links
1120 * through ->cset_link.  Returns 0 on success or -errno.
1121 */
1122static int allocate_cgrp_cset_links(int count, struct list_head *tmp_links)
1123{
1124	struct cgrp_cset_link *link;
1125	int i;
1126
1127	INIT_LIST_HEAD(tmp_links);
1128
1129	for (i = 0; i < count; i++) {
1130		link = kzalloc(sizeof(*link), GFP_KERNEL);
1131		if (!link) {
1132			free_cgrp_cset_links(tmp_links);
1133			return -ENOMEM;
1134		}
1135		list_add(&link->cset_link, tmp_links);
1136	}
1137	return 0;
1138}
1139
1140/**
1141 * link_css_set - a helper function to link a css_set to a cgroup
1142 * @tmp_links: cgrp_cset_link objects allocated by allocate_cgrp_cset_links()
1143 * @cset: the css_set to be linked
1144 * @cgrp: the destination cgroup
1145 */
1146static void link_css_set(struct list_head *tmp_links, struct css_set *cset,
1147			 struct cgroup *cgrp)
1148{
1149	struct cgrp_cset_link *link;
1150
1151	BUG_ON(list_empty(tmp_links));
1152
1153	if (cgroup_on_dfl(cgrp))
1154		cset->dfl_cgrp = cgrp;
1155
1156	link = list_first_entry(tmp_links, struct cgrp_cset_link, cset_link);
1157	link->cset = cset;
1158	link->cgrp = cgrp;
1159
1160	/*
1161	 * Always add links to the tail of the lists so that the lists are
1162	 * in choronological order.
1163	 */
1164	list_move_tail(&link->cset_link, &cgrp->cset_links);
1165	list_add_tail(&link->cgrp_link, &cset->cgrp_links);
1166
1167	if (cgroup_parent(cgrp))
1168		cgroup_get_live(cgrp);
1169}
1170
1171/**
1172 * find_css_set - return a new css_set with one cgroup updated
1173 * @old_cset: the baseline css_set
1174 * @cgrp: the cgroup to be updated
1175 *
1176 * Return a new css_set that's equivalent to @old_cset, but with @cgrp
1177 * substituted into the appropriate hierarchy.
1178 */
1179static struct css_set *find_css_set(struct css_set *old_cset,
1180				    struct cgroup *cgrp)
1181{
1182	struct cgroup_subsys_state *template[CGROUP_SUBSYS_COUNT] = { };
1183	struct css_set *cset;
1184	struct list_head tmp_links;
1185	struct cgrp_cset_link *link;
1186	struct cgroup_subsys *ss;
1187	unsigned long key;
1188	int ssid;
1189
1190	lockdep_assert_held(&cgroup_mutex);
1191
1192	/* First see if we already have a cgroup group that matches
1193	 * the desired set */
1194	spin_lock_irq(&css_set_lock);
1195	cset = find_existing_css_set(old_cset, cgrp, template);
1196	if (cset)
1197		get_css_set(cset);
1198	spin_unlock_irq(&css_set_lock);
1199
1200	if (cset)
1201		return cset;
1202
1203	cset = kzalloc(sizeof(*cset), GFP_KERNEL);
1204	if (!cset)
1205		return NULL;
1206
1207	/* Allocate all the cgrp_cset_link objects that we'll need */
1208	if (allocate_cgrp_cset_links(cgroup_root_count, &tmp_links) < 0) {
1209		kfree(cset);
1210		return NULL;
1211	}
1212
1213	refcount_set(&cset->refcount, 1);
1214	cset->dom_cset = cset;
1215	INIT_LIST_HEAD(&cset->tasks);
1216	INIT_LIST_HEAD(&cset->mg_tasks);
1217	INIT_LIST_HEAD(&cset->dying_tasks);
1218	INIT_LIST_HEAD(&cset->task_iters);
1219	INIT_LIST_HEAD(&cset->threaded_csets);
1220	INIT_HLIST_NODE(&cset->hlist);
1221	INIT_LIST_HEAD(&cset->cgrp_links);
1222	INIT_LIST_HEAD(&cset->mg_preload_node);
1223	INIT_LIST_HEAD(&cset->mg_node);
1224
1225	/* Copy the set of subsystem state objects generated in
1226	 * find_existing_css_set() */
1227	memcpy(cset->subsys, template, sizeof(cset->subsys));
1228
1229	spin_lock_irq(&css_set_lock);
1230	/* Add reference counts and links from the new css_set. */
1231	list_for_each_entry(link, &old_cset->cgrp_links, cgrp_link) {
1232		struct cgroup *c = link->cgrp;
1233
1234		if (c->root == cgrp->root)
1235			c = cgrp;
1236		link_css_set(&tmp_links, cset, c);
1237	}
1238
1239	BUG_ON(!list_empty(&tmp_links));
1240
1241	css_set_count++;
1242
1243	/* Add @cset to the hash table */
1244	key = css_set_hash(cset->subsys);
1245	hash_add(css_set_table, &cset->hlist, key);
1246
1247	for_each_subsys(ss, ssid) {
1248		struct cgroup_subsys_state *css = cset->subsys[ssid];
1249
1250		list_add_tail(&cset->e_cset_node[ssid],
1251			      &css->cgroup->e_csets[ssid]);
1252		css_get(css);
1253	}
1254
1255	spin_unlock_irq(&css_set_lock);
1256
1257	/*
1258	 * If @cset should be threaded, look up the matching dom_cset and
1259	 * link them up.  We first fully initialize @cset then look for the
1260	 * dom_cset.  It's simpler this way and safe as @cset is guaranteed
1261	 * to stay empty until we return.
1262	 */
1263	if (cgroup_is_threaded(cset->dfl_cgrp)) {
1264		struct css_set *dcset;
1265
1266		dcset = find_css_set(cset, cset->dfl_cgrp->dom_cgrp);
1267		if (!dcset) {
1268			put_css_set(cset);
1269			return NULL;
1270		}
1271
1272		spin_lock_irq(&css_set_lock);
1273		cset->dom_cset = dcset;
1274		list_add_tail(&cset->threaded_csets_node,
1275			      &dcset->threaded_csets);
1276		spin_unlock_irq(&css_set_lock);
1277	}
1278
1279	return cset;
1280}
1281
1282struct cgroup_root *cgroup_root_from_kf(struct kernfs_root *kf_root)
1283{
1284	struct cgroup *root_cgrp = kf_root->kn->priv;
1285
1286	return root_cgrp->root;
1287}
1288
1289static int cgroup_init_root_id(struct cgroup_root *root)
1290{
1291	int id;
1292
1293	lockdep_assert_held(&cgroup_mutex);
1294
1295	id = idr_alloc_cyclic(&cgroup_hierarchy_idr, root, 0, 0, GFP_KERNEL);
1296	if (id < 0)
1297		return id;
1298
1299	root->hierarchy_id = id;
1300	return 0;
1301}
1302
1303static void cgroup_exit_root_id(struct cgroup_root *root)
1304{
1305	lockdep_assert_held(&cgroup_mutex);
1306
1307	idr_remove(&cgroup_hierarchy_idr, root->hierarchy_id);
1308}
1309
1310void cgroup_free_root(struct cgroup_root *root)
1311{
1312	if (root) {
1313		idr_destroy(&root->cgroup_idr);
1314		kfree(root);
1315	}
1316}
1317
1318static void cgroup_destroy_root(struct cgroup_root *root)
1319{
1320	struct cgroup *cgrp = &root->cgrp;
1321	struct cgrp_cset_link *link, *tmp_link;
1322
1323	trace_cgroup_destroy_root(root);
1324
1325	cgroup_lock_and_drain_offline(&cgrp_dfl_root.cgrp);
1326
1327	BUG_ON(atomic_read(&root->nr_cgrps));
1328	BUG_ON(!list_empty(&cgrp->self.children));
1329
1330	/* Rebind all subsystems back to the default hierarchy */
1331	WARN_ON(rebind_subsystems(&cgrp_dfl_root, root->subsys_mask));
1332
1333	/*
1334	 * Release all the links from cset_links to this hierarchy's
1335	 * root cgroup
1336	 */
1337	spin_lock_irq(&css_set_lock);
1338
1339	list_for_each_entry_safe(link, tmp_link, &cgrp->cset_links, cset_link) {
1340		list_del(&link->cset_link);
1341		list_del(&link->cgrp_link);
1342		kfree(link);
1343	}
1344
1345	spin_unlock_irq(&css_set_lock);
1346
1347	if (!list_empty(&root->root_list)) {
1348		list_del(&root->root_list);
1349		cgroup_root_count--;
1350	}
1351
1352	cgroup_exit_root_id(root);
1353
1354	mutex_unlock(&cgroup_mutex);
1355
1356	kernfs_destroy_root(root->kf_root);
1357	cgroup_free_root(root);
1358}
1359
1360/*
1361 * look up cgroup associated with current task's cgroup namespace on the
1362 * specified hierarchy
1363 */
1364static struct cgroup *
1365current_cgns_cgroup_from_root(struct cgroup_root *root)
1366{
1367	struct cgroup *res = NULL;
1368	struct css_set *cset;
1369
1370	lockdep_assert_held(&css_set_lock);
1371
1372	rcu_read_lock();
1373
1374	cset = current->nsproxy->cgroup_ns->root_cset;
1375	if (cset == &init_css_set) {
1376		res = &root->cgrp;
1377	} else {
1378		struct cgrp_cset_link *link;
1379
1380		list_for_each_entry(link, &cset->cgrp_links, cgrp_link) {
1381			struct cgroup *c = link->cgrp;
1382
1383			if (c->root == root) {
1384				res = c;
1385				break;
1386			}
1387		}
1388	}
1389	rcu_read_unlock();
1390
1391	BUG_ON(!res);
1392	return res;
1393}
1394
1395/* look up cgroup associated with given css_set on the specified hierarchy */
1396static struct cgroup *cset_cgroup_from_root(struct css_set *cset,
1397					    struct cgroup_root *root)
1398{
1399	struct cgroup *res = NULL;
1400
1401	lockdep_assert_held(&cgroup_mutex);
1402	lockdep_assert_held(&css_set_lock);
1403
1404	if (cset == &init_css_set) {
1405		res = &root->cgrp;
1406	} else if (root == &cgrp_dfl_root) {
1407		res = cset->dfl_cgrp;
1408	} else {
1409		struct cgrp_cset_link *link;
1410
1411		list_for_each_entry(link, &cset->cgrp_links, cgrp_link) {
1412			struct cgroup *c = link->cgrp;
1413
1414			if (c->root == root) {
1415				res = c;
1416				break;
1417			}
1418		}
1419	}
1420
1421	BUG_ON(!res);
1422	return res;
1423}
1424
1425/*
1426 * Return the cgroup for "task" from the given hierarchy. Must be
1427 * called with cgroup_mutex and css_set_lock held.
1428 */
1429struct cgroup *task_cgroup_from_root(struct task_struct *task,
1430				     struct cgroup_root *root)
1431{
1432	/*
1433	 * No need to lock the task - since we hold cgroup_mutex the
1434	 * task can't change groups, so the only thing that can happen
1435	 * is that it exits and its css is set back to init_css_set.
1436	 */
1437	return cset_cgroup_from_root(task_css_set(task), root);
1438}
1439
1440/*
1441 * A task must hold cgroup_mutex to modify cgroups.
1442 *
1443 * Any task can increment and decrement the count field without lock.
1444 * So in general, code holding cgroup_mutex can't rely on the count
1445 * field not changing.  However, if the count goes to zero, then only
1446 * cgroup_attach_task() can increment it again.  Because a count of zero
1447 * means that no tasks are currently attached, therefore there is no
1448 * way a task attached to that cgroup can fork (the other way to
1449 * increment the count).  So code holding cgroup_mutex can safely
1450 * assume that if the count is zero, it will stay zero. Similarly, if
1451 * a task holds cgroup_mutex on a cgroup with zero count, it
1452 * knows that the cgroup won't be removed, as cgroup_rmdir()
1453 * needs that mutex.
1454 *
1455 * A cgroup can only be deleted if both its 'count' of using tasks
1456 * is zero, and its list of 'children' cgroups is empty.  Since all
1457 * tasks in the system use _some_ cgroup, and since there is always at
1458 * least one task in the system (init, pid == 1), therefore, root cgroup
1459 * always has either children cgroups and/or using tasks.  So we don't
1460 * need a special hack to ensure that root cgroup cannot be deleted.
1461 *
1462 * P.S.  One more locking exception.  RCU is used to guard the
1463 * update of a tasks cgroup pointer by cgroup_attach_task()
1464 */
1465
1466static struct kernfs_syscall_ops cgroup_kf_syscall_ops;
1467
1468static char *cgroup_file_name(struct cgroup *cgrp, const struct cftype *cft,
1469			      char *buf)
1470{
1471	struct cgroup_subsys *ss = cft->ss;
1472
1473	if (cft->ss && !(cft->flags & CFTYPE_NO_PREFIX) &&
1474	    !(cgrp->root->flags & CGRP_ROOT_NOPREFIX)) {
1475		const char *dbg = (cft->flags & CFTYPE_DEBUG) ? ".__DEBUG__." : "";
1476
1477		snprintf(buf, CGROUP_FILE_NAME_MAX, "%s%s.%s",
1478			 dbg, cgroup_on_dfl(cgrp) ? ss->name : ss->legacy_name,
1479			 cft->name);
1480	} else {
1481		strscpy(buf, cft->name, CGROUP_FILE_NAME_MAX);
1482	}
1483	return buf;
1484}
1485
1486/**
1487 * cgroup_file_mode - deduce file mode of a control file
1488 * @cft: the control file in question
1489 *
1490 * S_IRUGO for read, S_IWUSR for write.
1491 */
1492static umode_t cgroup_file_mode(const struct cftype *cft)
1493{
1494	umode_t mode = 0;
1495
1496	if (cft->read_u64 || cft->read_s64 || cft->seq_show)
1497		mode |= S_IRUGO;
1498
1499	if (cft->write_u64 || cft->write_s64 || cft->write) {
1500		if (cft->flags & CFTYPE_WORLD_WRITABLE)
1501			mode |= S_IWUGO;
1502		else
1503			mode |= S_IWUSR;
1504	}
1505
1506	return mode;
1507}
1508
1509/**
1510 * cgroup_calc_subtree_ss_mask - calculate subtree_ss_mask
1511 * @subtree_control: the new subtree_control mask to consider
1512 * @this_ss_mask: available subsystems
1513 *
1514 * On the default hierarchy, a subsystem may request other subsystems to be
1515 * enabled together through its ->depends_on mask.  In such cases, more
1516 * subsystems than specified in "cgroup.subtree_control" may be enabled.
1517 *
1518 * This function calculates which subsystems need to be enabled if
1519 * @subtree_control is to be applied while restricted to @this_ss_mask.
1520 */
1521static u16 cgroup_calc_subtree_ss_mask(u16 subtree_control, u16 this_ss_mask)
1522{
1523	u16 cur_ss_mask = subtree_control;
1524	struct cgroup_subsys *ss;
1525	int ssid;
1526
1527	lockdep_assert_held(&cgroup_mutex);
1528
1529	cur_ss_mask |= cgrp_dfl_implicit_ss_mask;
1530
1531	while (true) {
1532		u16 new_ss_mask = cur_ss_mask;
1533
1534		do_each_subsys_mask(ss, ssid, cur_ss_mask) {
1535			new_ss_mask |= ss->depends_on;
1536		} while_each_subsys_mask();
1537
1538		/*
1539		 * Mask out subsystems which aren't available.  This can
1540		 * happen only if some depended-upon subsystems were bound
1541		 * to non-default hierarchies.
1542		 */
1543		new_ss_mask &= this_ss_mask;
1544
1545		if (new_ss_mask == cur_ss_mask)
1546			break;
1547		cur_ss_mask = new_ss_mask;
1548	}
1549
1550	return cur_ss_mask;
1551}
1552
1553/**
1554 * cgroup_kn_unlock - unlocking helper for cgroup kernfs methods
1555 * @kn: the kernfs_node being serviced
1556 *
1557 * This helper undoes cgroup_kn_lock_live() and should be invoked before
1558 * the method finishes if locking succeeded.  Note that once this function
1559 * returns the cgroup returned by cgroup_kn_lock_live() may become
1560 * inaccessible any time.  If the caller intends to continue to access the
1561 * cgroup, it should pin it before invoking this function.
1562 */
1563void cgroup_kn_unlock(struct kernfs_node *kn)
1564{
1565	struct cgroup *cgrp;
1566
1567	if (kernfs_type(kn) == KERNFS_DIR)
1568		cgrp = kn->priv;
1569	else
1570		cgrp = kn->parent->priv;
1571
1572	mutex_unlock(&cgroup_mutex);
1573
1574	kernfs_unbreak_active_protection(kn);
1575	cgroup_put(cgrp);
1576}
1577
1578/**
1579 * cgroup_kn_lock_live - locking helper for cgroup kernfs methods
1580 * @kn: the kernfs_node being serviced
1581 * @drain_offline: perform offline draining on the cgroup
1582 *
1583 * This helper is to be used by a cgroup kernfs method currently servicing
1584 * @kn.  It breaks the active protection, performs cgroup locking and
1585 * verifies that the associated cgroup is alive.  Returns the cgroup if
1586 * alive; otherwise, %NULL.  A successful return should be undone by a
1587 * matching cgroup_kn_unlock() invocation.  If @drain_offline is %true, the
1588 * cgroup is drained of offlining csses before return.
1589 *
1590 * Any cgroup kernfs method implementation which requires locking the
1591 * associated cgroup should use this helper.  It avoids nesting cgroup
1592 * locking under kernfs active protection and allows all kernfs operations
1593 * including self-removal.
1594 */
1595struct cgroup *cgroup_kn_lock_live(struct kernfs_node *kn, bool drain_offline)
1596{
1597	struct cgroup *cgrp;
1598
1599	if (kernfs_type(kn) == KERNFS_DIR)
1600		cgrp = kn->priv;
1601	else
1602		cgrp = kn->parent->priv;
1603
1604	/*
1605	 * We're gonna grab cgroup_mutex which nests outside kernfs
1606	 * active_ref.  cgroup liveliness check alone provides enough
1607	 * protection against removal.  Ensure @cgrp stays accessible and
1608	 * break the active_ref protection.
1609	 */
1610	if (!cgroup_tryget(cgrp))
1611		return NULL;
1612	kernfs_break_active_protection(kn);
1613
1614	if (drain_offline)
1615		cgroup_lock_and_drain_offline(cgrp);
1616	else
1617		mutex_lock(&cgroup_mutex);
1618
1619	if (!cgroup_is_dead(cgrp))
1620		return cgrp;
1621
1622	cgroup_kn_unlock(kn);
1623	return NULL;
1624}
1625
1626static void cgroup_rm_file(struct cgroup *cgrp, const struct cftype *cft)
1627{
1628	char name[CGROUP_FILE_NAME_MAX];
1629
1630	lockdep_assert_held(&cgroup_mutex);
1631
1632	if (cft->file_offset) {
1633		struct cgroup_subsys_state *css = cgroup_css(cgrp, cft->ss);
1634		struct cgroup_file *cfile = (void *)css + cft->file_offset;
1635
1636		spin_lock_irq(&cgroup_file_kn_lock);
1637		cfile->kn = NULL;
1638		spin_unlock_irq(&cgroup_file_kn_lock);
1639
1640		del_timer_sync(&cfile->notify_timer);
1641	}
1642
1643	kernfs_remove_by_name(cgrp->kn, cgroup_file_name(cgrp, cft, name));
1644}
1645
1646/**
1647 * css_clear_dir - remove subsys files in a cgroup directory
1648 * @css: taget css
1649 */
1650static void css_clear_dir(struct cgroup_subsys_state *css)
1651{
1652	struct cgroup *cgrp = css->cgroup;
1653	struct cftype *cfts;
1654
1655	if (!(css->flags & CSS_VISIBLE))
1656		return;
1657
1658	css->flags &= ~CSS_VISIBLE;
1659
1660	if (!css->ss) {
1661		if (cgroup_on_dfl(cgrp))
1662			cfts = cgroup_base_files;
1663		else
1664			cfts = cgroup1_base_files;
1665
1666		cgroup_addrm_files(css, cgrp, cfts, false);
1667	} else {
1668		list_for_each_entry(cfts, &css->ss->cfts, node)
1669			cgroup_addrm_files(css, cgrp, cfts, false);
1670	}
1671}
1672
1673/**
1674 * css_populate_dir - create subsys files in a cgroup directory
1675 * @css: target css
1676 *
1677 * On failure, no file is added.
1678 */
1679static int css_populate_dir(struct cgroup_subsys_state *css)
1680{
1681	struct cgroup *cgrp = css->cgroup;
1682	struct cftype *cfts, *failed_cfts;
1683	int ret;
1684
1685	if ((css->flags & CSS_VISIBLE) || !cgrp->kn)
1686		return 0;
1687
1688	if (!css->ss) {
1689		if (cgroup_on_dfl(cgrp))
1690			cfts = cgroup_base_files;
1691		else
1692			cfts = cgroup1_base_files;
1693
1694		ret = cgroup_addrm_files(&cgrp->self, cgrp, cfts, true);
1695		if (ret < 0)
1696			return ret;
1697	} else {
1698		list_for_each_entry(cfts, &css->ss->cfts, node) {
1699			ret = cgroup_addrm_files(css, cgrp, cfts, true);
1700			if (ret < 0) {
1701				failed_cfts = cfts;
1702				goto err;
1703			}
1704		}
1705	}
1706
1707	css->flags |= CSS_VISIBLE;
1708
1709	return 0;
1710err:
1711	list_for_each_entry(cfts, &css->ss->cfts, node) {
1712		if (cfts == failed_cfts)
1713			break;
1714		cgroup_addrm_files(css, cgrp, cfts, false);
1715	}
1716	return ret;
1717}
1718
1719int rebind_subsystems(struct cgroup_root *dst_root, u16 ss_mask)
1720{
1721	struct cgroup *dcgrp = &dst_root->cgrp;
1722	struct cgroup_subsys *ss;
1723	int ssid, i, ret;
1724
1725	lockdep_assert_held(&cgroup_mutex);
1726
1727	do_each_subsys_mask(ss, ssid, ss_mask) {
1728		/*
1729		 * If @ss has non-root csses attached to it, can't move.
1730		 * If @ss is an implicit controller, it is exempt from this
1731		 * rule and can be stolen.
1732		 */
1733		if (css_next_child(NULL, cgroup_css(&ss->root->cgrp, ss)) &&
1734		    !ss->implicit_on_dfl)
1735			return -EBUSY;
1736
1737		/* can't move between two non-dummy roots either */
1738		if (ss->root != &cgrp_dfl_root && dst_root != &cgrp_dfl_root)
1739			return -EBUSY;
1740	} while_each_subsys_mask();
1741
1742	do_each_subsys_mask(ss, ssid, ss_mask) {
1743		struct cgroup_root *src_root = ss->root;
1744		struct cgroup *scgrp = &src_root->cgrp;
1745		struct cgroup_subsys_state *css = cgroup_css(scgrp, ss);
1746		struct css_set *cset;
1747
1748		WARN_ON(!css || cgroup_css(dcgrp, ss));
1749
1750		/* disable from the source */
1751		src_root->subsys_mask &= ~(1 << ssid);
1752		WARN_ON(cgroup_apply_control(scgrp));
1753		cgroup_finalize_control(scgrp, 0);
1754
1755		/* rebind */
1756		RCU_INIT_POINTER(scgrp->subsys[ssid], NULL);
1757		rcu_assign_pointer(dcgrp->subsys[ssid], css);
1758		ss->root = dst_root;
1759		css->cgroup = dcgrp;
1760
1761		spin_lock_irq(&css_set_lock);
1762		hash_for_each(css_set_table, i, cset, hlist)
1763			list_move_tail(&cset->e_cset_node[ss->id],
1764				       &dcgrp->e_csets[ss->id]);
1765		spin_unlock_irq(&css_set_lock);
1766
1767		/* default hierarchy doesn't enable controllers by default */
1768		dst_root->subsys_mask |= 1 << ssid;
1769		if (dst_root == &cgrp_dfl_root) {
1770			static_branch_enable(cgroup_subsys_on_dfl_key[ssid]);
1771		} else {
1772			dcgrp->subtree_control |= 1 << ssid;
1773			static_branch_disable(cgroup_subsys_on_dfl_key[ssid]);
1774		}
1775
1776		ret = cgroup_apply_control(dcgrp);
1777		if (ret)
1778			pr_warn("partial failure to rebind %s controller (err=%d)\n",
1779				ss->name, ret);
1780
1781		if (ss->bind)
1782			ss->bind(css);
1783	} while_each_subsys_mask();
1784
1785	kernfs_activate(dcgrp->kn);
1786	return 0;
1787}
1788
1789int cgroup_show_path(struct seq_file *sf, struct kernfs_node *kf_node,
1790		     struct kernfs_root *kf_root)
1791{
1792	int len = 0;
1793	char *buf = NULL;
1794	struct cgroup_root *kf_cgroot = cgroup_root_from_kf(kf_root);
1795	struct cgroup *ns_cgroup;
1796
1797	buf = kmalloc(PATH_MAX, GFP_KERNEL);
1798	if (!buf)
1799		return -ENOMEM;
1800
1801	spin_lock_irq(&css_set_lock);
1802	ns_cgroup = current_cgns_cgroup_from_root(kf_cgroot);
1803	len = kernfs_path_from_node(kf_node, ns_cgroup->kn, buf, PATH_MAX);
1804	spin_unlock_irq(&css_set_lock);
1805
1806	if (len >= PATH_MAX)
1807		len = -ERANGE;
1808	else if (len > 0) {
1809		seq_escape(sf, buf, " \t\n\\");
1810		len = 0;
1811	}
1812	kfree(buf);
1813	return len;
1814}
1815
1816enum cgroup2_param {
1817	Opt_nsdelegate,
1818	Opt_memory_localevents,
1819	nr__cgroup2_params
1820};
1821
1822static const struct fs_parameter_spec cgroup2_param_specs[] = {
1823	fsparam_flag("nsdelegate",		Opt_nsdelegate),
1824	fsparam_flag("memory_localevents",	Opt_memory_localevents),
1825	{}
1826};
1827
1828static const struct fs_parameter_description cgroup2_fs_parameters = {
1829	.name		= "cgroup2",
1830	.specs		= cgroup2_param_specs,
1831};
1832
1833static int cgroup2_parse_param(struct fs_context *fc, struct fs_parameter *param)
1834{
1835	struct cgroup_fs_context *ctx = cgroup_fc2context(fc);
1836	struct fs_parse_result result;
1837	int opt;
1838
1839	opt = fs_parse(fc, &cgroup2_fs_parameters, param, &result);
1840	if (opt < 0)
1841		return opt;
1842
1843	switch (opt) {
1844	case Opt_nsdelegate:
1845		ctx->flags |= CGRP_ROOT_NS_DELEGATE;
1846		return 0;
1847	case Opt_memory_localevents:
1848		ctx->flags |= CGRP_ROOT_MEMORY_LOCAL_EVENTS;
1849		return 0;
 
