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 <linux/cgroup.h>
  32#include <linux/cred.h>
  33#include <linux/ctype.h>
  34#include <linux/errno.h>
  35#include <linux/init_task.h>
  36#include <linux/kernel.h>
  37#include <linux/list.h>
  38#include <linux/magic.h>
  39#include <linux/mm.h>
  40#include <linux/mutex.h>
  41#include <linux/mount.h>
  42#include <linux/pagemap.h>
  43#include <linux/proc_fs.h>
  44#include <linux/rcupdate.h>
  45#include <linux/sched.h>
  46#include <linux/slab.h>
  47#include <linux/spinlock.h>
  48#include <linux/percpu-rwsem.h>
  49#include <linux/string.h>
  50#include <linux/sort.h>
  51#include <linux/kmod.h>
  52#include <linux/delayacct.h>
  53#include <linux/cgroupstats.h>
  54#include <linux/hashtable.h>
  55#include <linux/pid_namespace.h>
  56#include <linux/idr.h>
  57#include <linux/vmalloc.h> /* TODO: replace with more sophisticated array */
  58#include <linux/kthread.h>
  59#include <linux/delay.h>
  60#include <linux/atomic.h>
  61#include <linux/cpuset.h>
  62#include <linux/proc_ns.h>
  63#include <linux/nsproxy.h>
  64#include <linux/file.h>
  65#include <net/sock.h>
  66
  67#define CREATE_TRACE_POINTS
  68#include <trace/events/cgroup.h>
  69
  70/*
  71 * pidlists linger the following amount before being destroyed.  The goal
  72 * is avoiding frequent destruction in the middle of consecutive read calls
  73 * Expiring in the middle is a performance problem not a correctness one.
  74 * 1 sec should be enough.
  75 */
  76#define CGROUP_PIDLIST_DESTROY_DELAY	HZ
  77
  78#define CGROUP_FILE_NAME_MAX		(MAX_CGROUP_TYPE_NAMELEN +	\
  79					 MAX_CFTYPE_NAME + 2)
  80
  81/*
  82 * cgroup_mutex is the master lock.  Any modification to cgroup or its
  83 * hierarchy must be performed while holding it.
  84 *
  85 * css_set_lock protects task->cgroups pointer, the list of css_set
  86 * objects, and the chain of tasks off each css_set.
  87 *
  88 * These locks are exported if CONFIG_PROVE_RCU so that accessors in
  89 * cgroup.h can use them for lockdep annotations.
  90 */
  91#ifdef CONFIG_PROVE_RCU
  92DEFINE_MUTEX(cgroup_mutex);
  93DEFINE_SPINLOCK(css_set_lock);
  94EXPORT_SYMBOL_GPL(cgroup_mutex);
  95EXPORT_SYMBOL_GPL(css_set_lock);
  96#else
  97static DEFINE_MUTEX(cgroup_mutex);
  98static DEFINE_SPINLOCK(css_set_lock);
  99#endif
 100
 101/*
 102 * Protects cgroup_idr and css_idr so that IDs can be released without
 103 * grabbing cgroup_mutex.
 104 */
 105static DEFINE_SPINLOCK(cgroup_idr_lock);
 106
 107/*
 108 * Protects cgroup_file->kn for !self csses.  It synchronizes notifications
 109 * against file removal/re-creation across css hiding.
 110 */
 111static DEFINE_SPINLOCK(cgroup_file_kn_lock);
 112
 113/*
 114 * Protects cgroup_subsys->release_agent_path.  Modifying it also requires
 115 * cgroup_mutex.  Reading requires either cgroup_mutex or this spinlock.
 116 */
 117static DEFINE_SPINLOCK(release_agent_path_lock);
 118
 119struct percpu_rw_semaphore cgroup_threadgroup_rwsem;
 120
 121#define cgroup_assert_mutex_or_rcu_locked()				\
 122	RCU_LOCKDEP_WARN(!rcu_read_lock_held() &&			\
 123			   !lockdep_is_held(&cgroup_mutex),		\
 124			   "cgroup_mutex or RCU read lock required");
 125
 126/*
 127 * cgroup destruction makes heavy use of work items and there can be a lot
 128 * of concurrent destructions.  Use a separate workqueue so that cgroup
 129 * destruction work items don't end up filling up max_active of system_wq
 130 * which may lead to deadlock.
 131 */
 132static struct workqueue_struct *cgroup_destroy_wq;
 133
 134/*
 135 * pidlist destructions need to be flushed on cgroup destruction.  Use a
 136 * separate workqueue as flush domain.
 137 */
 138static struct workqueue_struct *cgroup_pidlist_destroy_wq;
 139
 140/* generate an array of cgroup subsystem pointers */
 141#define SUBSYS(_x) [_x ## _cgrp_id] = &_x ## _cgrp_subsys,
 142static struct cgroup_subsys *cgroup_subsys[] = {
 143#include <linux/cgroup_subsys.h>
 144};
 145#undef SUBSYS
 146
 147/* array of cgroup subsystem names */
 148#define SUBSYS(_x) [_x ## _cgrp_id] = #_x,
 149static const char *cgroup_subsys_name[] = {
 150#include <linux/cgroup_subsys.h>
 151};
 152#undef SUBSYS
 153
 154/* array of static_keys for cgroup_subsys_enabled() and cgroup_subsys_on_dfl() */
 155#define SUBSYS(_x)								\
 156	DEFINE_STATIC_KEY_TRUE(_x ## _cgrp_subsys_enabled_key);			\
 157	DEFINE_STATIC_KEY_TRUE(_x ## _cgrp_subsys_on_dfl_key);			\
 158	EXPORT_SYMBOL_GPL(_x ## _cgrp_subsys_enabled_key);			\
 159	EXPORT_SYMBOL_GPL(_x ## _cgrp_subsys_on_dfl_key);
 160#include <linux/cgroup_subsys.h>
 161#undef SUBSYS
 162
 163#define SUBSYS(_x) [_x ## _cgrp_id] = &_x ## _cgrp_subsys_enabled_key,
 164static struct static_key_true *cgroup_subsys_enabled_key[] = {
 165#include <linux/cgroup_subsys.h>
 166};
 167#undef SUBSYS
 168
 169#define SUBSYS(_x) [_x ## _cgrp_id] = &_x ## _cgrp_subsys_on_dfl_key,
 170static struct static_key_true *cgroup_subsys_on_dfl_key[] = {
 171#include <linux/cgroup_subsys.h>
 172};
 173#undef SUBSYS
 174
 175/*
 176 * The default hierarchy, reserved for the subsystems that are otherwise
 177 * unattached - it never has more than a single cgroup, and all tasks are
 178 * part of that cgroup.
 179 */
 180struct cgroup_root cgrp_dfl_root;
 181EXPORT_SYMBOL_GPL(cgrp_dfl_root);
 182
 183/*
 184 * The default hierarchy always exists but is hidden until mounted for the
 185 * first time.  This is for backward compatibility.
 186 */
 187static bool cgrp_dfl_visible;
 188
 189/* Controllers blocked by the commandline in v1 */
 190static u16 cgroup_no_v1_mask;
 191
 192/* some controllers are not supported in the default hierarchy */
 193static u16 cgrp_dfl_inhibit_ss_mask;
 194
 195/* some controllers are implicitly enabled on the default hierarchy */
 196static unsigned long cgrp_dfl_implicit_ss_mask;
 197
 198/* The list of hierarchy roots */
 199
 200static LIST_HEAD(cgroup_roots);
 201static int cgroup_root_count;
 202
 203/* hierarchy ID allocation and mapping, protected by cgroup_mutex */
 204static DEFINE_IDR(cgroup_hierarchy_idr);
 205
 206/*
 207 * Assign a monotonically increasing serial number to csses.  It guarantees
 208 * cgroups with bigger numbers are newer than those with smaller numbers.
 209 * Also, as csses are always appended to the parent's ->children list, it
 210 * guarantees that sibling csses are always sorted in the ascending serial
 211 * number order on the list.  Protected by cgroup_mutex.
 212 */
 213static u64 css_serial_nr_next = 1;
 214
 215/*
 216 * These bitmask flags indicate whether tasks in the fork and exit paths have
 217 * fork/exit handlers to call. This avoids us having to do extra work in the
 218 * fork/exit path to check which subsystems have fork/exit callbacks.
 219 */
 220static u16 have_fork_callback __read_mostly;
 221static u16 have_exit_callback __read_mostly;
 222static u16 have_free_callback __read_mostly;
 223
 224/* cgroup namespace for init task */
 225struct cgroup_namespace init_cgroup_ns = {
 226	.count		= { .counter = 2, },
 227	.user_ns	= &init_user_ns,
 228	.ns.ops		= &cgroupns_operations,
 229	.ns.inum	= PROC_CGROUP_INIT_INO,
 230	.root_cset	= &init_css_set,
 231};
 232
 233/* Ditto for the can_fork callback. */
 234static u16 have_canfork_callback __read_mostly;
 235
 236static struct file_system_type cgroup2_fs_type;
 237static struct cftype cgroup_dfl_base_files[];
 238static struct cftype cgroup_legacy_base_files[];
 239
 240static int rebind_subsystems(struct cgroup_root *dst_root, u16 ss_mask);
 241static void cgroup_lock_and_drain_offline(struct cgroup *cgrp);
 242static int cgroup_apply_control(struct cgroup *cgrp);
 243static void cgroup_finalize_control(struct cgroup *cgrp, int ret);
 244static void css_task_iter_advance(struct css_task_iter *it);
 245static int cgroup_destroy_locked(struct cgroup *cgrp);
 246static struct cgroup_subsys_state *css_create(struct cgroup *cgrp,
 247					      struct cgroup_subsys *ss);
 248static void css_release(struct percpu_ref *ref);
 249static void kill_css(struct cgroup_subsys_state *css);
 250static int cgroup_addrm_files(struct cgroup_subsys_state *css,
 251			      struct cgroup *cgrp, struct cftype cfts[],
 252			      bool is_add);
 253
 254/**
 255 * cgroup_ssid_enabled - cgroup subsys enabled test by subsys ID
 256 * @ssid: subsys ID of interest
 257 *
 258 * cgroup_subsys_enabled() can only be used with literal subsys names which
 259 * is fine for individual subsystems but unsuitable for cgroup core.  This
 260 * is slower static_key_enabled() based test indexed by @ssid.
 261 */
 262static bool cgroup_ssid_enabled(int ssid)
 263{
 264	if (CGROUP_SUBSYS_COUNT == 0)
 265		return false;
 266
 267	return static_key_enabled(cgroup_subsys_enabled_key[ssid]);
 268}
 269
 270static bool cgroup_ssid_no_v1(int ssid)
 271{
 272	return cgroup_no_v1_mask & (1 << ssid);
 273}
 274
 275/**
 276 * cgroup_on_dfl - test whether a cgroup is on the default hierarchy
 277 * @cgrp: the cgroup of interest
 278 *
 279 * The default hierarchy is the v2 interface of cgroup and this function
 280 * can be used to test whether a cgroup is on the default hierarchy for
 281 * cases where a subsystem should behave differnetly depending on the
 282 * interface version.
 283 *
 284 * The set of behaviors which change on the default hierarchy are still
 285 * being determined and the mount option is prefixed with __DEVEL__.
 286 *
 287 * List of changed behaviors:
 288 *
 289 * - Mount options "noprefix", "xattr", "clone_children", "release_agent"
 290 *   and "name" are disallowed.
 291 *
 292 * - When mounting an existing superblock, mount options should match.
 293 *
 294 * - Remount is disallowed.
 295 *
 296 * - rename(2) is disallowed.
 297 *
 298 * - "tasks" is removed.  Everything should be at process granularity.  Use
 299 *   "cgroup.procs" instead.
 300 *
 301 * - "cgroup.procs" is not sorted.  pids will be unique unless they got
 302 *   recycled inbetween reads.
 303 *
 304 * - "release_agent" and "notify_on_release" are removed.  Replacement
 305 *   notification mechanism will be implemented.
 306 *
 307 * - "cgroup.clone_children" is removed.
 308 *
 309 * - "cgroup.subtree_populated" is available.  Its value is 0 if the cgroup
 310 *   and its descendants contain no task; otherwise, 1.  The file also
 311 *   generates kernfs notification which can be monitored through poll and
 312 *   [di]notify when the value of the file changes.
 313 *
 314 * - cpuset: tasks will be kept in empty cpusets when hotplug happens and
 315 *   take masks of ancestors with non-empty cpus/mems, instead of being
 316 *   moved to an ancestor.
 317 *
 318 * - cpuset: a task can be moved into an empty cpuset, and again it takes
 319 *   masks of ancestors.
 320 *
 321 * - memcg: use_hierarchy is on by default and the cgroup file for the flag
 322 *   is not created.
 323 *
 324 * - blkcg: blk-throttle becomes properly hierarchical.
 325 *
 326 * - debug: disallowed on the default hierarchy.
 327 */
 328static bool cgroup_on_dfl(const struct cgroup *cgrp)
 329{
 330	return cgrp->root == &cgrp_dfl_root;
 331}
 332
 333/* IDR wrappers which synchronize using cgroup_idr_lock */
 334static int cgroup_idr_alloc(struct idr *idr, void *ptr, int start, int end,
 335			    gfp_t gfp_mask)
 336{
 337	int ret;
 338
 339	idr_preload(gfp_mask);
 340	spin_lock_bh(&cgroup_idr_lock);
 341	ret = idr_alloc(idr, ptr, start, end, gfp_mask & ~__GFP_DIRECT_RECLAIM);
 342	spin_unlock_bh(&cgroup_idr_lock);
 343	idr_preload_end();
 344	return ret;
 345}
 346
 347static void *cgroup_idr_replace(struct idr *idr, void *ptr, int id)
 348{
 349	void *ret;
 350
 351	spin_lock_bh(&cgroup_idr_lock);
 352	ret = idr_replace(idr, ptr, id);
 353	spin_unlock_bh(&cgroup_idr_lock);
 354	return ret;
 355}
 356
 357static void cgroup_idr_remove(struct idr *idr, int id)
 358{
 359	spin_lock_bh(&cgroup_idr_lock);
 360	idr_remove(idr, id);
 361	spin_unlock_bh(&cgroup_idr_lock);
 362}
 363
 364static struct cgroup *cgroup_parent(struct cgroup *cgrp)
 365{
 366	struct cgroup_subsys_state *parent_css = cgrp->self.parent;
 367
 368	if (parent_css)
 369		return container_of(parent_css, struct cgroup, self);
 370	return NULL;
 371}
 372
 373/* subsystems visibly enabled on a cgroup */
 374static u16 cgroup_control(struct cgroup *cgrp)
 375{
 376	struct cgroup *parent = cgroup_parent(cgrp);
 377	u16 root_ss_mask = cgrp->root->subsys_mask;
 378
 379	if (parent)
 380		return parent->subtree_control;
 381
 382	if (cgroup_on_dfl(cgrp))
 383		root_ss_mask &= ~(cgrp_dfl_inhibit_ss_mask |
 384				  cgrp_dfl_implicit_ss_mask);
 385	return root_ss_mask;
 386}
 387
 388/* subsystems enabled on a cgroup */
 389static u16 cgroup_ss_mask(struct cgroup *cgrp)
 390{
 391	struct cgroup *parent = cgroup_parent(cgrp);
 392
 393	if (parent)
 394		return parent->subtree_ss_mask;
 395
 396	return cgrp->root->subsys_mask;
 397}
 398
 399/**
 400 * cgroup_css - obtain a cgroup's css for the specified subsystem
 401 * @cgrp: the cgroup of interest
 402 * @ss: the subsystem of interest (%NULL returns @cgrp->self)
 403 *
 404 * Return @cgrp's css (cgroup_subsys_state) associated with @ss.  This
 405 * function must be called either under cgroup_mutex or rcu_read_lock() and
 406 * the caller is responsible for pinning the returned css if it wants to
 407 * keep accessing it outside the said locks.  This function may return
 408 * %NULL if @cgrp doesn't have @subsys_id enabled.
 409 */
 410static struct cgroup_subsys_state *cgroup_css(struct cgroup *cgrp,
 411					      struct cgroup_subsys *ss)
 412{
 413	if (ss)
 414		return rcu_dereference_check(cgrp->subsys[ss->id],
 415					lockdep_is_held(&cgroup_mutex));
 416	else
 417		return &cgrp->self;
 418}
 419
 420/**
 421 * cgroup_e_css - obtain a cgroup's effective css for the specified subsystem
 422 * @cgrp: the cgroup of interest
 423 * @ss: the subsystem of interest (%NULL returns @cgrp->self)
 424 *
 425 * Similar to cgroup_css() but returns the effective css, which is defined
 426 * as the matching css of the nearest ancestor including self which has @ss
 427 * enabled.  If @ss is associated with the hierarchy @cgrp is on, this
 428 * function is guaranteed to return non-NULL css.
 429 */
 430static struct cgroup_subsys_state *cgroup_e_css(struct cgroup *cgrp,
 431						struct cgroup_subsys *ss)
 432{
 433	lockdep_assert_held(&cgroup_mutex);
 434
 435	if (!ss)
 436		return &cgrp->self;
 437
 438	/*
 439	 * This function is used while updating css associations and thus
 440	 * can't test the csses directly.  Test ss_mask.
 441	 */
 442	while (!(cgroup_ss_mask(cgrp) & (1 << ss->id))) {
 443		cgrp = cgroup_parent(cgrp);
 444		if (!cgrp)
 445			return NULL;
 446	}
 447
 448	return cgroup_css(cgrp, ss);
 449}
 450
 451/**
 452 * cgroup_get_e_css - get a cgroup's effective css for the specified subsystem
 453 * @cgrp: the cgroup of interest
 454 * @ss: the subsystem of interest
 455 *
 456 * Find and get the effective css of @cgrp for @ss.  The effective css is
 457 * defined as the matching css of the nearest ancestor including self which
 458 * has @ss enabled.  If @ss is not mounted on the hierarchy @cgrp is on,
 459 * the root css is returned, so this function always returns a valid css.
 460 * The returned css must be put using css_put().
 461 */
 462struct cgroup_subsys_state *cgroup_get_e_css(struct cgroup *cgrp,
 463					     struct cgroup_subsys *ss)
 464{
 465	struct cgroup_subsys_state *css;
 466
 467	rcu_read_lock();
 468
 469	do {
 470		css = cgroup_css(cgrp, ss);
 471
 472		if (css && css_tryget_online(css))
 473			goto out_unlock;
 474		cgrp = cgroup_parent(cgrp);
 475	} while (cgrp);
 476
 477	css = init_css_set.subsys[ss->id];
 478	css_get(css);
 479out_unlock:
 480	rcu_read_unlock();
 481	return css;
 482}
 483
 484/* convenient tests for these bits */
 485static inline bool cgroup_is_dead(const struct cgroup *cgrp)
 486{
 487	return !(cgrp->self.flags & CSS_ONLINE);
 488}
 489
 490static void cgroup_get(struct cgroup *cgrp)
 491{
 492	WARN_ON_ONCE(cgroup_is_dead(cgrp));
 493	css_get(&cgrp->self);
 494}
 495
 496static bool cgroup_tryget(struct cgroup *cgrp)
 497{
 498	return css_tryget(&cgrp->self);
 499}
 500
 501struct cgroup_subsys_state *of_css(struct kernfs_open_file *of)
 502{
 503	struct cgroup *cgrp = of->kn->parent->priv;
 504	struct cftype *cft = of_cft(of);
 505
 506	/*
 507	 * This is open and unprotected implementation of cgroup_css().