 
 
 
 
 
 
 
 
1850	}
1851	return -EINVAL;
 
1852}
1853
1854static void apply_cgroup_root_flags(unsigned int root_flags)
1855{
1856	if (current->nsproxy->cgroup_ns == &init_cgroup_ns) {
1857		if (root_flags & CGRP_ROOT_NS_DELEGATE)
1858			cgrp_dfl_root.flags |= CGRP_ROOT_NS_DELEGATE;
1859		else
1860			cgrp_dfl_root.flags &= ~CGRP_ROOT_NS_DELEGATE;
1861
1862		if (root_flags & CGRP_ROOT_MEMORY_LOCAL_EVENTS)
1863			cgrp_dfl_root.flags |= CGRP_ROOT_MEMORY_LOCAL_EVENTS;
1864		else
1865			cgrp_dfl_root.flags &= ~CGRP_ROOT_MEMORY_LOCAL_EVENTS;
1866	}
1867}
1868
1869static int cgroup_show_options(struct seq_file *seq, struct kernfs_root *kf_root)
1870{
1871	if (cgrp_dfl_root.flags & CGRP_ROOT_NS_DELEGATE)
1872		seq_puts(seq, ",nsdelegate");
1873	if (cgrp_dfl_root.flags & CGRP_ROOT_MEMORY_LOCAL_EVENTS)
1874		seq_puts(seq, ",memory_localevents");
1875	return 0;
1876}
1877
1878static int cgroup_reconfigure(struct fs_context *fc)
1879{
1880	struct cgroup_fs_context *ctx = cgroup_fc2context(fc);
 
1881
1882	apply_cgroup_root_flags(ctx->flags);
 
 
 
 
1883	return 0;
1884}
1885
1886/*
1887 * To reduce the fork() overhead for systems that are not actually using
1888 * their cgroups capability, we don't maintain the lists running through
1889 * each css_set to its tasks until we see the list actually used - in other
1890 * words after the first mount.
1891 */
1892static bool use_task_css_set_links __read_mostly;
1893
1894void cgroup_enable_task_cg_lists(void)
1895{
1896	struct task_struct *p, *g;
1897
 
 
 
 
 
 
 
1898	/*
1899	 * We need tasklist_lock because RCU is not safe against
1900	 * while_each_thread(). Besides, a forking task that has passed
1901	 * cgroup_post_fork() without seeing use_task_css_set_links = 1
1902	 * is not guaranteed to have its child immediately visible in the
1903	 * tasklist if we walk through it with RCU.
1904	 */
1905	read_lock(&tasklist_lock);
1906	spin_lock_irq(&css_set_lock);
1907
1908	if (use_task_css_set_links)
1909		goto out_unlock;
1910
1911	use_task_css_set_links = true;
1912
1913	do_each_thread(g, p) {
1914		WARN_ON_ONCE(!list_empty(&p->cg_list) ||
1915			     task_css_set(p) != &init_css_set);
1916
1917		/*
1918		 * We should check if the process is exiting, otherwise
1919		 * it will race with cgroup_exit() in that the list
1920		 * entry won't be deleted though the process has exited.
1921		 * Do it while holding siglock so that we don't end up
1922		 * racing against cgroup_exit().
1923		 *
1924		 * Interrupts were already disabled while acquiring
1925		 * the css_set_lock, so we do not need to disable it
1926		 * again when acquiring the sighand->siglock here.
1927		 */
1928		spin_lock(&p->sighand->siglock);
1929		if (!(p->flags & PF_EXITING)) {
1930			struct css_set *cset = task_css_set(p);
1931
1932			if (!css_set_populated(cset))
1933				css_set_update_populated(cset, true);
1934			list_add_tail(&p->cg_list, &cset->tasks);
1935			get_css_set(cset);
1936			cset->nr_tasks++;
1937		}
1938		spin_unlock(&p->sighand->siglock);
1939	} while_each_thread(g, p);
 
1940out_unlock:
1941	spin_unlock_irq(&css_set_lock);
1942	read_unlock(&tasklist_lock);
1943}
1944
1945static void init_cgroup_housekeeping(struct cgroup *cgrp)
1946{
1947	struct cgroup_subsys *ss;
1948	int ssid;
1949
1950	INIT_LIST_HEAD(&cgrp->self.sibling);
1951	INIT_LIST_HEAD(&cgrp->self.children);
1952	INIT_LIST_HEAD(&cgrp->cset_links);
1953	INIT_LIST_HEAD(&cgrp->pidlists);
1954	mutex_init(&cgrp->pidlist_mutex);
1955	cgrp->self.cgroup = cgrp;
1956	cgrp->self.flags |= CSS_ONLINE;
1957	cgrp->dom_cgrp = cgrp;
1958	cgrp->max_descendants = INT_MAX;
1959	cgrp->max_depth = INT_MAX;
1960	INIT_LIST_HEAD(&cgrp->rstat_css_list);
1961	prev_cputime_init(&cgrp->prev_cputime);
1962
1963	for_each_subsys(ss, ssid)
1964		INIT_LIST_HEAD(&cgrp->e_csets[ssid]);
1965
1966	init_waitqueue_head(&cgrp->offline_waitq);
1967	INIT_WORK(&cgrp->release_agent_work, cgroup1_release_agent);
1968}
1969
1970void init_cgroup_root(struct cgroup_fs_context *ctx)
1971{
1972	struct cgroup_root *root = ctx->root;
1973	struct cgroup *cgrp = &root->cgrp;
1974
1975	INIT_LIST_HEAD(&root->root_list);
1976	atomic_set(&root->nr_cgrps, 1);
1977	cgrp->root = root;
1978	init_cgroup_housekeeping(cgrp);
1979	idr_init(&root->cgroup_idr);
1980
1981	root->flags = ctx->flags;
1982	if (ctx->release_agent)
1983		strscpy(root->release_agent_path, ctx->release_agent, PATH_MAX);
1984	if (ctx->name)
1985		strscpy(root->name, ctx->name, MAX_CGROUP_ROOT_NAMELEN);
1986	if (ctx->cpuset_clone_children)
1987		set_bit(CGRP_CPUSET_CLONE_CHILDREN, &root->cgrp.flags);
1988}
1989
1990int cgroup_setup_root(struct cgroup_root *root, u16 ss_mask)
1991{
1992	LIST_HEAD(tmp_links);
1993	struct cgroup *root_cgrp = &root->cgrp;
1994	struct kernfs_syscall_ops *kf_sops;
1995	struct css_set *cset;
1996	int i, ret;
1997
1998	lockdep_assert_held(&cgroup_mutex);
1999
2000	ret = cgroup_idr_alloc(&root->cgroup_idr, root_cgrp, 1, 2, GFP_KERNEL);
2001	if (ret < 0)
2002		goto out;
2003	root_cgrp->id = ret;
2004	root_cgrp->ancestor_ids[0] = ret;
2005
2006	ret = percpu_ref_init(&root_cgrp->self.refcnt, css_release,
2007			      0, GFP_KERNEL);
2008	if (ret)
2009		goto out;
2010
2011	/*
2012	 * We're accessing css_set_count without locking css_set_lock here,
2013	 * but that's OK - it can only be increased by someone holding
2014	 * cgroup_lock, and that's us.  Later rebinding may disable
2015	 * controllers on the default hierarchy and thus create new csets,
2016	 * which can't be more than the existing ones.  Allocate 2x.
2017	 */
2018	ret = allocate_cgrp_cset_links(2 * css_set_count, &tmp_links);
2019	if (ret)
2020		goto cancel_ref;
2021
2022	ret = cgroup_init_root_id(root);
2023	if (ret)
2024		goto cancel_ref;
2025
2026	kf_sops = root == &cgrp_dfl_root ?
2027		&cgroup_kf_syscall_ops : &cgroup1_kf_syscall_ops;
2028
2029	root->kf_root = kernfs_create_root(kf_sops,
2030					   KERNFS_ROOT_CREATE_DEACTIVATED |
2031					   KERNFS_ROOT_SUPPORT_EXPORTOP,
2032					   root_cgrp);
2033	if (IS_ERR(root->kf_root)) {
2034		ret = PTR_ERR(root->kf_root);
2035		goto exit_root_id;
2036	}
2037	root_cgrp->kn = root->kf_root->kn;
2038
2039	ret = css_populate_dir(&root_cgrp->self);
2040	if (ret)
2041		goto destroy_root;
2042
2043	ret = rebind_subsystems(root, ss_mask);
2044	if (ret)
2045		goto destroy_root;
2046
2047	ret = cgroup_bpf_inherit(root_cgrp);
2048	WARN_ON_ONCE(ret);
2049
2050	trace_cgroup_setup_root(root);
2051
2052	/*
2053	 * There must be no failure case after here, since rebinding takes
2054	 * care of subsystems' refcounts, which are explicitly dropped in
2055	 * the failure exit path.
2056	 */
2057	list_add(&root->root_list, &cgroup_roots);
2058	cgroup_root_count++;
2059
2060	/*
2061	 * Link the root cgroup in this hierarchy into all the css_set
2062	 * objects.
2063	 */
2064	spin_lock_irq(&css_set_lock);
2065	hash_for_each(css_set_table, i, cset, hlist) {
2066		link_css_set(&tmp_links, cset, root_cgrp);
2067		if (css_set_populated(cset))
2068			cgroup_update_populated(root_cgrp, true);
2069	}
2070	spin_unlock_irq(&css_set_lock);
2071
2072	BUG_ON(!list_empty(&root_cgrp->self.children));
2073	BUG_ON(atomic_read(&root->nr_cgrps) != 1);
2074
2075	kernfs_activate(root_cgrp->kn);
2076	ret = 0;
2077	goto out;
2078
2079destroy_root:
2080	kernfs_destroy_root(root->kf_root);
2081	root->kf_root = NULL;
2082exit_root_id:
2083	cgroup_exit_root_id(root);
2084cancel_ref:
2085	percpu_ref_exit(&root_cgrp->self.refcnt);
2086out:
2087	free_cgrp_cset_links(&tmp_links);
2088	return ret;
2089}
2090
2091int cgroup_do_get_tree(struct fs_context *fc)
 
 
2092{
2093	struct cgroup_fs_context *ctx = cgroup_fc2context(fc);
2094	int ret;
2095
2096	ctx->kfc.root = ctx->root->kf_root;
2097	if (fc->fs_type == &cgroup2_fs_type)
2098		ctx->kfc.magic = CGROUP2_SUPER_MAGIC;
2099	else
2100		ctx->kfc.magic = CGROUP_SUPER_MAGIC;
2101	ret = kernfs_get_tree(fc);
2102
2103	/*
2104	 * In non-init cgroup namespace, instead of root cgroup's dentry,
2105	 * we return the dentry corresponding to the cgroupns->root_cgrp.
2106	 */
2107	if (!ret && ctx->ns != &init_cgroup_ns) {
2108		struct dentry *nsdentry;
2109		struct super_block *sb = fc->root->d_sb;
2110		struct cgroup *cgrp;
2111
2112		mutex_lock(&cgroup_mutex);
2113		spin_lock_irq(&css_set_lock);
2114
2115		cgrp = cset_cgroup_from_root(ctx->ns->root_cset, ctx->root);
2116
2117		spin_unlock_irq(&css_set_lock);
2118		mutex_unlock(&cgroup_mutex);
2119
2120		nsdentry = kernfs_node_dentry(cgrp->kn, sb);
2121		dput(fc->root);
2122		if (IS_ERR(nsdentry)) {
2123			deactivate_locked_super(sb);
2124			ret = PTR_ERR(nsdentry);
2125			nsdentry = NULL;
2126		}
2127		fc->root = nsdentry;
2128	}
2129
2130	if (!ctx->kfc.new_sb_created)
2131		cgroup_put(&ctx->root->cgrp);
2132
2133	return ret;
2134}
2135
2136/*
2137 * Destroy a cgroup filesystem context.
2138 */
2139static void cgroup_fs_context_free(struct fs_context *fc)
2140{
2141	struct cgroup_fs_context *ctx = cgroup_fc2context(fc);
2142
2143	kfree(ctx->name);
2144	kfree(ctx->release_agent);
2145	put_cgroup_ns(ctx->ns);
2146	kernfs_free_fs_context(fc);
2147	kfree(ctx);
2148}
2149
2150static int cgroup_get_tree(struct fs_context *fc)
 
 
2151{
2152	struct cgroup_fs_context *ctx = cgroup_fc2context(fc);
 
2153	int ret;
2154
2155	cgrp_dfl_visible = true;
2156	cgroup_get_live(&cgrp_dfl_root.cgrp);
2157	ctx->root = &cgrp_dfl_root;
2158
2159	ret = cgroup_do_get_tree(fc);
2160	if (!ret)
2161		apply_cgroup_root_flags(ctx->flags);
2162	return ret;
2163}
2164
2165static const struct fs_context_operations cgroup_fs_context_ops = {
2166	.free		= cgroup_fs_context_free,
2167	.parse_param	= cgroup2_parse_param,
2168	.get_tree	= cgroup_get_tree,
2169	.reconfigure	= cgroup_reconfigure,
2170};
2171
2172static const struct fs_context_operations cgroup1_fs_context_ops = {
2173	.free		= cgroup_fs_context_free,
2174	.parse_param	= cgroup1_parse_param,
2175	.get_tree	= cgroup1_get_tree,
2176	.reconfigure	= cgroup1_reconfigure,
2177};
2178
2179/*
2180 * Initialise the cgroup filesystem creation/reconfiguration context.  Notably,
2181 * we select the namespace we're going to use.
2182 */
2183static int cgroup_init_fs_context(struct fs_context *fc)
2184{
2185	struct cgroup_fs_context *ctx;
2186
2187	ctx = kzalloc(sizeof(struct cgroup_fs_context), GFP_KERNEL);
2188	if (!ctx)
2189		return -ENOMEM;
 
 
2190
2191	/*
2192	 * The first time anyone tries to mount a cgroup, enable the list
2193	 * linking each css_set to its tasks and fix up all existing tasks.
2194	 */
2195	if (!use_task_css_set_links)
2196		cgroup_enable_task_cg_lists();
2197
2198	ctx->ns = current->nsproxy->cgroup_ns;
2199	get_cgroup_ns(ctx->ns);
2200	fc->fs_private = &ctx->kfc;
2201	if (fc->fs_type == &cgroup2_fs_type)
2202		fc->ops = &cgroup_fs_context_ops;
2203	else
2204		fc->ops = &cgroup1_fs_context_ops;
2205	put_user_ns(fc->user_ns);
2206	fc->user_ns = get_user_ns(ctx->ns->user_ns);
2207	fc->global = true;
2208	return 0;
 
 
 
 
 
 
 
 
 
 
 
 
2209}
2210
2211static void cgroup_kill_sb(struct super_block *sb)
2212{
2213	struct kernfs_root *kf_root = kernfs_root_from_sb(sb);
2214	struct cgroup_root *root = cgroup_root_from_kf(kf_root);
2215
2216	/*
2217	 * If @root doesn't have any children, start killing it.
2218	 * This prevents new mounts by disabling percpu_ref_tryget_live().
2219	 * cgroup_mount() may wait for @root's release.
2220	 *
2221	 * And don't kill the default root.
2222	 */
2223	if (list_empty(&root->cgrp.self.children) && root != &cgrp_dfl_root &&
2224	    !percpu_ref_is_dying(&root->cgrp.self.refcnt))
 