 508	 * seq_css() is only called from a kernfs file operation which has
 509	 * an active reference on the file.  Because all the subsystem
 510	 * files are drained before a css is disassociated with a cgroup,
 511	 * the matching css from the cgroup's subsys table is guaranteed to
 512	 * be and stay valid until the enclosing operation is complete.
 513	 */
 514	if (cft->ss)
 515		return rcu_dereference_raw(cgrp->subsys[cft->ss->id]);
 516	else
 517		return &cgrp->self;
 518}
 519EXPORT_SYMBOL_GPL(of_css);
 520
 521static int notify_on_release(const struct cgroup *cgrp)
 522{
 523	return test_bit(CGRP_NOTIFY_ON_RELEASE, &cgrp->flags);
 524}
 525
 526/**
 527 * for_each_css - iterate all css's of a cgroup
 528 * @css: the iteration cursor
 529 * @ssid: the index of the subsystem, CGROUP_SUBSYS_COUNT after reaching the end
 530 * @cgrp: the target cgroup to iterate css's of
 531 *
 532 * Should be called under cgroup_[tree_]mutex.
 533 */
 534#define for_each_css(css, ssid, cgrp)					\
 535	for ((ssid) = 0; (ssid) < CGROUP_SUBSYS_COUNT; (ssid)++)	\
 536		if (!((css) = rcu_dereference_check(			\
 537				(cgrp)->subsys[(ssid)],			\
 538				lockdep_is_held(&cgroup_mutex)))) { }	\
 539		else
 540
 541/**
 542 * for_each_e_css - iterate all effective css's of a cgroup
 543 * @css: the iteration cursor
 544 * @ssid: the index of the subsystem, CGROUP_SUBSYS_COUNT after reaching the end
 545 * @cgrp: the target cgroup to iterate css's of
 546 *
 547 * Should be called under cgroup_[tree_]mutex.
 548 */
 549#define for_each_e_css(css, ssid, cgrp)					\
 550	for ((ssid) = 0; (ssid) < CGROUP_SUBSYS_COUNT; (ssid)++)	\
 551		if (!((css) = cgroup_e_css(cgrp, cgroup_subsys[(ssid)]))) \
 552			;						\
 553		else
 554
 555/**
 556 * for_each_subsys - iterate all enabled cgroup subsystems
 557 * @ss: the iteration cursor
 558 * @ssid: the index of @ss, CGROUP_SUBSYS_COUNT after reaching the end
 559 */
 560#define for_each_subsys(ss, ssid)					\
 561	for ((ssid) = 0; (ssid) < CGROUP_SUBSYS_COUNT &&		\
 562	     (((ss) = cgroup_subsys[ssid]) || true); (ssid)++)
 563
 564/**
 565 * do_each_subsys_mask - filter for_each_subsys with a bitmask
 566 * @ss: the iteration cursor
 567 * @ssid: the index of @ss, CGROUP_SUBSYS_COUNT after reaching the end
 568 * @ss_mask: the bitmask
 569 *
 570 * The block will only run for cases where the ssid-th bit (1 << ssid) of
 571 * @ss_mask is set.
 572 */
 573#define do_each_subsys_mask(ss, ssid, ss_mask) do {			\
 574	unsigned long __ss_mask = (ss_mask);				\
 575	if (!CGROUP_SUBSYS_COUNT) { /* to avoid spurious gcc warning */	\
 576		(ssid) = 0;						\
 577		break;							\
 578	}								\
 579	for_each_set_bit(ssid, &__ss_mask, CGROUP_SUBSYS_COUNT) {	\
 580		(ss) = cgroup_subsys[ssid];				\
 581		{
 582
 583#define while_each_subsys_mask()					\
 584		}							\
 585	}								\
 586} while (false)
 587
 588/* iterate across the hierarchies */
 589#define for_each_root(root)						\
 590	list_for_each_entry((root), &cgroup_roots, root_list)
 591
 592/* iterate over child cgrps, lock should be held throughout iteration */
 593#define cgroup_for_each_live_child(child, cgrp)				\
 594	list_for_each_entry((child), &(cgrp)->self.children, self.sibling) \
 595		if (({ lockdep_assert_held(&cgroup_mutex);		\
 596		       cgroup_is_dead(child); }))			\
 597			;						\
 598		else
 599
 600/* walk live descendants in preorder */
 601#define cgroup_for_each_live_descendant_pre(dsct, d_css, cgrp)		\
 602	css_for_each_descendant_pre((d_css), cgroup_css((cgrp), NULL))	\
 603		if (({ lockdep_assert_held(&cgroup_mutex);		\
 604		       (dsct) = (d_css)->cgroup;			\
 605		       cgroup_is_dead(dsct); }))			\
 606			;						\
 607		else
 608
 609/* walk live descendants in postorder */
 610#define cgroup_for_each_live_descendant_post(dsct, d_css, cgrp)		\
 611	css_for_each_descendant_post((d_css), cgroup_css((cgrp), NULL))	\
 612		if (({ lockdep_assert_held(&cgroup_mutex);		\
 613		       (dsct) = (d_css)->cgroup;			\
 614		       cgroup_is_dead(dsct); }))			\
 615			;						\
 616		else
 617
 618static void cgroup_release_agent(struct work_struct *work);
 619static void check_for_release(struct cgroup *cgrp);
 620
 621/*
 622 * A cgroup can be associated with multiple css_sets as different tasks may
 623 * belong to different cgroups on different hierarchies.  In the other
 624 * direction, a css_set is naturally associated with multiple cgroups.
 625 * This M:N relationship is represented by the following link structure
 626 * which exists for each association and allows traversing the associations
 627 * from both sides.
 628 */
 629struct cgrp_cset_link {
 630	/* the cgroup and css_set this link associates */
 631	struct cgroup		*cgrp;
 632	struct css_set		*cset;
 633
 634	/* list of cgrp_cset_links anchored at cgrp->cset_links */
 635	struct list_head	cset_link;
 636
 637	/* list of cgrp_cset_links anchored at css_set->cgrp_links */
 638	struct list_head	cgrp_link;
 639};
 640
 641/*
 642 * The default css_set - used by init and its children prior to any
 643 * hierarchies being mounted. It contains a pointer to the root state
 644 * for each subsystem. Also used to anchor the list of css_sets. Not
 645 * reference-counted, to improve performance when child cgroups
 646 * haven't been created.
 647 */
 648struct css_set init_css_set = {
 649	.refcount		= ATOMIC_INIT(1),
 650	.cgrp_links		= LIST_HEAD_INIT(init_css_set.cgrp_links),
 651	.tasks			= LIST_HEAD_INIT(init_css_set.tasks),
 652	.mg_tasks		= LIST_HEAD_INIT(init_css_set.mg_tasks),
 653	.mg_preload_node	= LIST_HEAD_INIT(init_css_set.mg_preload_node),
 654	.mg_node		= LIST_HEAD_INIT(init_css_set.mg_node),
 655	.task_iters		= LIST_HEAD_INIT(init_css_set.task_iters),
 656};
 657
 658static int css_set_count	= 1;	/* 1 for init_css_set */
 659
 660/**
 661 * css_set_populated - does a css_set contain any tasks?
 662 * @cset: target css_set
 663 */
 664static bool css_set_populated(struct css_set *cset)
 665{
 666	lockdep_assert_held(&css_set_lock);
 667
 668	return !list_empty(&cset->tasks) || !list_empty(&cset->mg_tasks);
 669}
 670
 671/**
 672 * cgroup_update_populated - updated populated count of a cgroup
 673 * @cgrp: the target cgroup
 674 * @populated: inc or dec populated count
 675 *
 676 * One of the css_sets associated with @cgrp is either getting its first
 677 * task or losing the last.  Update @cgrp->populated_cnt accordingly.  The
 678 * count is propagated towards root so that a given cgroup's populated_cnt
 679 * is zero iff the cgroup and all its descendants don't contain any tasks.
 680 *
 681 * @cgrp's interface file "cgroup.populated" is zero if
 682 * @cgrp->populated_cnt is zero and 1 otherwise.  When @cgrp->populated_cnt
 683 * changes from or to zero, userland is notified that the content of the
 684 * interface file has changed.  This can be used to detect when @cgrp and
 685 * its descendants become populated or empty.
 686 */
 687static void cgroup_update_populated(struct cgroup *cgrp, bool populated)
 688{
 689	lockdep_assert_held(&css_set_lock);
 690
 691	do {
 692		bool trigger;
 693
 694		if (populated)
 695			trigger = !cgrp->populated_cnt++;
 696		else
 697			trigger = !--cgrp->populated_cnt;
 698
 699		if (!trigger)
 700			break;
 701
 702		check_for_release(cgrp);
 703		cgroup_file_notify(&cgrp->events_file);
 704
 705		cgrp = cgroup_parent(cgrp);
 706	} while (cgrp);
 707}
 708
 709/**
 710 * css_set_update_populated - update populated state of a css_set
 711 * @cset: target css_set
 712 * @populated: whether @cset is populated or depopulated
 713 *
 714 * @cset is either getting the first task or losing the last.  Update the
 715 * ->populated_cnt of all associated cgroups accordingly.
 716 */
 717static void css_set_update_populated(struct css_set *cset, bool populated)
 718{
 719	struct cgrp_cset_link *link;
 720
 721	lockdep_assert_held(&css_set_lock);
 722
 723	list_for_each_entry(link, &cset->cgrp_links, cgrp_link)
 724		cgroup_update_populated(link->cgrp, populated);
 725}
 726
 727/**
 728 * css_set_move_task - move a task from one css_set to another
 729 * @task: task being moved
 730 * @from_cset: css_set @task currently belongs to (may be NULL)
 731 * @to_cset: new css_set @task is being moved to (may be NULL)
 732 * @use_mg_tasks: move to @to_cset->mg_tasks instead of ->tasks
 733 *
 734 * Move @task from @from_cset to @to_cset.  If @task didn't belong to any
 735 * css_set, @from_cset can be NULL.  If @task is being disassociated
 736 * instead of moved, @to_cset can be NULL.
 737 *
 738 * This function automatically handles populated_cnt updates and
 739 * css_task_iter adjustments but the caller is responsible for managing
 740 * @from_cset and @to_cset's reference counts.
 741 */
 742static void css_set_move_task(struct task_struct *task,
 743			      struct css_set *from_cset, struct css_set *to_cset,
 744			      bool use_mg_tasks)
 745{
 746	lockdep_assert_held(&css_set_lock);
 747
 748	if (to_cset && !css_set_populated(to_cset))
 749		css_set_update_populated(to_cset, true);
 750
 751	if (from_cset) {
 752		struct css_task_iter *it, *pos;
 753
 754		WARN_ON_ONCE(list_empty(&task->cg_list));
 755
 756		/*
 757		 * @task is leaving, advance task iterators which are
 758		 * pointing to it so that they can resume at the next
 759		 * position.  Advancing an iterator might remove it from
 760		 * the list, use safe walk.  See css_task_iter_advance*()
 761		 * for details.
 762		 */
 763		list_for_each_entry_safe(it, pos, &from_cset->task_iters,
 764					 iters_node)
 765			if (it->task_pos == &task->cg_list)
 766				css_task_iter_advance(it);
 767
 768		list_del_init(&task->cg_list);
 769		if (!css_set_populated(from_cset))
 770			css_set_update_populated(from_cset, false);
 771	} else {
 772		WARN_ON_ONCE(!list_empty(&task->cg_list));
 773	}
 774
 775	if (to_cset) {
 776		/*
 777		 * We are synchronized through cgroup_threadgroup_rwsem
 778		 * against PF_EXITING setting such that we can't race
 779		 * against cgroup_exit() changing the css_set to
 780		 * init_css_set and dropping the old one.
 781		 */
 782		WARN_ON_ONCE(task->flags & PF_EXITING);
 783
 784		rcu_assign_pointer(task->cgroups, to_cset);
 785		list_add_tail(&task->cg_list, use_mg_tasks ? &to_cset->mg_tasks :
 786							     &to_cset->tasks);
 787	}
 788}
 789
 790/*
 791 * hash table for cgroup groups. This improves the performance to find
 792 * an existing css_set. This hash doesn't (currently) take into
 793 * account cgroups in empty hierarchies.
 794 */
 795#define CSS_SET_HASH_BITS	7
 796static DEFINE_HASHTABLE(css_set_table, CSS_SET_HASH_BITS);
 797
 798static unsigned long css_set_hash(struct cgroup_subsys_state *css[])
 799{
 800	unsigned long key = 0UL;
 801	struct cgroup_subsys *ss;
 802	int i;
 803
 804	for_each_subsys(ss, i)
 805		key += (unsigned long)css[i];
 806	key = (key >> 16) ^ key;
 807
 808	return key;
 809}
 810
 811static void put_css_set_locked(struct css_set *cset)
 812{
 813	struct cgrp_cset_link *link, *tmp_link;
 814	struct cgroup_subsys *ss;
 815	int ssid;
 816
 817	lockdep_assert_held(&css_set_lock);
 818
 819	if (!atomic_dec_and_test(&cset->refcount))
 820		return;
 821
 822	/* This css_set is dead. unlink it and release cgroup and css refs */
 823	for_each_subsys(ss, ssid) {
 824		list_del(&cset->e_cset_node[ssid]);
 825		css_put(cset->subsys[ssid]);
 826	}
 827	hash_del(&cset->hlist);
 828	css_set_count--;
 829
 830	list_for_each_entry_safe(link, tmp_link, &cset->cgrp_links, cgrp_link) {
 831		list_del(&link->cset_link);
 832		list_del(&link->cgrp_link);
 833		if (cgroup_parent(link->cgrp))
 834			cgroup_put(link->cgrp);
 835		kfree(link);
 836	}
 837
 838	kfree_rcu(cset, rcu_head);
 839}
 840
 841static void put_css_set(struct css_set *cset)
 842{
 843	unsigned long flags;
 844
 845	/*
 846	 * Ensure that the refcount doesn't hit zero while any readers
 847	 * can see it. Similar to atomic_dec_and_lock(), but for an
 848	 * rwlock
 849	 */
 850	if (atomic_add_unless(&cset->refcount, -1, 1))
 851		return;
 852
 853	spin_lock_irqsave(&css_set_lock, flags);
 854	put_css_set_locked(cset);
 855	spin_unlock_irqrestore(&css_set_lock, flags);
 856}
 857
 858/*
 859 * refcounted get/put for css_set objects
 860 */
 861static inline void get_css_set(struct css_set *cset)
 862{
 863	atomic_inc(&cset->refcount);
 864}
 865
 866/**
 867 * compare_css_sets - helper function for find_existing_css_set().
 868 * @cset: candidate css_set being tested
 869 * @old_cset: existing css_set for a task
 870 * @new_cgrp: cgroup that's being entered by the task
 871 * @template: desired set of css pointers in css_set (pre-calculated)
 872 *
 873 * Returns true if "cset" matches "old_cset" except for the hierarchy
 874 * which "new_cgrp" belongs to, for which it should match "new_cgrp".
 875 */
 876static bool compare_css_sets(struct css_set *cset,
 877			     struct css_set *old_cset,
 878			     struct cgroup *new_cgrp,
 879			     struct cgroup_subsys_state *template[])
 880{
 881	struct list_head *l1, *l2;
 882
 883	/*
 884	 * On the default hierarchy, there can be csets which are
 885	 * associated with the same set of cgroups but different csses.
 886	 * Let's first ensure that csses match.
 887	 */
 888	if (memcmp(template, cset->subsys, sizeof(cset->subsys)))
 889		return false;
 890
 891	/*
 892	 * Compare cgroup pointers in order to distinguish between
 893	 * different cgroups in hierarchies.  As different cgroups may
 894	 * share the same effective css, this comparison is always
 895	 * necessary.
 896	 */
 897	l1 = &cset->cgrp_links;
 898	l2 = &old_cset->cgrp_links;
 899	while (1) {
 900		struct cgrp_cset_link *link1, *link2;
 901		struct cgroup *cgrp1, *cgrp2;
 902
 903		l1 = l1->next;
 904		l2 = l2->next;
 905		/* See if we reached the end - both lists are equal length. */
 906		if (l1 == &cset->cgrp_links) {
 907			BUG_ON(l2 != &old_cset->cgrp_links);
 908			break;
 909		} else {
 910			BUG_ON(l2 == &old_cset->cgrp_links);
 911		}
 912		/* Locate the cgroups associated with these links. */
 913		link1 = list_entry(l1, struct cgrp_cset_link, cgrp_link);
 914		link2 = list_entry(l2, struct cgrp_cset_link, cgrp_link);
 915		cgrp1 = link1->cgrp;
 916		cgrp2 = link2->cgrp;
 917		/* Hierarchies should be linked in the same order. */
 918		BUG_ON(cgrp1->root != cgrp2->root);
 919
 920		/*
 921		 * If this hierarchy is the hierarchy of the cgroup
 922		 * that's changing, then we need to check that this
 923		 * css_set points to the new cgroup; if it's any other
 924		 * hierarchy, then this css_set should point to the
 925		 * same cgroup as the old css_set.
 926		 */
 927		if (cgrp1->root == new_cgrp->root) {
 928			if (cgrp1 != new_cgrp)
 929				return false;
 930		} else {
 931			if (cgrp1 != cgrp2)
 932				return false;
 933		}
 934	}
 935	return true;
 936}
 937
 938/**
 939 * find_existing_css_set - init css array and find the matching css_set
 940 * @old_cset: the css_set that we're using before the cgroup transition
 941 * @cgrp: the cgroup that we're moving into
 942 * @template: out param for the new set of csses, should be clear on entry
 943 */
 944static struct css_set *find_existing_css_set(struct css_set *old_cset,
 945					struct cgroup *cgrp,
 946					struct cgroup_subsys_state *template[])
 947{
 948	struct cgroup_root *root = cgrp->root;
 949	struct cgroup_subsys *ss;
 950	struct css_set *cset;
 951	unsigned long key;
 952	int i;
 953
 954	/*
 955	 * Build the set of subsystem state objects that we want to see in the
 956	 * new css_set. while subsystems can change globally, the entries here
 957	 * won't change, so no need for locking.
 958	 */
 959	for_each_subsys(ss, i) {
 960		if (root->subsys_mask & (1UL << i)) {
 961			/*
 962			 * @ss is in this hierarchy, so we want the
 963			 * effective css from @cgrp.
 964			 */
 965			template[i] = cgroup_e_css(cgrp, ss);
 966		} else {
 967			/*
 968			 * @ss is not in this hierarchy, so we don't want
 969			 * to change the css.
 970			 */
 971			template[i] = old_cset->subsys[i];
 972		}
 973	}
 974
 975	key = css_set_hash(template);
 976	hash_for_each_possible(css_set_table, cset, hlist, key) {
 977		if (!compare_css_sets(cset, old_cset, cgrp, template))
 978			continue;
 979
 980		/* This css_set matches what we need */
 981		return cset;
 982	}
 983
 984	/* No existing cgroup group matched */
 985	return NULL;
 986}
 987
 988static void free_cgrp_cset_links(struct list_head *links_to_free)
 989{
 990	struct cgrp_cset_link *link, *tmp_link;
 991
 992	list_for_each_entry_safe(link, tmp_link, links_to_free, cset_link) {
 993		list_del(&link->cset_link);
 994		kfree(link);
 995	}
 996}
 997
 998/**
 999 * allocate_cgrp_cset_links - allocate cgrp_cset_links
1000 * @count: the number of links to allocate
1001 * @tmp_links: list_head the allocated links are put on
1002 *
1003 * Allocate @count cgrp_cset_link structures and chain them on @tmp_links
1004 * through ->cset_link.  Returns 0 on success or -errno.