 
2225		percpu_ref_kill(&root->cgrp.self.refcnt);
2226	cgroup_put(&root->cgrp);
2227	kernfs_kill_sb(sb);
2228}
2229
2230struct file_system_type cgroup_fs_type = {
2231	.name			= "cgroup",
2232	.init_fs_context	= cgroup_init_fs_context,
2233	.parameters		= &cgroup1_fs_parameters,
2234	.kill_sb		= cgroup_kill_sb,
2235	.fs_flags		= FS_USERNS_MOUNT,
2236};
2237
2238static struct file_system_type cgroup2_fs_type = {
2239	.name			= "cgroup2",
2240	.init_fs_context	= cgroup_init_fs_context,
2241	.parameters		= &cgroup2_fs_parameters,
2242	.kill_sb		= cgroup_kill_sb,
2243	.fs_flags		= FS_USERNS_MOUNT,
2244};
2245
2246#ifdef CONFIG_CPUSETS
2247static const struct fs_context_operations cpuset_fs_context_ops = {
2248	.get_tree	= cgroup1_get_tree,
2249	.free		= cgroup_fs_context_free,
2250};
2251
2252/*
2253 * This is ugly, but preserves the userspace API for existing cpuset
2254 * users. If someone tries to mount the "cpuset" filesystem, we
2255 * silently switch it to mount "cgroup" instead
2256 */
2257static int cpuset_init_fs_context(struct fs_context *fc)
2258{
2259	char *agent = kstrdup("/sbin/cpuset_release_agent", GFP_USER);
2260	struct cgroup_fs_context *ctx;
2261	int err;
2262
2263	err = cgroup_init_fs_context(fc);
2264	if (err) {
2265		kfree(agent);
2266		return err;
2267	}
2268
2269	fc->ops = &cpuset_fs_context_ops;
2270
2271	ctx = cgroup_fc2context(fc);
2272	ctx->subsys_mask = 1 << cpuset_cgrp_id;
2273	ctx->flags |= CGRP_ROOT_NOPREFIX;
2274	ctx->release_agent = agent;
2275
2276	get_filesystem(&cgroup_fs_type);
2277	put_filesystem(fc->fs_type);
2278	fc->fs_type = &cgroup_fs_type;
2279
2280	return 0;
2281}
2282
2283static struct file_system_type cpuset_fs_type = {
2284	.name			= "cpuset",
2285	.init_fs_context	= cpuset_init_fs_context,
2286	.fs_flags		= FS_USERNS_MOUNT,
2287};
2288#endif
2289
2290int cgroup_path_ns_locked(struct cgroup *cgrp, char *buf, size_t buflen,
2291			  struct cgroup_namespace *ns)
2292{
2293	struct cgroup *root = cset_cgroup_from_root(ns->root_cset, cgrp->root);
2294
2295	return kernfs_path_from_node(cgrp->kn, root->kn, buf, buflen);
2296}
2297
2298int cgroup_path_ns(struct cgroup *cgrp, char *buf, size_t buflen,
2299		   struct cgroup_namespace *ns)
2300{
2301	int ret;
2302
2303	mutex_lock(&cgroup_mutex);
2304	spin_lock_irq(&css_set_lock);
2305
2306	ret = cgroup_path_ns_locked(cgrp, buf, buflen, ns);
2307
2308	spin_unlock_irq(&css_set_lock);
2309	mutex_unlock(&cgroup_mutex);
2310
2311	return ret;
2312}
2313EXPORT_SYMBOL_GPL(cgroup_path_ns);
2314
2315/**
2316 * task_cgroup_path - cgroup path of a task in the first cgroup hierarchy
2317 * @task: target task
2318 * @buf: the buffer to write the path into
2319 * @buflen: the length of the buffer
2320 *
2321 * Determine @task's cgroup on the first (the one with the lowest non-zero
2322 * hierarchy_id) cgroup hierarchy and copy its path into @buf.  This
2323 * function grabs cgroup_mutex and shouldn't be used inside locks used by
2324 * cgroup controller callbacks.
2325 *
2326 * Return value is the same as kernfs_path().
2327 */
2328int task_cgroup_path(struct task_struct *task, char *buf, size_t buflen)
2329{
2330	struct cgroup_root *root;
2331	struct cgroup *cgrp;
2332	int hierarchy_id = 1;
2333	int ret;
2334
2335	mutex_lock(&cgroup_mutex);
2336	spin_lock_irq(&css_set_lock);
2337
2338	root = idr_get_next(&cgroup_hierarchy_idr, &hierarchy_id);
2339
2340	if (root) {
2341		cgrp = task_cgroup_from_root(task, root);
2342		ret = cgroup_path_ns_locked(cgrp, buf, buflen, &init_cgroup_ns);
2343	} else {
2344		/* if no hierarchy exists, everyone is in "/" */
2345		ret = strlcpy(buf, "/", buflen);
2346	}
2347
2348	spin_unlock_irq(&css_set_lock);
2349	mutex_unlock(&cgroup_mutex);
2350	return ret;
2351}
2352EXPORT_SYMBOL_GPL(task_cgroup_path);
2353
2354/**
2355 * cgroup_migrate_add_task - add a migration target task to a migration context
2356 * @task: target task
2357 * @mgctx: target migration context
2358 *
2359 * Add @task, which is a migration target, to @mgctx->tset.  This function
2360 * becomes noop if @task doesn't need to be migrated.  @task's css_set
2361 * should have been added as a migration source and @task->cg_list will be
2362 * moved from the css_set's tasks list to mg_tasks one.
2363 */
2364static void cgroup_migrate_add_task(struct task_struct *task,
2365				    struct cgroup_mgctx *mgctx)
2366{
2367	struct css_set *cset;
2368
2369	lockdep_assert_held(&css_set_lock);
2370
2371	/* @task either already exited or can't exit until the end */
2372	if (task->flags & PF_EXITING)
2373		return;
2374
2375	/* leave @task alone if post_fork() hasn't linked it yet */
2376	if (list_empty(&task->cg_list))
2377		return;
2378
2379	cset = task_css_set(task);
2380	if (!cset->mg_src_cgrp)
2381		return;
2382
2383	mgctx->tset.nr_tasks++;
2384
2385	list_move_tail(&task->cg_list, &cset->mg_tasks);
2386	if (list_empty(&cset->mg_node))
2387		list_add_tail(&cset->mg_node,
2388			      &mgctx->tset.src_csets);
2389	if (list_empty(&cset->mg_dst_cset->mg_node))
2390		list_add_tail(&cset->mg_dst_cset->mg_node,
2391			      &mgctx->tset.dst_csets);
2392}
2393
2394/**
2395 * cgroup_taskset_first - reset taskset and return the first task
2396 * @tset: taskset of interest
2397 * @dst_cssp: output variable for the destination css
2398 *
2399 * @tset iteration is initialized and the first task is returned.
2400 */
2401struct task_struct *cgroup_taskset_first(struct cgroup_taskset *tset,
2402					 struct cgroup_subsys_state **dst_cssp)
2403{
2404	tset->cur_cset = list_first_entry(tset->csets, struct css_set, mg_node);
2405	tset->cur_task = NULL;
2406
2407	return cgroup_taskset_next(tset, dst_cssp);
2408}
2409
2410/**
2411 * cgroup_taskset_next - iterate to the next task in taskset
2412 * @tset: taskset of interest
2413 * @dst_cssp: output variable for the destination css
2414 *
2415 * Return the next task in @tset.  Iteration must have been initialized
2416 * with cgroup_taskset_first().
2417 */
2418struct task_struct *cgroup_taskset_next(struct cgroup_taskset *tset,
2419					struct cgroup_subsys_state **dst_cssp)
2420{
2421	struct css_set *cset = tset->cur_cset;
2422	struct task_struct *task = tset->cur_task;
2423
2424	while (&cset->mg_node != tset->csets) {
2425		if (!task)
2426			task = list_first_entry(&cset->mg_tasks,
2427						struct task_struct, cg_list);
2428		else
2429			task = list_next_entry(task, cg_list);
2430
2431		if (&task->cg_list != &cset->mg_tasks) {
2432			tset->cur_cset = cset;
2433			tset->cur_task = task;
2434
2435			/*
2436			 * This function may be called both before and
2437			 * after cgroup_taskset_migrate().  The two cases
2438			 * can be distinguished by looking at whether @cset
2439			 * has its ->mg_dst_cset set.
2440			 */
2441			if (cset->mg_dst_cset)
2442				*dst_cssp = cset->mg_dst_cset->subsys[tset->ssid];
2443			else
2444				*dst_cssp = cset->subsys[tset->ssid];
2445
2446			return task;
2447		}
2448
2449		cset = list_next_entry(cset, mg_node);
2450		task = NULL;
2451	}
2452
2453	return NULL;
2454}
2455
2456/**
2457 * cgroup_taskset_migrate - migrate a taskset
2458 * @mgctx: migration context
2459 *
2460 * Migrate tasks in @mgctx as setup by migration preparation functions.
2461 * This function fails iff one of the ->can_attach callbacks fails and
2462 * guarantees that either all or none of the tasks in @mgctx are migrated.
2463 * @mgctx is consumed regardless of success.
2464 */
2465static int cgroup_migrate_execute(struct cgroup_mgctx *mgctx)
2466{
2467	struct cgroup_taskset *tset = &mgctx->tset;
2468	struct cgroup_subsys *ss;
2469	struct task_struct *task, *tmp_task;
2470	struct css_set *cset, *tmp_cset;
2471	int ssid, failed_ssid, ret;
2472
2473	/* check that we can legitimately attach to the cgroup */
2474	if (tset->nr_tasks) {
2475		do_each_subsys_mask(ss, ssid, mgctx->ss_mask) {
2476			if (ss->can_attach) {
2477				tset->ssid = ssid;
2478				ret = ss->can_attach(tset);
2479				if (ret) {
2480					failed_ssid = ssid;
2481					goto out_cancel_attach;
2482				}
2483			}
2484		} while_each_subsys_mask();
2485	}
2486
2487	/*
2488	 * Now that we're guaranteed success, proceed to move all tasks to
2489	 * the new cgroup.  There are no failure cases after here, so this
2490	 * is the commit point.
2491	 */
2492	spin_lock_irq(&css_set_lock);
2493	list_for_each_entry(cset, &tset->src_csets, mg_node) {
2494		list_for_each_entry_safe(task, tmp_task, &cset->mg_tasks, cg_list) {
2495			struct css_set *from_cset = task_css_set(task);
2496			struct css_set *to_cset = cset->mg_dst_cset;
2497
2498			get_css_set(to_cset);
2499			to_cset->nr_tasks++;
2500			css_set_move_task(task, from_cset, to_cset, true);
2501			from_cset->nr_tasks--;
2502			/*
2503			 * If the source or destination cgroup is frozen,
2504			 * the task might require to change its state.
2505			 */
2506			cgroup_freezer_migrate_task(task, from_cset->dfl_cgrp,
2507						    to_cset->dfl_cgrp);
2508			put_css_set_locked(from_cset);
2509
2510		}
2511	}
2512	spin_unlock_irq(&css_set_lock);
2513
2514	/*
2515	 * Migration is committed, all target tasks are now on dst_csets.
2516	 * Nothing is sensitive to fork() after this point.  Notify
2517	 * controllers that migration is complete.
2518	 */
2519	tset->csets = &tset->dst_csets;
2520
2521	if (tset->nr_tasks) {
2522		do_each_subsys_mask(ss, ssid, mgctx->ss_mask) {
2523			if (ss->attach) {
2524				tset->ssid = ssid;
2525				ss->attach(tset);
2526			}
2527		} while_each_subsys_mask();
2528	}
2529
2530	ret = 0;
2531	goto out_release_tset;
2532
2533out_cancel_attach:
2534	if (tset->nr_tasks) {
2535		do_each_subsys_mask(ss, ssid, mgctx->ss_mask) {
2536			if (ssid == failed_ssid)
2537				break;
2538			if (ss->cancel_attach) {
2539				tset->ssid = ssid;
2540				ss->cancel_attach(tset);
2541			}
2542		} while_each_subsys_mask();
2543	}
2544out_release_tset:
2545	spin_lock_irq(&css_set_lock);
2546	list_splice_init(&tset->dst_csets, &tset->src_csets);
2547	list_for_each_entry_safe(cset, tmp_cset, &tset->src_csets, mg_node) {
2548		list_splice_tail_init(&cset->mg_tasks, &cset->tasks);
2549		list_del_init(&cset->mg_node);
2550	}
2551	spin_unlock_irq(&css_set_lock);
2552
2553	/*
2554	 * Re-initialize the cgroup_taskset structure in case it is reused
2555	 * again in another cgroup_migrate_add_task()/cgroup_migrate_execute()
2556	 * iteration.
2557	 */
2558	tset->nr_tasks = 0;
2559	tset->csets    = &tset->src_csets;
2560	return ret;
2561}
2562
2563/**
2564 * cgroup_migrate_vet_dst - verify whether a cgroup can be migration destination
2565 * @dst_cgrp: destination cgroup to test
2566 *
2567 * On the default hierarchy, except for the mixable, (possible) thread root
2568 * and threaded cgroups, subtree_control must be zero for migration
2569 * destination cgroups with tasks so that child cgroups don't compete
2570 * against tasks.
2571 */
2572int cgroup_migrate_vet_dst(struct cgroup *dst_cgrp)
2573{
2574	/* v1 doesn't have any restriction */
2575	if (!cgroup_on_dfl(dst_cgrp))
2576		return 0;
2577
2578	/* verify @dst_cgrp can host resources */
2579	if (!cgroup_is_valid_domain(dst_cgrp->dom_cgrp))
2580		return -EOPNOTSUPP;
2581
2582	/* mixables don't care */
2583	if (cgroup_is_mixable(dst_cgrp))
2584		return 0;
2585
2586	/*
2587	 * If @dst_cgrp is already or can become a thread root or is
2588	 * threaded, it doesn't matter.
2589	 */
2590	if (cgroup_can_be_thread_root(dst_cgrp) || cgroup_is_threaded(dst_cgrp))
2591		return 0;
2592
2593	/* apply no-internal-process constraint */
2594	if (dst_cgrp->subtree_control)
2595		return -EBUSY;
2596
2597	return 0;
2598}
2599
2600/**
2601 * cgroup_migrate_finish - cleanup after attach
2602 * @mgctx: migration context
2603 *
2604 * Undo cgroup_migrate_add_src() and cgroup_migrate_prepare_dst().  See
2605 * those functions for details.
2606 */
2607void cgroup_migrate_finish(struct cgroup_mgctx *mgctx)
2608{
2609	LIST_HEAD(preloaded);
2610	struct css_set *cset, *tmp_cset;
2611
2612	lockdep_assert_held(&cgroup_mutex);
2613
2614	spin_lock_irq(&css_set_lock);
2615
2616	list_splice_tail_init(&mgctx->preloaded_src_csets, &preloaded);
2617	list_splice_tail_init(&mgctx->preloaded_dst_csets, &preloaded);
2618
2619	list_for_each_entry_safe(cset, tmp_cset, &preloaded, mg_preload_node) {
2620		cset->mg_src_cgrp = NULL;
2621		cset->mg_dst_cgrp = NULL;
2622		cset->mg_dst_cset = NULL;
2623		list_del_init(&cset->mg_preload_node);
2624		put_css_set_locked(cset);
2625	}
2626
2627	spin_unlock_irq(&css_set_lock);
2628}
2629
2630/**
2631 * cgroup_migrate_add_src - add a migration source css_set
2632 * @src_cset: the source css_set to add
2633 * @dst_cgrp: the destination cgroup
2634 * @mgctx: migration context
2635 *
2636 * Tasks belonging to @src_cset are about to be migrated to @dst_cgrp.  Pin
2637 * @src_cset and add it to @mgctx->src_csets, which should later be cleaned
2638 * up by cgroup_migrate_finish().
2639 *
2640 * This function may be called without holding cgroup_threadgroup_rwsem
2641 * even if the target is a process.  Threads may be created and destroyed
2642 * but as long as cgroup_mutex is not dropped, no new css_set can be put
2643 * into play and the preloaded css_sets are guaranteed to cover all
2644 * migrations.
2645 */
2646void cgroup_migrate_add_src(struct css_set *src_cset,
2647			    struct cgroup *dst_cgrp,
2648			    struct cgroup_mgctx *mgctx)
2649{
2650	struct cgroup *src_cgrp;
2651
2652	lockdep_assert_held(&cgroup_mutex);
2653	lockdep_assert_held(&css_set_lock);
2654
2655	/*
2656	 * If ->dead, @src_set is associated with one or more dead cgroups
2657	 * and doesn't contain any migratable tasks.  Ignore it early so
2658	 * that the rest of migration path doesn't get confused by it.
2659	 */
2660	if (src_cset->dead)
2661		return;
2662
2663	src_cgrp = cset_cgroup_from_root(src_cset, dst_cgrp->root);
2664
2665	if (!list_empty(&src_cset->mg_preload_node))
2666		return;
2667
2668	WARN_ON(src_cset->mg_src_cgrp);
2669	WARN_ON(src_cset->mg_dst_cgrp);
2670	WARN_ON(!list_empty(&src_cset->mg_tasks));
2671	WARN_ON(!list_empty(&src_cset->mg_node));
2672
2673	src_cset->mg_src_cgrp = src_cgrp;
2674	src_cset->mg_dst_cgrp = dst_cgrp;
2675	get_css_set(src_cset);
2676	list_add_tail(&src_cset->mg_preload_node, &mgctx->preloaded_src_csets);
2677}
2678
2679/**
2680 * cgroup_migrate_prepare_dst - prepare destination css_sets for migration
2681 * @mgctx: migration context
2682 *
2683 * Tasks are about to be moved and all the source css_sets have been
2684 * preloaded to @mgctx->preloaded_src_csets.  This function looks up and
2685 * pins all destination css_sets, links each to its source, and append them
2686 * to @mgctx->preloaded_dst_csets.
2687 *
2688 * This function must be called after cgroup_migrate_add_src() has been
2689 * called on each migration source css_set.  After migration is performed
2690 * using cgroup_migrate(), cgroup_migrate_finish() must be called on
2691 * @mgctx.
2692 */
2693int cgroup_migrate_prepare_dst(struct cgroup_mgctx *mgctx)
2694{
2695	struct css_set *src_cset, *tmp_cset;
2696
2697	lockdep_assert_held(&cgroup_mutex);
2698
2699	/* look up the dst cset for each src cset and link it to src */
2700	list_for_each_entry_safe(src_cset, tmp_cset, &mgctx->preloaded_src_csets,
2701				 mg_preload_node) {
2702		struct css_set *dst_cset;
2703		struct cgroup_subsys *ss;
2704		int ssid;
2705
2706		dst_cset = find_css_set(src_cset, src_cset->mg_dst_cgrp);
2707		if (!dst_cset)
2708			return -ENOMEM;
2709
2710		WARN_ON_ONCE(src_cset->mg_dst_cset || dst_cset->mg_dst_cset);
2711
2712		/*
2713		 * If src cset equals dst, it's noop.  Drop the src.
2714		 * cgroup_migrate() will skip the cset too.  Note that we
2715		 * can't handle src == dst as some nodes are used by both.
2716		 */
2717		if (src_cset == dst_cset) {
2718			src_cset->mg_src_cgrp = NULL;
2719			src_cset->mg_dst_cgrp = NULL;
2720			list_del_init(&src_cset->mg_preload_node);
2721			put_css_set(src_cset);
2722			put_css_set(dst_cset);
2723			continue;
2724		}
2725
2726		src_cset->mg_dst_cset = dst_cset;
2727
2728		if (list_empty(&dst_cset->mg_preload_node))
2729			list_add_tail(&dst_cset->mg_preload_node,
2730				      &mgctx->preloaded_dst_csets);
2731		else
2732			put_css_set(dst_cset);
2733
2734		for_each_subsys(ss, ssid)
2735			if (src_cset->subsys[ssid] != dst_cset->subsys[ssid])
2736				mgctx->ss_mask |= 1 << ssid;
2737	}
2738
2739	return 0;
 
 
 
2740}
2741
2742/**
2743 * cgroup_migrate - migrate a process or task to a cgroup
2744 * @leader: the leader of the process or the task to migrate
2745 * @threadgroup: whether @leader points to the whole process or a single task
2746 * @mgctx: migration context
2747 *
2748 * Migrate a process or task denoted by @leader.  If migrating a process,
2749 * the caller must be holding cgroup_threadgroup_rwsem.  The caller is also
2750 * responsible for invoking cgroup_migrate_add_src() and
2751 * cgroup_migrate_prepare_dst() on the targets before invoking this
2752 * function and following up with cgroup_migrate_finish().
2753 *
2754 * As long as a controller's ->can_attach() doesn't fail, this function is
2755 * guaranteed to succeed.  This means that, excluding ->can_attach()
2756 * failure, when migrating multiple targets, the success or failure can be
2757 * decided for all targets by invoking group_migrate_prepare_dst() before
2758 * actually starting migrating.
2759 */
2760int cgroup_migrate(struct task_struct *leader, bool threadgroup,
2761		   struct cgroup_mgctx *mgctx)
2762{
2763	struct task_struct *task;
2764
2765	/*
2766	 * Prevent freeing of tasks while we take a snapshot. Tasks that are
2767	 * already PF_EXITING could be freed from underneath us unless we
2768	 * take an rcu_read_lock.
2769	 */
2770	spin_lock_irq(&css_set_lock);
2771	rcu_read_lock();
2772	task = leader;
2773	do {
2774		cgroup_migrate_add_task(task, mgctx);
2775		if (!threadgroup)
2776			break;
2777	} while_each_thread(leader, task);
2778	rcu_read_unlock();
2779	spin_unlock_irq(&css_set_lock);
2780
2781	return cgroup_migrate_execute(mgctx);
2782}
2783
2784/**
2785 * cgroup_attach_task - attach a task or a whole threadgroup to a cgroup
2786 * @dst_cgrp: the cgroup to attach to
2787 * @leader: the task or the leader of the threadgroup to be attached
2788 * @threadgroup: attach the whole threadgroup?
2789 *
2790 * Call holding cgroup_mutex and cgroup_threadgroup_rwsem.
2791 */
2792int cgroup_attach_task(struct cgroup *dst_cgrp, struct task_struct *leader,
2793		       bool threadgroup)
2794{
2795	DEFINE_CGROUP_MGCTX(mgctx);
2796	struct task_struct *task;
2797	int ret;
2798
2799	ret = cgroup_migrate_vet_dst(dst_cgrp);
2800	if (ret)
2801		return ret;
2802
2803	/* look up all src csets */
2804	spin_lock_irq(&css_set_lock);
2805	rcu_read_lock();
2806	task = leader;
2807	do {
2808		cgroup_migrate_add_src(task_css_set(task), dst_cgrp, &mgctx);
2809		if (!threadgroup)
2810			break;
2811	} while_each_thread(leader, task);
2812	rcu_read_unlock();
2813	spin_unlock_irq(&css_set_lock);
2814
2815	/* prepare dst csets and commit */
2816	ret = cgroup_migrate_prepare_dst(&mgctx);
2817	if (!ret)
2818		ret = cgroup_migrate(leader, threadgroup, &mgctx);
2819
2820	cgroup_migrate_finish(&mgctx);
2821
2822	if (!ret)
2823		TRACE_CGROUP_PATH(attach_task, dst_cgrp, leader, threadgroup);
2824
2825	return ret;
2826}
2827
2828struct task_struct *cgroup_procs_write_start(char *buf, bool threadgroup)
2829	__acquires(&cgroup_threadgroup_rwsem)
2830{
2831	struct task_struct *tsk;
2832	pid_t pid;
2833
2834	if (kstrtoint(strstrip(buf), 0, &pid) || pid < 0)
2835		return ERR_PTR(-EINVAL);
2836
2837	percpu_down_write(&cgroup_threadgroup_rwsem);
2838
2839	rcu_read_lock();
2840	if (pid) {
2841		tsk = find_task_by_vpid(pid);
2842		if (!tsk) {
2843			tsk = ERR_PTR(-ESRCH);
2844			goto out_unlock_threadgroup;
2845		}
2846	} else {
2847		tsk = current;
2848	}
2849
2850	if (threadgroup)
2851		tsk = tsk->group_leader;
2852
2853	/*
2854	 * kthreads may acquire PF_NO_SETAFFINITY during initialization.
2855	 * If userland migrates such a kthread to a non-root cgroup, it can
2856	 * become trapped in a cpuset, or RT kthread may be born in a
2857	 * cgroup with no rt_runtime allocated.  Just say no.
2858	 */
2859	if (tsk->no_cgroup_migration || (tsk->flags & PF_NO_SETAFFINITY)) {
2860		tsk = ERR_PTR(-EINVAL);
2861		goto out_unlock_threadgroup;
2862	}
2863
2864	get_task_struct(tsk);
2865	goto out_unlock_rcu;
2866
2867out_unlock_threadgroup:
2868	percpu_up_write(&cgroup_threadgroup_rwsem);
2869out_unlock_rcu:
2870	rcu_read_unlock();
2871	return tsk;
2872}
2873
2874void cgroup_procs_write_finish(struct task_struct *task)
2875	__releases(&cgroup_threadgroup_rwsem)
2876{
2877	struct cgroup_subsys *ss;
2878	int ssid;
2879
2880	/* release reference from cgroup_procs_write_start() */
2881	put_task_struct(task);
2882
2883	percpu_up_write(&cgroup_threadgroup_rwsem);
2884	for_each_subsys(ss, ssid)
2885		if (ss->post_attach)
2886			ss->post_attach();
2887}
2888
2889static void cgroup_print_ss_mask(struct seq_file *seq, u16 ss_mask)
2890{
2891	struct cgroup_subsys *ss;
2892	bool printed = false;
2893	int ssid;
2894
2895	do_each_subsys_mask(ss, ssid, ss_mask) {
2896		if (printed)
2897			seq_putc(seq, ' ');
2898		seq_puts(seq, ss->name);
2899		printed = true;
2900	} while_each_subsys_mask();
2901	if (printed)
2902		seq_putc(seq, '\n');
2903}
2904
2905/* show controllers which are enabled from the parent */
2906static int cgroup_controllers_show(struct seq_file *seq, void *v)
2907{
2908	struct cgroup *cgrp = seq_css(seq)->cgroup;
2909
2910	cgroup_print_ss_mask(seq, cgroup_control(cgrp));
2911	return 0;
2912}
2913
2914/* show controllers which are enabled for a given cgroup's children */
2915static int cgroup_subtree_control_show(struct seq_file *seq, void *v)
2916{
2917	struct cgroup *cgrp = seq_css(seq)->cgroup;
2918
2919	cgroup_print_ss_mask(seq, cgrp->subtree_control);
2920	return 0;
2921}
2922
2923/**
2924 * cgroup_update_dfl_csses - update css assoc of a subtree in default hierarchy
2925 * @cgrp: root of the subtree to update csses for
2926 *
2927 * @cgrp's control masks have changed and its subtree's css associations
2928 * need to be updated accordingly.  This function looks up all css_sets
2929 * which are attached to the subtree, creates the matching updated css_sets
2930 * and migrates the tasks to the new ones.
2931 */
2932static int cgroup_update_dfl_csses(struct cgroup *cgrp)
2933{
2934	DEFINE_CGROUP_MGCTX(mgctx);
2935	struct cgroup_subsys_state *d_css;
2936	struct cgroup *dsct;
2937	struct css_set *src_cset;
2938	int ret;
2939
2940	lockdep_assert_held(&cgroup_mutex);
2941
2942	percpu_down_write(&cgroup_threadgroup_rwsem);
2943
2944	/* look up all csses currently attached to @cgrp's subtree */
2945	spin_lock_irq(&css_set_lock);
2946	cgroup_for_each_live_descendant_pre(dsct, d_css, cgrp) {
2947		struct cgrp_cset_link *link;
2948
2949		list_for_each_entry(link, &dsct->cset_links, cset_link)
2950			cgroup_migrate_add_src(link->cset, dsct, &mgctx);
2951	}
2952	spin_unlock_irq(&css_set_lock);
2953
2954	/* NULL dst indicates self on default hierarchy */
2955	ret = cgroup_migrate_prepare_dst(&mgctx);
2956	if (ret)
2957		goto out_finish;
2958
2959	spin_lock_irq(&css_set_lock);
2960	list_for_each_entry(src_cset, &mgctx.preloaded_src_csets, mg_preload_node) {
2961		struct task_struct *task, *ntask;
2962
2963		/* all tasks in src_csets need to be migrated */
2964		list_for_each_entry_safe(task, ntask, &src_cset->tasks, cg_list)
2965			cgroup_migrate_add_task(task, &mgctx);
2966	}
2967	spin_unlock_irq(&css_set_lock);
2968
2969	ret = cgroup_migrate_execute(&mgctx);
2970out_finish:
2971	cgroup_migrate_finish(&mgctx);
2972	percpu_up_write(&cgroup_threadgroup_rwsem);
2973	return ret;
2974}
2975
2976/**
2977 * cgroup_lock_and_drain_offline - lock cgroup_mutex and drain offlined csses
2978 * @cgrp: root of the target subtree
2979 *
2980 * Because css offlining is asynchronous, userland may try to re-enable a
2981 * controller while the previous css is still around.  This function grabs
2982 * cgroup_mutex and drains the previous css instances of @cgrp's subtree.
2983 */
2984void cgroup_lock_and_drain_offline(struct cgroup *cgrp)
2985	__acquires(&cgroup_mutex)
2986{
2987	struct cgroup *dsct;
2988	struct cgroup_subsys_state *d_css;
2989	struct cgroup_subsys *ss;
2990	int ssid;
2991
2992restart:
2993	mutex_lock(&cgroup_mutex);
2994
2995	cgroup_for_each_live_descendant_post(dsct, d_css, cgrp) {
2996		for_each_subsys(ss, ssid) {
2997			struct cgroup_subsys_state *css = cgroup_css(dsct, ss);
2998			DEFINE_WAIT(wait);
2999
3000			if (!css || !percpu_ref_is_dying(&css->refcnt))
3001				continue;
3002
3003			cgroup_get_live(dsct);
3004			prepare_to_wait(&dsct->offline_waitq, &wait,
3005					TASK_UNINTERRUPTIBLE);
3006
3007			mutex_unlock(&cgroup_mutex);
3008			schedule();
3009			finish_wait(&dsct->offline_waitq, &wait);
3010
3011			cgroup_put(dsct);
3012			goto restart;
3013		}
3014	}
3015}
3016
3017/**
3018 * cgroup_save_control - save control masks and dom_cgrp of a subtree
3019 * @cgrp: root of the target subtree
3020 *
3021 * Save ->subtree_control, ->subtree_ss_mask and ->dom_cgrp to the
3022 * respective old_ prefixed fields for @cgrp's subtree including @cgrp
3023 * itself.
3024 */
3025static void cgroup_save_control(struct cgroup *cgrp)
3026{
3027	struct cgroup *dsct;
3028	struct cgroup_subsys_state *d_css;
3029
3030	cgroup_for_each_live_descendant_pre(dsct, d_css, cgrp) {
3031		dsct->old_subtree_control = dsct->subtree_control;
3032		dsct->old_subtree_ss_mask = dsct->subtree_ss_mask;
3033		dsct->old_dom_cgrp = dsct->dom_cgrp;
3034	}
3035}
3036
3037/**
3038 * cgroup_propagate_control - refresh control masks of a subtree
3039 * @cgrp: root of the target subtree
3040 *
3041 * For @cgrp and its subtree, ensure ->subtree_ss_mask matches
3042 * ->subtree_control and propagate controller availability through the
3043 * subtree so that descendants don't have unavailable controllers enabled.
3044 */
3045static void cgroup_propagate_control(struct cgroup *cgrp)
3046{
3047	struct cgroup *dsct;
3048	struct cgroup_subsys_state *d_css;
3049
3050	cgroup_for_each_live_descendant_pre(dsct, d_css, cgrp) {
3051		dsct->subtree_control &= cgroup_control(dsct);
3052		dsct->subtree_ss_mask =
3053			cgroup_calc_subtree_ss_mask(dsct->subtree_control,
3054						    cgroup_ss_mask(dsct));
3055	}
3056}
3057
3058/**
3059 * cgroup_restore_control - restore control masks and dom_cgrp of a subtree
3060 * @cgrp: root of the target subtree
3061 *
3062 * Restore ->subtree_control, ->subtree_ss_mask and ->dom_cgrp from the
3063 * respective old_ prefixed fields for @cgrp's subtree including @cgrp
3064 * itself.
3065 */
3066static void cgroup_restore_control(struct cgroup *cgrp)
3067{
3068	struct cgroup *dsct;
3069	struct cgroup_subsys_state *d_css;
3070
3071	cgroup_for_each_live_descendant_post(dsct, d_css, cgrp) {
3072		dsct->subtree_control = dsct->old_subtree_control;
3073		dsct->subtree_ss_mask = dsct->old_subtree_ss_mask;
3074		dsct->dom_cgrp = dsct->old_dom_cgrp;
3075	}
3076}
3077
3078static bool css_visible(struct cgroup_subsys_state *css)
3079{
3080	struct cgroup_subsys *ss = css->ss;
3081	struct cgroup *cgrp = css->cgroup;
3082
3083	if (cgroup_control(cgrp) & (1 << ss->id))
3084		return true;
3085	if (!(cgroup_ss_mask(cgrp) & (1 << ss->id)))
3086		return false;
3087	return cgroup_on_dfl(cgrp) && ss->implicit_on_dfl;
3088}
3089
3090/**
3091 * cgroup_apply_control_enable - enable or show csses according to control
3092 * @cgrp: root of the target subtree
3093 *
3094 * Walk @cgrp's subtree and create new csses or make the existing ones
3095 * visible.  A css is created invisible if it's being implicitly enabled
3096 * through dependency.  An invisible css is made visible when the userland
3097 * explicitly enables it.
3098 *
3099 * Returns 0 on success, -errno on failure.  On failure, csses which have
3100 * been processed already aren't cleaned up.  The caller is responsible for
3101 * cleaning up with cgroup_apply_control_disable().
3102 */
3103static int cgroup_apply_control_enable(struct cgroup *cgrp)
3104{
3105	struct cgroup *dsct;
3106	struct cgroup_subsys_state *d_css;
3107	struct cgroup_subsys *ss;
3108	int ssid, ret;
3109
3110	cgroup_for_each_live_descendant_pre(dsct, d_css, cgrp) {
3111		for_each_subsys(ss, ssid) {
3112			struct cgroup_subsys_state *css = cgroup_css(dsct, ss);
3113
3114			WARN_ON_ONCE(css && percpu_ref_is_dying(&css->refcnt));
3115
3116			if (!(cgroup_ss_mask(dsct) & (1 << ss->id)))
3117				continue;
3118
3119			if (!css) {
3120				css = css_create(dsct, ss);
3121				if (IS_ERR(css))
3122					return PTR_ERR(css);
3123			}
3124
3125			if (css_visible(css)) {
3126				ret = css_populate_dir(css);
3127				if (ret)
3128					return ret;
3129			}
3130		}
3131	}
3132
3133	return 0;
3134}
3135
3136/**
3137 * cgroup_apply_control_disable - kill or hide csses according to control
3138 * @cgrp: root of the target subtree
3139 *
3140 * Walk @cgrp's subtree and kill and hide csses so that they match
3141 * cgroup_ss_mask() and cgroup_visible_mask().
3142 *
3143 * A css is hidden when the userland requests it to be disabled while other
3144 * subsystems are still depending on it.  The css must not actively control
3145 * resources and be in the vanilla state if it's made visible again later.
3146 * Controllers which may be depended upon should provide ->css_reset() for
3147 * this purpose.
3148 */
3149static void cgroup_apply_control_disable(struct cgroup *cgrp)
3150{
3151	struct cgroup *dsct;
3152	struct cgroup_subsys_state *d_css;
3153	struct cgroup_subsys *ss;
3154	int ssid;
3155
3156	cgroup_for_each_live_descendant_post(dsct, d_css, cgrp) {
3157		for_each_subsys(ss, ssid) {
3158			struct cgroup_subsys_state *css = cgroup_css(dsct, ss);
3159
3160			WARN_ON_ONCE(css && percpu_ref_is_dying(&css->refcnt));
3161
3162			if (!css)
3163				continue;
3164
3165			if (css->parent &&
3166			    !(cgroup_ss_mask(dsct) & (1 << ss->id))) {
3167				kill_css(css);
3168			} else if (!css_visible(css)) {
3169				css_clear_dir(css);
3170				if (ss->css_reset)
3171					ss->css_reset(css);
3172			}
3173		}
3174	}
3175}
3176
3177/**
3178 * cgroup_apply_control - apply control mask updates to the subtree
3179 * @cgrp: root of the target subtree
3180 *
3181 * subsystems can be enabled and disabled in a subtree using the following
3182 * steps.
3183 *
3184 * 1. Call cgroup_save_control() to stash the current state.
3185 * 2. Update ->subtree_control masks in the subtree as desired.
3186 * 3. Call cgroup_apply_control() to apply the changes.
3187 * 4. Optionally perform other related operations.
3188 * 5. Call cgroup_finalize_control() to finish up.
3189 *
3190 * This function implements step 3 and propagates the mask changes
3191 * throughout @cgrp's subtree, updates csses accordingly and perform
3192 * process migrations.
3193 */
3194static int cgroup_apply_control(struct cgroup *cgrp)
3195{
3196	int ret;
3197
3198	cgroup_propagate_control(cgrp);
3199
3200	ret = cgroup_apply_control_enable(cgrp);
3201	if (ret)
3202		return ret;
3203
3204	/*
3205	 * At this point, cgroup_e_css_by_mask() results reflect the new csses
3206	 * making the following cgroup_update_dfl_csses() properly update
3207	 * css associations of all tasks in the subtree.
3208	 */
3209	ret = cgroup_update_dfl_csses(cgrp);
3210	if (ret)
3211		return ret;
3212
3213	return 0;
3214}
3215
3216/**
3217 * cgroup_finalize_control - finalize control mask update
3218 * @cgrp: root of the target subtree
3219 * @ret: the result of the update
3220 *
3221 * Finalize control mask update.  See cgroup_apply_control() for more info.
3222 */
3223static void cgroup_finalize_control(struct cgroup *cgrp, int ret)
3224{
3225	if (ret) {
3226		cgroup_restore_control(cgrp);
3227		cgroup_propagate_control(cgrp);
3228	}
3229
3230	cgroup_apply_control_disable(cgrp);
3231}
3232
3233static int cgroup_vet_subtree_control_enable(struct cgroup *cgrp, u16 enable)
3234{
3235	u16 domain_enable = enable & ~cgrp_dfl_threaded_ss_mask;
3236
3237	/* if nothing is getting enabled, nothing to worry about */
3238	if (!enable)
3239		return 0;
3240
3241	/* can @cgrp host any resources? */
3242	if (!cgroup_is_valid_domain(cgrp->dom_cgrp))
3243		return -EOPNOTSUPP;
3244
3245	/* mixables don't care */
3246	if (cgroup_is_mixable(cgrp))
3247		return 0;
3248
3249	if (domain_enable) {
3250		/* can't enable domain controllers inside a thread subtree */
3251		if (cgroup_is_thread_root(cgrp) || cgroup_is_threaded(cgrp))
3252			return -EOPNOTSUPP;
3253	} else {
3254		/*
3255		 * Threaded controllers can handle internal competitions
3256		 * and are always allowed inside a (prospective) thread
3257		 * subtree.
3258		 */
3259		if (cgroup_can_be_thread_root(cgrp) || cgroup_is_threaded(cgrp))
3260			return 0;
3261	}
3262
3263	/*
3264	 * Controllers can't be enabled for a cgroup with tasks to avoid
3265	 * child cgroups competing against tasks.
3266	 */
3267	if (cgroup_has_tasks(cgrp))
3268		return -EBUSY;
3269
3270	return 0;
3271}
3272
3273/* change the enabled child controllers for a cgroup in the default hierarchy */
3274static ssize_t cgroup_subtree_control_write(struct kernfs_open_file *of,
3275					    char *buf, size_t nbytes,
3276					    loff_t off)
3277{
3278	u16 enable = 0, disable = 0;
3279	struct cgroup *cgrp, *child;
3280	struct cgroup_subsys *ss;
3281	char *tok;
3282	int ssid, ret;
3283
3284	/*
3285	 * Parse input - space separated list of subsystem names prefixed
3286	 * with either + or -.
3287	 */
3288	buf = strstrip(buf);
3289	while ((tok = strsep(&buf, " "))) {
3290		if (tok[0] == '\0')
3291			continue;
3292		do_each_subsys_mask(ss, ssid, ~cgrp_dfl_inhibit_ss_mask) {
3293			if (!cgroup_ssid_enabled(ssid) ||
3294			    strcmp(tok + 1, ss->name))
3295				continue;
3296
3297			if (*tok == '+') {
3298				enable |= 1 << ssid;
3299				disable &= ~(1 << ssid);
3300			} else if (*tok == '-') {
3301				disable |= 1 << ssid;
3302				enable &= ~(1 << ssid);
3303			} else {
3304				return -EINVAL;
3305			}
3306			break;
3307		} while_each_subsys_mask();
3308		if (ssid == CGROUP_SUBSYS_COUNT)
3309			return -EINVAL;
3310	}
3311
3312	cgrp = cgroup_kn_lock_live(of->kn, true);
3313	if (!cgrp)
3314		return -ENODEV;
3315
3316	for_each_subsys(ss, ssid) {
3317		if (enable & (1 << ssid)) {
3318			if (cgrp->subtree_control & (1 << ssid)) {
3319				enable &= ~(1 << ssid);
3320				continue;
3321			}
3322
3323			if (!(cgroup_control(cgrp) & (1 << ssid))) {
3324				ret = -ENOENT;
3325				goto out_unlock;
3326			}
3327		} else if (disable & (1 << ssid)) {
3328			if (!(cgrp->subtree_control & (1 << ssid))) {
3329				disable &= ~(1 << ssid);
3330				continue;
3331			}
3332
3333			/* a child has it enabled? */
3334			cgroup_for_each_live_child(child, cgrp) {
3335				if (child->subtree_control & (1 << ssid)) {
3336					ret = -EBUSY;
3337					goto out_unlock;
3338				}
3339			}
3340		}
3341	}
3342
3343	if (!enable && !disable) {
3344		ret = 0;
3345		goto out_unlock;
3346	}
3347
3348	ret = cgroup_vet_subtree_control_enable(cgrp, enable);
3349	if (ret)
3350		goto out_unlock;
3351
3352	/* save and update control masks and prepare csses */
3353	cgroup_save_control(cgrp);
3354
3355	cgrp->subtree_control |= enable;
3356	cgrp->subtree_control &= ~disable;
3357
3358	ret = cgroup_apply_control(cgrp);
3359	cgroup_finalize_control(cgrp, ret);
3360	if (ret)
3361		goto out_unlock;
3362
3363	kernfs_activate(cgrp->kn);
3364out_unlock:
3365	cgroup_kn_unlock(of->kn);
3366	return ret ?: nbytes;
3367}
3368
3369/**
3370 * cgroup_enable_threaded - make @cgrp threaded
3371 * @cgrp: the target cgroup
3372 *
3373 * Called when "threaded" is written to the cgroup.type interface file and
3374 * tries to make @cgrp threaded and join the parent's resource domain.
3375 * This function is never called on the root cgroup as cgroup.type doesn't
3376 * exist on it.
3377 */
3378static int cgroup_enable_threaded(struct cgroup *cgrp)
3379{
3380	struct cgroup *parent = cgroup_parent(cgrp);
3381	struct cgroup *dom_cgrp = parent->dom_cgrp;
3382	struct cgroup *dsct;
3383	struct cgroup_subsys_state *d_css;
3384	int ret;
3385
3386	lockdep_assert_held(&cgroup_mutex);
3387
3388	/* noop if already threaded */
3389	if (cgroup_is_threaded(cgrp))
3390		return 0;
3391
3392	/*
3393	 * If @cgroup is populated or has domain controllers enabled, it
3394	 * can't be switched.  While the below cgroup_can_be_thread_root()
3395	 * test can catch the same conditions, that's only when @parent is
3396	 * not mixable, so let's check it explicitly.
3397	 */
3398	if (cgroup_is_populated(cgrp) ||
3399	    cgrp->subtree_control & ~cgrp_dfl_threaded_ss_mask)
3400		return -EOPNOTSUPP;
3401
3402	/* we're joining the parent's domain, ensure its validity */
3403	if (!cgroup_is_valid_domain(dom_cgrp) ||
3404	    !cgroup_can_be_thread_root(dom_cgrp))
3405		return -EOPNOTSUPP;
3406
3407	/*
3408	 * The following shouldn't cause actual migrations and should
3409	 * always succeed.
3410	 */
3411	cgroup_save_control(cgrp);
3412
3413	cgroup_for_each_live_descendant_pre(dsct, d_css, cgrp)
3414		if (dsct == cgrp || cgroup_is_threaded(dsct))
3415			dsct->dom_cgrp = dom_cgrp;
3416
3417	ret = cgroup_apply_control(cgrp);
3418	if (!ret)
3419		parent->nr_threaded_children++;
 