1005 */
1006static int allocate_cgrp_cset_links(int count, struct list_head *tmp_links)
1007{
1008	struct cgrp_cset_link *link;
1009	int i;
1010
1011	INIT_LIST_HEAD(tmp_links);
1012
1013	for (i = 0; i < count; i++) {
1014		link = kzalloc(sizeof(*link), GFP_KERNEL);
1015		if (!link) {
1016			free_cgrp_cset_links(tmp_links);
1017			return -ENOMEM;
1018		}
1019		list_add(&link->cset_link, tmp_links);
1020	}
1021	return 0;
1022}
1023
1024/**
1025 * link_css_set - a helper function to link a css_set to a cgroup
1026 * @tmp_links: cgrp_cset_link objects allocated by allocate_cgrp_cset_links()
1027 * @cset: the css_set to be linked
1028 * @cgrp: the destination cgroup
1029 */
1030static void link_css_set(struct list_head *tmp_links, struct css_set *cset,
1031			 struct cgroup *cgrp)
1032{
1033	struct cgrp_cset_link *link;
1034
1035	BUG_ON(list_empty(tmp_links));
1036
1037	if (cgroup_on_dfl(cgrp))
1038		cset->dfl_cgrp = cgrp;
1039
1040	link = list_first_entry(tmp_links, struct cgrp_cset_link, cset_link);
1041	link->cset = cset;
1042	link->cgrp = cgrp;
1043
1044	/*
1045	 * Always add links to the tail of the lists so that the lists are
1046	 * in choronological order.
1047	 */
1048	list_move_tail(&link->cset_link, &cgrp->cset_links);
1049	list_add_tail(&link->cgrp_link, &cset->cgrp_links);
1050
1051	if (cgroup_parent(cgrp))
1052		cgroup_get(cgrp);
1053}
1054
1055/**
1056 * find_css_set - return a new css_set with one cgroup updated
1057 * @old_cset: the baseline css_set
1058 * @cgrp: the cgroup to be updated
1059 *
1060 * Return a new css_set that's equivalent to @old_cset, but with @cgrp
1061 * substituted into the appropriate hierarchy.
1062 */
1063static struct css_set *find_css_set(struct css_set *old_cset,
1064				    struct cgroup *cgrp)
1065{
1066	struct cgroup_subsys_state *template[CGROUP_SUBSYS_COUNT] = { };
1067	struct css_set *cset;
1068	struct list_head tmp_links;
1069	struct cgrp_cset_link *link;
1070	struct cgroup_subsys *ss;
1071	unsigned long key;
1072	int ssid;
1073
1074	lockdep_assert_held(&cgroup_mutex);
1075
1076	/* First see if we already have a cgroup group that matches
1077	 * the desired set */
1078	spin_lock_irq(&css_set_lock);
1079	cset = find_existing_css_set(old_cset, cgrp, template);
1080	if (cset)
1081		get_css_set(cset);
1082	spin_unlock_irq(&css_set_lock);
1083
1084	if (cset)
1085		return cset;
1086
1087	cset = kzalloc(sizeof(*cset), GFP_KERNEL);
1088	if (!cset)
1089		return NULL;
1090
1091	/* Allocate all the cgrp_cset_link objects that we'll need */
1092	if (allocate_cgrp_cset_links(cgroup_root_count, &tmp_links) < 0) {
1093		kfree(cset);
1094		return NULL;
1095	}
1096
1097	atomic_set(&cset->refcount, 1);
1098	INIT_LIST_HEAD(&cset->cgrp_links);
1099	INIT_LIST_HEAD(&cset->tasks);
1100	INIT_LIST_HEAD(&cset->mg_tasks);
1101	INIT_LIST_HEAD(&cset->mg_preload_node);
1102	INIT_LIST_HEAD(&cset->mg_node);
1103	INIT_LIST_HEAD(&cset->task_iters);
1104	INIT_HLIST_NODE(&cset->hlist);
1105
1106	/* Copy the set of subsystem state objects generated in
1107	 * find_existing_css_set() */
1108	memcpy(cset->subsys, template, sizeof(cset->subsys));
1109
1110	spin_lock_irq(&css_set_lock);
1111	/* Add reference counts and links from the new css_set. */
1112	list_for_each_entry(link, &old_cset->cgrp_links, cgrp_link) {
1113		struct cgroup *c = link->cgrp;
1114
1115		if (c->root == cgrp->root)
1116			c = cgrp;
1117		link_css_set(&tmp_links, cset, c);
1118	}
1119
1120	BUG_ON(!list_empty(&tmp_links));
1121
1122	css_set_count++;
1123
1124	/* Add @cset to the hash table */
1125	key = css_set_hash(cset->subsys);
1126	hash_add(css_set_table, &cset->hlist, key);
1127
1128	for_each_subsys(ss, ssid) {
1129		struct cgroup_subsys_state *css = cset->subsys[ssid];
1130
1131		list_add_tail(&cset->e_cset_node[ssid],
1132			      &css->cgroup->e_csets[ssid]);
1133		css_get(css);
1134	}
1135
1136	spin_unlock_irq(&css_set_lock);
1137
1138	return cset;
1139}
1140
1141static struct cgroup_root *cgroup_root_from_kf(struct kernfs_root *kf_root)
1142{
1143	struct cgroup *root_cgrp = kf_root->kn->priv;
1144
1145	return root_cgrp->root;
1146}
1147
1148static int cgroup_init_root_id(struct cgroup_root *root)
1149{
1150	int id;
1151
1152	lockdep_assert_held(&cgroup_mutex);
1153
1154	id = idr_alloc_cyclic(&cgroup_hierarchy_idr, root, 0, 0, GFP_KERNEL);
1155	if (id < 0)
1156		return id;
1157
1158	root->hierarchy_id = id;
1159	return 0;
1160}
1161
1162static void cgroup_exit_root_id(struct cgroup_root *root)
1163{
1164	lockdep_assert_held(&cgroup_mutex);
1165
1166	idr_remove(&cgroup_hierarchy_idr, root->hierarchy_id);
 
 
 
1167}
1168
1169static void cgroup_free_root(struct cgroup_root *root)
1170{
1171	if (root) {
 
 
 
1172		idr_destroy(&root->cgroup_idr);
1173		kfree(root);
1174	}
1175}
1176
1177static void cgroup_destroy_root(struct cgroup_root *root)
1178{
1179	struct cgroup *cgrp = &root->cgrp;
1180	struct cgrp_cset_link *link, *tmp_link;
1181
1182	trace_cgroup_destroy_root(root);
1183
1184	cgroup_lock_and_drain_offline(&cgrp_dfl_root.cgrp);
1185
1186	BUG_ON(atomic_read(&root->nr_cgrps));
1187	BUG_ON(!list_empty(&cgrp->self.children));
1188
1189	/* Rebind all subsystems back to the default hierarchy */
1190	WARN_ON(rebind_subsystems(&cgrp_dfl_root, root->subsys_mask));
1191
1192	/*
1193	 * Release all the links from cset_links to this hierarchy's
1194	 * root cgroup
1195	 */
1196	spin_lock_irq(&css_set_lock);
1197
1198	list_for_each_entry_safe(link, tmp_link, &cgrp->cset_links, cset_link) {
1199		list_del(&link->cset_link);
1200		list_del(&link->cgrp_link);
1201		kfree(link);
1202	}
1203
1204	spin_unlock_irq(&css_set_lock);
1205
1206	if (!list_empty(&root->root_list)) {
1207		list_del(&root->root_list);
1208		cgroup_root_count--;
1209	}
1210
1211	cgroup_exit_root_id(root);
1212
1213	mutex_unlock(&cgroup_mutex);
1214
1215	kernfs_destroy_root(root->kf_root);
1216	cgroup_free_root(root);
1217}
1218
1219/*
1220 * look up cgroup associated with current task's cgroup namespace on the
1221 * specified hierarchy
1222 */
1223static struct cgroup *
1224current_cgns_cgroup_from_root(struct cgroup_root *root)
1225{
1226	struct cgroup *res = NULL;
1227	struct css_set *cset;
1228
1229	lockdep_assert_held(&css_set_lock);
1230
1231	rcu_read_lock();
1232
1233	cset = current->nsproxy->cgroup_ns->root_cset;
1234	if (cset == &init_css_set) {
1235		res = &root->cgrp;
1236	} else {
1237		struct cgrp_cset_link *link;
1238
1239		list_for_each_entry(link, &cset->cgrp_links, cgrp_link) {
1240			struct cgroup *c = link->cgrp;
1241
1242			if (c->root == root) {
1243				res = c;
1244				break;
1245			}
1246		}
1247	}
1248	rcu_read_unlock();
1249
1250	BUG_ON(!res);
1251	return res;
1252}
1253
1254/* look up cgroup associated with given css_set on the specified hierarchy */
1255static struct cgroup *cset_cgroup_from_root(struct css_set *cset,
1256					    struct cgroup_root *root)
1257{
1258	struct cgroup *res = NULL;
1259
1260	lockdep_assert_held(&cgroup_mutex);
1261	lockdep_assert_held(&css_set_lock);
1262
1263	if (cset == &init_css_set) {
1264		res = &root->cgrp;
1265	} else {
1266		struct cgrp_cset_link *link;
1267
1268		list_for_each_entry(link, &cset->cgrp_links, cgrp_link) {
1269			struct cgroup *c = link->cgrp;
1270
1271			if (c->root == root) {
1272				res = c;
1273				break;
1274			}
1275		}
1276	}
1277
1278	BUG_ON(!res);
1279	return res;
1280}
1281
1282/*
1283 * Return the cgroup for "task" from the given hierarchy. Must be
1284 * called with cgroup_mutex and css_set_lock held.
1285 */
1286static struct cgroup *task_cgroup_from_root(struct task_struct *task,
1287					    struct cgroup_root *root)
1288{
1289	/*
1290	 * No need to lock the task - since we hold cgroup_mutex the
1291	 * task can't change groups, so the only thing that can happen
1292	 * is that it exits and its css is set back to init_css_set.
1293	 */
1294	return cset_cgroup_from_root(task_css_set(task), root);
1295}
1296
1297/*
1298 * A task must hold cgroup_mutex to modify cgroups.
1299 *
1300 * Any task can increment and decrement the count field without lock.
1301 * So in general, code holding cgroup_mutex can't rely on the count
1302 * field not changing.  However, if the count goes to zero, then only
1303 * cgroup_attach_task() can increment it again.  Because a count of zero
1304 * means that no tasks are currently attached, therefore there is no
1305 * way a task attached to that cgroup can fork (the other way to
1306 * increment the count).  So code holding cgroup_mutex can safely
1307 * assume that if the count is zero, it will stay zero. Similarly, if
1308 * a task holds cgroup_mutex on a cgroup with zero count, it
1309 * knows that the cgroup won't be removed, as cgroup_rmdir()
1310 * needs that mutex.
1311 *
1312 * A cgroup can only be deleted if both its 'count' of using tasks
1313 * is zero, and its list of 'children' cgroups is empty.  Since all
1314 * tasks in the system use _some_ cgroup, and since there is always at
1315 * least one task in the system (init, pid == 1), therefore, root cgroup
1316 * always has either children cgroups and/or using tasks.  So we don't
1317 * need a special hack to ensure that root cgroup cannot be deleted.
1318 *
1319 * P.S.  One more locking exception.  RCU is used to guard the
1320 * update of a tasks cgroup pointer by cgroup_attach_task()
1321 */
1322
1323static struct kernfs_syscall_ops cgroup_kf_syscall_ops;
1324static const struct file_operations proc_cgroupstats_operations;
1325
1326static char *cgroup_file_name(struct cgroup *cgrp, const struct cftype *cft,
1327			      char *buf)
1328{
1329	struct cgroup_subsys *ss = cft->ss;
1330
1331	if (cft->ss && !(cft->flags & CFTYPE_NO_PREFIX) &&
1332	    !(cgrp->root->flags & CGRP_ROOT_NOPREFIX))
1333		snprintf(buf, CGROUP_FILE_NAME_MAX, "%s.%s",
1334			 cgroup_on_dfl(cgrp) ? ss->name : ss->legacy_name,
1335			 cft->name);
1336	else
1337		strncpy(buf, cft->name, CGROUP_FILE_NAME_MAX);
1338	return buf;
1339}
1340
1341/**
1342 * cgroup_file_mode - deduce file mode of a control file
1343 * @cft: the control file in question
1344 *
1345 * S_IRUGO for read, S_IWUSR for write.
1346 */
1347static umode_t cgroup_file_mode(const struct cftype *cft)
1348{
1349	umode_t mode = 0;
1350
1351	if (cft->read_u64 || cft->read_s64 || cft->seq_show)
1352		mode |= S_IRUGO;
1353
1354	if (cft->write_u64 || cft->write_s64 || cft->write) {
1355		if (cft->flags & CFTYPE_WORLD_WRITABLE)
1356			mode |= S_IWUGO;
1357		else
1358			mode |= S_IWUSR;
1359	}
1360
1361	return mode;
1362}
1363
1364/**
1365 * cgroup_calc_subtree_ss_mask - calculate subtree_ss_mask
1366 * @subtree_control: the new subtree_control mask to consider
1367 * @this_ss_mask: available subsystems
1368 *
1369 * On the default hierarchy, a subsystem may request other subsystems to be
1370 * enabled together through its ->depends_on mask.  In such cases, more
1371 * subsystems than specified in "cgroup.subtree_control" may be enabled.
1372 *
1373 * This function calculates which subsystems need to be enabled if
1374 * @subtree_control is to be applied while restricted to @this_ss_mask.
1375 */
1376static u16 cgroup_calc_subtree_ss_mask(u16 subtree_control, u16 this_ss_mask)
1377{
1378	u16 cur_ss_mask = subtree_control;
1379	struct cgroup_subsys *ss;
1380	int ssid;
1381
1382	lockdep_assert_held(&cgroup_mutex);
1383
1384	cur_ss_mask |= cgrp_dfl_implicit_ss_mask;
1385
1386	while (true) {
1387		u16 new_ss_mask = cur_ss_mask;
1388
1389		do_each_subsys_mask(ss, ssid, cur_ss_mask) {
1390			new_ss_mask |= ss->depends_on;
1391		} while_each_subsys_mask();
1392
1393		/*
1394		 * Mask out subsystems which aren't available.  This can
1395		 * happen only if some depended-upon subsystems were bound
1396		 * to non-default hierarchies.
1397		 */
1398		new_ss_mask &= this_ss_mask;
1399
1400		if (new_ss_mask == cur_ss_mask)
1401			break;
1402		cur_ss_mask = new_ss_mask;
1403	}
1404
1405	return cur_ss_mask;
1406}
1407
1408/**
1409 * cgroup_kn_unlock - unlocking helper for cgroup kernfs methods
1410 * @kn: the kernfs_node being serviced
1411 *
1412 * This helper undoes cgroup_kn_lock_live() and should be invoked before
1413 * the method finishes if locking succeeded.  Note that once this function
1414 * returns the cgroup returned by cgroup_kn_lock_live() may become
1415 * inaccessible any time.  If the caller intends to continue to access the
1416 * cgroup, it should pin it before invoking this function.
1417 */
1418static void cgroup_kn_unlock(struct kernfs_node *kn)
1419{
1420	struct cgroup *cgrp;
1421
1422	if (kernfs_type(kn) == KERNFS_DIR)
1423		cgrp = kn->priv;
1424	else
1425		cgrp = kn->parent->priv;
1426
1427	mutex_unlock(&cgroup_mutex);
1428
1429	kernfs_unbreak_active_protection(kn);
1430	cgroup_put(cgrp);
1431}
1432
1433/**
1434 * cgroup_kn_lock_live - locking helper for cgroup kernfs methods
1435 * @kn: the kernfs_node being serviced
1436 * @drain_offline: perform offline draining on the cgroup
1437 *
1438 * This helper is to be used by a cgroup kernfs method currently servicing
1439 * @kn.  It breaks the active protection, performs cgroup locking and
1440 * verifies that the associated cgroup is alive.  Returns the cgroup if
1441 * alive; otherwise, %NULL.  A successful return should be undone by a
1442 * matching cgroup_kn_unlock() invocation.  If @drain_offline is %true, the
1443 * cgroup is drained of offlining csses before return.
1444 *
1445 * Any cgroup kernfs method implementation which requires locking the
1446 * associated cgroup should use this helper.  It avoids nesting cgroup
1447 * locking under kernfs active protection and allows all kernfs operations
1448 * including self-removal.
1449 */
1450static struct cgroup *cgroup_kn_lock_live(struct kernfs_node *kn,
1451					  bool drain_offline)
1452{
1453	struct cgroup *cgrp;
1454
1455	if (kernfs_type(kn) == KERNFS_DIR)
1456		cgrp = kn->priv;
1457	else
1458		cgrp = kn->parent->priv;
1459
1460	/*
1461	 * We're gonna grab cgroup_mutex which nests outside kernfs
1462	 * active_ref.  cgroup liveliness check alone provides enough
1463	 * protection against removal.  Ensure @cgrp stays accessible and
1464	 * break the active_ref protection.
1465	 */
1466	if (!cgroup_tryget(cgrp))
1467		return NULL;
1468	kernfs_break_active_protection(kn);
1469
1470	if (drain_offline)
1471		cgroup_lock_and_drain_offline(cgrp);
1472	else
1473		mutex_lock(&cgroup_mutex);
1474
1475	if (!cgroup_is_dead(cgrp))
1476		return cgrp;
1477
1478	cgroup_kn_unlock(kn);
1479	return NULL;
1480}
1481
1482static void cgroup_rm_file(struct cgroup *cgrp, const struct cftype *cft)
1483{
1484	char name[CGROUP_FILE_NAME_MAX];
1485
1486	lockdep_assert_held(&cgroup_mutex);
1487
1488	if (cft->file_offset) {
1489		struct cgroup_subsys_state *css = cgroup_css(cgrp, cft->ss);
1490		struct cgroup_file *cfile = (void *)css + cft->file_offset;
1491
1492		spin_lock_irq(&cgroup_file_kn_lock);
1493		cfile->kn = NULL;
1494		spin_unlock_irq(&cgroup_file_kn_lock);
1495	}
1496
1497	kernfs_remove_by_name(cgrp->kn, cgroup_file_name(cgrp, cft, name));
1498}
1499
1500/**
1501 * css_clear_dir - remove subsys files in a cgroup directory
1502 * @css: taget css
1503 */
1504static void css_clear_dir(struct cgroup_subsys_state *css)
1505{
1506	struct cgroup *cgrp = css->cgroup;
1507	struct cftype *cfts;
1508
1509	if (!(css->flags & CSS_VISIBLE))
1510		return;
1511
1512	css->flags &= ~CSS_VISIBLE;
1513
1514	list_for_each_entry(cfts, &css->ss->cfts, node)
1515		cgroup_addrm_files(css, cgrp, cfts, false);
1516}
1517
1518/**
1519 * css_populate_dir - create subsys files in a cgroup directory
1520 * @css: target css
1521 *
1522 * On failure, no file is added.