 
3420
3421	cgroup_finalize_control(cgrp, ret);
3422	return ret;
3423}
3424
3425static int cgroup_type_show(struct seq_file *seq, void *v)
3426{
3427	struct cgroup *cgrp = seq_css(seq)->cgroup;
3428
3429	if (cgroup_is_threaded(cgrp))
3430		seq_puts(seq, "threaded\n");
3431	else if (!cgroup_is_valid_domain(cgrp))
3432		seq_puts(seq, "domain invalid\n");
3433	else if (cgroup_is_thread_root(cgrp))
3434		seq_puts(seq, "domain threaded\n");
3435	else
3436		seq_puts(seq, "domain\n");
3437
3438	return 0;
3439}
3440
3441static ssize_t cgroup_type_write(struct kernfs_open_file *of, char *buf,
3442				 size_t nbytes, loff_t off)
3443{
3444	struct cgroup *cgrp;
3445	int ret;
3446
3447	/* only switching to threaded mode is supported */
3448	if (strcmp(strstrip(buf), "threaded"))
3449		return -EINVAL;
3450
3451	cgrp = cgroup_kn_lock_live(of->kn, false);
3452	if (!cgrp)
3453		return -ENOENT;
3454
3455	/* threaded can only be enabled */
3456	ret = cgroup_enable_threaded(cgrp);
3457
3458	cgroup_kn_unlock(of->kn);
3459	return ret ?: nbytes;
3460}
3461
3462static int cgroup_max_descendants_show(struct seq_file *seq, void *v)
3463{
3464	struct cgroup *cgrp = seq_css(seq)->cgroup;
3465	int descendants = READ_ONCE(cgrp->max_descendants);
3466
3467	if (descendants == INT_MAX)
3468		seq_puts(seq, "max\n");
3469	else
3470		seq_printf(seq, "%d\n", descendants);
3471
3472	return 0;
3473}
3474
3475static ssize_t cgroup_max_descendants_write(struct kernfs_open_file *of,
3476					   char *buf, size_t nbytes, loff_t off)
3477{
3478	struct cgroup *cgrp;
3479	int descendants;
3480	ssize_t ret;
3481
3482	buf = strstrip(buf);
3483	if (!strcmp(buf, "max")) {
3484		descendants = INT_MAX;
3485	} else {
3486		ret = kstrtoint(buf, 0, &descendants);
3487		if (ret)
3488			return ret;
3489	}
3490
3491	if (descendants < 0)
3492		return -ERANGE;
3493
3494	cgrp = cgroup_kn_lock_live(of->kn, false);
3495	if (!cgrp)
3496		return -ENOENT;
3497
3498	cgrp->max_descendants = descendants;
3499
3500	cgroup_kn_unlock(of->kn);
3501
3502	return nbytes;
3503}
3504
3505static int cgroup_max_depth_show(struct seq_file *seq, void *v)
3506{
3507	struct cgroup *cgrp = seq_css(seq)->cgroup;
3508	int depth = READ_ONCE(cgrp->max_depth);
3509
3510	if (depth == INT_MAX)
3511		seq_puts(seq, "max\n");
3512	else
3513		seq_printf(seq, "%d\n", depth);
3514
3515	return 0;
3516}
3517
3518static ssize_t cgroup_max_depth_write(struct kernfs_open_file *of,
3519				      char *buf, size_t nbytes, loff_t off)
3520{
3521	struct cgroup *cgrp;
3522	ssize_t ret;
3523	int depth;
3524
3525	buf = strstrip(buf);
3526	if (!strcmp(buf, "max")) {
3527		depth = INT_MAX;
3528	} else {
3529		ret = kstrtoint(buf, 0, &depth);
3530		if (ret)
3531			return ret;
3532	}
3533
3534	if (depth < 0)
3535		return -ERANGE;
3536
3537	cgrp = cgroup_kn_lock_live(of->kn, false);
3538	if (!cgrp)
3539		return -ENOENT;
3540
3541	cgrp->max_depth = depth;
3542
3543	cgroup_kn_unlock(of->kn);
3544
3545	return nbytes;
3546}
3547
3548static int cgroup_events_show(struct seq_file *seq, void *v)
3549{
3550	struct cgroup *cgrp = seq_css(seq)->cgroup;
3551
3552	seq_printf(seq, "populated %d\n", cgroup_is_populated(cgrp));
3553	seq_printf(seq, "frozen %d\n", test_bit(CGRP_FROZEN, &cgrp->flags));
3554
3555	return 0;
3556}
3557
3558static int cgroup_stat_show(struct seq_file *seq, void *v)
3559{
3560	struct cgroup *cgroup = seq_css(seq)->cgroup;
3561
3562	seq_printf(seq, "nr_descendants %d\n",
3563		   cgroup->nr_descendants);
3564	seq_printf(seq, "nr_dying_descendants %d\n",
3565		   cgroup->nr_dying_descendants);
3566
3567	return 0;
3568}
3569
3570static int __maybe_unused cgroup_extra_stat_show(struct seq_file *seq,
3571						 struct cgroup *cgrp, int ssid)
3572{
3573	struct cgroup_subsys *ss = cgroup_subsys[ssid];
3574	struct cgroup_subsys_state *css;
3575	int ret;
3576
3577	if (!ss->css_extra_stat_show)
3578		return 0;
3579
3580	css = cgroup_tryget_css(cgrp, ss);
3581	if (!css)
3582		return 0;
3583
3584	ret = ss->css_extra_stat_show(seq, css);
3585	css_put(css);
3586	return ret;
3587}
3588
3589static int cpu_stat_show(struct seq_file *seq, void *v)
3590{
3591	struct cgroup __maybe_unused *cgrp = seq_css(seq)->cgroup;
3592	int ret = 0;
3593
3594	cgroup_base_stat_cputime_show(seq);
3595#ifdef CONFIG_CGROUP_SCHED
3596	ret = cgroup_extra_stat_show(seq, cgrp, cpu_cgrp_id);
3597#endif
3598	return ret;
3599}
3600
3601#ifdef CONFIG_PSI
3602static int cgroup_io_pressure_show(struct seq_file *seq, void *v)
3603{
3604	struct cgroup *cgroup = seq_css(seq)->cgroup;
3605	struct psi_group *psi = cgroup->id == 1 ? &psi_system : &cgroup->psi;
3606
3607	return psi_show(seq, psi, PSI_IO);
3608}
3609static int cgroup_memory_pressure_show(struct seq_file *seq, void *v)
3610{
3611	struct cgroup *cgroup = seq_css(seq)->cgroup;
3612	struct psi_group *psi = cgroup->id == 1 ? &psi_system : &cgroup->psi;
3613
3614	return psi_show(seq, psi, PSI_MEM);
3615}
3616static int cgroup_cpu_pressure_show(struct seq_file *seq, void *v)
3617{
3618	struct cgroup *cgroup = seq_css(seq)->cgroup;
3619	struct psi_group *psi = cgroup->id == 1 ? &psi_system : &cgroup->psi;
3620
3621	return psi_show(seq, psi, PSI_CPU);
3622}
3623
3624static ssize_t cgroup_pressure_write(struct kernfs_open_file *of, char *buf,
3625					  size_t nbytes, enum psi_res res)
3626{
3627	struct psi_trigger *new;
3628	struct cgroup *cgrp;
3629
3630	cgrp = cgroup_kn_lock_live(of->kn, false);
3631	if (!cgrp)
3632		return -ENODEV;
3633
3634	cgroup_get(cgrp);
3635	cgroup_kn_unlock(of->kn);
3636
3637	new = psi_trigger_create(&cgrp->psi, buf, nbytes, res);
3638	if (IS_ERR(new)) {
3639		cgroup_put(cgrp);
3640		return PTR_ERR(new);
3641	}
3642
3643	psi_trigger_replace(&of->priv, new);
3644
3645	cgroup_put(cgrp);
3646
3647	return nbytes;
3648}
3649
3650static ssize_t cgroup_io_pressure_write(struct kernfs_open_file *of,
3651					  char *buf, size_t nbytes,
3652					  loff_t off)
3653{
3654	return cgroup_pressure_write(of, buf, nbytes, PSI_IO);
3655}
3656
3657static ssize_t cgroup_memory_pressure_write(struct kernfs_open_file *of,
3658					  char *buf, size_t nbytes,
3659					  loff_t off)
3660{
3661	return cgroup_pressure_write(of, buf, nbytes, PSI_MEM);
3662}
3663
3664static ssize_t cgroup_cpu_pressure_write(struct kernfs_open_file *of,
3665					  char *buf, size_t nbytes,
3666					  loff_t off)
3667{
3668	return cgroup_pressure_write(of, buf, nbytes, PSI_CPU);
3669}
3670
3671static __poll_t cgroup_pressure_poll(struct kernfs_open_file *of,
3672					  poll_table *pt)
3673{
3674	return psi_trigger_poll(&of->priv, of->file, pt);
3675}
3676
3677static void cgroup_pressure_release(struct kernfs_open_file *of)
3678{
3679	psi_trigger_replace(&of->priv, NULL);
3680}
3681#endif /* CONFIG_PSI */
3682
3683static int cgroup_freeze_show(struct seq_file *seq, void *v)
3684{
3685	struct cgroup *cgrp = seq_css(seq)->cgroup;
3686
3687	seq_printf(seq, "%d\n", cgrp->freezer.freeze);
3688
3689	return 0;
3690}
3691
3692static ssize_t cgroup_freeze_write(struct kernfs_open_file *of,
3693				   char *buf, size_t nbytes, loff_t off)
3694{
3695	struct cgroup *cgrp;
3696	ssize_t ret;
3697	int freeze;
3698
3699	ret = kstrtoint(strstrip(buf), 0, &freeze);
3700	if (ret)
3701		return ret;
3702
3703	if (freeze < 0 || freeze > 1)
3704		return -ERANGE;
3705
3706	cgrp = cgroup_kn_lock_live(of->kn, false);
3707	if (!cgrp)
3708		return -ENOENT;
3709
3710	cgroup_freeze(cgrp, freeze);
3711
3712	cgroup_kn_unlock(of->kn);
3713
3714	return nbytes;
3715}
3716
3717static int cgroup_file_open(struct kernfs_open_file *of)
3718{
3719	struct cftype *cft = of->kn->priv;
3720
3721	if (cft->open)
3722		return cft->open(of);
3723	return 0;
3724}
3725
3726static void cgroup_file_release(struct kernfs_open_file *of)
3727{
3728	struct cftype *cft = of->kn->priv;
3729
3730	if (cft->release)
3731		cft->release(of);
3732}
3733
3734static ssize_t cgroup_file_write(struct kernfs_open_file *of, char *buf,
3735				 size_t nbytes, loff_t off)
3736{
3737	struct cgroup_namespace *ns = current->nsproxy->cgroup_ns;
3738	struct cgroup *cgrp = of->kn->parent->priv;
3739	struct cftype *cft = of->kn->priv;
3740	struct cgroup_subsys_state *css;
3741	int ret;
3742
3743	/*
3744	 * If namespaces are delegation boundaries, disallow writes to
3745	 * files in an non-init namespace root from inside the namespace
3746	 * except for the files explicitly marked delegatable -
3747	 * cgroup.procs and cgroup.subtree_control.
3748	 */
3749	if ((cgrp->root->flags & CGRP_ROOT_NS_DELEGATE) &&
3750	    !(cft->flags & CFTYPE_NS_DELEGATABLE) &&
3751	    ns != &init_cgroup_ns && ns->root_cset->dfl_cgrp == cgrp)
3752		return -EPERM;
3753
3754	if (cft->write)
3755		return cft->write(of, buf, nbytes, off);
3756
3757	/*
3758	 * kernfs guarantees that a file isn't deleted with operations in
3759	 * flight, which means that the matching css is and stays alive and
3760	 * doesn't need to be pinned.  The RCU locking is not necessary
3761	 * either.  It's just for the convenience of using cgroup_css().
3762	 */
3763	rcu_read_lock();
3764	css = cgroup_css(cgrp, cft->ss);
3765	rcu_read_unlock();
3766
3767	if (cft->write_u64) {
3768		unsigned long long v;
3769		ret = kstrtoull(buf, 0, &v);
3770		if (!ret)
3771			ret = cft->write_u64(css, cft, v);
3772	} else if (cft->write_s64) {
3773		long long v;
3774		ret = kstrtoll(buf, 0, &v);
3775		if (!ret)
3776			ret = cft->write_s64(css, cft, v);
3777	} else {
3778		ret = -EINVAL;
3779	}
3780
3781	return ret ?: nbytes;
3782}
3783
3784static __poll_t cgroup_file_poll(struct kernfs_open_file *of, poll_table *pt)
3785{
3786	struct cftype *cft = of->kn->priv;
3787
3788	if (cft->poll)
3789		return cft->poll(of, pt);
3790
3791	return kernfs_generic_poll(of, pt);
3792}
3793
3794static void *cgroup_seqfile_start(struct seq_file *seq, loff_t *ppos)
3795{
3796	return seq_cft(seq)->seq_start(seq, ppos);
3797}
3798
3799static void *cgroup_seqfile_next(struct seq_file *seq, void *v, loff_t *ppos)
3800{
3801	return seq_cft(seq)->seq_next(seq, v, ppos);
3802}
3803
3804static void cgroup_seqfile_stop(struct seq_file *seq, void *v)
3805{
3806	if (seq_cft(seq)->seq_stop)
3807		seq_cft(seq)->seq_stop(seq, v);
3808}
3809
3810static int cgroup_seqfile_show(struct seq_file *m, void *arg)
3811{
3812	struct cftype *cft = seq_cft(m);
3813	struct cgroup_subsys_state *css = seq_css(m);
3814
3815	if (cft->seq_show)
3816		return cft->seq_show(m, arg);
3817
3818	if (cft->read_u64)
3819		seq_printf(m, "%llu\n", cft->read_u64(css, cft));
3820	else if (cft->read_s64)
3821		seq_printf(m, "%lld\n", cft->read_s64(css, cft));
3822	else
3823		return -EINVAL;
3824	return 0;
3825}
3826
3827static struct kernfs_ops cgroup_kf_single_ops = {
3828	.atomic_write_len	= PAGE_SIZE,
3829	.open			= cgroup_file_open,
3830	.release		= cgroup_file_release,
3831	.write			= cgroup_file_write,
3832	.poll			= cgroup_file_poll,
3833	.seq_show		= cgroup_seqfile_show,
3834};
3835
3836static struct kernfs_ops cgroup_kf_ops = {
3837	.atomic_write_len	= PAGE_SIZE,
3838	.open			= cgroup_file_open,
3839	.release		= cgroup_file_release,
3840	.write			= cgroup_file_write,
3841	.poll			= cgroup_file_poll,
3842	.seq_start		= cgroup_seqfile_start,
3843	.seq_next		= cgroup_seqfile_next,
3844	.seq_stop		= cgroup_seqfile_stop,
3845	.seq_show		= cgroup_seqfile_show,
3846};
3847
3848/* set uid and gid of cgroup dirs and files to that of the creator */
3849static int cgroup_kn_set_ugid(struct kernfs_node *kn)
3850{
3851	struct iattr iattr = { .ia_valid = ATTR_UID | ATTR_GID,
3852			       .ia_uid = current_fsuid(),
3853			       .ia_gid = current_fsgid(), };
3854
3855	if (uid_eq(iattr.ia_uid, GLOBAL_ROOT_UID) &&
3856	    gid_eq(iattr.ia_gid, GLOBAL_ROOT_GID))
3857		return 0;
3858
3859	return kernfs_setattr(kn, &iattr);
3860}
3861
3862static void cgroup_file_notify_timer(struct timer_list *timer)
3863{
3864	cgroup_file_notify(container_of(timer, struct cgroup_file,
3865					notify_timer));
3866}
3867
3868static int cgroup_add_file(struct cgroup_subsys_state *css, struct cgroup *cgrp,
3869			   struct cftype *cft)
3870{
3871	char name[CGROUP_FILE_NAME_MAX];
3872	struct kernfs_node *kn;
3873	struct lock_class_key *key = NULL;
3874	int ret;
3875
3876#ifdef CONFIG_DEBUG_LOCK_ALLOC
3877	key = &cft->lockdep_key;
3878#endif
3879	kn = __kernfs_create_file(cgrp->kn, cgroup_file_name(cgrp, cft, name),
3880				  cgroup_file_mode(cft),
3881				  GLOBAL_ROOT_UID, GLOBAL_ROOT_GID,
3882				  0, cft->kf_ops, cft,
3883				  NULL, key);
3884	if (IS_ERR(kn))
3885		return PTR_ERR(kn);
3886
3887	ret = cgroup_kn_set_ugid(kn);
3888	if (ret) {
3889		kernfs_remove(kn);
3890		return ret;
3891	}
3892
3893	if (cft->file_offset) {
3894		struct cgroup_file *cfile = (void *)css + cft->file_offset;
3895
3896		timer_setup(&cfile->notify_timer, cgroup_file_notify_timer, 0);
3897
3898		spin_lock_irq(&cgroup_file_kn_lock);
3899		cfile->kn = kn;
3900		spin_unlock_irq(&cgroup_file_kn_lock);
3901	}
3902
3903	return 0;
3904}
3905
3906/**
3907 * cgroup_addrm_files - add or remove files to a cgroup directory
3908 * @css: the target css
3909 * @cgrp: the target cgroup (usually css->cgroup)
3910 * @cfts: array of cftypes to be added
3911 * @is_add: whether to add or remove
3912 *
3913 * Depending on @is_add, add or remove files defined by @cfts on @cgrp.
3914 * For removals, this function never fails.
3915 */
3916static int cgroup_addrm_files(struct cgroup_subsys_state *css,
3917			      struct cgroup *cgrp, struct cftype cfts[],
3918			      bool is_add)
3919{
3920	struct cftype *cft, *cft_end = NULL;
3921	int ret = 0;
3922
3923	lockdep_assert_held(&cgroup_mutex);
3924
3925restart:
3926	for (cft = cfts; cft != cft_end && cft->name[0] != '\0'; cft++) {
3927		/* does cft->flags tell us to skip this file on @cgrp? */
3928		if ((cft->flags & __CFTYPE_ONLY_ON_DFL) && !cgroup_on_dfl(cgrp))
3929			continue;
3930		if ((cft->flags & __CFTYPE_NOT_ON_DFL) && cgroup_on_dfl(cgrp))
3931			continue;
3932		if ((cft->flags & CFTYPE_NOT_ON_ROOT) && !cgroup_parent(cgrp))
3933			continue;
3934		if ((cft->flags & CFTYPE_ONLY_ON_ROOT) && cgroup_parent(cgrp))
3935			continue;
3936		if ((cft->flags & CFTYPE_DEBUG) && !cgroup_debug)
3937			continue;
3938		if (is_add) {
3939			ret = cgroup_add_file(css, cgrp, cft);
3940			if (ret) {
3941				pr_warn("%s: failed to add %s, err=%d\n",
3942					__func__, cft->name, ret);
3943				cft_end = cft;
3944				is_add = false;
3945				goto restart;
3946			}
3947		} else {
3948			cgroup_rm_file(cgrp, cft);
3949		}
3950	}
3951	return ret;
3952}
3953
3954static int cgroup_apply_cftypes(struct cftype *cfts, bool is_add)
3955{
3956	struct cgroup_subsys *ss = cfts[0].ss;
3957	struct cgroup *root = &ss->root->cgrp;
3958	struct cgroup_subsys_state *css;
3959	int ret = 0;
3960
3961	lockdep_assert_held(&cgroup_mutex);
3962
3963	/* add/rm files for all cgroups created before */
3964	css_for_each_descendant_pre(css, cgroup_css(root, ss)) {
3965		struct cgroup *cgrp = css->cgroup;
3966
3967		if (!(css->flags & CSS_VISIBLE))
3968			continue;
3969
3970		ret = cgroup_addrm_files(css, cgrp, cfts, is_add);
3971		if (ret)
3972			break;
3973	}
3974
3975	if (is_add && !ret)
3976		kernfs_activate(root->kn);
3977	return ret;
3978}
3979
3980static void cgroup_exit_cftypes(struct cftype *cfts)
3981{
3982	struct cftype *cft;
3983
3984	for (cft = cfts; cft->name[0] != '\0'; cft++) {
3985		/* free copy for custom atomic_write_len, see init_cftypes() */
3986		if (cft->max_write_len && cft->max_write_len != PAGE_SIZE)
3987			kfree(cft->kf_ops);
3988		cft->kf_ops = NULL;
3989		cft->ss = NULL;
3990
3991		/* revert flags set by cgroup core while adding @cfts */
3992		cft->flags &= ~(__CFTYPE_ONLY_ON_DFL | __CFTYPE_NOT_ON_DFL);
3993	}
3994}
3995
3996static int cgroup_init_cftypes(struct cgroup_subsys *ss, struct cftype *cfts)
3997{
3998	struct cftype *cft;
3999
4000	for (cft = cfts; cft->name[0] != '\0'; cft++) {
4001		struct kernfs_ops *kf_ops;
4002
4003		WARN_ON(cft->ss || cft->kf_ops);
4004
4005		if (cft->seq_start)
4006			kf_ops = &cgroup_kf_ops;
4007		else
4008			kf_ops = &cgroup_kf_single_ops;
4009
4010		/*
4011		 * Ugh... if @cft wants a custom max_write_len, we need to
4012		 * make a copy of kf_ops to set its atomic_write_len.
4013		 */
4014		if (cft->max_write_len && cft->max_write_len != PAGE_SIZE) {
4015			kf_ops = kmemdup(kf_ops, sizeof(*kf_ops), GFP_KERNEL);
4016			if (!kf_ops) {
4017				cgroup_exit_cftypes(cfts);
4018				return -ENOMEM;
4019			}
4020			kf_ops->atomic_write_len = cft->max_write_len;
4021		}
4022
4023		cft->kf_ops = kf_ops;
4024		cft->ss = ss;
4025	}
4026
4027	return 0;
4028}
4029
4030static int cgroup_rm_cftypes_locked(struct cftype *cfts)
4031{
4032	lockdep_assert_held(&cgroup_mutex);
4033
4034	if (!cfts || !cfts[0].ss)
4035		return -ENOENT;
4036
4037	list_del(&cfts->node);
4038	cgroup_apply_cftypes(cfts, false);
4039	cgroup_exit_cftypes(cfts);
4040	return 0;
4041}
4042
4043/**
4044 * cgroup_rm_cftypes - remove an array of cftypes from a subsystem
4045 * @cfts: zero-length name terminated array of cftypes
4046 *
4047 * Unregister @cfts.  Files described by @cfts are removed from all
4048 * existing cgroups and all future cgroups won't have them either.  This
4049 * function can be called anytime whether @cfts' subsys is attached or not.
4050 *
4051 * Returns 0 on successful unregistration, -ENOENT if @cfts is not
4052 * registered.
4053 */
4054int cgroup_rm_cftypes(struct cftype *cfts)
4055{
4056	int ret;
4057
4058	mutex_lock(&cgroup_mutex);
4059	ret = cgroup_rm_cftypes_locked(cfts);
4060	mutex_unlock(&cgroup_mutex);
4061	return ret;
4062}
4063
4064/**
4065 * cgroup_add_cftypes - add an array of cftypes to a subsystem
4066 * @ss: target cgroup subsystem
4067 * @cfts: zero-length name terminated array of cftypes
4068 *
4069 * Register @cfts to @ss.  Files described by @cfts are created for all
4070 * existing cgroups to which @ss is attached and all future cgroups will
4071 * have them too.  This function can be called anytime whether @ss is
4072 * attached or not.
4073 *
4074 * Returns 0 on successful registration, -errno on failure.  Note that this
4075 * function currently returns 0 as long as @cfts registration is successful
4076 * even if some file creation attempts on existing cgroups fail.
4077 */
4078static int cgroup_add_cftypes(struct cgroup_subsys *ss, struct cftype *cfts)
4079{
4080	int ret;
4081
4082	if (!cgroup_ssid_enabled(ss->id))
4083		return 0;
4084
4085	if (!cfts || cfts[0].name[0] == '\0')
4086		return 0;
4087
4088	ret = cgroup_init_cftypes(ss, cfts);
4089	if (ret)
4090		return ret;
4091
4092	mutex_lock(&cgroup_mutex);
4093
4094	list_add_tail(&cfts->node, &ss->cfts);
4095	ret = cgroup_apply_cftypes(cfts, true);
4096	if (ret)
4097		cgroup_rm_cftypes_locked(cfts);
4098
4099	mutex_unlock(&cgroup_mutex);
4100	return ret;
4101}
4102
4103/**
4104 * cgroup_add_dfl_cftypes - add an array of cftypes for default hierarchy
4105 * @ss: target cgroup subsystem
4106 * @cfts: zero-length name terminated array of cftypes
4107 *
4108 * Similar to cgroup_add_cftypes() but the added files are only used for
4109 * the default hierarchy.
4110 */
4111int cgroup_add_dfl_cftypes(struct cgroup_subsys *ss, struct cftype *cfts)
4112{
4113	struct cftype *cft;
4114
4115	for (cft = cfts; cft && cft->name[0] != '\0'; cft++)
4116		cft->flags |= __CFTYPE_ONLY_ON_DFL;
4117	return cgroup_add_cftypes(ss, cfts);
4118}
4119
4120/**
4121 * cgroup_add_legacy_cftypes - add an array of cftypes for legacy hierarchies
4122 * @ss: target cgroup subsystem
4123 * @cfts: zero-length name terminated array of cftypes
4124 *
4125 * Similar to cgroup_add_cftypes() but the added files are only used for
4126 * the legacy hierarchies.
4127 */
4128int cgroup_add_legacy_cftypes(struct cgroup_subsys *ss, struct cftype *cfts)
4129{
4130	struct cftype *cft;
4131
4132	for (cft = cfts; cft && cft->name[0] != '\0'; cft++)
4133		cft->flags |= __CFTYPE_NOT_ON_DFL;
4134	return cgroup_add_cftypes(ss, cfts);
4135}
4136
4137/**
4138 * cgroup_file_notify - generate a file modified event for a cgroup_file
4139 * @cfile: target cgroup_file
4140 *
4141 * @cfile must have been obtained by setting cftype->file_offset.
4142 */
4143void cgroup_file_notify(struct cgroup_file *cfile)
4144{
4145	unsigned long flags;
4146
4147	spin_lock_irqsave(&cgroup_file_kn_lock, flags);
4148	if (cfile->kn) {
4149		unsigned long last = cfile->notified_at;
4150		unsigned long next = last + CGROUP_FILE_NOTIFY_MIN_INTV;
4151
4152		if (time_in_range(jiffies, last, next)) {
4153			timer_reduce(&cfile->notify_timer, next);
4154		} else {
4155			kernfs_notify(cfile->kn);
4156			cfile->notified_at = jiffies;
4157		}
4158	}
4159	spin_unlock_irqrestore(&cgroup_file_kn_lock, flags);
4160}
4161
4162/**
4163 * css_next_child - find the next child of a given css
4164 * @pos: the current position (%NULL to initiate traversal)
4165 * @parent: css whose children to walk
4166 *
4167 * This function returns the next child of @parent and should be called
4168 * under either cgroup_mutex or RCU read lock.  The only requirement is
4169 * that @parent and @pos are accessible.  The next sibling is guaranteed to
4170 * be returned regardless of their states.
4171 *
4172 * If a subsystem synchronizes ->css_online() and the start of iteration, a
4173 * css which finished ->css_online() is guaranteed to be visible in the
4174 * future iterations and will stay visible until the last reference is put.
4175 * A css which hasn't finished ->css_online() or already finished
4176 * ->css_offline() may show up during traversal.  It's each subsystem's
4177 * responsibility to synchronize against on/offlining.
4178 */
4179struct cgroup_subsys_state *css_next_child(struct cgroup_subsys_state *pos,
4180					   struct cgroup_subsys_state *parent)
4181{
4182	struct cgroup_subsys_state *next;
4183
4184	cgroup_assert_mutex_or_rcu_locked();
4185
4186	/*
4187	 * @pos could already have been unlinked from the sibling list.
4188	 * Once a cgroup is removed, its ->sibling.next is no longer
4189	 * updated when its next sibling changes.  CSS_RELEASED is set when
4190	 * @pos is taken off list, at which time its next pointer is valid,
4191	 * and, as releases are serialized, the one pointed to by the next
4192	 * pointer is guaranteed to not have started release yet.  This
4193	 * implies that if we observe !CSS_RELEASED on @pos in this RCU
4194	 * critical section, the one pointed to by its next pointer is
4195	 * guaranteed to not have finished its RCU grace period even if we
4196	 * have dropped rcu_read_lock() inbetween iterations.
4197	 *
4198	 * If @pos has CSS_RELEASED set, its next pointer can't be
4199	 * dereferenced; however, as each css is given a monotonically
4200	 * increasing unique serial number and always appended to the
4201	 * sibling list, the next one can be found by walking the parent's
4202	 * children until the first css with higher serial number than
4203	 * @pos's.  While this path can be slower, it happens iff iteration
4204	 * races against release and the race window is very small.
4205	 */
4206	if (!pos) {
4207		next = list_entry_rcu(parent->children.next, struct cgroup_subsys_state, sibling);
4208	} else if (likely(!(pos->flags & CSS_RELEASED))) {
4209		next = list_entry_rcu(pos->sibling.next, struct cgroup_subsys_state, sibling);
4210	} else {
4211		list_for_each_entry_rcu(next, &parent->children, sibling)
4212			if (next->serial_nr > pos->serial_nr)
4213				break;
4214	}
4215
4216	/*
4217	 * @next, if not pointing to the head, can be dereferenced and is
4218	 * the next sibling.
4219	 */
4220	if (&next->sibling != &parent->children)
4221		return next;
4222	return NULL;
4223}
4224
4225/**
4226 * css_next_descendant_pre - find the next descendant for pre-order walk
4227 * @pos: the current position (%NULL to initiate traversal)
4228 * @root: css whose descendants to walk
4229 *
4230 * To be used by css_for_each_descendant_pre().  Find the next descendant
4231 * to visit for pre-order traversal of @root's descendants.  @root is
4232 * included in the iteration and the first node to be visited.
4233 *
4234 * While this function requires cgroup_mutex or RCU read locking, it
4235 * doesn't require the whole traversal to be contained in a single critical
4236 * section.  This function will return the correct next descendant as long
4237 * as both @pos and @root are accessible and @pos is a descendant of @root.
4238 *
4239 * If a subsystem synchronizes ->css_online() and the start of iteration, a
4240 * css which finished ->css_online() is guaranteed to be visible in the
4241 * future iterations and will stay visible until the last reference is put.
4242 * A css which hasn't finished ->css_online() or already finished
4243 * ->css_offline() may show up during traversal.  It's each subsystem's
4244 * responsibility to synchronize against on/offlining.
4245 */
4246struct cgroup_subsys_state *
4247css_next_descendant_pre(struct cgroup_subsys_state *pos,
4248			struct cgroup_subsys_state *root)
4249{
4250	struct cgroup_subsys_state *next;
4251
4252	cgroup_assert_mutex_or_rcu_locked();
4253
4254	/* if first iteration, visit @root */
4255	if (!pos)
4256		return root;
4257
4258	/* visit the first child if exists */
4259	next = css_next_child(NULL, pos);
4260	if (next)
4261		return next;
4262
4263	/* no child, visit my or the closest ancestor's next sibling */
4264	while (pos != root) {
4265		next = css_next_child(pos, pos->parent);
4266		if (next)
4267			return next;
4268		pos = pos->parent;
4269	}
4270
4271	return NULL;
4272}
4273EXPORT_SYMBOL_GPL(css_next_descendant_pre);
4274
4275/**
4276 * css_rightmost_descendant - return the rightmost descendant of a css
4277 * @pos: css of interest
4278 *
4279 * Return the rightmost descendant of @pos.  If there's no descendant, @pos
4280 * is returned.  This can be used during pre-order traversal to skip
4281 * subtree of @pos.
4282 *
4283 * While this function requires cgroup_mutex or RCU read locking, it
4284 * doesn't require the whole traversal to be contained in a single critical
4285 * section.  This function will return the correct rightmost descendant as
4286 * long as @pos is accessible.
4287 */
4288struct cgroup_subsys_state *
4289css_rightmost_descendant(struct cgroup_subsys_state *pos)
4290{
4291	struct cgroup_subsys_state *last, *tmp;
4292
4293	cgroup_assert_mutex_or_rcu_locked();
4294
4295	do {
4296		last = pos;
4297		/* ->prev isn't RCU safe, walk ->next till the end */
4298		pos = NULL;
4299		css_for_each_child(tmp, last)
4300			pos = tmp;
4301	} while (pos);
4302
4303	return last;
4304}
4305
4306static struct cgroup_subsys_state *
4307css_leftmost_descendant(struct cgroup_subsys_state *pos)
4308{
4309	struct cgroup_subsys_state *last;
4310
4311	do {
4312		last = pos;
4313		pos = css_next_child(NULL, pos);
4314	} while (pos);
4315
4316	return last;
4317}
4318
4319/**
4320 * css_next_descendant_post - find the next descendant for post-order walk
4321 * @pos: the current position (%NULL to initiate traversal)
4322 * @root: css whose descendants to walk
4323 *
4324 * To be used by css_for_each_descendant_post().  Find the next descendant
4325 * to visit for post-order traversal of @root's descendants.  @root is
4326 * included in the iteration and the last node to be visited.
4327 *
4328 * While this function requires cgroup_mutex or RCU read locking, it
4329 * doesn't require the whole traversal to be contained in a single critical
4330 * section.  This function will return the correct next descendant as long
4331 * as both @pos and @cgroup are accessible and @pos is a descendant of
4332 * @cgroup.
4333 *
4334 * If a subsystem synchronizes ->css_online() and the start of iteration, a
4335 * css which finished ->css_online() is guaranteed to be visible in the
4336 * future iterations and will stay visible until the last reference is put.
4337 * A css which hasn't finished ->css_online() or already finished
4338 * ->css_offline() may show up during traversal.  It's each subsystem's
4339 * responsibility to synchronize against on/offlining.
4340 */
4341struct cgroup_subsys_state *
4342css_next_descendant_post(struct cgroup_subsys_state *pos,
4343			 struct cgroup_subsys_state *root)
4344{
4345	struct cgroup_subsys_state *next;
4346
4347	cgroup_assert_mutex_or_rcu_locked();
4348
4349	/* if first iteration, visit leftmost descendant which may be @root */
4350	if (!pos)
4351		return css_leftmost_descendant(root);
4352
4353	/* if we visited @root, we're done */
4354	if (pos == root)
4355		return NULL;
4356
4357	/* if there's an unvisited sibling, visit its leftmost descendant */
4358	next = css_next_child(pos, pos->parent);
4359	if (next)
4360		return css_leftmost_descendant(next);
4361
4362	/* no sibling left, visit parent */
4363	return pos->parent;
4364}
4365
4366/**
4367 * css_has_online_children - does a css have online children
4368 * @css: the target css
4369 *
4370 * Returns %true if @css has any online children; otherwise, %false.  This
4371 * function can be called from any context but the caller is responsible
4372 * for synchronizing against on/offlining as necessary.
4373 */
4374bool css_has_online_children(struct cgroup_subsys_state *css)
4375{
4376	struct cgroup_subsys_state *child;
4377	bool ret = false;
4378
4379	rcu_read_lock();
4380	css_for_each_child(child, css) {
4381		if (child->flags & CSS_ONLINE) {
4382			ret = true;
4383			break;
4384		}
4385	}
4386	rcu_read_unlock();
4387	return ret;
4388}
4389
4390static struct css_set *css_task_iter_next_css_set(struct css_task_iter *it)
4391{
4392	struct list_head *l;
4393	struct cgrp_cset_link *link;
4394	struct css_set *cset;
4395
4396	lockdep_assert_held(&css_set_lock);
4397
4398	/* find the next threaded cset */
4399	if (it->tcset_pos) {
4400		l = it->tcset_pos->next;
4401
4402		if (l != it->tcset_head) {
4403			it->tcset_pos = l;
4404			return container_of(l, struct css_set,
4405					    threaded_csets_node);
4406		}
4407
4408		it->tcset_pos = NULL;
4409	}
4410
4411	/* find the next cset */
4412	l = it->cset_pos;
4413	l = l->next;
4414	if (l == it->cset_head) {
4415		it->cset_pos = NULL;
4416		return NULL;
4417	}
4418
4419	if (it->ss) {
4420		cset = container_of(l, struct css_set, e_cset_node[it->ss->id]);
4421	} else {
4422		link = list_entry(l, struct cgrp_cset_link, cset_link);
4423		cset = link->cset;
4424	}
4425
4426	it->cset_pos = l;
4427
4428	/* initialize threaded css_set walking */
4429	if (it->flags & CSS_TASK_ITER_THREADED) {
4430		if (it->cur_dcset)
4431			put_css_set_locked(it->cur_dcset);
4432		it->cur_dcset = cset;
4433		get_css_set(cset);
4434
4435		it->tcset_head = &cset->threaded_csets;
4436		it->tcset_pos = &cset->threaded_csets;
4437	}
4438
4439	return cset;
4440}
4441
4442/**
4443 * css_task_iter_advance_css_set - advance a task itererator to the next css_set
4444 * @it: the iterator to advance
4445 *
4446 * Advance @it to the next css_set to walk.
4447 */
4448static void css_task_iter_advance_css_set(struct css_task_iter *it)
4449{
4450	struct css_set *cset;
4451
4452	lockdep_assert_held(&css_set_lock);
4453
4454	/* Advance to the next non-empty css_set */
4455	do {
4456		cset = css_task_iter_next_css_set(it);
4457		if (!cset) {
4458			it->task_pos = NULL;
4459			return;
4460		}
4461	} while (!css_set_populated(cset) && list_empty(&cset->dying_tasks));
4462
4463	if (!list_empty(&cset->tasks))
4464		it->task_pos = cset->tasks.next;
4465	else if (!list_empty(&cset->mg_tasks))
4466		it->task_pos = cset->mg_tasks.next;
4467	else
4468		it->task_pos = cset->dying_tasks.next;
4469
4470	it->tasks_head = &cset->tasks;
4471	it->mg_tasks_head = &cset->mg_tasks;
4472	it->dying_tasks_head = &cset->dying_tasks;
4473
4474	/*
4475	 * We don't keep css_sets locked across iteration steps and thus
4476	 * need to take steps to ensure that iteration can be resumed after
4477	 * the lock is re-acquired.  Iteration is performed at two levels -
4478	 * css_sets and tasks in them.
4479	 *
4480	 * Once created, a css_set never leaves its cgroup lists, so a
4481	 * pinned css_set is guaranteed to stay put and we can resume
4482	 * iteration afterwards.
4483	 *
4484	 * Tasks may leave @cset across iteration steps.  This is resolved
4485	 * by registering each iterator with the css_set currently being
4486	 * walked and making css_set_move_task() advance iterators whose
4487	 * next task is leaving.
4488	 */
4489	if (it->cur_cset) {
4490		list_del(&it->iters_node);
4491		put_css_set_locked(it->cur_cset);
4492	}
4493	get_css_set(cset);
4494	it->cur_cset = cset;
4495	list_add(&it->iters_node, &cset->task_iters);
4496}
4497
4498static void css_task_iter_skip(struct css_task_iter *it,
4499			       struct task_struct *task)
4500{
4501	lockdep_assert_held(&css_set_lock);
4502
4503	if (it->task_pos == &task->cg_list) {
4504		it->task_pos = it->task_pos->next;
4505		it->flags |= CSS_TASK_ITER_SKIPPED;
4506	}
4507}
4508
4509static void css_task_iter_advance(struct css_task_iter *it)
4510{
4511	struct task_struct *task;
4512
4513	lockdep_assert_held(&css_set_lock);
4514repeat:
4515	if (it->task_pos) {
4516		/*
4517		 * Advance iterator to find next entry.  cset->tasks is
4518		 * consumed first and then ->mg_tasks.  After ->mg_tasks,
4519		 * we move onto the next cset.
4520		 */
4521		if (it->flags & CSS_TASK_ITER_SKIPPED)
4522			it->flags &= ~CSS_TASK_ITER_SKIPPED;
4523		else
4524			it->task_pos = it->task_pos->next;
4525
4526		if (it->task_pos == it->tasks_head)
4527			it->task_pos = it->mg_tasks_head->next;
4528		if (it->task_pos == it->mg_tasks_head)
4529			it->task_pos = it->dying_tasks_head->next;
4530		if (it->task_pos == it->dying_tasks_head)
4531			css_task_iter_advance_css_set(it);
4532	} else {
4533		/* called from start, proceed to the first cset */
4534		css_task_iter_advance_css_set(it);
4535	}
4536
4537	if (!it->task_pos)
4538		return;
4539
4540	task = list_entry(it->task_pos, struct task_struct, cg_list);
 