1523 */
1524static int css_populate_dir(struct cgroup_subsys_state *css)
1525{
1526	struct cgroup *cgrp = css->cgroup;
1527	struct cftype *cfts, *failed_cfts;
1528	int ret;
1529
1530	if ((css->flags & CSS_VISIBLE) || !cgrp->kn)
1531		return 0;
1532
1533	if (!css->ss) {
1534		if (cgroup_on_dfl(cgrp))
1535			cfts = cgroup_dfl_base_files;
1536		else
1537			cfts = cgroup_legacy_base_files;
1538
1539		return cgroup_addrm_files(&cgrp->self, cgrp, cfts, true);
1540	}
1541
1542	list_for_each_entry(cfts, &css->ss->cfts, node) {
1543		ret = cgroup_addrm_files(css, cgrp, cfts, true);
1544		if (ret < 0) {
1545			failed_cfts = cfts;
1546			goto err;
1547		}
1548	}
1549
1550	css->flags |= CSS_VISIBLE;
1551
1552	return 0;
1553err:
1554	list_for_each_entry(cfts, &css->ss->cfts, node) {
1555		if (cfts == failed_cfts)
1556			break;
1557		cgroup_addrm_files(css, cgrp, cfts, false);
1558	}
1559	return ret;
1560}
1561
1562static int rebind_subsystems(struct cgroup_root *dst_root, u16 ss_mask)
1563{
1564	struct cgroup *dcgrp = &dst_root->cgrp;
1565	struct cgroup_subsys *ss;
1566	int ssid, i, ret;
1567
1568	lockdep_assert_held(&cgroup_mutex);
1569
1570	do_each_subsys_mask(ss, ssid, ss_mask) {
1571		/*
1572		 * If @ss has non-root csses attached to it, can't move.
1573		 * If @ss is an implicit controller, it is exempt from this
1574		 * rule and can be stolen.
1575		 */
1576		if (css_next_child(NULL, cgroup_css(&ss->root->cgrp, ss)) &&
1577		    !ss->implicit_on_dfl)
1578			return -EBUSY;
1579
1580		/* can't move between two non-dummy roots either */
1581		if (ss->root != &cgrp_dfl_root && dst_root != &cgrp_dfl_root)
1582			return -EBUSY;
1583	} while_each_subsys_mask();
1584
1585	do_each_subsys_mask(ss, ssid, ss_mask) {
1586		struct cgroup_root *src_root = ss->root;
1587		struct cgroup *scgrp = &src_root->cgrp;
1588		struct cgroup_subsys_state *css = cgroup_css(scgrp, ss);
1589		struct css_set *cset;
1590
1591		WARN_ON(!css || cgroup_css(dcgrp, ss));
1592
1593		/* disable from the source */
1594		src_root->subsys_mask &= ~(1 << ssid);
1595		WARN_ON(cgroup_apply_control(scgrp));
1596		cgroup_finalize_control(scgrp, 0);
1597
1598		/* rebind */
1599		RCU_INIT_POINTER(scgrp->subsys[ssid], NULL);
1600		rcu_assign_pointer(dcgrp->subsys[ssid], css);
1601		ss->root = dst_root;
1602		css->cgroup = dcgrp;
1603
1604		spin_lock_irq(&css_set_lock);
1605		hash_for_each(css_set_table, i, cset, hlist)
1606			list_move_tail(&cset->e_cset_node[ss->id],
1607				       &dcgrp->e_csets[ss->id]);
1608		spin_unlock_irq(&css_set_lock);
1609
1610		/* default hierarchy doesn't enable controllers by default */
1611		dst_root->subsys_mask |= 1 << ssid;
1612		if (dst_root == &cgrp_dfl_root) {
1613			static_branch_enable(cgroup_subsys_on_dfl_key[ssid]);
1614		} else {
1615			dcgrp->subtree_control |= 1 << ssid;
1616			static_branch_disable(cgroup_subsys_on_dfl_key[ssid]);
1617		}
1618
1619		ret = cgroup_apply_control(dcgrp);
1620		if (ret)
1621			pr_warn("partial failure to rebind %s controller (err=%d)\n",
1622				ss->name, ret);
1623
1624		if (ss->bind)
1625			ss->bind(css);
1626	} while_each_subsys_mask();
1627
1628	kernfs_activate(dcgrp->kn);
1629	return 0;
1630}
1631
1632static int cgroup_show_path(struct seq_file *sf, struct kernfs_node *kf_node,
1633			    struct kernfs_root *kf_root)
1634{
1635	int len = 0;
1636	char *buf = NULL;
1637	struct cgroup_root *kf_cgroot = cgroup_root_from_kf(kf_root);
1638	struct cgroup *ns_cgroup;
1639
1640	buf = kmalloc(PATH_MAX, GFP_KERNEL);
1641	if (!buf)
1642		return -ENOMEM;
1643
1644	spin_lock_irq(&css_set_lock);
1645	ns_cgroup = current_cgns_cgroup_from_root(kf_cgroot);
1646	len = kernfs_path_from_node(kf_node, ns_cgroup->kn, buf, PATH_MAX);
1647	spin_unlock_irq(&css_set_lock);
1648
1649	if (len >= PATH_MAX)
1650		len = -ERANGE;
1651	else if (len > 0) {
1652		seq_escape(sf, buf, " \t\n\\");
1653		len = 0;
1654	}
1655	kfree(buf);
1656	return len;
1657}
1658
1659static int cgroup_show_options(struct seq_file *seq,
1660			       struct kernfs_root *kf_root)
1661{
1662	struct cgroup_root *root = cgroup_root_from_kf(kf_root);
1663	struct cgroup_subsys *ss;
1664	int ssid;
1665
1666	if (root != &cgrp_dfl_root)
1667		for_each_subsys(ss, ssid)
1668			if (root->subsys_mask & (1 << ssid))
1669				seq_show_option(seq, ss->legacy_name, NULL);
1670	if (root->flags & CGRP_ROOT_NOPREFIX)
1671		seq_puts(seq, ",noprefix");
1672	if (root->flags & CGRP_ROOT_XATTR)
1673		seq_puts(seq, ",xattr");
1674
1675	spin_lock(&release_agent_path_lock);
1676	if (strlen(root->release_agent_path))
1677		seq_show_option(seq, "release_agent",
1678				root->release_agent_path);
1679	spin_unlock(&release_agent_path_lock);
1680
1681	if (test_bit(CGRP_CPUSET_CLONE_CHILDREN, &root->cgrp.flags))
1682		seq_puts(seq, ",clone_children");
1683	if (strlen(root->name))
1684		seq_show_option(seq, "name", root->name);
1685	return 0;
1686}
1687
1688struct cgroup_sb_opts {
1689	u16 subsys_mask;
1690	unsigned int flags;
1691	char *release_agent;
1692	bool cpuset_clone_children;
1693	char *name;
1694	/* User explicitly requested empty subsystem */
1695	bool none;
1696};
1697
1698static int parse_cgroupfs_options(char *data, struct cgroup_sb_opts *opts)
1699{
1700	char *token, *o = data;
1701	bool all_ss = false, one_ss = false;
1702	u16 mask = U16_MAX;
1703	struct cgroup_subsys *ss;
1704	int nr_opts = 0;
1705	int i;
1706
1707#ifdef CONFIG_CPUSETS
1708	mask = ~((u16)1 << cpuset_cgrp_id);
1709#endif
1710
1711	memset(opts, 0, sizeof(*opts));
1712
1713	while ((token = strsep(&o, ",")) != NULL) {
1714		nr_opts++;
1715
1716		if (!*token)
1717			return -EINVAL;
1718		if (!strcmp(token, "none")) {
1719			/* Explicitly have no subsystems */
1720			opts->none = true;
1721			continue;
1722		}
1723		if (!strcmp(token, "all")) {
1724			/* Mutually exclusive option 'all' + subsystem name */
1725			if (one_ss)
1726				return -EINVAL;
1727			all_ss = true;
1728			continue;
1729		}
1730		if (!strcmp(token, "noprefix")) {
1731			opts->flags |= CGRP_ROOT_NOPREFIX;
1732			continue;
1733		}
1734		if (!strcmp(token, "clone_children")) {
1735			opts->cpuset_clone_children = true;
1736			continue;
1737		}
1738		if (!strcmp(token, "xattr")) {
1739			opts->flags |= CGRP_ROOT_XATTR;
1740			continue;
1741		}
1742		if (!strncmp(token, "release_agent=", 14)) {
1743			/* Specifying two release agents is forbidden */
1744			if (opts->release_agent)
1745				return -EINVAL;
1746			opts->release_agent =
1747				kstrndup(token + 14, PATH_MAX - 1, GFP_KERNEL);
1748			if (!opts->release_agent)
1749				return -ENOMEM;
1750			continue;
1751		}
1752		if (!strncmp(token, "name=", 5)) {
1753			const char *name = token + 5;
1754			/* Can't specify an empty name */
1755			if (!strlen(name))
1756				return -EINVAL;
1757			/* Must match [\w.-]+ */
1758			for (i = 0; i < strlen(name); i++) {
1759				char c = name[i];
1760				if (isalnum(c))
1761					continue;
1762				if ((c == '.') || (c == '-') || (c == '_'))
1763					continue;
1764				return -EINVAL;
1765			}
1766			/* Specifying two names is forbidden */
1767			if (opts->name)
1768				return -EINVAL;
1769			opts->name = kstrndup(name,
1770					      MAX_CGROUP_ROOT_NAMELEN - 1,
1771					      GFP_KERNEL);
1772			if (!opts->name)
1773				return -ENOMEM;
1774
1775			continue;
1776		}
1777
1778		for_each_subsys(ss, i) {
1779			if (strcmp(token, ss->legacy_name))
1780				continue;
1781			if (!cgroup_ssid_enabled(i))
1782				continue;
1783			if (cgroup_ssid_no_v1(i))
1784				continue;
1785
1786			/* Mutually exclusive option 'all' + subsystem name */
1787			if (all_ss)
1788				return -EINVAL;
1789			opts->subsys_mask |= (1 << i);
1790			one_ss = true;
1791
1792			break;
1793		}
1794		if (i == CGROUP_SUBSYS_COUNT)
1795			return -ENOENT;
1796	}
1797
1798	/*
1799	 * If the 'all' option was specified select all the subsystems,
1800	 * otherwise if 'none', 'name=' and a subsystem name options were
1801	 * not specified, let's default to 'all'
1802	 */
1803	if (all_ss || (!one_ss && !opts->none && !opts->name))
1804		for_each_subsys(ss, i)
1805			if (cgroup_ssid_enabled(i) && !cgroup_ssid_no_v1(i))
1806				opts->subsys_mask |= (1 << i);
1807
1808	/*
1809	 * We either have to specify by name or by subsystems. (So all
1810	 * empty hierarchies must have a name).
1811	 */
1812	if (!opts->subsys_mask && !opts->name)
1813		return -EINVAL;
1814
1815	/*
1816	 * Option noprefix was introduced just for backward compatibility
1817	 * with the old cpuset, so we allow noprefix only if mounting just
1818	 * the cpuset subsystem.
1819	 */
1820	if ((opts->flags & CGRP_ROOT_NOPREFIX) && (opts->subsys_mask & mask))
1821		return -EINVAL;
1822
1823	/* Can't specify "none" and some subsystems */
1824	if (opts->subsys_mask && opts->none)
1825		return -EINVAL;
1826
1827	return 0;
1828}
1829
1830static int cgroup_remount(struct kernfs_root *kf_root, int *flags, char *data)
1831{
1832	int ret = 0;
1833	struct cgroup_root *root = cgroup_root_from_kf(kf_root);
1834	struct cgroup_sb_opts opts;
1835	u16 added_mask, removed_mask;
1836
1837	if (root == &cgrp_dfl_root) {
1838		pr_err("remount is not allowed\n");
1839		return -EINVAL;
1840	}
1841
1842	cgroup_lock_and_drain_offline(&cgrp_dfl_root.cgrp);
1843
1844	/* See what subsystems are wanted */
1845	ret = parse_cgroupfs_options(data, &opts);
1846	if (ret)
1847		goto out_unlock;
1848
1849	if (opts.subsys_mask != root->subsys_mask || opts.release_agent)
1850		pr_warn("option changes via remount are deprecated (pid=%d comm=%s)\n",
1851			task_tgid_nr(current), current->comm);
1852
1853	added_mask = opts.subsys_mask & ~root->subsys_mask;
1854	removed_mask = root->subsys_mask & ~opts.subsys_mask;
1855
1856	/* Don't allow flags or name to change at remount */
1857	if ((opts.flags ^ root->flags) ||
1858	    (opts.name && strcmp(opts.name, root->name))) {
1859		pr_err("option or name mismatch, new: 0x%x \"%s\", old: 0x%x \"%s\"\n",
1860		       opts.flags, opts.name ?: "", root->flags, root->name);
1861		ret = -EINVAL;
1862		goto out_unlock;
1863	}
1864
1865	/* remounting is not allowed for populated hierarchies */
1866	if (!list_empty(&root->cgrp.self.children)) {
1867		ret = -EBUSY;
1868		goto out_unlock;
1869	}
1870
1871	ret = rebind_subsystems(root, added_mask);
1872	if (ret)
1873		goto out_unlock;
1874
1875	WARN_ON(rebind_subsystems(&cgrp_dfl_root, removed_mask));
1876
1877	if (opts.release_agent) {
1878		spin_lock(&release_agent_path_lock);
1879		strcpy(root->release_agent_path, opts.release_agent);
1880		spin_unlock(&release_agent_path_lock);
1881	}
1882
1883	trace_cgroup_remount(root);
1884
1885 out_unlock:
1886	kfree(opts.release_agent);
1887	kfree(opts.name);
1888	mutex_unlock(&cgroup_mutex);
1889	return ret;
1890}
1891
1892/*
1893 * To reduce the fork() overhead for systems that are not actually using
1894 * their cgroups capability, we don't maintain the lists running through
1895 * each css_set to its tasks until we see the list actually used - in other
1896 * words after the first mount.
1897 */
1898static bool use_task_css_set_links __read_mostly;
1899
1900static void cgroup_enable_task_cg_lists(void)
1901{
1902	struct task_struct *p, *g;
1903
1904	spin_lock_irq(&css_set_lock);
1905
1906	if (use_task_css_set_links)
1907		goto out_unlock;
1908
1909	use_task_css_set_links = true;
1910
1911	/*
1912	 * We need tasklist_lock because RCU is not safe against
1913	 * while_each_thread(). Besides, a forking task that has passed
1914	 * cgroup_post_fork() without seeing use_task_css_set_links = 1
1915	 * is not guaranteed to have its child immediately visible in the
1916	 * tasklist if we walk through it with RCU.
1917	 */
1918	read_lock(&tasklist_lock);
1919	do_each_thread(g, p) {
1920		WARN_ON_ONCE(!list_empty(&p->cg_list) ||
1921			     task_css_set(p) != &init_css_set);
1922
1923		/*
1924		 * We should check if the process is exiting, otherwise
1925		 * it will race with cgroup_exit() in that the list
1926		 * entry won't be deleted though the process has exited.
1927		 * Do it while holding siglock so that we don't end up
1928		 * racing against cgroup_exit().
1929		 *
1930		 * Interrupts were already disabled while acquiring
1931		 * the css_set_lock, so we do not need to disable it
1932		 * again when acquiring the sighand->siglock here.
1933		 */
1934		spin_lock(&p->sighand->siglock);
1935		if (!(p->flags & PF_EXITING)) {
1936			struct css_set *cset = task_css_set(p);
1937
1938			if (!css_set_populated(cset))
1939				css_set_update_populated(cset, true);
1940			list_add_tail(&p->cg_list, &cset->tasks);
1941			get_css_set(cset);
1942		}
1943		spin_unlock(&p->sighand->siglock);
1944	} while_each_thread(g, p);
1945	read_unlock(&tasklist_lock);
1946out_unlock:
1947	spin_unlock_irq(&css_set_lock);
1948}
1949
1950static void init_cgroup_housekeeping(struct cgroup *cgrp)
1951{
1952	struct cgroup_subsys *ss;
1953	int ssid;
1954
1955	INIT_LIST_HEAD(&cgrp->self.sibling);
1956	INIT_LIST_HEAD(&cgrp->self.children);
1957	INIT_LIST_HEAD(&cgrp->cset_links);
1958	INIT_LIST_HEAD(&cgrp->pidlists);
1959	mutex_init(&cgrp->pidlist_mutex);
1960	cgrp->self.cgroup = cgrp;
1961	cgrp->self.flags |= CSS_ONLINE;
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, cgroup_release_agent);
1968}
1969
1970static void init_cgroup_root(struct cgroup_root *root,
1971			     struct cgroup_sb_opts *opts)
1972{
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 = opts->flags;
1982	if (opts->release_agent)
1983		strcpy(root->release_agent_path, opts->release_agent);
1984	if (opts->name)
1985		strcpy(root->name, opts->name);
1986	if (opts->cpuset_clone_children)
1987		set_bit(CGRP_CPUSET_CLONE_CHILDREN, &root->cgrp.flags);
1988}
1989
1990static int 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 css_set *cset;
1995	int i, ret;
1996
1997	lockdep_assert_held(&cgroup_mutex);
1998
1999	ret = cgroup_idr_alloc(&root->cgroup_idr, root_cgrp, 1, 2, GFP_KERNEL);
2000	if (ret < 0)
2001		goto out;
2002	root_cgrp->id = ret;
2003	root_cgrp->ancestor_ids[0] = ret;
2004
2005	ret = percpu_ref_init(&root_cgrp->self.refcnt, css_release, 0,
2006			      GFP_KERNEL);
2007	if (ret)
2008		goto out;
2009
2010	/*
2011	 * We're accessing css_set_count without locking css_set_lock here,
2012	 * but that's OK - it can only be increased by someone holding
2013	 * cgroup_lock, and that's us.  Later rebinding may disable
2014	 * controllers on the default hierarchy and thus create new csets,
2015	 * which can't be more than the existing ones.  Allocate 2x.
2016	 */
2017	ret = allocate_cgrp_cset_links(2 * css_set_count, &tmp_links);
2018	if (ret)
2019		goto cancel_ref;
2020
2021	ret = cgroup_init_root_id(root);
2022	if (ret)
2023		goto cancel_ref;
2024
2025	root->kf_root = kernfs_create_root(&cgroup_kf_syscall_ops,
2026					   KERNFS_ROOT_CREATE_DEACTIVATED,
2027					   root_cgrp);
2028	if (IS_ERR(root->kf_root)) {
2029		ret = PTR_ERR(root->kf_root);
2030		goto exit_root_id;
2031	}
2032	root_cgrp->kn = root->kf_root->kn;
2033
2034	ret = css_populate_dir(&root_cgrp->self);
2035	if (ret)
2036		goto destroy_root;
2037
2038	ret = rebind_subsystems(root, ss_mask);
2039	if (ret)
2040		goto destroy_root;
2041
2042	trace_cgroup_setup_root(root);
2043
2044	/*
2045	 * There must be no failure case after here, since rebinding takes
2046	 * care of subsystems' refcounts, which are explicitly dropped in
2047	 * the failure exit path.
2048	 */
2049	list_add(&root->root_list, &cgroup_roots);
2050	cgroup_root_count++;
2051
2052	/*
2053	 * Link the root cgroup in this hierarchy into all the css_set
2054	 * objects.
2055	 */
2056	spin_lock_irq(&css_set_lock);
2057	hash_for_each(css_set_table, i, cset, hlist) {
2058		link_css_set(&tmp_links, cset, root_cgrp);
2059		if (css_set_populated(cset))
2060			cgroup_update_populated(root_cgrp, true);
2061	}
2062	spin_unlock_irq(&css_set_lock);
2063
2064	BUG_ON(!list_empty(&root_cgrp->self.children));
2065	BUG_ON(atomic_read(&root->nr_cgrps) != 1);
2066
2067	kernfs_activate(root_cgrp->kn);
2068	ret = 0;
2069	goto out;
2070
2071destroy_root:
2072	kernfs_destroy_root(root->kf_root);
2073	root->kf_root = NULL;
2074exit_root_id:
2075	cgroup_exit_root_id(root);
2076cancel_ref:
2077	percpu_ref_exit(&root_cgrp->self.refcnt);
2078out:
2079	free_cgrp_cset_links(&tmp_links);
2080	return ret;
2081}
2082
2083static struct dentry *cgroup_mount(struct file_system_type *fs_type,
2084			 int flags, const char *unused_dev_name,
2085			 void *data)
2086{
2087	bool is_v2 = fs_type == &cgroup2_fs_type;
2088	struct super_block *pinned_sb = NULL;
2089	struct cgroup_namespace *ns = current->nsproxy->cgroup_ns;
2090	struct cgroup_subsys *ss;
2091	struct cgroup_root *root;
2092	struct cgroup_sb_opts opts;
2093	struct dentry *dentry;
2094	int ret;
2095	int i;
2096	bool new_sb;
2097
2098	get_cgroup_ns(ns);
2099
2100	/* Check if the caller has permission to mount. */
2101	if (!ns_capable(ns->user_ns, CAP_SYS_ADMIN)) {
2102		put_cgroup_ns(ns);
2103		return ERR_PTR(-EPERM);
2104	}
2105
2106	/*
2107	 * The first time anyone tries to mount a cgroup, enable the list
2108	 * linking each css_set to its tasks and fix up all existing tasks.
2109	 */
2110	if (!use_task_css_set_links)
2111		cgroup_enable_task_cg_lists();
2112
2113	if (is_v2) {
2114		if (data) {
2115			pr_err("cgroup2: unknown option \"%s\"\n", (char *)data);
2116			put_cgroup_ns(ns);
2117			return ERR_PTR(-EINVAL);
2118		}
2119		cgrp_dfl_visible = true;
2120		root = &cgrp_dfl_root;
2121		cgroup_get(&root->cgrp);
2122		goto out_mount;
2123	}
2124
2125	cgroup_lock_and_drain_offline(&cgrp_dfl_root.cgrp);
2126
2127	/* First find the desired set of subsystems */
2128	ret = parse_cgroupfs_options(data, &opts);
2129	if (ret)
2130		goto out_unlock;
2131
2132	/*
2133	 * Destruction of cgroup root is asynchronous, so subsystems may
2134	 * still be dying after the previous unmount.  Let's drain the
2135	 * dying subsystems.  We just need to ensure that the ones
2136	 * unmounted previously finish dying and don't care about new ones
2137	 * starting.  Testing ref liveliness is good enough.
2138	 */
2139	for_each_subsys(ss, i) {
2140		if (!(opts.subsys_mask & (1 << i)) ||
2141		    ss->root == &cgrp_dfl_root)
2142			continue;
2143
2144		if (!percpu_ref_tryget_live(&ss->root->cgrp.self.refcnt)) {
2145			mutex_unlock(&cgroup_mutex);
2146			msleep(10);
2147			ret = restart_syscall();
2148			goto out_free;
2149		}
2150		cgroup_put(&ss->root->cgrp);
2151	}
2152
2153	for_each_root(root) {
2154		bool name_match = false;
2155
2156		if (root == &cgrp_dfl_root)
2157			continue;
2158
2159		/*
2160		 * If we asked for a name then it must match.  Also, if
2161		 * name matches but sybsys_mask doesn't, we should fail.
2162		 * Remember whether name matched.
2163		 */
2164		if (opts.name) {
2165			if (strcmp(opts.name, root->name))
2166				continue;
2167			name_match = true;
2168		}
2169
2170		/*
2171		 * If we asked for subsystems (or explicitly for no
2172		 * subsystems) then they must match.
2173		 */
2174		if ((opts.subsys_mask || opts.none) &&
2175		    (opts.subsys_mask != root->subsys_mask)) {
2176			if (!name_match)
2177				continue;
2178			ret = -EBUSY;
2179			goto out_unlock;
2180		}
2181
2182		if (root->flags ^ opts.flags)
2183			pr_warn("new mount options do not match the existing superblock, will be ignored\n");
2184
2185		/*
2186		 * We want to reuse @root whose lifetime is governed by its
2187		 * ->cgrp.  Let's check whether @root is alive and keep it
2188		 * that way.  As cgroup_kill_sb() can happen anytime, we
2189		 * want to block it by pinning the sb so that @root doesn't
2190		 * get killed before mount is complete.
2191		 *
2192		 * With the sb pinned, tryget_live can reliably indicate
2193		 * whether @root can be reused.  If it's being killed,
2194		 * drain it.  We can use wait_queue for the wait but this
2195		 * path is super cold.  Let's just sleep a bit and retry.
2196		 */
2197		pinned_sb = kernfs_pin_sb(root->kf_root, NULL);
2198		if (IS_ERR(pinned_sb) ||
2199		    !percpu_ref_tryget_live(&root->cgrp.self.refcnt)) {
2200			mutex_unlock(&cgroup_mutex);
2201			if (!IS_ERR_OR_NULL(pinned_sb))
2202				deactivate_super(pinned_sb);
2203			msleep(10);
2204			ret = restart_syscall();
2205			goto out_free;
2206		}
2207
2208		ret = 0;
2209		goto out_unlock;
2210	}
2211
2212	/*
2213	 * No such thing, create a new one.  name= matching without subsys
2214	 * specification is allowed for already existing hierarchies but we
2215	 * can't create new one without subsys specification.
2216	 */
2217	if (!opts.subsys_mask && !opts.none) {
2218		ret = -EINVAL;
2219		goto out_unlock;
2220	}
2221
2222	/* Hierarchies may only be created in the initial cgroup namespace. */
2223	if (ns != &init_cgroup_ns) {
 
 
 
 
2224		ret = -EPERM;
2225		goto out_unlock;
2226	}
2227
2228	root = kzalloc(sizeof(*root), GFP_KERNEL);
2229	if (!root) {
2230		ret = -ENOMEM;
2231		goto out_unlock;
2232	}
2233
2234	init_cgroup_root(root, &opts);
2235
2236	ret = cgroup_setup_root(root, opts.subsys_mask);
2237	if (ret)
2238		cgroup_free_root(root);
2239
2240out_unlock:
2241	mutex_unlock(&cgroup_mutex);
2242out_free:
2243	kfree(opts.release_agent);
2244	kfree(opts.name);
2245
2246	if (ret) {
2247		put_cgroup_ns(ns);
2248		return ERR_PTR(ret);
2249	}
2250out_mount:
2251	dentry = kernfs_mount(fs_type, flags, root->kf_root,
2252			      is_v2 ? CGROUP2_SUPER_MAGIC : CGROUP_SUPER_MAGIC,
2253			      &new_sb);
2254
2255	/*
2256	 * In non-init cgroup namespace, instead of root cgroup's
2257	 * dentry, we return the dentry corresponding to the
2258	 * cgroupns->root_cgrp.
2259	 */
2260	if (!IS_ERR(dentry) && ns != &init_cgroup_ns) {
2261		struct dentry *nsdentry;
2262		struct cgroup *cgrp;
2263
2264		mutex_lock(&cgroup_mutex);
2265		spin_lock_irq(&css_set_lock);
2266
2267		cgrp = cset_cgroup_from_root(ns->root_cset, root);
2268
2269		spin_unlock_irq(&css_set_lock);
2270		mutex_unlock(&cgroup_mutex);
2271
2272		nsdentry = kernfs_node_dentry(cgrp->kn, dentry->d_sb);
2273		dput(dentry);
2274		dentry = nsdentry;
2275	}
2276
2277	if (IS_ERR(dentry) || !new_sb)
2278		cgroup_put(&root->cgrp);
2279
2280	/*
2281	 * If @pinned_sb, we're reusing an existing root and holding an
2282	 * extra ref on its sb.  Mount is complete.  Put the extra ref.
2283	 */
2284	if (pinned_sb) {
2285		WARN_ON(new_sb);
2286		deactivate_super(pinned_sb);
2287	}
2288
2289	put_cgroup_ns(ns);
2290	return dentry;
2291}
2292
2293static void cgroup_kill_sb(struct super_block *sb)
2294{
2295	struct kernfs_root *kf_root = kernfs_root_from_sb(sb);
2296	struct cgroup_root *root = cgroup_root_from_kf(kf_root);
2297
2298	/*
2299	 * If @root doesn't have any mounts or children, start killing it.
2300	 * This prevents new mounts by disabling percpu_ref_tryget_live().
2301	 * cgroup_mount() may wait for @root's release.
2302	 *
2303	 * And don't kill the default root.
2304	 */
2305	if (!list_empty(&root->cgrp.self.children) ||
2306	    root == &cgrp_dfl_root)
2307		cgroup_put(&root->cgrp);
2308	else
2309		percpu_ref_kill(&root->cgrp.self.refcnt);
2310
2311	kernfs_kill_sb(sb);
2312}
2313
2314static struct file_system_type cgroup_fs_type = {
2315	.name = "cgroup",
2316	.mount = cgroup_mount,
2317	.kill_sb = cgroup_kill_sb,
2318	.fs_flags = FS_USERNS_MOUNT,
2319};
2320
2321static struct file_system_type cgroup2_fs_type = {
2322	.name = "cgroup2",
2323	.mount = cgroup_mount,
2324	.kill_sb = cgroup_kill_sb,
2325	.fs_flags = FS_USERNS_MOUNT,
2326};
2327
2328static int cgroup_path_ns_locked(struct cgroup *cgrp, char *buf, size_t buflen,
2329				 struct cgroup_namespace *ns)
2330{
2331	struct cgroup *root = cset_cgroup_from_root(ns->root_cset, cgrp->root);
 
2332
2333	return kernfs_path_from_node(cgrp->kn, root->kn, buf, buflen);
 
 
 
2334}
2335
2336int cgroup_path_ns(struct cgroup *cgrp, char *buf, size_t buflen,
2337		   struct cgroup_namespace *ns)
2338{
2339	int ret;
2340
2341	mutex_lock(&cgroup_mutex);
2342	spin_lock_irq(&css_set_lock);
2343
2344	ret = cgroup_path_ns_locked(cgrp, buf, buflen, ns);
2345
2346	spin_unlock_irq(&css_set_lock);
2347	mutex_unlock(&cgroup_mutex);
2348
2349	return ret;
2350}
2351EXPORT_SYMBOL_GPL(cgroup_path_ns);
2352
2353/**
2354 * task_cgroup_path - cgroup path of a task in the first cgroup hierarchy
2355 * @task: target task
2356 * @buf: the buffer to write the path into
2357 * @buflen: the length of the buffer
2358 *
2359 * Determine @task's cgroup on the first (the one with the lowest non-zero
2360 * hierarchy_id) cgroup hierarchy and copy its path into @buf.  This
2361 * function grabs cgroup_mutex and shouldn't be used inside locks used by
2362 * cgroup controller callbacks.
2363 *
2364 * Return value is the same as kernfs_path().
2365 */
2366int task_cgroup_path(struct task_struct *task, char *buf, size_t buflen)
2367{
2368	struct cgroup_root *root;
2369	struct cgroup *cgrp;
2370	int hierarchy_id = 1;
2371	int ret;
2372
2373	mutex_lock(&cgroup_mutex);
2374	spin_lock_irq(&css_set_lock);
2375
2376	root = idr_get_next(&cgroup_hierarchy_idr, &hierarchy_id);
2377
2378	if (root) {
2379		cgrp = task_cgroup_from_root(task, root);
2380		ret = cgroup_path_ns_locked(cgrp, buf, buflen, &init_cgroup_ns);
2381	} else {
2382		/* if no hierarchy exists, everyone is in "/" */
2383		ret = strlcpy(buf, "/", buflen);
 
2384	}
2385
2386	spin_unlock_irq(&css_set_lock);
2387	mutex_unlock(&cgroup_mutex);
2388	return ret;
2389}
2390EXPORT_SYMBOL_GPL(task_cgroup_path);
2391
2392/* used to track tasks and other necessary states during migration */
2393struct cgroup_taskset {
2394	/* the src and dst cset list running through cset->mg_node */
2395	struct list_head	src_csets;
2396	struct list_head	dst_csets;
2397
2398	/* the subsys currently being processed */
2399	int			ssid;
2400
2401	/*
2402	 * Fields for cgroup_taskset_*() iteration.
2403	 *
2404	 * Before migration is committed, the target migration tasks are on
2405	 * ->mg_tasks of the csets on ->src_csets.  After, on ->mg_tasks of
2406	 * the csets on ->dst_csets.  ->csets point to either ->src_csets
2407	 * or ->dst_csets depending on whether migration is committed.
2408	 *
2409	 * ->cur_csets and ->cur_task point to the current task position
2410	 * during iteration.
2411	 */
2412	struct list_head	*csets;
2413	struct css_set		*cur_cset;
2414	struct task_struct	*cur_task;
2415};
2416
2417#define CGROUP_TASKSET_INIT(tset)	(struct cgroup_taskset){	\
2418	.src_csets		= LIST_HEAD_INIT(tset.src_csets),	\
2419	.dst_csets		= LIST_HEAD_INIT(tset.dst_csets),	\
2420	.csets			= &tset.src_csets,			\
2421}
2422
2423/**
2424 * cgroup_taskset_add - try to add a migration target task to a taskset
2425 * @task: target task
2426 * @tset: target taskset
2427 *
2428 * Add @task, which is a migration target, to @tset.  This function becomes
2429 * noop if @task doesn't need to be migrated.  @task's css_set should have
2430 * been added as a migration source and @task->cg_list will be moved from
2431 * the css_set's tasks list to mg_tasks one.
2432 */
2433static void cgroup_taskset_add(struct task_struct *task,
2434			       struct cgroup_taskset *tset)
2435{
2436	struct css_set *cset;
2437
2438	lockdep_assert_held(&css_set_lock);
2439
2440	/* @task either already exited or can't exit until the end */
2441	if (task->flags & PF_EXITING)
2442		return;
2443
2444	/* leave @task alone if post_fork() hasn't linked it yet */
2445	if (list_empty(&task->cg_list))
2446		return;
2447
2448	cset = task_css_set(task);
2449	if (!cset->mg_src_cgrp)
2450		return;
2451
2452	list_move_tail(&task->cg_list, &cset->mg_tasks);
2453	if (list_empty(&cset->mg_node))
2454		list_add_tail(&cset->mg_node, &tset->src_csets);
2455	if (list_empty(&cset->mg_dst_cset->mg_node))
2456		list_move_tail(&cset->mg_dst_cset->mg_node,
2457			       &tset->dst_csets);
2458}
2459
2460/**
2461 * cgroup_taskset_first - reset taskset and return the first task
2462 * @tset: taskset of interest
2463 * @dst_cssp: output variable for the destination css
2464 *
2465 * @tset iteration is initialized and the first task is returned.
2466 */
2467struct task_struct *cgroup_taskset_first(struct cgroup_taskset *tset,
2468					 struct cgroup_subsys_state **dst_cssp)
2469{
2470	tset->cur_cset = list_first_entry(tset->csets, struct css_set, mg_node);
2471	tset->cur_task = NULL;
2472
2473	return cgroup_taskset_next(tset, dst_cssp);
2474}
2475
2476/**
2477 * cgroup_taskset_next - iterate to the next task in taskset
2478 * @tset: taskset of interest
2479 * @dst_cssp: output variable for the destination css
2480 *
2481 * Return the next task in @tset.  Iteration must have been initialized
2482 * with cgroup_taskset_first().
2483 */
2484struct task_struct *cgroup_taskset_next(struct cgroup_taskset *tset,
2485					struct cgroup_subsys_state **dst_cssp)
2486{
2487	struct css_set *cset = tset->cur_cset;
2488	struct task_struct *task = tset->cur_task;
2489
2490	while (&cset->mg_node != tset->csets) {
2491		if (!task)
2492			task = list_first_entry(&cset->mg_tasks,
2493						struct task_struct, cg_list);
2494		else
2495			task = list_next_entry(task, cg_list);
2496
2497		if (&task->cg_list != &cset->mg_tasks) {
2498			tset->cur_cset = cset;
2499			tset->cur_task = task;
2500
2501			/*
2502			 * This function may be called both before and
2503			 * after cgroup_taskset_migrate().  The two cases
2504			 * can be distinguished by looking at whether @cset
2505			 * has its ->mg_dst_cset set.
2506			 */
2507			if (cset->mg_dst_cset)
2508				*dst_cssp = cset->mg_dst_cset->subsys[tset->ssid];
2509			else
2510				*dst_cssp = cset->subsys[tset->ssid];
2511
2512			return task;
2513		}
2514
2515		cset = list_next_entry(cset, mg_node);
2516		task = NULL;
2517	}
2518
2519	return NULL;
2520}
2521
2522/**
2523 * cgroup_taskset_migrate - migrate a taskset
2524 * @tset: taget taskset
2525 * @root: cgroup root the migration is taking place on
2526 *
2527 * Migrate tasks in @tset as setup by migration preparation functions.
2528 * This function fails iff one of the ->can_attach callbacks fails and
2529 * guarantees that either all or none of the tasks in @tset are migrated.
2530 * @tset is consumed regardless of success.
2531 */
2532static int cgroup_taskset_migrate(struct cgroup_taskset *tset,
2533				  struct cgroup_root *root)
2534{
2535	struct cgroup_subsys *ss;
2536	struct task_struct *task, *tmp_task;
2537	struct css_set *cset, *tmp_cset;
2538	int ssid, failed_ssid, ret;
2539
2540	/* methods shouldn't be called if no task is actually migrating */
2541	if (list_empty(&tset->src_csets))
2542		return 0;
2543
2544	/* check that we can legitimately attach to the cgroup */
2545	do_each_subsys_mask(ss, ssid, root->subsys_mask) {
2546		if (ss->can_attach) {
2547			tset->ssid = ssid;
2548			ret = ss->can_attach(tset);
2549			if (ret) {
2550				failed_ssid = ssid;
2551				goto out_cancel_attach;
2552			}
2553		}
2554	} while_each_subsys_mask();
2555
2556	/*
2557	 * Now that we're guaranteed success, proceed to move all tasks to
2558	 * the new cgroup.  There are no failure cases after here, so this
2559	 * is the commit point.
2560	 */
2561	spin_lock_irq(&css_set_lock);
2562	list_for_each_entry(cset, &tset->src_csets, mg_node) {
2563		list_for_each_entry_safe(task, tmp_task, &cset->mg_tasks, cg_list) {
2564			struct css_set *from_cset = task_css_set(task);
2565			struct css_set *to_cset = cset->mg_dst_cset;
2566
2567			get_css_set(to_cset);
2568			css_set_move_task(task, from_cset, to_cset, true);
2569			put_css_set_locked(from_cset);
2570		}
2571	}
2572	spin_unlock_irq(&css_set_lock);
2573
2574	/*
2575	 * Migration is committed, all target tasks are now on dst_csets.
2576	 * Nothing is sensitive to fork() after this point.  Notify
2577	 * controllers that migration is complete.
2578	 */
2579	tset->csets = &tset->dst_csets;
2580
2581	do_each_subsys_mask(ss, ssid, root->subsys_mask) {
2582		if (ss->attach) {
2583			tset->ssid = ssid;
2584			ss->attach(tset);
2585		}
2586	} while_each_subsys_mask();
2587
2588	ret = 0;
2589	goto out_release_tset;
2590
2591out_cancel_attach:
2592	do_each_subsys_mask(ss, ssid, root->subsys_mask) {
2593		if (ssid == failed_ssid)
2594			break;
2595		if (ss->cancel_attach) {
2596			tset->ssid = ssid;
2597			ss->cancel_attach(tset);
2598		}
2599	} while_each_subsys_mask();
2600out_release_tset:
2601	spin_lock_irq(&css_set_lock);
2602	list_splice_init(&tset->dst_csets, &tset->src_csets);
2603	list_for_each_entry_safe(cset, tmp_cset, &tset->src_csets, mg_node) {
2604		list_splice_tail_init(&cset->mg_tasks, &cset->tasks);
2605		list_del_init(&cset->mg_node);
2606	}
2607	spin_unlock_irq(&css_set_lock);
2608	return ret;
2609}
2610
2611/**
2612 * cgroup_may_migrate_to - verify whether a cgroup can be migration destination
2613 * @dst_cgrp: destination cgroup to test
2614 *
2615 * On the default hierarchy, except for the root, subtree_control must be
2616 * zero for migration destination cgroups with tasks so that child cgroups
2617 * don't compete against tasks.