 
 
4541
4542	if (it->flags & CSS_TASK_ITER_PROCS) {
4543		/* if PROCS, skip over tasks which aren't group leaders */
4544		if (!thread_group_leader(task))
4545			goto repeat;
4546
4547		/* and dying leaders w/o live member threads */
4548		if (!atomic_read(&task->signal->live))
4549			goto repeat;
4550	} else {
4551		/* skip all dying ones */
4552		if (task->flags & PF_EXITING)
4553			goto repeat;
4554	}
4555}
4556
4557/**
4558 * css_task_iter_start - initiate task iteration
4559 * @css: the css to walk tasks of
4560 * @flags: CSS_TASK_ITER_* flags
4561 * @it: the task iterator to use
4562 *
4563 * Initiate iteration through the tasks of @css.  The caller can call
4564 * css_task_iter_next() to walk through the tasks until the function
4565 * returns NULL.  On completion of iteration, css_task_iter_end() must be
4566 * called.
4567 */
4568void css_task_iter_start(struct cgroup_subsys_state *css, unsigned int flags,
4569			 struct css_task_iter *it)
4570{
4571	/* no one should try to iterate before mounting cgroups */
4572	WARN_ON_ONCE(!use_task_css_set_links);
4573
4574	memset(it, 0, sizeof(*it));
4575
4576	spin_lock_irq(&css_set_lock);
4577
4578	it->ss = css->ss;
4579	it->flags = flags;
4580
4581	if (it->ss)
4582		it->cset_pos = &css->cgroup->e_csets[css->ss->id];
4583	else
4584		it->cset_pos = &css->cgroup->cset_links;
4585
4586	it->cset_head = it->cset_pos;
4587
4588	css_task_iter_advance(it);
4589
4590	spin_unlock_irq(&css_set_lock);
4591}
4592
4593/**
4594 * css_task_iter_next - return the next task for the iterator
4595 * @it: the task iterator being iterated
4596 *
4597 * The "next" function for task iteration.  @it should have been
4598 * initialized via css_task_iter_start().  Returns NULL when the iteration
4599 * reaches the end.
4600 */
4601struct task_struct *css_task_iter_next(struct css_task_iter *it)
4602{
4603	if (it->cur_task) {
4604		put_task_struct(it->cur_task);
4605		it->cur_task = NULL;
4606	}
4607
4608	spin_lock_irq(&css_set_lock);
4609
4610	/* @it may be half-advanced by skips, finish advancing */
4611	if (it->flags & CSS_TASK_ITER_SKIPPED)
4612		css_task_iter_advance(it);
4613
4614	if (it->task_pos) {
4615		it->cur_task = list_entry(it->task_pos, struct task_struct,
4616					  cg_list);
4617		get_task_struct(it->cur_task);
4618		css_task_iter_advance(it);
4619	}
4620
4621	spin_unlock_irq(&css_set_lock);
4622
4623	return it->cur_task;
4624}
4625
4626/**
4627 * css_task_iter_end - finish task iteration
4628 * @it: the task iterator to finish
4629 *
4630 * Finish task iteration started by css_task_iter_start().
4631 */
4632void css_task_iter_end(struct css_task_iter *it)
4633{
4634	if (it->cur_cset) {
4635		spin_lock_irq(&css_set_lock);
4636		list_del(&it->iters_node);
4637		put_css_set_locked(it->cur_cset);
4638		spin_unlock_irq(&css_set_lock);
4639	}
4640
4641	if (it->cur_dcset)
4642		put_css_set(it->cur_dcset);
4643
4644	if (it->cur_task)
4645		put_task_struct(it->cur_task);
4646}
4647
4648static void cgroup_procs_release(struct kernfs_open_file *of)
4649{
4650	if (of->priv) {
4651		css_task_iter_end(of->priv);
4652		kfree(of->priv);
4653	}
4654}
4655
4656static void *cgroup_procs_next(struct seq_file *s, void *v, loff_t *pos)
4657{
4658	struct kernfs_open_file *of = s->private;
4659	struct css_task_iter *it = of->priv;
4660
4661	return css_task_iter_next(it);
4662}
4663
4664static void *__cgroup_procs_start(struct seq_file *s, loff_t *pos,
4665				  unsigned int iter_flags)
4666{
4667	struct kernfs_open_file *of = s->private;
4668	struct cgroup *cgrp = seq_css(s)->cgroup;
4669	struct css_task_iter *it = of->priv;
4670
4671	/*
4672	 * When a seq_file is seeked, it's always traversed sequentially
4673	 * from position 0, so we can simply keep iterating on !0 *pos.
4674	 */
4675	if (!it) {
4676		if (WARN_ON_ONCE((*pos)++))
4677			return ERR_PTR(-EINVAL);
4678
4679		it = kzalloc(sizeof(*it), GFP_KERNEL);
4680		if (!it)
4681			return ERR_PTR(-ENOMEM);
4682		of->priv = it;
4683		css_task_iter_start(&cgrp->self, iter_flags, it);
4684	} else if (!(*pos)++) {
4685		css_task_iter_end(it);
4686		css_task_iter_start(&cgrp->self, iter_flags, it);
4687	}
4688
4689	return cgroup_procs_next(s, NULL, NULL);
4690}
4691
4692static void *cgroup_procs_start(struct seq_file *s, loff_t *pos)
4693{
4694	struct cgroup *cgrp = seq_css(s)->cgroup;
4695
4696	/*
4697	 * All processes of a threaded subtree belong to the domain cgroup
4698	 * of the subtree.  Only threads can be distributed across the
4699	 * subtree.  Reject reads on cgroup.procs in the subtree proper.
4700	 * They're always empty anyway.
4701	 */
4702	if (cgroup_is_threaded(cgrp))
4703		return ERR_PTR(-EOPNOTSUPP);
4704
4705	return __cgroup_procs_start(s, pos, CSS_TASK_ITER_PROCS |
4706					    CSS_TASK_ITER_THREADED);
4707}
4708
4709static int cgroup_procs_show(struct seq_file *s, void *v)
4710{
4711	seq_printf(s, "%d\n", task_pid_vnr(v));
4712	return 0;
4713}
4714
4715static int cgroup_procs_write_permission(struct cgroup *src_cgrp,
4716					 struct cgroup *dst_cgrp,
4717					 struct super_block *sb)
4718{
4719	struct cgroup_namespace *ns = current->nsproxy->cgroup_ns;
4720	struct cgroup *com_cgrp = src_cgrp;
4721	struct inode *inode;
4722	int ret;
4723
4724	lockdep_assert_held(&cgroup_mutex);
4725
4726	/* find the common ancestor */
4727	while (!cgroup_is_descendant(dst_cgrp, com_cgrp))
4728		com_cgrp = cgroup_parent(com_cgrp);
4729
4730	/* %current should be authorized to migrate to the common ancestor */
4731	inode = kernfs_get_inode(sb, com_cgrp->procs_file.kn);
4732	if (!inode)
4733		return -ENOMEM;
4734
4735	ret = inode_permission(inode, MAY_WRITE);
4736	iput(inode);
4737	if (ret)
4738		return ret;
4739
4740	/*
4741	 * If namespaces are delegation boundaries, %current must be able
4742	 * to see both source and destination cgroups from its namespace.
4743	 */
4744	if ((cgrp_dfl_root.flags & CGRP_ROOT_NS_DELEGATE) &&
4745	    (!cgroup_is_descendant(src_cgrp, ns->root_cset->dfl_cgrp) ||
4746	     !cgroup_is_descendant(dst_cgrp, ns->root_cset->dfl_cgrp)))
4747		return -ENOENT;
4748
4749	return 0;
4750}
4751
4752static ssize_t cgroup_procs_write(struct kernfs_open_file *of,
4753				  char *buf, size_t nbytes, loff_t off)
4754{
4755	struct cgroup *src_cgrp, *dst_cgrp;
4756	struct task_struct *task;
4757	ssize_t ret;
4758
4759	dst_cgrp = cgroup_kn_lock_live(of->kn, false);
4760	if (!dst_cgrp)
4761		return -ENODEV;
4762
4763	task = cgroup_procs_write_start(buf, true);
4764	ret = PTR_ERR_OR_ZERO(task);
4765	if (ret)
4766		goto out_unlock;
4767
4768	/* find the source cgroup */
4769	spin_lock_irq(&css_set_lock);
4770	src_cgrp = task_cgroup_from_root(task, &cgrp_dfl_root);
4771	spin_unlock_irq(&css_set_lock);
4772
4773	ret = cgroup_procs_write_permission(src_cgrp, dst_cgrp,
4774					    of->file->f_path.dentry->d_sb);
4775	if (ret)
4776		goto out_finish;
4777
4778	ret = cgroup_attach_task(dst_cgrp, task, true);
4779
4780out_finish:
4781	cgroup_procs_write_finish(task);
4782out_unlock:
4783	cgroup_kn_unlock(of->kn);
4784
4785	return ret ?: nbytes;
4786}
4787
4788static void *cgroup_threads_start(struct seq_file *s, loff_t *pos)
4789{
4790	return __cgroup_procs_start(s, pos, 0);
4791}
4792
4793static ssize_t cgroup_threads_write(struct kernfs_open_file *of,
4794				    char *buf, size_t nbytes, loff_t off)
4795{
4796	struct cgroup *src_cgrp, *dst_cgrp;
4797	struct task_struct *task;
4798	ssize_t ret;
4799
4800	buf = strstrip(buf);
4801
4802	dst_cgrp = cgroup_kn_lock_live(of->kn, false);
4803	if (!dst_cgrp)
4804		return -ENODEV;
4805
4806	task = cgroup_procs_write_start(buf, false);
4807	ret = PTR_ERR_OR_ZERO(task);
4808	if (ret)
4809		goto out_unlock;
4810
4811	/* find the source cgroup */
4812	spin_lock_irq(&css_set_lock);
4813	src_cgrp = task_cgroup_from_root(task, &cgrp_dfl_root);
4814	spin_unlock_irq(&css_set_lock);
4815
4816	/* thread migrations follow the cgroup.procs delegation rule */
4817	ret = cgroup_procs_write_permission(src_cgrp, dst_cgrp,
4818					    of->file->f_path.dentry->d_sb);
4819	if (ret)
4820		goto out_finish;
4821
4822	/* and must be contained in the same domain */
4823	ret = -EOPNOTSUPP;
4824	if (src_cgrp->dom_cgrp != dst_cgrp->dom_cgrp)
4825		goto out_finish;
4826
4827	ret = cgroup_attach_task(dst_cgrp, task, false);
4828
4829out_finish:
4830	cgroup_procs_write_finish(task);
4831out_unlock:
4832	cgroup_kn_unlock(of->kn);
4833
4834	return ret ?: nbytes;
4835}
4836
4837/* cgroup core interface files for the default hierarchy */
4838static struct cftype cgroup_base_files[] = {
4839	{
4840		.name = "cgroup.type",
4841		.flags = CFTYPE_NOT_ON_ROOT,
4842		.seq_show = cgroup_type_show,
4843		.write = cgroup_type_write,
4844	},
4845	{
4846		.name = "cgroup.procs",
4847		.flags = CFTYPE_NS_DELEGATABLE,
4848		.file_offset = offsetof(struct cgroup, procs_file),
4849		.release = cgroup_procs_release,
4850		.seq_start = cgroup_procs_start,
4851		.seq_next = cgroup_procs_next,
4852		.seq_show = cgroup_procs_show,
4853		.write = cgroup_procs_write,
4854	},
4855	{
4856		.name = "cgroup.threads",
4857		.flags = CFTYPE_NS_DELEGATABLE,
4858		.release = cgroup_procs_release,
4859		.seq_start = cgroup_threads_start,
4860		.seq_next = cgroup_procs_next,
4861		.seq_show = cgroup_procs_show,
4862		.write = cgroup_threads_write,
4863	},
4864	{
4865		.name = "cgroup.controllers",
4866		.seq_show = cgroup_controllers_show,
4867	},
4868	{
4869		.name = "cgroup.subtree_control",
4870		.flags = CFTYPE_NS_DELEGATABLE,
4871		.seq_show = cgroup_subtree_control_show,
4872		.write = cgroup_subtree_control_write,
4873	},
4874	{
4875		.name = "cgroup.events",
4876		.flags = CFTYPE_NOT_ON_ROOT,
4877		.file_offset = offsetof(struct cgroup, events_file),
4878		.seq_show = cgroup_events_show,
4879	},
4880	{
4881		.name = "cgroup.max.descendants",
4882		.seq_show = cgroup_max_descendants_show,
4883		.write = cgroup_max_descendants_write,
4884	},
4885	{
4886		.name = "cgroup.max.depth",
4887		.seq_show = cgroup_max_depth_show,
4888		.write = cgroup_max_depth_write,
4889	},
4890	{
4891		.name = "cgroup.stat",
4892		.seq_show = cgroup_stat_show,
4893	},
4894	{
4895		.name = "cgroup.freeze",
4896		.flags = CFTYPE_NOT_ON_ROOT,
4897		.seq_show = cgroup_freeze_show,
4898		.write = cgroup_freeze_write,
4899	},
4900	{
4901		.name = "cpu.stat",
4902		.flags = CFTYPE_NOT_ON_ROOT,
4903		.seq_show = cpu_stat_show,
4904	},
4905#ifdef CONFIG_PSI
4906	{
4907		.name = "io.pressure",
4908		.seq_show = cgroup_io_pressure_show,
4909		.write = cgroup_io_pressure_write,
4910		.poll = cgroup_pressure_poll,
4911		.release = cgroup_pressure_release,
4912	},
4913	{
4914		.name = "memory.pressure",
4915		.seq_show = cgroup_memory_pressure_show,
4916		.write = cgroup_memory_pressure_write,
4917		.poll = cgroup_pressure_poll,
4918		.release = cgroup_pressure_release,
4919	},
4920	{
4921		.name = "cpu.pressure",
4922		.seq_show = cgroup_cpu_pressure_show,
4923		.write = cgroup_cpu_pressure_write,
4924		.poll = cgroup_pressure_poll,
4925		.release = cgroup_pressure_release,
4926	},
4927#endif /* CONFIG_PSI */
4928	{ }	/* terminate */
4929};
4930
4931/*
4932 * css destruction is four-stage process.
4933 *
4934 * 1. Destruction starts.  Killing of the percpu_ref is initiated.
4935 *    Implemented in kill_css().
4936 *
4937 * 2. When the percpu_ref is confirmed to be visible as killed on all CPUs
4938 *    and thus css_tryget_online() is guaranteed to fail, the css can be
4939 *    offlined by invoking offline_css().  After offlining, the base ref is
4940 *    put.  Implemented in css_killed_work_fn().
4941 *
4942 * 3. When the percpu_ref reaches zero, the only possible remaining
4943 *    accessors are inside RCU read sections.  css_release() schedules the
4944 *    RCU callback.
4945 *
4946 * 4. After the grace period, the css can be freed.  Implemented in
4947 *    css_free_work_fn().
4948 *
4949 * It is actually hairier because both step 2 and 4 require process context
4950 * and thus involve punting to css->destroy_work adding two additional
4951 * steps to the already complex sequence.
4952 */
4953static void css_free_rwork_fn(struct work_struct *work)
4954{
4955	struct cgroup_subsys_state *css = container_of(to_rcu_work(work),
4956				struct cgroup_subsys_state, destroy_rwork);
4957	struct cgroup_subsys *ss = css->ss;
4958	struct cgroup *cgrp = css->cgroup;
4959
4960	percpu_ref_exit(&css->refcnt);
4961
4962	if (ss) {
4963		/* css free path */
4964		struct cgroup_subsys_state *parent = css->parent;
4965		int id = css->id;
4966
4967		ss->css_free(css);
4968		cgroup_idr_remove(&ss->css_idr, id);
4969		cgroup_put(cgrp);
4970
4971		if (parent)
4972			css_put(parent);
4973	} else {
4974		/* cgroup free path */
4975		atomic_dec(&cgrp->root->nr_cgrps);
4976		cgroup1_pidlist_destroy_all(cgrp);
4977		cancel_work_sync(&cgrp->release_agent_work);
4978
4979		if (cgroup_parent(cgrp)) {
4980			/*
4981			 * We get a ref to the parent, and put the ref when
4982			 * this cgroup is being freed, so it's guaranteed
4983			 * that the parent won't be destroyed before its
4984			 * children.
4985			 */
4986			cgroup_put(cgroup_parent(cgrp));
4987			kernfs_put(cgrp->kn);
4988			psi_cgroup_free(cgrp);
4989			if (cgroup_on_dfl(cgrp))
4990				cgroup_rstat_exit(cgrp);
4991			kfree(cgrp);
4992		} else {
4993			/*
4994			 * This is root cgroup's refcnt reaching zero,
4995			 * which indicates that the root should be
4996			 * released.
4997			 */
4998			cgroup_destroy_root(cgrp->root);
4999		}
5000	}
5001}
5002
5003static void css_release_work_fn(struct work_struct *work)
5004{
5005	struct cgroup_subsys_state *css =
5006		container_of(work, struct cgroup_subsys_state, destroy_work);
5007	struct cgroup_subsys *ss = css->ss;
5008	struct cgroup *cgrp = css->cgroup;
5009
5010	mutex_lock(&cgroup_mutex);
5011
5012	css->flags |= CSS_RELEASED;
5013	list_del_rcu(&css->sibling);
5014
5015	if (ss) {
5016		/* css release path */
5017		if (!list_empty(&css->rstat_css_node)) {
5018			cgroup_rstat_flush(cgrp);
5019			list_del_rcu(&css->rstat_css_node);
5020		}
5021
5022		cgroup_idr_replace(&ss->css_idr, NULL, css->id);
5023		if (ss->css_released)
5024			ss->css_released(css);
5025	} else {
5026		struct cgroup *tcgrp;
5027
5028		/* cgroup release path */
5029		TRACE_CGROUP_PATH(release, cgrp);
5030
5031		if (cgroup_on_dfl(cgrp))
5032			cgroup_rstat_flush(cgrp);
5033
5034		spin_lock_irq(&css_set_lock);
5035		for (tcgrp = cgroup_parent(cgrp); tcgrp;
5036		     tcgrp = cgroup_parent(tcgrp))
5037			tcgrp->nr_dying_descendants--;
5038		spin_unlock_irq(&css_set_lock);
5039
5040		cgroup_idr_remove(&cgrp->root->cgroup_idr, cgrp->id);
5041		cgrp->id = -1;
5042
5043		/*
5044		 * There are two control paths which try to determine
5045		 * cgroup from dentry without going through kernfs -
5046		 * cgroupstats_build() and css_tryget_online_from_dir().
5047		 * Those are supported by RCU protecting clearing of
5048		 * cgrp->kn->priv backpointer.
5049		 */
5050		if (cgrp->kn)
5051			RCU_INIT_POINTER(*(void __rcu __force **)&cgrp->kn->priv,
5052					 NULL);
 