2618 */
2619static bool cgroup_may_migrate_to(struct cgroup *dst_cgrp)
2620{
2621	return !cgroup_on_dfl(dst_cgrp) || !cgroup_parent(dst_cgrp) ||
2622		!dst_cgrp->subtree_control;
2623}
2624
2625/**
2626 * cgroup_migrate_finish - cleanup after attach
2627 * @preloaded_csets: list of preloaded css_sets
2628 *
2629 * Undo cgroup_migrate_add_src() and cgroup_migrate_prepare_dst().  See
2630 * those functions for details.
2631 */
2632static void cgroup_migrate_finish(struct list_head *preloaded_csets)
2633{
2634	struct css_set *cset, *tmp_cset;
2635
2636	lockdep_assert_held(&cgroup_mutex);
2637
2638	spin_lock_irq(&css_set_lock);
2639	list_for_each_entry_safe(cset, tmp_cset, preloaded_csets, mg_preload_node) {
2640		cset->mg_src_cgrp = NULL;
2641		cset->mg_dst_cgrp = NULL;
2642		cset->mg_dst_cset = NULL;
2643		list_del_init(&cset->mg_preload_node);
2644		put_css_set_locked(cset);
2645	}
2646	spin_unlock_irq(&css_set_lock);
2647}
2648
2649/**
2650 * cgroup_migrate_add_src - add a migration source css_set
2651 * @src_cset: the source css_set to add
2652 * @dst_cgrp: the destination cgroup
2653 * @preloaded_csets: list of preloaded css_sets
2654 *
2655 * Tasks belonging to @src_cset are about to be migrated to @dst_cgrp.  Pin
2656 * @src_cset and add it to @preloaded_csets, which should later be cleaned
2657 * up by cgroup_migrate_finish().
2658 *
2659 * This function may be called without holding cgroup_threadgroup_rwsem
2660 * even if the target is a process.  Threads may be created and destroyed
2661 * but as long as cgroup_mutex is not dropped, no new css_set can be put
2662 * into play and the preloaded css_sets are guaranteed to cover all
2663 * migrations.
2664 */
2665static void cgroup_migrate_add_src(struct css_set *src_cset,
2666				   struct cgroup *dst_cgrp,
2667				   struct list_head *preloaded_csets)
2668{
2669	struct cgroup *src_cgrp;
2670
2671	lockdep_assert_held(&cgroup_mutex);
2672	lockdep_assert_held(&css_set_lock);
2673
2674	/*
2675	 * If ->dead, @src_set is associated with one or more dead cgroups
2676	 * and doesn't contain any migratable tasks.  Ignore it early so
2677	 * that the rest of migration path doesn't get confused by it.
2678	 */
2679	if (src_cset->dead)
2680		return;
2681
2682	src_cgrp = cset_cgroup_from_root(src_cset, dst_cgrp->root);
2683
2684	if (!list_empty(&src_cset->mg_preload_node))
2685		return;
2686
2687	WARN_ON(src_cset->mg_src_cgrp);
2688	WARN_ON(src_cset->mg_dst_cgrp);
2689	WARN_ON(!list_empty(&src_cset->mg_tasks));
2690	WARN_ON(!list_empty(&src_cset->mg_node));
2691
2692	src_cset->mg_src_cgrp = src_cgrp;
2693	src_cset->mg_dst_cgrp = dst_cgrp;
2694	get_css_set(src_cset);
2695	list_add(&src_cset->mg_preload_node, preloaded_csets);
2696}
2697
2698/**
2699 * cgroup_migrate_prepare_dst - prepare destination css_sets for migration
2700 * @preloaded_csets: list of preloaded source css_sets
2701 *
2702 * Tasks are about to be moved and all the source css_sets have been
2703 * preloaded to @preloaded_csets.  This function looks up and pins all
2704 * destination css_sets, links each to its source, and append them to
2705 * @preloaded_csets.
2706 *
2707 * This function must be called after cgroup_migrate_add_src() has been
2708 * called on each migration source css_set.  After migration is performed
2709 * using cgroup_migrate(), cgroup_migrate_finish() must be called on
2710 * @preloaded_csets.
2711 */
2712static int cgroup_migrate_prepare_dst(struct list_head *preloaded_csets)
2713{
2714	LIST_HEAD(csets);
2715	struct css_set *src_cset, *tmp_cset;
2716
2717	lockdep_assert_held(&cgroup_mutex);
2718
2719	/* look up the dst cset for each src cset and link it to src */
2720	list_for_each_entry_safe(src_cset, tmp_cset, preloaded_csets, mg_preload_node) {
2721		struct css_set *dst_cset;
2722
2723		dst_cset = find_css_set(src_cset, src_cset->mg_dst_cgrp);
2724		if (!dst_cset)
2725			goto err;
2726
2727		WARN_ON_ONCE(src_cset->mg_dst_cset || dst_cset->mg_dst_cset);
2728
2729		/*
2730		 * If src cset equals dst, it's noop.  Drop the src.
2731		 * cgroup_migrate() will skip the cset too.  Note that we
2732		 * can't handle src == dst as some nodes are used by both.
2733		 */
2734		if (src_cset == dst_cset) {
2735			src_cset->mg_src_cgrp = NULL;
2736			src_cset->mg_dst_cgrp = NULL;
2737			list_del_init(&src_cset->mg_preload_node);
2738			put_css_set(src_cset);
2739			put_css_set(dst_cset);
2740			continue;
2741		}
2742
2743		src_cset->mg_dst_cset = dst_cset;
2744
2745		if (list_empty(&dst_cset->mg_preload_node))
2746			list_add(&dst_cset->mg_preload_node, &csets);
2747		else
2748			put_css_set(dst_cset);
2749	}
2750
2751	list_splice_tail(&csets, preloaded_csets);
2752	return 0;
2753err:
2754	cgroup_migrate_finish(&csets);
2755	return -ENOMEM;
2756}
2757
2758/**
2759 * cgroup_migrate - migrate a process or task to a cgroup
2760 * @leader: the leader of the process or the task to migrate
2761 * @threadgroup: whether @leader points to the whole process or a single task
2762 * @root: cgroup root migration is taking place on
2763 *
2764 * Migrate a process or task denoted by @leader.  If migrating a process,
2765 * the caller must be holding cgroup_threadgroup_rwsem.  The caller is also
2766 * responsible for invoking cgroup_migrate_add_src() and
2767 * cgroup_migrate_prepare_dst() on the targets before invoking this
2768 * function and following up with cgroup_migrate_finish().
2769 *
2770 * As long as a controller's ->can_attach() doesn't fail, this function is
2771 * guaranteed to succeed.  This means that, excluding ->can_attach()
2772 * failure, when migrating multiple targets, the success or failure can be
2773 * decided for all targets by invoking group_migrate_prepare_dst() before
2774 * actually starting migrating.
2775 */
2776static int cgroup_migrate(struct task_struct *leader, bool threadgroup,
2777			  struct cgroup_root *root)
2778{
2779	struct cgroup_taskset tset = CGROUP_TASKSET_INIT(tset);
2780	struct task_struct *task;
2781
2782	/*
2783	 * Prevent freeing of tasks while we take a snapshot. Tasks that are
2784	 * already PF_EXITING could be freed from underneath us unless we
2785	 * take an rcu_read_lock.
2786	 */
2787	spin_lock_irq(&css_set_lock);
2788	rcu_read_lock();
2789	task = leader;
2790	do {
2791		cgroup_taskset_add(task, &tset);
2792		if (!threadgroup)
2793			break;
2794	} while_each_thread(leader, task);
2795	rcu_read_unlock();
2796	spin_unlock_irq(&css_set_lock);
2797
2798	return cgroup_taskset_migrate(&tset, root);
2799}
2800
2801/**
2802 * cgroup_attach_task - attach a task or a whole threadgroup to a cgroup
2803 * @dst_cgrp: the cgroup to attach to
2804 * @leader: the task or the leader of the threadgroup to be attached
2805 * @threadgroup: attach the whole threadgroup?
2806 *
2807 * Call holding cgroup_mutex and cgroup_threadgroup_rwsem.
2808 */
2809static int cgroup_attach_task(struct cgroup *dst_cgrp,
2810			      struct task_struct *leader, bool threadgroup)
2811{
2812	LIST_HEAD(preloaded_csets);
2813	struct task_struct *task;
2814	int ret;
2815
2816	if (!cgroup_may_migrate_to(dst_cgrp))
2817		return -EBUSY;
2818
2819	/* look up all src csets */
2820	spin_lock_irq(&css_set_lock);
2821	rcu_read_lock();
2822	task = leader;
2823	do {
2824		cgroup_migrate_add_src(task_css_set(task), dst_cgrp,
2825				       &preloaded_csets);
2826		if (!threadgroup)
2827			break;
2828	} while_each_thread(leader, task);
2829	rcu_read_unlock();
2830	spin_unlock_irq(&css_set_lock);
2831
2832	/* prepare dst csets and commit */
2833	ret = cgroup_migrate_prepare_dst(&preloaded_csets);
2834	if (!ret)
2835		ret = cgroup_migrate(leader, threadgroup, dst_cgrp->root);
2836
2837	cgroup_migrate_finish(&preloaded_csets);
2838
2839	if (!ret)
2840		trace_cgroup_attach_task(dst_cgrp, leader, threadgroup);
2841
2842	return ret;
2843}
2844
2845static int cgroup_procs_write_permission(struct task_struct *task,
2846					 struct cgroup *dst_cgrp,
2847					 struct kernfs_open_file *of)
2848{
2849	const struct cred *cred = current_cred();
2850	const struct cred *tcred = get_task_cred(task);
2851	int ret = 0;
2852
2853	/*
2854	 * even if we're attaching all tasks in the thread group, we only
2855	 * need to check permissions on one of them.
2856	 */
2857	if (!uid_eq(cred->euid, GLOBAL_ROOT_UID) &&
2858	    !uid_eq(cred->euid, tcred->uid) &&
2859	    !uid_eq(cred->euid, tcred->suid))
2860		ret = -EACCES;
2861
2862	if (!ret && cgroup_on_dfl(dst_cgrp)) {
2863		struct super_block *sb = of->file->f_path.dentry->d_sb;
2864		struct cgroup *cgrp;
2865		struct inode *inode;
2866
2867		spin_lock_irq(&css_set_lock);
2868		cgrp = task_cgroup_from_root(task, &cgrp_dfl_root);
2869		spin_unlock_irq(&css_set_lock);
2870
2871		while (!cgroup_is_descendant(dst_cgrp, cgrp))
2872			cgrp = cgroup_parent(cgrp);
2873
2874		ret = -ENOMEM;
2875		inode = kernfs_get_inode(sb, cgrp->procs_file.kn);
2876		if (inode) {
2877			ret = inode_permission(inode, MAY_WRITE);
2878			iput(inode);
2879		}
2880	}
2881
2882	put_cred(tcred);
2883	return ret;
2884}
2885
2886/*
2887 * Find the task_struct of the task to attach by vpid and pass it along to the
2888 * function to attach either it or all tasks in its threadgroup. Will lock
2889 * cgroup_mutex and threadgroup.
2890 */
2891static ssize_t __cgroup_procs_write(struct kernfs_open_file *of, char *buf,
2892				    size_t nbytes, loff_t off, bool threadgroup)
2893{
2894	struct task_struct *tsk;
2895	struct cgroup_subsys *ss;
2896	struct cgroup *cgrp;
2897	pid_t pid;
2898	int ssid, ret;
2899
2900	if (kstrtoint(strstrip(buf), 0, &pid) || pid < 0)
2901		return -EINVAL;
2902
2903	cgrp = cgroup_kn_lock_live(of->kn, false);
2904	if (!cgrp)
2905		return -ENODEV;
2906
2907	percpu_down_write(&cgroup_threadgroup_rwsem);
2908	rcu_read_lock();
2909	if (pid) {
2910		tsk = find_task_by_vpid(pid);
2911		if (!tsk) {
2912			ret = -ESRCH;
2913			goto out_unlock_rcu;
2914		}
2915	} else {
2916		tsk = current;
2917	}
2918
2919	if (threadgroup)
2920		tsk = tsk->group_leader;
2921
2922	/*
2923	 * Workqueue threads may acquire PF_NO_SETAFFINITY and become
2924	 * trapped in a cpuset, or RT worker may be born in a cgroup
2925	 * with no rt_runtime allocated.  Just say no.
2926	 */
2927	if (tsk == kthreadd_task || (tsk->flags & PF_NO_SETAFFINITY)) {
2928		ret = -EINVAL;
2929		goto out_unlock_rcu;
2930	}
2931
2932	get_task_struct(tsk);
2933	rcu_read_unlock();
2934
2935	ret = cgroup_procs_write_permission(tsk, cgrp, of);
2936	if (!ret)
2937		ret = cgroup_attach_task(cgrp, tsk, threadgroup);
2938
2939	put_task_struct(tsk);
2940	goto out_unlock_threadgroup;
2941
2942out_unlock_rcu:
2943	rcu_read_unlock();
2944out_unlock_threadgroup:
2945	percpu_up_write(&cgroup_threadgroup_rwsem);
2946	for_each_subsys(ss, ssid)
2947		if (ss->post_attach)
2948			ss->post_attach();
2949	cgroup_kn_unlock(of->kn);
2950	return ret ?: nbytes;
2951}
2952
2953/**
2954 * cgroup_attach_task_all - attach task 'tsk' to all cgroups of task 'from'
2955 * @from: attach to all cgroups of a given task
2956 * @tsk: the task to be attached
2957 */
2958int cgroup_attach_task_all(struct task_struct *from, struct task_struct *tsk)
2959{
2960	struct cgroup_root *root;
2961	int retval = 0;
2962
2963	mutex_lock(&cgroup_mutex);
2964	percpu_down_write(&cgroup_threadgroup_rwsem);
2965	for_each_root(root) {
2966		struct cgroup *from_cgrp;
2967
2968		if (root == &cgrp_dfl_root)
2969			continue;
2970
2971		spin_lock_irq(&css_set_lock);
2972		from_cgrp = task_cgroup_from_root(from, root);
2973		spin_unlock_irq(&css_set_lock);
2974
2975		retval = cgroup_attach_task(from_cgrp, tsk, false);
2976		if (retval)
2977			break;
2978	}
2979	percpu_up_write(&cgroup_threadgroup_rwsem);
2980	mutex_unlock(&cgroup_mutex);
2981
2982	return retval;
2983}
2984EXPORT_SYMBOL_GPL(cgroup_attach_task_all);
2985
2986static ssize_t cgroup_tasks_write(struct kernfs_open_file *of,
2987				  char *buf, size_t nbytes, loff_t off)
2988{
2989	return __cgroup_procs_write(of, buf, nbytes, off, false);
2990}
2991
2992static ssize_t cgroup_procs_write(struct kernfs_open_file *of,
2993				  char *buf, size_t nbytes, loff_t off)
2994{
2995	return __cgroup_procs_write(of, buf, nbytes, off, true);
2996}
2997
2998static ssize_t cgroup_release_agent_write(struct kernfs_open_file *of,
2999					  char *buf, size_t nbytes, loff_t off)
3000{
3001	struct cgroup *cgrp;
3002
3003	BUILD_BUG_ON(sizeof(cgrp->root->release_agent_path) < PATH_MAX);
3004
3005	cgrp = cgroup_kn_lock_live(of->kn, false);
3006	if (!cgrp)
3007		return -ENODEV;
3008	spin_lock(&release_agent_path_lock);
3009	strlcpy(cgrp->root->release_agent_path, strstrip(buf),
3010		sizeof(cgrp->root->release_agent_path));
3011	spin_unlock(&release_agent_path_lock);
3012	cgroup_kn_unlock(of->kn);
3013	return nbytes;
3014}
3015
3016static int cgroup_release_agent_show(struct seq_file *seq, void *v)
3017{
3018	struct cgroup *cgrp = seq_css(seq)->cgroup;
3019
3020	spin_lock(&release_agent_path_lock);
3021	seq_puts(seq, cgrp->root->release_agent_path);
3022	spin_unlock(&release_agent_path_lock);
3023	seq_putc(seq, '\n');
3024	return 0;
3025}
3026
3027static int cgroup_sane_behavior_show(struct seq_file *seq, void *v)
3028{
3029	seq_puts(seq, "0\n");
3030	return 0;
3031}
3032
3033static void cgroup_print_ss_mask(struct seq_file *seq, u16 ss_mask)
3034{
3035	struct cgroup_subsys *ss;
3036	bool printed = false;
3037	int ssid;
3038
3039	do_each_subsys_mask(ss, ssid, ss_mask) {
3040		if (printed)
3041			seq_putc(seq, ' ');
3042		seq_printf(seq, "%s", ss->name);
3043		printed = true;
3044	} while_each_subsys_mask();
3045	if (printed)
3046		seq_putc(seq, '\n');
3047}
3048
3049/* show controllers which are enabled from the parent */
3050static int cgroup_controllers_show(struct seq_file *seq, void *v)
3051{
3052	struct cgroup *cgrp = seq_css(seq)->cgroup;
3053
3054	cgroup_print_ss_mask(seq, cgroup_control(cgrp));
3055	return 0;
3056}
3057
3058/* show controllers which are enabled for a given cgroup's children */
3059static int cgroup_subtree_control_show(struct seq_file *seq, void *v)
3060{
3061	struct cgroup *cgrp = seq_css(seq)->cgroup;
3062
3063	cgroup_print_ss_mask(seq, cgrp->subtree_control);
3064	return 0;
3065}
3066
3067/**
3068 * cgroup_update_dfl_csses - update css assoc of a subtree in default hierarchy
3069 * @cgrp: root of the subtree to update csses for
3070 *
3071 * @cgrp's control masks have changed and its subtree's css associations
3072 * need to be updated accordingly.  This function looks up all css_sets
3073 * which are attached to the subtree, creates the matching updated css_sets
3074 * and migrates the tasks to the new ones.