 
5053	}
5054
5055	mutex_unlock(&cgroup_mutex);
5056
5057	INIT_RCU_WORK(&css->destroy_rwork, css_free_rwork_fn);
5058	queue_rcu_work(cgroup_destroy_wq, &css->destroy_rwork);
5059}
5060
5061static void css_release(struct percpu_ref *ref)
5062{
5063	struct cgroup_subsys_state *css =
5064		container_of(ref, struct cgroup_subsys_state, refcnt);
5065
5066	INIT_WORK(&css->destroy_work, css_release_work_fn);
5067	queue_work(cgroup_destroy_wq, &css->destroy_work);
5068}
5069
5070static void init_and_link_css(struct cgroup_subsys_state *css,
5071			      struct cgroup_subsys *ss, struct cgroup *cgrp)
5072{
5073	lockdep_assert_held(&cgroup_mutex);
5074
5075	cgroup_get_live(cgrp);
5076
5077	memset(css, 0, sizeof(*css));
5078	css->cgroup = cgrp;
5079	css->ss = ss;
5080	css->id = -1;
5081	INIT_LIST_HEAD(&css->sibling);
5082	INIT_LIST_HEAD(&css->children);
5083	INIT_LIST_HEAD(&css->rstat_css_node);
5084	css->serial_nr = css_serial_nr_next++;
5085	atomic_set(&css->online_cnt, 0);
5086
5087	if (cgroup_parent(cgrp)) {
5088		css->parent = cgroup_css(cgroup_parent(cgrp), ss);
5089		css_get(css->parent);
5090	}
5091
5092	if (cgroup_on_dfl(cgrp) && ss->css_rstat_flush)
5093		list_add_rcu(&css->rstat_css_node, &cgrp->rstat_css_list);
5094
5095	BUG_ON(cgroup_css(cgrp, ss));
5096}
5097
5098/* invoke ->css_online() on a new CSS and mark it online if successful */
5099static int online_css(struct cgroup_subsys_state *css)
5100{
5101	struct cgroup_subsys *ss = css->ss;
5102	int ret = 0;
5103
5104	lockdep_assert_held(&cgroup_mutex);
5105
5106	if (ss->css_online)
5107		ret = ss->css_online(css);
5108	if (!ret) {
5109		css->flags |= CSS_ONLINE;
5110		rcu_assign_pointer(css->cgroup->subsys[ss->id], css);
5111
5112		atomic_inc(&css->online_cnt);
5113		if (css->parent)
5114			atomic_inc(&css->parent->online_cnt);
5115	}
5116	return ret;
5117}
5118
5119/* if the CSS is online, invoke ->css_offline() on it and mark it offline */
5120static void offline_css(struct cgroup_subsys_state *css)
5121{
5122	struct cgroup_subsys *ss = css->ss;
5123
5124	lockdep_assert_held(&cgroup_mutex);
5125
5126	if (!(css->flags & CSS_ONLINE))
5127		return;
5128
5129	if (ss->css_offline)
5130		ss->css_offline(css);
5131
5132	css->flags &= ~CSS_ONLINE;
5133	RCU_INIT_POINTER(css->cgroup->subsys[ss->id], NULL);
5134
5135	wake_up_all(&css->cgroup->offline_waitq);
5136}
5137
5138/**
5139 * css_create - create a cgroup_subsys_state
5140 * @cgrp: the cgroup new css will be associated with
5141 * @ss: the subsys of new css
5142 *
5143 * Create a new css associated with @cgrp - @ss pair.  On success, the new
5144 * css is online and installed in @cgrp.  This function doesn't create the
5145 * interface files.  Returns 0 on success, -errno on failure.
5146 */
5147static struct cgroup_subsys_state *css_create(struct cgroup *cgrp,
5148					      struct cgroup_subsys *ss)
5149{
5150	struct cgroup *parent = cgroup_parent(cgrp);
5151	struct cgroup_subsys_state *parent_css = cgroup_css(parent, ss);
5152	struct cgroup_subsys_state *css;
5153	int err;
5154
5155	lockdep_assert_held(&cgroup_mutex);
5156
5157	css = ss->css_alloc(parent_css);
5158	if (!css)
5159		css = ERR_PTR(-ENOMEM);
5160	if (IS_ERR(css))
5161		return css;
5162
5163	init_and_link_css(css, ss, cgrp);
5164
5165	err = percpu_ref_init(&css->refcnt, css_release, 0, GFP_KERNEL);
5166	if (err)
5167		goto err_free_css;
5168
5169	err = cgroup_idr_alloc(&ss->css_idr, NULL, 2, 0, GFP_KERNEL);
5170	if (err < 0)
5171		goto err_free_css;
5172	css->id = err;
5173
5174	/* @css is ready to be brought online now, make it visible */
5175	list_add_tail_rcu(&css->sibling, &parent_css->children);
5176	cgroup_idr_replace(&ss->css_idr, css, css->id);
5177
5178	err = online_css(css);
5179	if (err)
5180		goto err_list_del;
5181
5182	if (ss->broken_hierarchy && !ss->warned_broken_hierarchy &&
5183	    cgroup_parent(parent)) {
5184		pr_warn("%s (%d) created nested cgroup for controller \"%s\" which has incomplete hierarchy support. Nested cgroups may change behavior in the future.\n",
5185			current->comm, current->pid, ss->name);
5186		if (!strcmp(ss->name, "memory"))
5187			pr_warn("\"memory\" requires setting use_hierarchy to 1 on the root\n");
5188		ss->warned_broken_hierarchy = true;
5189	}
5190
5191	return css;
5192
5193err_list_del:
5194	list_del_rcu(&css->sibling);
5195err_free_css:
5196	list_del_rcu(&css->rstat_css_node);
5197	INIT_RCU_WORK(&css->destroy_rwork, css_free_rwork_fn);
5198	queue_rcu_work(cgroup_destroy_wq, &css->destroy_rwork);
5199	return ERR_PTR(err);
5200}
5201
5202/*
5203 * The returned cgroup is fully initialized including its control mask, but
5204 * it isn't associated with its kernfs_node and doesn't have the control
5205 * mask applied.
5206 */
5207static struct cgroup *cgroup_create(struct cgroup *parent)
5208{
5209	struct cgroup_root *root = parent->root;
5210	struct cgroup *cgrp, *tcgrp;
5211	int level = parent->level + 1;
5212	int ret;
5213
5214	/* allocate the cgroup and its ID, 0 is reserved for the root */
5215	cgrp = kzalloc(struct_size(cgrp, ancestor_ids, (level + 1)),
5216		       GFP_KERNEL);
5217	if (!cgrp)
5218		return ERR_PTR(-ENOMEM);
5219
5220	ret = percpu_ref_init(&cgrp->self.refcnt, css_release, 0, GFP_KERNEL);
5221	if (ret)
5222		goto out_free_cgrp;
5223
5224	if (cgroup_on_dfl(parent)) {
5225		ret = cgroup_rstat_init(cgrp);
5226		if (ret)
5227			goto out_cancel_ref;
5228	}
5229
5230	/*
5231	 * Temporarily set the pointer to NULL, so idr_find() won't return
5232	 * a half-baked cgroup.
5233	 */
5234	cgrp->id = cgroup_idr_alloc(&root->cgroup_idr, NULL, 2, 0, GFP_KERNEL);
5235	if (cgrp->id < 0) {
5236		ret = -ENOMEM;
5237		goto out_stat_exit;
5238	}
5239
5240	init_cgroup_housekeeping(cgrp);
5241
5242	cgrp->self.parent = &parent->self;
5243	cgrp->root = root;
5244	cgrp->level = level;
5245
5246	ret = psi_cgroup_alloc(cgrp);
5247	if (ret)
5248		goto out_idr_free;
5249
5250	ret = cgroup_bpf_inherit(cgrp);
5251	if (ret)
5252		goto out_psi_free;
5253
5254	/*
5255	 * New cgroup inherits effective freeze counter, and
5256	 * if the parent has to be frozen, the child has too.
5257	 */
5258	cgrp->freezer.e_freeze = parent->freezer.e_freeze;
5259	if (cgrp->freezer.e_freeze) {
5260		/*
5261		 * Set the CGRP_FREEZE flag, so when a process will be
5262		 * attached to the child cgroup, it will become frozen.
5263		 * At this point the new cgroup is unpopulated, so we can
5264		 * consider it frozen immediately.
5265		 */
5266		set_bit(CGRP_FREEZE, &cgrp->flags);
5267		set_bit(CGRP_FROZEN, &cgrp->flags);
5268	}
5269
5270	spin_lock_irq(&css_set_lock);
5271	for (tcgrp = cgrp; tcgrp; tcgrp = cgroup_parent(tcgrp)) {
5272		cgrp->ancestor_ids[tcgrp->level] = tcgrp->id;
5273
5274		if (tcgrp != cgrp) {
5275			tcgrp->nr_descendants++;
5276
5277			/*
5278			 * If the new cgroup is frozen, all ancestor cgroups
5279			 * get a new frozen descendant, but their state can't
5280			 * change because of this.
5281			 */
5282			if (cgrp->freezer.e_freeze)
5283				tcgrp->freezer.nr_frozen_descendants++;
5284		}
5285	}
5286	spin_unlock_irq(&css_set_lock);
5287
5288	if (notify_on_release(parent))
5289		set_bit(CGRP_NOTIFY_ON_RELEASE, &cgrp->flags);
5290
5291	if (test_bit(CGRP_CPUSET_CLONE_CHILDREN, &parent->flags))
5292		set_bit(CGRP_CPUSET_CLONE_CHILDREN, &cgrp->flags);
5293
5294	cgrp->self.serial_nr = css_serial_nr_next++;
5295
5296	/* allocation complete, commit to creation */
5297	list_add_tail_rcu(&cgrp->self.sibling, &cgroup_parent(cgrp)->self.children);
5298	atomic_inc(&root->nr_cgrps);
5299	cgroup_get_live(parent);
5300
5301	/*
5302	 * @cgrp is now fully operational.  If something fails after this
5303	 * point, it'll be released via the normal destruction path.
5304	 */
5305	cgroup_idr_replace(&root->cgroup_idr, cgrp, cgrp->id);
5306
5307	/*
5308	 * On the default hierarchy, a child doesn't automatically inherit
5309	 * subtree_control from the parent.  Each is configured manually.
5310	 */
5311	if (!cgroup_on_dfl(cgrp))
5312		cgrp->subtree_control = cgroup_control(cgrp);
5313
5314	cgroup_propagate_control(cgrp);
5315
5316	return cgrp;
5317
5318out_psi_free:
5319	psi_cgroup_free(cgrp);
5320out_idr_free:
5321	cgroup_idr_remove(&root->cgroup_idr, cgrp->id);
5322out_stat_exit:
5323	if (cgroup_on_dfl(parent))
5324		cgroup_rstat_exit(cgrp);
5325out_cancel_ref:
5326	percpu_ref_exit(&cgrp->self.refcnt);
5327out_free_cgrp:
5328	kfree(cgrp);
5329	return ERR_PTR(ret);
5330}
5331
5332static bool cgroup_check_hierarchy_limits(struct cgroup *parent)
5333{
5334	struct cgroup *cgroup;
5335	int ret = false;
5336	int level = 1;
5337
5338	lockdep_assert_held(&cgroup_mutex);
5339
5340	for (cgroup = parent; cgroup; cgroup = cgroup_parent(cgroup)) {
5341		if (cgroup->nr_descendants >= cgroup->max_descendants)
5342			goto fail;
5343
5344		if (level > cgroup->max_depth)
5345			goto fail;
5346
5347		level++;
5348	}
5349
5350	ret = true;
5351fail:
5352	return ret;
5353}
5354
5355int cgroup_mkdir(struct kernfs_node *parent_kn, const char *name, umode_t mode)
5356{
5357	struct cgroup *parent, *cgrp;
5358	struct kernfs_node *kn;
5359	int ret;
5360
5361	/* do not accept '\n' to prevent making /proc/<pid>/cgroup unparsable */
5362	if (strchr(name, '\n'))
5363		return -EINVAL;
5364
5365	parent = cgroup_kn_lock_live(parent_kn, false);
5366	if (!parent)
5367		return -ENODEV;
5368
5369	if (!cgroup_check_hierarchy_limits(parent)) {
5370		ret = -EAGAIN;
5371		goto out_unlock;
5372	}
5373
5374	cgrp = cgroup_create(parent);
5375	if (IS_ERR(cgrp)) {
5376		ret = PTR_ERR(cgrp);
5377		goto out_unlock;
5378	}
5379
5380	/* create the directory */
5381	kn = kernfs_create_dir(parent->kn, name, mode, cgrp);
5382	if (IS_ERR(kn)) {
5383		ret = PTR_ERR(kn);
5384		goto out_destroy;
5385	}
5386	cgrp->kn = kn;
5387
5388	/*
5389	 * This extra ref will be put in cgroup_free_fn() and guarantees
5390	 * that @cgrp->kn is always accessible.
5391	 */
5392	kernfs_get(kn);
5393
5394	ret = cgroup_kn_set_ugid(kn);
5395	if (ret)
5396		goto out_destroy;
5397
5398	ret = css_populate_dir(&cgrp->self);
5399	if (ret)
5400		goto out_destroy;
5401
5402	ret = cgroup_apply_control_enable(cgrp);
5403	if (ret)
5404		goto out_destroy;
5405
5406	TRACE_CGROUP_PATH(mkdir, cgrp);
5407
5408	/* let's create and online css's */
5409	kernfs_activate(kn);
5410
5411	ret = 0;
5412	goto out_unlock;
5413
5414out_destroy:
5415	cgroup_destroy_locked(cgrp);
5416out_unlock:
5417	cgroup_kn_unlock(parent_kn);
5418	return ret;
5419}
5420
5421/*
5422 * This is called when the refcnt of a css is confirmed to be killed.
5423 * css_tryget_online() is now guaranteed to fail.  Tell the subsystem to
5424 * initate destruction and put the css ref from kill_css().
5425 */
5426static void css_killed_work_fn(struct work_struct *work)
5427{
5428	struct cgroup_subsys_state *css =
5429		container_of(work, struct cgroup_subsys_state, destroy_work);
5430
5431	mutex_lock(&cgroup_mutex);
5432
5433	do {
5434		offline_css(css);
5435		css_put(css);
5436		/* @css can't go away while we're holding cgroup_mutex */
5437		css = css->parent;
5438	} while (css && atomic_dec_and_test(&css->online_cnt));
5439
5440	mutex_unlock(&cgroup_mutex);
5441}
5442
5443/* css kill confirmation processing requires process context, bounce */
5444static void css_killed_ref_fn(struct percpu_ref *ref)
5445{
5446	struct cgroup_subsys_state *css =
5447		container_of(ref, struct cgroup_subsys_state, refcnt);
5448
5449	if (atomic_dec_and_test(&css->online_cnt)) {
5450		INIT_WORK(&css->destroy_work, css_killed_work_fn);
5451		queue_work(cgroup_destroy_wq, &css->destroy_work);
5452	}
5453}
5454
5455/**
5456 * kill_css - destroy a css
5457 * @css: css to destroy
5458 *
5459 * This function initiates destruction of @css by removing cgroup interface
5460 * files and putting its base reference.  ->css_offline() will be invoked
5461 * asynchronously once css_tryget_online() is guaranteed to fail and when
5462 * the reference count reaches zero, @css will be released.
5463 */
5464static void kill_css(struct cgroup_subsys_state *css)
5465{
5466	lockdep_assert_held(&cgroup_mutex);
5467
5468	if (css->flags & CSS_DYING)
5469		return;
5470
5471	css->flags |= CSS_DYING;
5472
5473	/*
5474	 * This must happen before css is disassociated with its cgroup.
5475	 * See seq_css() for details.
5476	 */
5477	css_clear_dir(css);
5478
5479	/*
5480	 * Killing would put the base ref, but we need to keep it alive
5481	 * until after ->css_offline().
5482	 */
5483	css_get(css);
5484
5485	/*
5486	 * cgroup core guarantees that, by the time ->css_offline() is
5487	 * invoked, no new css reference will be given out via
5488	 * css_tryget_online().  We can't simply call percpu_ref_kill() and
5489	 * proceed to offlining css's because percpu_ref_kill() doesn't
5490	 * guarantee that the ref is seen as killed on all CPUs on return.
5491	 *
5492	 * Use percpu_ref_kill_and_confirm() to get notifications as each
5493	 * css is confirmed to be seen as killed on all CPUs.
5494	 */
5495	percpu_ref_kill_and_confirm(&css->refcnt, css_killed_ref_fn);
5496}
5497
5498/**
5499 * cgroup_destroy_locked - the first stage of cgroup destruction
5500 * @cgrp: cgroup to be destroyed
5501 *
5502 * css's make use of percpu refcnts whose killing latency shouldn't be
5503 * exposed to userland and are RCU protected.  Also, cgroup core needs to
5504 * guarantee that css_tryget_online() won't succeed by the time
5505 * ->css_offline() is invoked.  To satisfy all the requirements,
5506 * destruction is implemented in the following two steps.
5507 *
5508 * s1. Verify @cgrp can be destroyed and mark it dying.  Remove all
5509 *     userland visible parts and start killing the percpu refcnts of
5510 *     css's.  Set up so that the next stage will be kicked off once all
5511 *     the percpu refcnts are confirmed to be killed.
5512 *
5513 * s2. Invoke ->css_offline(), mark the cgroup dead and proceed with the
5514 *     rest of destruction.  Once all cgroup references are gone, the
5515 *     cgroup is RCU-freed.
5516 *
5517 * This function implements s1.  After this step, @cgrp is gone as far as
5518 * the userland is concerned and a new cgroup with the same name may be
5519 * created.  As cgroup doesn't care about the names internally, this
5520 * doesn't cause any problem.
5521 */
5522static int cgroup_destroy_locked(struct cgroup *cgrp)
5523	__releases(&cgroup_mutex) __acquires(&cgroup_mutex)
5524{
5525	struct cgroup *tcgrp, *parent = cgroup_parent(cgrp);
5526	struct cgroup_subsys_state *css;
5527	struct cgrp_cset_link *link;
5528	int ssid;
5529
5530	lockdep_assert_held(&cgroup_mutex);
5531
5532	/*
5533	 * Only migration can raise populated from zero and we're already
5534	 * holding cgroup_mutex.
5535	 */
5536	if (cgroup_is_populated(cgrp))
5537		return -EBUSY;
5538
5539	/*
5540	 * Make sure there's no live children.  We can't test emptiness of
5541	 * ->self.children as dead children linger on it while being
5542	 * drained; otherwise, "rmdir parent/child parent" may fail.
5543	 */
5544	if (css_has_online_children(&cgrp->self))
5545		return -EBUSY;
5546
5547	/*
5548	 * Mark @cgrp and the associated csets dead.  The former prevents
5549	 * further task migration and child creation by disabling
5550	 * cgroup_lock_live_group().  The latter makes the csets ignored by
5551	 * the migration path.
5552	 */
5553	cgrp->self.flags &= ~CSS_ONLINE;
5554
5555	spin_lock_irq(&css_set_lock);
5556	list_for_each_entry(link, &cgrp->cset_links, cset_link)
5557		link->cset->dead = true;
5558	spin_unlock_irq(&css_set_lock);
5559
5560	/* initiate massacre of all css's */
5561	for_each_css(css, ssid, cgrp)
5562		kill_css(css);
5563
5564	/* clear and remove @cgrp dir, @cgrp has an extra ref on its kn */
5565	css_clear_dir(&cgrp->self);
 
 
5566	kernfs_remove(cgrp->kn);
5567
5568	if (parent && cgroup_is_threaded(cgrp))
5569		parent->nr_threaded_children--;
5570
5571	spin_lock_irq(&css_set_lock);
5572	for (tcgrp = cgroup_parent(cgrp); tcgrp; tcgrp = cgroup_parent(tcgrp)) {
5573		tcgrp->nr_descendants--;
5574		tcgrp->nr_dying_descendants++;
5575		/*
5576		 * If the dying cgroup is frozen, decrease frozen descendants
5577		 * counters of ancestor cgroups.
5578		 */
5579		if (test_bit(CGRP_FROZEN, &cgrp->flags))
5580			tcgrp->freezer.nr_frozen_descendants--;
5581	}
5582	spin_unlock_irq(&css_set_lock);
5583
5584	cgroup1_check_for_release(parent);
5585
5586	cgroup_bpf_offline(cgrp);
5587
5588	/* put the base reference */
5589	percpu_ref_kill(&cgrp->self.refcnt);
5590
5591	return 0;
5592};
5593
5594int cgroup_rmdir(struct kernfs_node *kn)
5595{
5596	struct cgroup *cgrp;
5597	int ret = 0;
5598
5599	cgrp = cgroup_kn_lock_live(kn, false);
5600	if (!cgrp)
5601		return 0;
5602
5603	ret = cgroup_destroy_locked(cgrp);
 
5604	if (!ret)
5605		TRACE_CGROUP_PATH(rmdir, cgrp);
5606
5607	cgroup_kn_unlock(kn);
5608	return ret;
5609}
5610
5611static struct kernfs_syscall_ops cgroup_kf_syscall_ops = {
5612	.show_options		= cgroup_show_options,
 
5613	.mkdir			= cgroup_mkdir,
5614	.rmdir			= cgroup_rmdir,
5615	.show_path		= cgroup_show_path,
5616};
5617
5618static void __init cgroup_init_subsys(struct cgroup_subsys *ss, bool early)
5619{
5620	struct cgroup_subsys_state *css;
5621
5622	pr_debug("Initializing cgroup subsys %s\n", ss->name);
5623
5624	mutex_lock(&cgroup_mutex);
5625
5626	idr_init(&ss->css_idr);
5627	INIT_LIST_HEAD(&ss->cfts);
5628
5629	/* Create the root cgroup state for this subsystem */
5630	ss->root = &cgrp_dfl_root;
5631	css = ss->css_alloc(cgroup_css(&cgrp_dfl_root.cgrp, ss));
5632	/* We don't handle early failures gracefully */
5633	BUG_ON(IS_ERR(css));
5634	init_and_link_css(css, ss, &cgrp_dfl_root.cgrp);
5635
5636	/*
5637	 * Root csses are never destroyed and we can't initialize
5638	 * percpu_ref during early init.  Disable refcnting.
5639	 */
5640	css->flags |= CSS_NO_REF;
5641
5642	if (early) {
5643		/* allocation can't be done safely during early init */
5644		css->id = 1;
5645	} else {
5646		css->id = cgroup_idr_alloc(&ss->css_idr, css, 1, 2, GFP_KERNEL);
5647		BUG_ON(css->id < 0);
5648	}
5649
5650	/* Update the init_css_set to contain a subsys
5651	 * pointer to this state - since the subsystem is
5652	 * newly registered, all tasks and hence the
5653	 * init_css_set is in the subsystem's root cgroup. */
5654	init_css_set.subsys[ss->id] = css;
5655
5656	have_fork_callback |= (bool)ss->fork << ss->id;
5657	have_exit_callback |= (bool)ss->exit << ss->id;
5658	have_release_callback |= (bool)ss->release << ss->id;
5659	have_canfork_callback |= (bool)ss->can_fork << ss->id;
5660
5661	/* At system boot, before all subsystems have been
5662	 * registered, no tasks have been forked, so we don't
5663	 * need to invoke fork callbacks here. */
5664	BUG_ON(!list_empty(&init_task.tasks));
5665
5666	BUG_ON(online_css(css));
5667
5668	mutex_unlock(&cgroup_mutex);
5669}
5670
5671/**
5672 * cgroup_init_early - cgroup initialization at system boot
5673 *
5674 * Initialize cgroups at system boot, and initialize any
5675 * subsystems that request early init.
5676 */
5677int __init cgroup_init_early(void)
5678{
5679	static struct cgroup_fs_context __initdata ctx;
5680	struct cgroup_subsys *ss;
5681	int i;
5682
5683	ctx.root = &cgrp_dfl_root;
5684	init_cgroup_root(&ctx);
5685	cgrp_dfl_root.cgrp.self.flags |= CSS_NO_REF;
5686
5687	RCU_INIT_POINTER(init_task.cgroups, &init_css_set);
5688
5689	for_each_subsys(ss, i) {
5690		WARN(!ss->css_alloc || !ss->css_free || ss->name || ss->id,
5691		     "invalid cgroup_subsys %d:%s css_alloc=%p css_free=%p id:name=%d:%s\n",
5692		     i, cgroup_subsys_name[i], ss->css_alloc, ss->css_free,
5693		     ss->id, ss->name);
5694		WARN(strlen(cgroup_subsys_name[i]) > MAX_CGROUP_TYPE_NAMELEN,
5695		     "cgroup_subsys_name %s too long\n", cgroup_subsys_name[i]);
5696
5697		ss->id = i;
5698		ss->name = cgroup_subsys_name[i];
5699		if (!ss->legacy_name)
5700			ss->legacy_name = cgroup_subsys_name[i];
5701
5702		if (ss->early_init)
5703			cgroup_init_subsys(ss, true);
5704	}
5705	return 0;
5706}
5707
5708static u16 cgroup_disable_mask __initdata;
5709
5710/**
5711 * cgroup_init - cgroup initialization
5712 *
5713 * Register cgroup filesystem and /proc file, and initialize
5714 * any subsystems that didn't request early init.
5715 */
5716int __init cgroup_init(void)
5717{
5718	struct cgroup_subsys *ss;
5719	int ssid;
5720
5721	BUILD_BUG_ON(CGROUP_SUBSYS_COUNT > 16);
 