3075 */
3076static int cgroup_update_dfl_csses(struct cgroup *cgrp)
3077{
3078	LIST_HEAD(preloaded_csets);
3079	struct cgroup_taskset tset = CGROUP_TASKSET_INIT(tset);
3080	struct cgroup_subsys_state *d_css;
3081	struct cgroup *dsct;
3082	struct css_set *src_cset;
3083	int ret;
3084
3085	lockdep_assert_held(&cgroup_mutex);
3086
3087	percpu_down_write(&cgroup_threadgroup_rwsem);
3088
3089	/* look up all csses currently attached to @cgrp's subtree */
3090	spin_lock_irq(&css_set_lock);
3091	cgroup_for_each_live_descendant_pre(dsct, d_css, cgrp) {
3092		struct cgrp_cset_link *link;
3093
3094		list_for_each_entry(link, &dsct->cset_links, cset_link)
3095			cgroup_migrate_add_src(link->cset, dsct,
3096					       &preloaded_csets);
3097	}
3098	spin_unlock_irq(&css_set_lock);
3099
3100	/* NULL dst indicates self on default hierarchy */
3101	ret = cgroup_migrate_prepare_dst(&preloaded_csets);
3102	if (ret)
3103		goto out_finish;
3104
3105	spin_lock_irq(&css_set_lock);
3106	list_for_each_entry(src_cset, &preloaded_csets, mg_preload_node) {
3107		struct task_struct *task, *ntask;
3108
3109		/* src_csets precede dst_csets, break on the first dst_cset */
3110		if (!src_cset->mg_src_cgrp)
3111			break;
3112
3113		/* all tasks in src_csets need to be migrated */
3114		list_for_each_entry_safe(task, ntask, &src_cset->tasks, cg_list)
3115			cgroup_taskset_add(task, &tset);
3116	}
3117	spin_unlock_irq(&css_set_lock);
3118
3119	ret = cgroup_taskset_migrate(&tset, cgrp->root);
3120out_finish:
3121	cgroup_migrate_finish(&preloaded_csets);
3122	percpu_up_write(&cgroup_threadgroup_rwsem);
3123	return ret;
3124}
3125
3126/**
3127 * cgroup_lock_and_drain_offline - lock cgroup_mutex and drain offlined csses
3128 * @cgrp: root of the target subtree
3129 *
3130 * Because css offlining is asynchronous, userland may try to re-enable a
3131 * controller while the previous css is still around.  This function grabs
3132 * cgroup_mutex and drains the previous css instances of @cgrp's subtree.
3133 */
3134static void cgroup_lock_and_drain_offline(struct cgroup *cgrp)
3135	__acquires(&cgroup_mutex)
3136{
3137	struct cgroup *dsct;
3138	struct cgroup_subsys_state *d_css;
3139	struct cgroup_subsys *ss;
3140	int ssid;
3141
3142restart:
3143	mutex_lock(&cgroup_mutex);
3144
3145	cgroup_for_each_live_descendant_post(dsct, d_css, cgrp) {
3146		for_each_subsys(ss, ssid) {
3147			struct cgroup_subsys_state *css = cgroup_css(dsct, ss);
3148			DEFINE_WAIT(wait);
3149
3150			if (!css || !percpu_ref_is_dying(&css->refcnt))
3151				continue;
3152
3153			cgroup_get(dsct);
3154			prepare_to_wait(&dsct->offline_waitq, &wait,
3155					TASK_UNINTERRUPTIBLE);
3156
3157			mutex_unlock(&cgroup_mutex);
3158			schedule();
3159			finish_wait(&dsct->offline_waitq, &wait);
3160
3161			cgroup_put(dsct);
3162			goto restart;
3163		}
3164	}
3165}
3166
3167/**
3168 * cgroup_save_control - save control masks of a subtree
3169 * @cgrp: root of the target subtree
3170 *
3171 * Save ->subtree_control and ->subtree_ss_mask to the respective old_
3172 * prefixed fields for @cgrp's subtree including @cgrp itself.
3173 */
3174static void cgroup_save_control(struct cgroup *cgrp)
3175{
3176	struct cgroup *dsct;
3177	struct cgroup_subsys_state *d_css;
3178
3179	cgroup_for_each_live_descendant_pre(dsct, d_css, cgrp) {
3180		dsct->old_subtree_control = dsct->subtree_control;
3181		dsct->old_subtree_ss_mask = dsct->subtree_ss_mask;
3182	}
3183}
3184
3185/**
3186 * cgroup_propagate_control - refresh control masks of a subtree
3187 * @cgrp: root of the target subtree
3188 *
3189 * For @cgrp and its subtree, ensure ->subtree_ss_mask matches
3190 * ->subtree_control and propagate controller availability through the
3191 * subtree so that descendants don't have unavailable controllers enabled.
3192 */
3193static void cgroup_propagate_control(struct cgroup *cgrp)
3194{
3195	struct cgroup *dsct;
3196	struct cgroup_subsys_state *d_css;
3197
3198	cgroup_for_each_live_descendant_pre(dsct, d_css, cgrp) {
3199		dsct->subtree_control &= cgroup_control(dsct);
3200		dsct->subtree_ss_mask =
3201			cgroup_calc_subtree_ss_mask(dsct->subtree_control,
3202						    cgroup_ss_mask(dsct));
3203	}
3204}
3205
3206/**
3207 * cgroup_restore_control - restore control masks of a subtree
3208 * @cgrp: root of the target subtree
3209 *
3210 * Restore ->subtree_control and ->subtree_ss_mask from the respective old_
3211 * prefixed fields for @cgrp's subtree including @cgrp itself.
3212 */
3213static void cgroup_restore_control(struct cgroup *cgrp)
3214{
3215	struct cgroup *dsct;
3216	struct cgroup_subsys_state *d_css;
3217
3218	cgroup_for_each_live_descendant_post(dsct, d_css, cgrp) {
3219		dsct->subtree_control = dsct->old_subtree_control;
3220		dsct->subtree_ss_mask = dsct->old_subtree_ss_mask;
3221	}
3222}
3223
3224static bool css_visible(struct cgroup_subsys_state *css)
3225{
3226	struct cgroup_subsys *ss = css->ss;
3227	struct cgroup *cgrp = css->cgroup;
3228
3229	if (cgroup_control(cgrp) & (1 << ss->id))
3230		return true;
3231	if (!(cgroup_ss_mask(cgrp) & (1 << ss->id)))
3232		return false;
3233	return cgroup_on_dfl(cgrp) && ss->implicit_on_dfl;
3234}
3235
3236/**
3237 * cgroup_apply_control_enable - enable or show csses according to control
3238 * @cgrp: root of the target subtree
3239 *
3240 * Walk @cgrp's subtree and create new csses or make the existing ones
3241 * visible.  A css is created invisible if it's being implicitly enabled
3242 * through dependency.  An invisible css is made visible when the userland
3243 * explicitly enables it.
3244 *
3245 * Returns 0 on success, -errno on failure.  On failure, csses which have
3246 * been processed already aren't cleaned up.  The caller is responsible for
3247 * cleaning up with cgroup_apply_control_disble().
3248 */
3249static int cgroup_apply_control_enable(struct cgroup *cgrp)
3250{
3251	struct cgroup *dsct;
3252	struct cgroup_subsys_state *d_css;
3253	struct cgroup_subsys *ss;
3254	int ssid, ret;
3255
3256	cgroup_for_each_live_descendant_pre(dsct, d_css, cgrp) {
3257		for_each_subsys(ss, ssid) {
3258			struct cgroup_subsys_state *css = cgroup_css(dsct, ss);
3259
3260			WARN_ON_ONCE(css && percpu_ref_is_dying(&css->refcnt));
3261
3262			if (!(cgroup_ss_mask(dsct) & (1 << ss->id)))
3263				continue;
3264
3265			if (!css) {
3266				css = css_create(dsct, ss);
3267				if (IS_ERR(css))
3268					return PTR_ERR(css);
3269			}
3270
3271			if (css_visible(css)) {
3272				ret = css_populate_dir(css);
3273				if (ret)
3274					return ret;
3275			}
3276		}
3277	}
3278
3279	return 0;
3280}
3281
3282/**
3283 * cgroup_apply_control_disable - kill or hide csses according to control
3284 * @cgrp: root of the target subtree
3285 *
3286 * Walk @cgrp's subtree and kill and hide csses so that they match
3287 * cgroup_ss_mask() and cgroup_visible_mask().
3288 *
3289 * A css is hidden when the userland requests it to be disabled while other
3290 * subsystems are still depending on it.  The css must not actively control
3291 * resources and be in the vanilla state if it's made visible again later.
3292 * Controllers which may be depended upon should provide ->css_reset() for
3293 * this purpose.
3294 */
3295static void cgroup_apply_control_disable(struct cgroup *cgrp)
3296{
3297	struct cgroup *dsct;
3298	struct cgroup_subsys_state *d_css;
3299	struct cgroup_subsys *ss;
3300	int ssid;
3301
3302	cgroup_for_each_live_descendant_post(dsct, d_css, cgrp) {
3303		for_each_subsys(ss, ssid) {
3304			struct cgroup_subsys_state *css = cgroup_css(dsct, ss);
3305
3306			WARN_ON_ONCE(css && percpu_ref_is_dying(&css->refcnt));
3307
3308			if (!css)
3309				continue;
3310
3311			if (css->parent &&
3312			    !(cgroup_ss_mask(dsct) & (1 << ss->id))) {
3313				kill_css(css);
3314			} else if (!css_visible(css)) {
3315				css_clear_dir(css);
3316				if (ss->css_reset)
3317					ss->css_reset(css);
3318			}
3319		}
3320	}
3321}
3322
3323/**
3324 * cgroup_apply_control - apply control mask updates to the subtree
3325 * @cgrp: root of the target subtree
3326 *
3327 * subsystems can be enabled and disabled in a subtree using the following
3328 * steps.
3329 *
3330 * 1. Call cgroup_save_control() to stash the current state.
3331 * 2. Update ->subtree_control masks in the subtree as desired.
3332 * 3. Call cgroup_apply_control() to apply the changes.
3333 * 4. Optionally perform other related operations.
3334 * 5. Call cgroup_finalize_control() to finish up.
3335 *
3336 * This function implements step 3 and propagates the mask changes
3337 * throughout @cgrp's subtree, updates csses accordingly and perform
3338 * process migrations.
3339 */
3340static int cgroup_apply_control(struct cgroup *cgrp)
3341{
3342	int ret;
3343
3344	cgroup_propagate_control(cgrp);
3345
3346	ret = cgroup_apply_control_enable(cgrp);
3347	if (ret)
3348		return ret;
3349
3350	/*
3351	 * At this point, cgroup_e_css() results reflect the new csses
3352	 * making the following cgroup_update_dfl_csses() properly update
3353	 * css associations of all tasks in the subtree.
3354	 */
3355	ret = cgroup_update_dfl_csses(cgrp);
3356	if (ret)
3357		return ret;
3358
3359	return 0;
3360}
3361
3362/**
3363 * cgroup_finalize_control - finalize control mask update
3364 * @cgrp: root of the target subtree
3365 * @ret: the result of the update
3366 *
3367 * Finalize control mask update.  See cgroup_apply_control() for more info.
3368 */
3369static void cgroup_finalize_control(struct cgroup *cgrp, int ret)
3370{
3371	if (ret) {
3372		cgroup_restore_control(cgrp);
3373		cgroup_propagate_control(cgrp);
3374	}
3375
3376	cgroup_apply_control_disable(cgrp);
3377}
3378
3379/* change the enabled child controllers for a cgroup in the default hierarchy */
3380static ssize_t cgroup_subtree_control_write(struct kernfs_open_file *of,
3381					    char *buf, size_t nbytes,
3382					    loff_t off)
3383{
3384	u16 enable = 0, disable = 0;
3385	struct cgroup *cgrp, *child;
3386	struct cgroup_subsys *ss;
3387	char *tok;
3388	int ssid, ret;
3389
3390	/*
3391	 * Parse input - space separated list of subsystem names prefixed
3392	 * with either + or -.
3393	 */
3394	buf = strstrip(buf);
3395	while ((tok = strsep(&buf, " "))) {
3396		if (tok[0] == '\0')
3397			continue;
3398		do_each_subsys_mask(ss, ssid, ~cgrp_dfl_inhibit_ss_mask) {
3399			if (!cgroup_ssid_enabled(ssid) ||
3400			    strcmp(tok + 1, ss->name))
3401				continue;
3402
3403			if (*tok == '+') {
3404				enable |= 1 << ssid;
3405				disable &= ~(1 << ssid);
3406			} else if (*tok == '-') {
3407				disable |= 1 << ssid;
3408				enable &= ~(1 << ssid);
3409			} else {
3410				return -EINVAL;
3411			}
3412			break;
3413		} while_each_subsys_mask();
3414		if (ssid == CGROUP_SUBSYS_COUNT)
3415			return -EINVAL;
3416	}
3417
3418	cgrp = cgroup_kn_lock_live(of->kn, true);
3419	if (!cgrp)
3420		return -ENODEV;
3421
3422	for_each_subsys(ss, ssid) {
3423		if (enable & (1 << ssid)) {
3424			if (cgrp->subtree_control & (1 << ssid)) {
3425				enable &= ~(1 << ssid);
3426				continue;
3427			}
3428
3429			if (!(cgroup_control(cgrp) & (1 << ssid))) {
3430				ret = -ENOENT;
3431				goto out_unlock;
3432			}
3433		} else if (disable & (1 << ssid)) {
3434			if (!(cgrp->subtree_control & (1 << ssid))) {
3435				disable &= ~(1 << ssid);
3436				continue;
3437			}
3438
3439			/* a child has it enabled? */
3440			cgroup_for_each_live_child(child, cgrp) {
3441				if (child->subtree_control & (1 << ssid)) {
3442					ret = -EBUSY;
3443					goto out_unlock;
3444				}
3445			}
3446		}
3447	}
3448
3449	if (!enable && !disable) {
3450		ret = 0;
3451		goto out_unlock;
3452	}
3453
3454	/*
3455	 * Except for the root, subtree_control must be zero for a cgroup
3456	 * with tasks so that child cgroups don't compete against tasks.
3457	 */
3458	if (enable && cgroup_parent(cgrp)) {
3459		struct cgrp_cset_link *link;
3460
3461		/*
3462		 * Because namespaces pin csets too, @cgrp->cset_links
3463		 * might not be empty even when @cgrp is empty.  Walk and
3464		 * verify each cset.
3465		 */
3466		spin_lock_irq(&css_set_lock);
3467
3468		ret = 0;
3469		list_for_each_entry(link, &cgrp->cset_links, cset_link) {
3470			if (css_set_populated(link->cset)) {
3471				ret = -EBUSY;
3472				break;
3473			}
3474		}
3475
3476		spin_unlock_irq(&css_set_lock);
3477
3478		if (ret)
3479			goto out_unlock;
3480	}
3481
3482	/* save and update control masks and prepare csses */
3483	cgroup_save_control(cgrp);
3484
3485	cgrp->subtree_control |= enable;
3486	cgrp->subtree_control &= ~disable;
3487
3488	ret = cgroup_apply_control(cgrp);
3489
3490	cgroup_finalize_control(cgrp, ret);
3491
3492	kernfs_activate(cgrp->kn);
3493	ret = 0;
3494out_unlock:
3495	cgroup_kn_unlock(of->kn);
3496	return ret ?: nbytes;
3497}
3498
3499static int cgroup_events_show(struct seq_file *seq, void *v)
3500{
3501	seq_printf(seq, "populated %d\n",
3502		   cgroup_is_populated(seq_css(seq)->cgroup));
3503	return 0;
3504}
3505
3506static ssize_t cgroup_file_write(struct kernfs_open_file *of, char *buf,
3507				 size_t nbytes, loff_t off)
3508{
3509	struct cgroup *cgrp = of->kn->parent->priv;
3510	struct cftype *cft = of->kn->priv;
3511	struct cgroup_subsys_state *css;
3512	int ret;
3513
3514	if (cft->write)
3515		return cft->write(of, buf, nbytes, off);
3516
3517	/*
3518	 * kernfs guarantees that a file isn't deleted with operations in
3519	 * flight, which means that the matching css is and stays alive and
3520	 * doesn't need to be pinned.  The RCU locking is not necessary
3521	 * either.  It's just for the convenience of using cgroup_css().
3522	 */
3523	rcu_read_lock();
3524	css = cgroup_css(cgrp, cft->ss);
3525	rcu_read_unlock();
3526
3527	if (cft->write_u64) {
3528		unsigned long long v;
3529		ret = kstrtoull(buf, 0, &v);
3530		if (!ret)
3531			ret = cft->write_u64(css, cft, v);
3532	} else if (cft->write_s64) {
3533		long long v;
3534		ret = kstrtoll(buf, 0, &v);
3535		if (!ret)
3536			ret = cft->write_s64(css, cft, v);
3537	} else {
3538		ret = -EINVAL;
3539	}
3540
3541	return ret ?: nbytes;
3542}
3543
3544static void *cgroup_seqfile_start(struct seq_file *seq, loff_t *ppos)
3545{
3546	return seq_cft(seq)->seq_start(seq, ppos);
3547}
3548
3549static void *cgroup_seqfile_next(struct seq_file *seq, void *v, loff_t *ppos)
3550{
3551	return seq_cft(seq)->seq_next(seq, v, ppos);
3552}
3553
3554static void cgroup_seqfile_stop(struct seq_file *seq, void *v)
3555{
3556	seq_cft(seq)->seq_stop(seq, v);
3557}
3558
3559static int cgroup_seqfile_show(struct seq_file *m, void *arg)
3560{
3561	struct cftype *cft = seq_cft(m);
3562	struct cgroup_subsys_state *css = seq_css(m);
3563
3564	if (cft->seq_show)
3565		return cft->seq_show(m, arg);
3566
3567	if (cft->read_u64)
3568		seq_printf(m, "%llu\n", cft->read_u64(css, cft));
3569	else if (cft->read_s64)
3570		seq_printf(m, "%lld\n", cft->read_s64(css, cft));
3571	else
3572		return -EINVAL;
3573	return 0;
3574}
3575
3576static struct kernfs_ops cgroup_kf_single_ops = {
3577	.atomic_write_len	= PAGE_SIZE,
3578	.write			= cgroup_file_write,
3579	.seq_show		= cgroup_seqfile_show,
3580};
3581
3582static struct kernfs_ops cgroup_kf_ops = {
3583	.atomic_write_len	= PAGE_SIZE,
3584	.write			= cgroup_file_write,
3585	.seq_start		= cgroup_seqfile_start,
3586	.seq_next		= cgroup_seqfile_next,
3587	.seq_stop		= cgroup_seqfile_stop,
3588	.seq_show		= cgroup_seqfile_show,
3589};
3590
3591/*
3592 * cgroup_rename - Only allow simple rename of directories in place.
3593 */
3594static int cgroup_rename(struct kernfs_node *kn, struct kernfs_node *new_parent,
3595			 const char *new_name_str)
3596{
3597	struct cgroup *cgrp = kn->priv;
3598	int ret;
3599
3600	if (kernfs_type(kn) != KERNFS_DIR)
3601		return -ENOTDIR;
3602	if (kn->parent != new_parent)
3603		return -EIO;
3604
3605	/*
3606	 * This isn't a proper migration and its usefulness is very
3607	 * limited.  Disallow on the default hierarchy.
3608	 */
3609	if (cgroup_on_dfl(cgrp))
3610		return -EPERM;
3611
3612	/*
3613	 * We're gonna grab cgroup_mutex which nests outside kernfs
3614	 * active_ref.  kernfs_rename() doesn't require active_ref
3615	 * protection.  Break them before grabbing cgroup_mutex.