5722	BUG_ON(cgroup_init_cftypes(NULL, cgroup_base_files));
5723	BUG_ON(cgroup_init_cftypes(NULL, cgroup1_base_files));
5724
5725	cgroup_rstat_boot();
5726
5727	/*
5728	 * The latency of the synchronize_rcu() is too high for cgroups,
5729	 * avoid it at the cost of forcing all readers into the slow path.
5730	 */
5731	rcu_sync_enter_start(&cgroup_threadgroup_rwsem.rss);
5732
5733	get_user_ns(init_cgroup_ns.user_ns);
5734
5735	mutex_lock(&cgroup_mutex);
5736
5737	/*
5738	 * Add init_css_set to the hash table so that dfl_root can link to
5739	 * it during init.
5740	 */
5741	hash_add(css_set_table, &init_css_set.hlist,
5742		 css_set_hash(init_css_set.subsys));
5743
5744	BUG_ON(cgroup_setup_root(&cgrp_dfl_root, 0));
5745
5746	mutex_unlock(&cgroup_mutex);
5747
5748	for_each_subsys(ss, ssid) {
5749		if (ss->early_init) {
5750			struct cgroup_subsys_state *css =
5751				init_css_set.subsys[ss->id];
5752
5753			css->id = cgroup_idr_alloc(&ss->css_idr, css, 1, 2,
5754						   GFP_KERNEL);
5755			BUG_ON(css->id < 0);
5756		} else {
5757			cgroup_init_subsys(ss, false);
5758		}
5759
5760		list_add_tail(&init_css_set.e_cset_node[ssid],
5761			      &cgrp_dfl_root.cgrp.e_csets[ssid]);
5762
5763		/*
5764		 * Setting dfl_root subsys_mask needs to consider the
5765		 * disabled flag and cftype registration needs kmalloc,
5766		 * both of which aren't available during early_init.
5767		 */
5768		if (cgroup_disable_mask & (1 << ssid)) {
5769			static_branch_disable(cgroup_subsys_enabled_key[ssid]);
5770			printk(KERN_INFO "Disabling %s control group subsystem\n",
5771			       ss->name);
5772			continue;
5773		}
5774
5775		if (cgroup1_ssid_disabled(ssid))
5776			printk(KERN_INFO "Disabling %s control group subsystem in v1 mounts\n",
5777			       ss->name);
5778
5779		cgrp_dfl_root.subsys_mask |= 1 << ss->id;
5780
5781		/* implicit controllers must be threaded too */
5782		WARN_ON(ss->implicit_on_dfl && !ss->threaded);
5783
5784		if (ss->implicit_on_dfl)
5785			cgrp_dfl_implicit_ss_mask |= 1 << ss->id;
5786		else if (!ss->dfl_cftypes)
5787			cgrp_dfl_inhibit_ss_mask |= 1 << ss->id;
5788
5789		if (ss->threaded)
5790			cgrp_dfl_threaded_ss_mask |= 1 << ss->id;
5791
5792		if (ss->dfl_cftypes == ss->legacy_cftypes) {
5793			WARN_ON(cgroup_add_cftypes(ss, ss->dfl_cftypes));
5794		} else {
5795			WARN_ON(cgroup_add_dfl_cftypes(ss, ss->dfl_cftypes));
5796			WARN_ON(cgroup_add_legacy_cftypes(ss, ss->legacy_cftypes));
5797		}
5798
5799		if (ss->bind)
5800			ss->bind(init_css_set.subsys[ssid]);
5801
5802		mutex_lock(&cgroup_mutex);
5803		css_populate_dir(init_css_set.subsys[ssid]);
5804		mutex_unlock(&cgroup_mutex);
5805	}
5806
5807	/* init_css_set.subsys[] has been updated, re-hash */
5808	hash_del(&init_css_set.hlist);
5809	hash_add(css_set_table, &init_css_set.hlist,
5810		 css_set_hash(init_css_set.subsys));
5811
5812	WARN_ON(sysfs_create_mount_point(fs_kobj, "cgroup"));
5813	WARN_ON(register_filesystem(&cgroup_fs_type));
5814	WARN_ON(register_filesystem(&cgroup2_fs_type));
5815	WARN_ON(!proc_create_single("cgroups", 0, NULL, proc_cgroupstats_show));
5816#ifdef CONFIG_CPUSETS
5817	WARN_ON(register_filesystem(&cpuset_fs_type));
5818#endif
5819
5820	return 0;
5821}
5822
5823static int __init cgroup_wq_init(void)
5824{
5825	/*
5826	 * There isn't much point in executing destruction path in
5827	 * parallel.  Good chunk is serialized with cgroup_mutex anyway.
5828	 * Use 1 for @max_active.
5829	 *
5830	 * We would prefer to do this in cgroup_init() above, but that
5831	 * is called before init_workqueues(): so leave this until after.
5832	 */
5833	cgroup_destroy_wq = alloc_workqueue("cgroup_destroy", 0, 1);
5834	BUG_ON(!cgroup_destroy_wq);
5835	return 0;
5836}
5837core_initcall(cgroup_wq_init);
5838
5839void cgroup_path_from_kernfs_id(const union kernfs_node_id *id,
5840					char *buf, size_t buflen)
5841{
5842	struct kernfs_node *kn;
5843
5844	kn = kernfs_get_node_by_id(cgrp_dfl_root.kf_root, id);
5845	if (!kn)
5846		return;
5847	kernfs_path(kn, buf, buflen);
5848	kernfs_put(kn);
5849}
5850
5851/*
5852 * proc_cgroup_show()
5853 *  - Print task's cgroup paths into seq_file, one line for each hierarchy
5854 *  - Used for /proc/<pid>/cgroup.
5855 */
5856int proc_cgroup_show(struct seq_file *m, struct pid_namespace *ns,
5857		     struct pid *pid, struct task_struct *tsk)
5858{
5859	char *buf;
5860	int retval;
5861	struct cgroup_root *root;
5862
5863	retval = -ENOMEM;
5864	buf = kmalloc(PATH_MAX, GFP_KERNEL);
5865	if (!buf)
5866		goto out;
5867
5868	mutex_lock(&cgroup_mutex);
5869	spin_lock_irq(&css_set_lock);
5870
5871	for_each_root(root) {
5872		struct cgroup_subsys *ss;
5873		struct cgroup *cgrp;
5874		int ssid, count = 0;
5875
5876		if (root == &cgrp_dfl_root && !cgrp_dfl_visible)
5877			continue;
5878
5879		seq_printf(m, "%d:", root->hierarchy_id);
5880		if (root != &cgrp_dfl_root)
5881			for_each_subsys(ss, ssid)
5882				if (root->subsys_mask & (1 << ssid))
5883					seq_printf(m, "%s%s", count++ ? "," : "",
5884						   ss->legacy_name);
5885		if (strlen(root->name))
5886			seq_printf(m, "%sname=%s", count ? "," : "",
5887				   root->name);
5888		seq_putc(m, ':');
5889
5890		cgrp = task_cgroup_from_root(tsk, root);
5891
5892		/*
5893		 * On traditional hierarchies, all zombie tasks show up as
5894		 * belonging to the root cgroup.  On the default hierarchy,
5895		 * while a zombie doesn't show up in "cgroup.procs" and
5896		 * thus can't be migrated, its /proc/PID/cgroup keeps
5897		 * reporting the cgroup it belonged to before exiting.  If
5898		 * the cgroup is removed before the zombie is reaped,
5899		 * " (deleted)" is appended to the cgroup path.
5900		 */
5901		if (cgroup_on_dfl(cgrp) || !(tsk->flags & PF_EXITING)) {
5902			retval = cgroup_path_ns_locked(cgrp, buf, PATH_MAX,
5903						current->nsproxy->cgroup_ns);
5904			if (retval >= PATH_MAX)
5905				retval = -ENAMETOOLONG;
5906			if (retval < 0)
5907				goto out_unlock;
5908
5909			seq_puts(m, buf);
5910		} else {
5911			seq_puts(m, "/");
5912		}
5913
5914		if (cgroup_on_dfl(cgrp) && cgroup_is_dead(cgrp))
5915			seq_puts(m, " (deleted)\n");
5916		else
5917			seq_putc(m, '\n');
5918	}
5919
5920	retval = 0;
5921out_unlock:
5922	spin_unlock_irq(&css_set_lock);
5923	mutex_unlock(&cgroup_mutex);
5924	kfree(buf);
5925out:
5926	return retval;
5927}
5928
5929/**
5930 * cgroup_fork - initialize cgroup related fields during copy_process()
5931 * @child: pointer to task_struct of forking parent process.
5932 *
5933 * A task is associated with the init_css_set until cgroup_post_fork()
5934 * attaches it to the parent's css_set.  Empty cg_list indicates that
5935 * @child isn't holding reference to its css_set.
5936 */
5937void cgroup_fork(struct task_struct *child)
5938{
5939	RCU_INIT_POINTER(child->cgroups, &init_css_set);
5940	INIT_LIST_HEAD(&child->cg_list);
5941}
5942
5943/**
5944 * cgroup_can_fork - called on a new task before the process is exposed
5945 * @child: the task in question.
5946 *
5947 * This calls the subsystem can_fork() callbacks. If the can_fork() callback
5948 * returns an error, the fork aborts with that error code. This allows for
5949 * a cgroup subsystem to conditionally allow or deny new forks.
5950 */
5951int cgroup_can_fork(struct task_struct *child)
5952{
5953	struct cgroup_subsys *ss;
5954	int i, j, ret;
5955
5956	do_each_subsys_mask(ss, i, have_canfork_callback) {
5957		ret = ss->can_fork(child);
5958		if (ret)
5959			goto out_revert;
5960	} while_each_subsys_mask();
5961
5962	return 0;
5963
5964out_revert:
5965	for_each_subsys(ss, j) {
5966		if (j >= i)
5967			break;
5968		if (ss->cancel_fork)
5969			ss->cancel_fork(child);
5970	}
5971
5972	return ret;
5973}
5974
5975/**
5976 * cgroup_cancel_fork - called if a fork failed after cgroup_can_fork()
5977 * @child: the task in question
5978 *
5979 * This calls the cancel_fork() callbacks if a fork failed *after*
5980 * cgroup_can_fork() succeded.
5981 */
5982void cgroup_cancel_fork(struct task_struct *child)
5983{
5984	struct cgroup_subsys *ss;
5985	int i;
5986
5987	for_each_subsys(ss, i)
5988		if (ss->cancel_fork)
5989			ss->cancel_fork(child);
5990}
5991
5992/**
5993 * cgroup_post_fork - called on a new task after adding it to the task list
5994 * @child: the task in question
5995 *
5996 * Adds the task to the list running through its css_set if necessary and
5997 * call the subsystem fork() callbacks.  Has to be after the task is
5998 * visible on the task list in case we race with the first call to
5999 * cgroup_task_iter_start() - to guarantee that the new task ends up on its
6000 * list.
6001 */
6002void cgroup_post_fork(struct task_struct *child)
6003{
6004	struct cgroup_subsys *ss;
6005	int i;
6006
6007	/*
6008	 * This may race against cgroup_enable_task_cg_lists().  As that
6009	 * function sets use_task_css_set_links before grabbing
6010	 * tasklist_lock and we just went through tasklist_lock to add
6011	 * @child, it's guaranteed that either we see the set
6012	 * use_task_css_set_links or cgroup_enable_task_cg_lists() sees
6013	 * @child during its iteration.
6014	 *
6015	 * If we won the race, @child is associated with %current's
6016	 * css_set.  Grabbing css_set_lock guarantees both that the
6017	 * association is stable, and, on completion of the parent's
6018	 * migration, @child is visible in the source of migration or
6019	 * already in the destination cgroup.  This guarantee is necessary
6020	 * when implementing operations which need to migrate all tasks of
6021	 * a cgroup to another.
6022	 *
6023	 * Note that if we lose to cgroup_enable_task_cg_lists(), @child
6024	 * will remain in init_css_set.  This is safe because all tasks are
6025	 * in the init_css_set before cg_links is enabled and there's no
6026	 * operation which transfers all tasks out of init_css_set.
6027	 */
6028	if (use_task_css_set_links) {
6029		struct css_set *cset;
6030
6031		spin_lock_irq(&css_set_lock);
6032		cset = task_css_set(current);
6033		if (list_empty(&child->cg_list)) {
6034			get_css_set(cset);
6035			cset->nr_tasks++;
6036			css_set_move_task(child, NULL, cset, false);
6037		}
6038
6039		/*
6040		 * If the cgroup has to be frozen, the new task has too.
6041		 * Let's set the JOBCTL_TRAP_FREEZE jobctl bit to get
6042		 * the task into the frozen state.
6043		 */
6044		if (unlikely(cgroup_task_freeze(child))) {
6045			spin_lock(&child->sighand->siglock);
6046			WARN_ON_ONCE(child->frozen);
6047			child->jobctl |= JOBCTL_TRAP_FREEZE;
6048			spin_unlock(&child->sighand->siglock);
6049
6050			/*
6051			 * Calling cgroup_update_frozen() isn't required here,
6052			 * because it will be called anyway a bit later
6053			 * from do_freezer_trap(). So we avoid cgroup's
6054			 * transient switch from the frozen state and back.
6055			 */
6056		}
6057
6058		spin_unlock_irq(&css_set_lock);
6059	}
6060
6061	/*
6062	 * Call ss->fork().  This must happen after @child is linked on
6063	 * css_set; otherwise, @child might change state between ->fork()
6064	 * and addition to css_set.
6065	 */
6066	do_each_subsys_mask(ss, i, have_fork_callback) {
6067		ss->fork(child);
6068	} while_each_subsys_mask();
6069}
6070
6071/**
6072 * cgroup_exit - detach cgroup from exiting task
6073 * @tsk: pointer to task_struct of exiting process
6074 *
6075 * Description: Detach cgroup from @tsk and release it.
6076 *
6077 * Note that cgroups marked notify_on_release force every task in
6078 * them to take the global cgroup_mutex mutex when exiting.
6079 * This could impact scaling on very large systems.  Be reluctant to
6080 * use notify_on_release cgroups where very high task exit scaling
6081 * is required on large systems.
6082 *
6083 * We set the exiting tasks cgroup to the root cgroup (top_cgroup).  We
6084 * call cgroup_exit() while the task is still competent to handle
6085 * notify_on_release(), then leave the task attached to the root cgroup in
6086 * each hierarchy for the remainder of its exit.  No need to bother with
6087 * init_css_set refcnting.  init_css_set never goes away and we can't race
6088 * with migration path - PF_EXITING is visible to migration path.
6089 */
6090void cgroup_exit(struct task_struct *tsk)
6091{
6092	struct cgroup_subsys *ss;
6093	struct css_set *cset;
6094	int i;
6095
6096	/*
6097	 * Unlink from @tsk from its css_set.  As migration path can't race
6098	 * with us, we can check css_set and cg_list without synchronization.
6099	 */
6100	cset = task_css_set(tsk);
6101
6102	if (!list_empty(&tsk->cg_list)) {
6103		spin_lock_irq(&css_set_lock);
6104		css_set_move_task(tsk, cset, NULL, false);
6105		list_add_tail(&tsk->cg_list, &cset->dying_tasks);
6106		cset->nr_tasks--;
6107
6108		WARN_ON_ONCE(cgroup_task_frozen(tsk));
6109		if (unlikely(cgroup_task_freeze(tsk)))
6110			cgroup_update_frozen(task_dfl_cgroup(tsk));
6111
6112		spin_unlock_irq(&css_set_lock);
6113	} else {
6114		get_css_set(cset);
6115	}
6116
6117	/* see cgroup_post_fork() for details */
6118	do_each_subsys_mask(ss, i, have_exit_callback) {
6119		ss->exit(tsk);
6120	} while_each_subsys_mask();
6121}
6122
6123void cgroup_release(struct task_struct *task)
6124{
 
6125	struct cgroup_subsys *ss;
6126	int ssid;
6127
6128	do_each_subsys_mask(ss, ssid, have_release_callback) {
6129		ss->release(task);
6130	} while_each_subsys_mask();
6131
6132	if (use_task_css_set_links) {
6133		spin_lock_irq(&css_set_lock);
6134		css_set_skip_task_iters(task_css_set(task), task);
6135		list_del_init(&task->cg_list);
6136		spin_unlock_irq(&css_set_lock);
6137	}
6138}
6139
6140void cgroup_free(struct task_struct *task)
6141{
6142	struct css_set *cset = task_css_set(task);
6143	put_css_set(cset);
6144}
6145
6146static int __init cgroup_disable(char *str)
6147{
6148	struct cgroup_subsys *ss;
6149	char *token;
6150	int i;
6151
6152	while ((token = strsep(&str, ",")) != NULL) {
6153		if (!*token)
6154			continue;
6155
6156		for_each_subsys(ss, i) {
6157			if (strcmp(token, ss->name) &&
6158			    strcmp(token, ss->legacy_name))
6159				continue;
6160			cgroup_disable_mask |= 1 << i;
6161		}
6162	}
6163	return 1;
6164}
6165__setup("cgroup_disable=", cgroup_disable);
6166
6167void __init __weak enable_debug_cgroup(void) { }
6168
6169static int __init enable_cgroup_debug(char *str)
6170{
6171	cgroup_debug = true;
6172	enable_debug_cgroup();
6173	return 1;
6174}
6175__setup("cgroup_debug", enable_cgroup_debug);
6176
6177/**
6178 * css_tryget_online_from_dir - get corresponding css from a cgroup dentry
6179 * @dentry: directory dentry of interest
6180 * @ss: subsystem of interest
6181 *
6182 * If @dentry is a directory for a cgroup which has @ss enabled on it, try
6183 * to get the corresponding css and return it.  If such css doesn't exist
6184 * or can't be pinned, an ERR_PTR value is returned.
6185 */
6186struct cgroup_subsys_state *css_tryget_online_from_dir(struct dentry *dentry,
6187						       struct cgroup_subsys *ss)
6188{
6189	struct kernfs_node *kn = kernfs_node_from_dentry(dentry);
6190	struct file_system_type *s_type = dentry->d_sb->s_type;
6191	struct cgroup_subsys_state *css = NULL;
6192	struct cgroup *cgrp;
6193
6194	/* is @dentry a cgroup dir? */
6195	if ((s_type != &cgroup_fs_type && s_type != &cgroup2_fs_type) ||
6196	    !kn || kernfs_type(kn) != KERNFS_DIR)
6197		return ERR_PTR(-EBADF);
6198
6199	rcu_read_lock();
6200
6201	/*
6202	 * This path doesn't originate from kernfs and @kn could already
6203	 * have been or be removed at any point.  @kn->priv is RCU
6204	 * protected for this access.  See css_release_work_fn() for details.
6205	 */
6206	cgrp = rcu_dereference(*(void __rcu __force **)&kn->priv);
6207	if (cgrp)
6208		css = cgroup_css(cgrp, ss);
6209
6210	if (!css || !css_tryget_online(css))
6211		css = ERR_PTR(-ENOENT);
6212
6213	rcu_read_unlock();
6214	return css;
6215}
6216
6217/**
6218 * css_from_id - lookup css by id
6219 * @id: the cgroup id
6220 * @ss: cgroup subsys to be looked into
6221 *
6222 * Returns the css if there's valid one with @id, otherwise returns NULL.
6223 * Should be called under rcu_read_lock().
6224 */
6225struct cgroup_subsys_state *css_from_id(int id, struct cgroup_subsys *ss)
6226{
6227	WARN_ON_ONCE(!rcu_read_lock_held());
6228	return idr_find(&ss->css_idr, id);
6229}
6230
6231/**
6232 * cgroup_get_from_path - lookup and get a cgroup from its default hierarchy path
6233 * @path: path on the default hierarchy
6234 *
6235 * Find the cgroup at @path on the default hierarchy, increment its
6236 * reference count and return it.  Returns pointer to the found cgroup on
6237 * success, ERR_PTR(-ENOENT) if @path doens't exist and ERR_PTR(-ENOTDIR)
6238 * if @path points to a non-directory.
6239 */
6240struct cgroup *cgroup_get_from_path(const char *path)
6241{
6242	struct kernfs_node *kn;
6243	struct cgroup *cgrp;
6244
6245	mutex_lock(&cgroup_mutex);
6246
6247	kn = kernfs_walk_and_get(cgrp_dfl_root.cgrp.kn, path);
6248	if (kn) {
6249		if (kernfs_type(kn) == KERNFS_DIR) {
6250			cgrp = kn->priv;
6251			cgroup_get_live(cgrp);
6252		} else {
6253			cgrp = ERR_PTR(-ENOTDIR);
6254		}
6255		kernfs_put(kn);
6256	} else {
6257		cgrp = ERR_PTR(-ENOENT);
6258	}
6259
6260	mutex_unlock(&cgroup_mutex);
6261	return cgrp;
6262}
6263EXPORT_SYMBOL_GPL(cgroup_get_from_path);
6264
6265/**
6266 * cgroup_get_from_fd - get a cgroup pointer from a fd
6267 * @fd: fd obtained by open(cgroup2_dir)
6268 *
6269 * Find the cgroup from a fd which should be obtained
6270 * by opening a cgroup directory.  Returns a pointer to the
6271 * cgroup on success. ERR_PTR is returned if the cgroup
6272 * cannot be found.
6273 */
6274struct cgroup *cgroup_get_from_fd(int fd)
6275{
6276	struct cgroup_subsys_state *css;
6277	struct cgroup *cgrp;
6278	struct file *f;
6279
6280	f = fget_raw(fd);
6281	if (!f)
6282		return ERR_PTR(-EBADF);
6283
6284	css = css_tryget_online_from_dir(f->f_path.dentry, NULL);
6285	fput(f);
6286	if (IS_ERR(css))
6287		return ERR_CAST(css);
6288
6289	cgrp = css->cgroup;
6290	if (!cgroup_on_dfl(cgrp)) {
6291		cgroup_put(cgrp);
6292		return ERR_PTR(-EBADF);
6293	}
6294
6295	return cgrp;
6296}
6297EXPORT_SYMBOL_GPL(cgroup_get_from_fd);
6298
6299static u64 power_of_ten(int power)
6300{
6301	u64 v = 1;
6302	while (power--)
6303		v *= 10;
6304	return v;
6305}
6306
6307/**
6308 * cgroup_parse_float - parse a floating number
6309 * @input: input string
6310 * @dec_shift: number of decimal digits to shift
6311 * @v: output
6312 *
6313 * Parse a decimal floating point number in @input and store the result in
6314 * @v with decimal point right shifted @dec_shift times.  For example, if
6315 * @input is "12.3456" and @dec_shift is 3, *@v will be set to 12345.
6316 * Returns 0 on success, -errno otherwise.
6317 *
6318 * There's nothing cgroup specific about this function except that it's
6319 * currently the only user.
6320 */
6321int cgroup_parse_float(const char *input, unsigned dec_shift, s64 *v)
6322{
6323	s64 whole, frac = 0;
6324	int fstart = 0, fend = 0, flen;
6325
6326	if (!sscanf(input, "%lld.%n%lld%n", &whole, &fstart, &frac, &fend))
6327		return -EINVAL;
6328	if (frac < 0)
6329		return -EINVAL;
6330
6331	flen = fend > fstart ? fend - fstart : 0;
6332	if (flen < dec_shift)
6333		frac *= power_of_ten(dec_shift - flen);
6334	else
6335		frac = DIV_ROUND_CLOSEST_ULL(frac, power_of_ten(flen - dec_shift));
6336
6337	*v = whole * power_of_ten(dec_shift) + frac;
6338	return 0;
6339}
6340
6341/*
6342 * sock->sk_cgrp_data handling.  For more info, see sock_cgroup_data
6343 * definition in cgroup-defs.h.
6344 */
6345#ifdef CONFIG_SOCK_CGROUP_DATA
6346
6347#if defined(CONFIG_CGROUP_NET_PRIO) || defined(CONFIG_CGROUP_NET_CLASSID)
6348
6349DEFINE_SPINLOCK(cgroup_sk_update_lock);
6350static bool cgroup_sk_alloc_disabled __read_mostly;
6351
6352void cgroup_sk_alloc_disable(void)
6353{
6354	if (cgroup_sk_alloc_disabled)
6355		return;
6356	pr_info("cgroup: disabling cgroup2 socket matching due to net_prio or net_cls activation\n");
6357	cgroup_sk_alloc_disabled = true;
6358}
6359
6360#else
6361
6362#define cgroup_sk_alloc_disabled	false
6363
6364#endif
6365
6366void cgroup_sk_alloc(struct sock_cgroup_data *skcd)
6367{
6368	if (cgroup_sk_alloc_disabled)
6369		return;
6370
6371	/* Socket clone path */
6372	if (skcd->val) {
6373		/*
6374		 * We might be cloning a socket which is left in an empty
6375		 * cgroup and the cgroup might have already been rmdir'd.
6376		 * Don't use cgroup_get_live().
6377		 */
6378		cgroup_get(sock_cgroup_ptr(skcd));
6379		cgroup_bpf_get(sock_cgroup_ptr(skcd));
6380		return;
6381	}
6382
6383	rcu_read_lock();
6384
6385	while (true) {
6386		struct css_set *cset;
6387
6388		cset = task_css_set(current);
6389		if (likely(cgroup_tryget(cset->dfl_cgrp))) {
6390			skcd->val = (unsigned long)cset->dfl_cgrp;
6391			cgroup_bpf_get(cset->dfl_cgrp);
6392			break;
6393		}
6394		cpu_relax();
6395	}
6396
6397	rcu_read_unlock();
6398}
6399
6400void cgroup_sk_free(struct sock_cgroup_data *skcd)
6401{
6402	struct cgroup *cgrp = sock_cgroup_ptr(skcd);
6403
6404	cgroup_bpf_put(cgrp);
6405	cgroup_put(cgrp);
6406}
6407
6408#endif	/* CONFIG_SOCK_CGROUP_DATA */
6409
6410#ifdef CONFIG_CGROUP_BPF
6411int cgroup_bpf_attach(struct cgroup *cgrp, struct bpf_prog *prog,
6412		      enum bpf_attach_type type, u32 flags)
6413{
6414	int ret;
6415
6416	mutex_lock(&cgroup_mutex);
6417	ret = __cgroup_bpf_attach(cgrp, prog, type, flags);
6418	mutex_unlock(&cgroup_mutex);
6419	return ret;
6420}
6421int cgroup_bpf_detach(struct cgroup *cgrp, struct bpf_prog *prog,
6422		      enum bpf_attach_type type, u32 flags)
6423{
6424	int ret;
6425
6426	mutex_lock(&cgroup_mutex);
6427	ret = __cgroup_bpf_detach(cgrp, prog, type);
6428	mutex_unlock(&cgroup_mutex);
6429	return ret;
6430}
6431int cgroup_bpf_query(struct cgroup *cgrp, const union bpf_attr *attr,
6432		     union bpf_attr __user *uattr)
6433{
6434	int ret;
6435
6436	mutex_lock(&cgroup_mutex);
6437	ret = __cgroup_bpf_query(cgrp, attr, uattr);
6438	mutex_unlock(&cgroup_mutex);
6439	return ret;
6440}
6441#endif /* CONFIG_CGROUP_BPF */
6442
6443#ifdef CONFIG_SYSFS
6444static ssize_t show_delegatable_files(struct cftype *files, char *buf,
6445				      ssize_t size, const char *prefix)
6446{
6447	struct cftype *cft;
6448	ssize_t ret = 0;
6449
6450	for (cft = files; cft && cft->name[0] != '\0'; cft++) {
6451		if (!(cft->flags & CFTYPE_NS_DELEGATABLE))
6452			continue;
6453
6454		if (prefix)
6455			ret += snprintf(buf + ret, size - ret, "%s.", prefix);
6456
6457		ret += snprintf(buf + ret, size - ret, "%s\n", cft->name);
6458
6459		if (WARN_ON(ret >= size))
 
6460			break;
 
6461	}
6462
6463	return ret;
6464}
6465
6466static ssize_t delegate_show(struct kobject *kobj, struct kobj_attribute *attr,
6467			      char *buf)
6468{
6469	struct cgroup_subsys *ss;
6470	int ssid;
6471	ssize_t ret = 0;
6472
6473	ret = show_delegatable_files(cgroup_base_files, buf, PAGE_SIZE - ret,
6474				     NULL);
6475
6476	for_each_subsys(ss, ssid)
6477		ret += show_delegatable_files(ss->dfl_cftypes, buf + ret,
6478					      PAGE_SIZE - ret,
6479					      cgroup_subsys_name[ssid]);
6480
6481	return ret;
6482}
6483static struct kobj_attribute cgroup_delegate_attr = __ATTR_RO(delegate);
6484
6485static ssize_t features_show(struct kobject *kobj, struct kobj_attribute *attr,
6486			     char *buf)
6487{
6488	return snprintf(buf, PAGE_SIZE, "nsdelegate\nmemory_localevents\n");
6489}
6490static struct kobj_attribute cgroup_features_attr = __ATTR_RO(features);
6491
6492static struct attribute *cgroup_sysfs_attrs[] = {
6493	&cgroup_delegate_attr.attr,
6494	&cgroup_features_attr.attr,
6495	NULL,
6496};
6497
6498static const struct attribute_group cgroup_sysfs_attr_group = {
6499	.attrs = cgroup_sysfs_attrs,
6500	.name = "cgroup",
6501};
6502
6503static int __init cgroup_sysfs_init(void)
6504{
6505	return sysfs_create_group(kernel_kobj, &cgroup_sysfs_attr_group);
6506}
6507subsys_initcall(cgroup_sysfs_init);
6508
6509#endif /* CONFIG_SYSFS */