3616	 */
3617	kernfs_break_active_protection(new_parent);
3618	kernfs_break_active_protection(kn);
3619
3620	mutex_lock(&cgroup_mutex);
3621
3622	ret = kernfs_rename(kn, new_parent, new_name_str);
3623	if (!ret)
3624		trace_cgroup_rename(cgrp);
3625
3626	mutex_unlock(&cgroup_mutex);
3627
3628	kernfs_unbreak_active_protection(kn);
3629	kernfs_unbreak_active_protection(new_parent);
3630	return ret;
3631}
3632
3633/* set uid and gid of cgroup dirs and files to that of the creator */
3634static int cgroup_kn_set_ugid(struct kernfs_node *kn)
3635{
3636	struct iattr iattr = { .ia_valid = ATTR_UID | ATTR_GID,
3637			       .ia_uid = current_fsuid(),
3638			       .ia_gid = current_fsgid(), };
3639
3640	if (uid_eq(iattr.ia_uid, GLOBAL_ROOT_UID) &&
3641	    gid_eq(iattr.ia_gid, GLOBAL_ROOT_GID))
3642		return 0;
3643
3644	return kernfs_setattr(kn, &iattr);
3645}
3646
3647static int cgroup_add_file(struct cgroup_subsys_state *css, struct cgroup *cgrp,
3648			   struct cftype *cft)
3649{
3650	char name[CGROUP_FILE_NAME_MAX];
3651	struct kernfs_node *kn;
3652	struct lock_class_key *key = NULL;
3653	int ret;
3654
3655#ifdef CONFIG_DEBUG_LOCK_ALLOC
3656	key = &cft->lockdep_key;
3657#endif
3658	kn = __kernfs_create_file(cgrp->kn, cgroup_file_name(cgrp, cft, name),
3659				  cgroup_file_mode(cft), 0, cft->kf_ops, cft,
3660				  NULL, key);
3661	if (IS_ERR(kn))
3662		return PTR_ERR(kn);
3663
3664	ret = cgroup_kn_set_ugid(kn);
3665	if (ret) {
3666		kernfs_remove(kn);
3667		return ret;
3668	}
3669
3670	if (cft->file_offset) {
3671		struct cgroup_file *cfile = (void *)css + cft->file_offset;
3672
3673		spin_lock_irq(&cgroup_file_kn_lock);
3674		cfile->kn = kn;
3675		spin_unlock_irq(&cgroup_file_kn_lock);
3676	}
3677
3678	return 0;
3679}
3680
3681/**
3682 * cgroup_addrm_files - add or remove files to a cgroup directory
3683 * @css: the target css
3684 * @cgrp: the target cgroup (usually css->cgroup)
3685 * @cfts: array of cftypes to be added
3686 * @is_add: whether to add or remove
3687 *
3688 * Depending on @is_add, add or remove files defined by @cfts on @cgrp.
3689 * For removals, this function never fails.
3690 */
3691static int cgroup_addrm_files(struct cgroup_subsys_state *css,
3692			      struct cgroup *cgrp, struct cftype cfts[],
3693			      bool is_add)
3694{
3695	struct cftype *cft, *cft_end = NULL;
3696	int ret = 0;
3697
3698	lockdep_assert_held(&cgroup_mutex);
3699
3700restart:
3701	for (cft = cfts; cft != cft_end && cft->name[0] != '\0'; cft++) {
3702		/* does cft->flags tell us to skip this file on @cgrp? */
3703		if ((cft->flags & __CFTYPE_ONLY_ON_DFL) && !cgroup_on_dfl(cgrp))
3704			continue;
3705		if ((cft->flags & __CFTYPE_NOT_ON_DFL) && cgroup_on_dfl(cgrp))
3706			continue;
3707		if ((cft->flags & CFTYPE_NOT_ON_ROOT) && !cgroup_parent(cgrp))
3708			continue;
3709		if ((cft->flags & CFTYPE_ONLY_ON_ROOT) && cgroup_parent(cgrp))
3710			continue;
3711
3712		if (is_add) {
3713			ret = cgroup_add_file(css, cgrp, cft);
3714			if (ret) {
3715				pr_warn("%s: failed to add %s, err=%d\n",
3716					__func__, cft->name, ret);
3717				cft_end = cft;
3718				is_add = false;
3719				goto restart;
3720			}
3721		} else {
3722			cgroup_rm_file(cgrp, cft);
3723		}
3724	}
3725	return ret;
3726}
3727
3728static int cgroup_apply_cftypes(struct cftype *cfts, bool is_add)
3729{
3730	LIST_HEAD(pending);
3731	struct cgroup_subsys *ss = cfts[0].ss;
3732	struct cgroup *root = &ss->root->cgrp;
3733	struct cgroup_subsys_state *css;
3734	int ret = 0;
3735
3736	lockdep_assert_held(&cgroup_mutex);
3737
3738	/* add/rm files for all cgroups created before */
3739	css_for_each_descendant_pre(css, cgroup_css(root, ss)) {
3740		struct cgroup *cgrp = css->cgroup;
3741
3742		if (!(css->flags & CSS_VISIBLE))
3743			continue;
3744
3745		ret = cgroup_addrm_files(css, cgrp, cfts, is_add);
3746		if (ret)
3747			break;
3748	}
3749
3750	if (is_add && !ret)
3751		kernfs_activate(root->kn);
3752	return ret;
3753}
3754
3755static void cgroup_exit_cftypes(struct cftype *cfts)
3756{
3757	struct cftype *cft;
3758
3759	for (cft = cfts; cft->name[0] != '\0'; cft++) {
3760		/* free copy for custom atomic_write_len, see init_cftypes() */
3761		if (cft->max_write_len && cft->max_write_len != PAGE_SIZE)
3762			kfree(cft->kf_ops);
3763		cft->kf_ops = NULL;
3764		cft->ss = NULL;
3765
3766		/* revert flags set by cgroup core while adding @cfts */
3767		cft->flags &= ~(__CFTYPE_ONLY_ON_DFL | __CFTYPE_NOT_ON_DFL);
3768	}
3769}
3770
3771static int cgroup_init_cftypes(struct cgroup_subsys *ss, struct cftype *cfts)
3772{
3773	struct cftype *cft;
3774
3775	for (cft = cfts; cft->name[0] != '\0'; cft++) {
3776		struct kernfs_ops *kf_ops;
3777
3778		WARN_ON(cft->ss || cft->kf_ops);
3779
3780		if (cft->seq_start)
3781			kf_ops = &cgroup_kf_ops;
3782		else
3783			kf_ops = &cgroup_kf_single_ops;
3784
3785		/*
3786		 * Ugh... if @cft wants a custom max_write_len, we need to
3787		 * make a copy of kf_ops to set its atomic_write_len.
3788		 */
3789		if (cft->max_write_len && cft->max_write_len != PAGE_SIZE) {
3790			kf_ops = kmemdup(kf_ops, sizeof(*kf_ops), GFP_KERNEL);
3791			if (!kf_ops) {
3792				cgroup_exit_cftypes(cfts);
3793				return -ENOMEM;
3794			}
3795			kf_ops->atomic_write_len = cft->max_write_len;
3796		}
3797
3798		cft->kf_ops = kf_ops;
3799		cft->ss = ss;
3800	}
3801
3802	return 0;
3803}
3804
3805static int cgroup_rm_cftypes_locked(struct cftype *cfts)
3806{
3807	lockdep_assert_held(&cgroup_mutex);
3808
3809	if (!cfts || !cfts[0].ss)
3810		return -ENOENT;
3811
3812	list_del(&cfts->node);
3813	cgroup_apply_cftypes(cfts, false);
3814	cgroup_exit_cftypes(cfts);
3815	return 0;
3816}
3817
3818/**
3819 * cgroup_rm_cftypes - remove an array of cftypes from a subsystem
3820 * @cfts: zero-length name terminated array of cftypes
3821 *
3822 * Unregister @cfts.  Files described by @cfts are removed from all
3823 * existing cgroups and all future cgroups won't have them either.  This
3824 * function can be called anytime whether @cfts' subsys is attached or not.
3825 *
3826 * Returns 0 on successful unregistration, -ENOENT if @cfts is not
3827 * registered.
3828 */
3829int cgroup_rm_cftypes(struct cftype *cfts)
3830{
3831	int ret;
3832
3833	mutex_lock(&cgroup_mutex);
3834	ret = cgroup_rm_cftypes_locked(cfts);
3835	mutex_unlock(&cgroup_mutex);
3836	return ret;
3837}
3838
3839/**
3840 * cgroup_add_cftypes - add an array of cftypes to a subsystem
3841 * @ss: target cgroup subsystem
3842 * @cfts: zero-length name terminated array of cftypes
3843 *
3844 * Register @cfts to @ss.  Files described by @cfts are created for all
3845 * existing cgroups to which @ss is attached and all future cgroups will
3846 * have them too.  This function can be called anytime whether @ss is
3847 * attached or not.
3848 *
3849 * Returns 0 on successful registration, -errno on failure.  Note that this
3850 * function currently returns 0 as long as @cfts registration is successful
3851 * even if some file creation attempts on existing cgroups fail.
3852 */
3853static int cgroup_add_cftypes(struct cgroup_subsys *ss, struct cftype *cfts)
3854{
3855	int ret;
3856
3857	if (!cgroup_ssid_enabled(ss->id))
3858		return 0;
3859
3860	if (!cfts || cfts[0].name[0] == '\0')
3861		return 0;
3862
3863	ret = cgroup_init_cftypes(ss, cfts);
3864	if (ret)
3865		return ret;
3866
3867	mutex_lock(&cgroup_mutex);
3868
3869	list_add_tail(&cfts->node, &ss->cfts);
3870	ret = cgroup_apply_cftypes(cfts, true);
3871	if (ret)
3872		cgroup_rm_cftypes_locked(cfts);
3873
3874	mutex_unlock(&cgroup_mutex);
3875	return ret;
3876}
3877
3878/**
3879 * cgroup_add_dfl_cftypes - add an array of cftypes for default hierarchy
3880 * @ss: target cgroup subsystem
3881 * @cfts: zero-length name terminated array of cftypes
3882 *
3883 * Similar to cgroup_add_cftypes() but the added files are only used for
3884 * the default hierarchy.
3885 */
3886int cgroup_add_dfl_cftypes(struct cgroup_subsys *ss, struct cftype *cfts)
3887{
3888	struct cftype *cft;
3889
3890	for (cft = cfts; cft && cft->name[0] != '\0'; cft++)
3891		cft->flags |= __CFTYPE_ONLY_ON_DFL;
3892	return cgroup_add_cftypes(ss, cfts);
3893}
3894
3895/**
3896 * cgroup_add_legacy_cftypes - add an array of cftypes for legacy hierarchies
3897 * @ss: target cgroup subsystem
3898 * @cfts: zero-length name terminated array of cftypes
3899 *
3900 * Similar to cgroup_add_cftypes() but the added files are only used for
3901 * the legacy hierarchies.
3902 */
3903int cgroup_add_legacy_cftypes(struct cgroup_subsys *ss, struct cftype *cfts)
3904{
3905	struct cftype *cft;
3906
3907	for (cft = cfts; cft && cft->name[0] != '\0'; cft++)
3908		cft->flags |= __CFTYPE_NOT_ON_DFL;
3909	return cgroup_add_cftypes(ss, cfts);
3910}
3911
3912/**
3913 * cgroup_file_notify - generate a file modified event for a cgroup_file
3914 * @cfile: target cgroup_file
3915 *
3916 * @cfile must have been obtained by setting cftype->file_offset.
3917 */
3918void cgroup_file_notify(struct cgroup_file *cfile)
3919{
3920	unsigned long flags;
3921
3922	spin_lock_irqsave(&cgroup_file_kn_lock, flags);
3923	if (cfile->kn)
3924		kernfs_notify(cfile->kn);
3925	spin_unlock_irqrestore(&cgroup_file_kn_lock, flags);
3926}
3927
3928/**
3929 * cgroup_task_count - count the number of tasks in a cgroup.
3930 * @cgrp: the cgroup in question
3931 *
3932 * Return the number of tasks in the cgroup.  The returned number can be
3933 * higher than the actual number of tasks due to css_set references from
3934 * namespace roots and temporary usages.
3935 */
3936static int cgroup_task_count(const struct cgroup *cgrp)
3937{
3938	int count = 0;
3939	struct cgrp_cset_link *link;
3940
3941	spin_lock_irq(&css_set_lock);
3942	list_for_each_entry(link, &cgrp->cset_links, cset_link)
3943		count += atomic_read(&link->cset->refcount);
3944	spin_unlock_irq(&css_set_lock);
3945	return count;
3946}
3947
3948/**
3949 * css_next_child - find the next child of a given css
3950 * @pos: the current position (%NULL to initiate traversal)
3951 * @parent: css whose children to walk
3952 *
3953 * This function returns the next child of @parent and should be called
3954 * under either cgroup_mutex or RCU read lock.  The only requirement is
3955 * that @parent and @pos are accessible.  The next sibling is guaranteed to
3956 * be returned regardless of their states.
3957 *
3958 * If a subsystem synchronizes ->css_online() and the start of iteration, a
3959 * css which finished ->css_online() is guaranteed to be visible in the
3960 * future iterations and will stay visible until the last reference is put.
3961 * A css which hasn't finished ->css_online() or already finished
3962 * ->css_offline() may show up during traversal.  It's each subsystem's
3963 * responsibility to synchronize against on/offlining.
3964 */
3965struct cgroup_subsys_state *css_next_child(struct cgroup_subsys_state *pos,
3966					   struct cgroup_subsys_state *parent)
3967{
3968	struct cgroup_subsys_state *next;
3969
3970	cgroup_assert_mutex_or_rcu_locked();
3971
3972	/*
3973	 * @pos could already have been unlinked from the sibling list.
3974	 * Once a cgroup is removed, its ->sibling.next is no longer
3975	 * updated when its next sibling changes.  CSS_RELEASED is set when
3976	 * @pos is taken off list, at which time its next pointer is valid,
3977	 * and, as releases are serialized, the one pointed to by the next
3978	 * pointer is guaranteed to not have started release yet.  This
3979	 * implies that if we observe !CSS_RELEASED on @pos in this RCU
3980	 * critical section, the one pointed to by its next pointer is
3981	 * guaranteed to not have finished its RCU grace period even if we
3982	 * have dropped rcu_read_lock() inbetween iterations.
3983	 *
3984	 * If @pos has CSS_RELEASED set, its next pointer can't be
3985	 * dereferenced; however, as each css is given a monotonically
3986	 * increasing unique serial number and always appended to the
3987	 * sibling list, the next one can be found by walking the parent's
3988	 * children until the first css with higher serial number than
3989	 * @pos's.  While this path can be slower, it happens iff iteration
3990	 * races against release and the race window is very small.
3991	 */
3992	if (!pos) {
3993		next = list_entry_rcu(parent->children.next, struct cgroup_subsys_state, sibling);
3994	} else if (likely(!(pos->flags & CSS_RELEASED))) {
3995		next = list_entry_rcu(pos->sibling.next, struct cgroup_subsys_state, sibling);
3996	} else {
3997		list_for_each_entry_rcu(next, &parent->children, sibling)
3998			if (next->serial_nr > pos->serial_nr)
3999				break;
4000	}
4001
4002	/*
4003	 * @next, if not pointing to the head, can be dereferenced and is
4004	 * the next sibling.
4005	 */
4006	if (&next->sibling != &parent->children)
4007		return next;
4008	return NULL;
4009}
4010
4011/**
4012 * css_next_descendant_pre - find the next descendant for pre-order walk
4013 * @pos: the current position (%NULL to initiate traversal)
4014 * @root: css whose descendants to walk
4015 *
4016 * To be used by css_for_each_descendant_pre().  Find the next descendant
4017 * to visit for pre-order traversal of @root's descendants.  @root is
4018 * included in the iteration and the first node to be visited.
4019 *
4020 * While this function requires cgroup_mutex or RCU read locking, it
4021 * doesn't require the whole traversal to be contained in a single critical
4022 * section.  This function will return the correct next descendant as long
4023 * as both @pos and @root are accessible and @pos is a descendant of @root.
4024 *
4025 * If a subsystem synchronizes ->css_online() and the start of iteration, a
4026 * css which finished ->css_online() is guaranteed to be visible in the
4027 * future iterations and will stay visible until the last reference is put.
4028 * A css which hasn't finished ->css_online() or already finished
4029 * ->css_offline() may show up during traversal.  It's each subsystem's
4030 * responsibility to synchronize against on/offlining.
4031 */
4032struct cgroup_subsys_state *
4033css_next_descendant_pre(struct cgroup_subsys_state *pos,
4034			struct cgroup_subsys_state *root)
4035{
4036	struct cgroup_subsys_state *next;
4037
4038	cgroup_assert_mutex_or_rcu_locked();
4039
4040	/* if first iteration, visit @root */
4041	if (!pos)
4042		return root;
4043
4044	/* visit the first child if exists */
4045	next = css_next_child(NULL, pos);
4046	if (next)
4047		return next;
4048
4049	/* no child, visit my or the closest ancestor's next sibling */
4050	while (pos != root) {
4051		next = css_next_child(pos, pos->parent);
4052		if (next)
4053			return next;
4054		pos = pos->parent;
4055	}
4056
4057	return NULL;
4058}
4059
4060/**
4061 * css_rightmost_descendant - return the rightmost descendant of a css
4062 * @pos: css of interest
4063 *
4064 * Return the rightmost descendant of @pos.  If there's no descendant, @pos
4065 * is returned.  This can be used during pre-order traversal to skip
4066 * subtree of @pos.
4067 *
4068 * While this function requires cgroup_mutex or RCU read locking, it
4069 * doesn't require the whole traversal to be contained in a single critical
4070 * section.  This function will return the correct rightmost descendant as
4071 * long as @pos is accessible.
4072 */
4073struct cgroup_subsys_state *
4074css_rightmost_descendant(struct cgroup_subsys_state *pos)
4075{
4076	struct cgroup_subsys_state *last, *tmp;
4077
4078	cgroup_assert_mutex_or_rcu_locked();
4079
4080	do {
4081		last = pos;
4082		/* ->prev isn't RCU safe, walk ->next till the end */
4083		pos = NULL;
4084		css_for_each_child(tmp, last)
4085			pos = tmp;
4086	} while (pos);
4087
4088	return last;
4089}
4090
4091static struct cgroup_subsys_state *
4092css_leftmost_descendant(struct cgroup_subsys_state *pos)
4093{
4094	struct cgroup_subsys_state *last;
4095
4096	do {
4097		last = pos;
4098		pos = css_next_child(NULL, pos);
4099	} while (pos);
4100
4101	return last;
4102}
4103
4104/**
4105 * css_next_descendant_post - find the next descendant for post-order walk
4106 * @pos: the current position (%NULL to initiate traversal)
4107 * @root: css whose descendants to walk
4108 *
4109 * To be used by css_for_each_descendant_post().  Find the next descendant
4110 * to visit for post-order traversal of @root's descendants.  @root is
4111 * included in the iteration and the last node to be visited.
4112 *
4113 * While this function requires cgroup_mutex or RCU read locking, it
4114 * doesn't require the whole traversal to be contained in a single critical
4115 * section.  This function will return the correct next descendant as long
4116 * as both @pos and @cgroup are accessible and @pos is a descendant of
4117 * @cgroup.
4118 *
4119 * If a subsystem synchronizes ->css_online() and the start of iteration, a
4120 * css which finished ->css_online() is guaranteed to be visible in the
4121 * future iterations and will stay visible until the last reference is put.
4122 * A css which hasn't finished ->css_online() or already finished
4123 * ->css_offline() may show up during traversal.  It's each subsystem's
4124 * responsibility to synchronize against on/offlining.
4125 */
4126struct cgroup_subsys_state *
4127css_next_descendant_post(struct cgroup_subsys_state *pos,
4128			 struct cgroup_subsys_state *root)
4129{
4130	struct cgroup_subsys_state *next;
4131
4132	cgroup_assert_mutex_or_rcu_locked();
4133
4134	/* if first iteration, visit leftmost descendant which may be @root */
4135	if (!pos)
4136		return css_leftmost_descendant(root);
4137
4138	/* if we visited @root, we're done */
4139	if (pos == root)
4140		return NULL;
4141
4142	/* if there's an unvisited sibling, visit its leftmost descendant */
4143	next = css_next_child(pos, pos->parent);
4144	if (next)
4145		return css_leftmost_descendant(next);
4146
4147	/* no sibling left, visit parent */
4148	return pos->parent;
4149}
4150
4151/**
4152 * css_has_online_children - does a css have online children
4153 * @css: the target css
4154 *
4155 * Returns %true if @css has any online children; otherwise, %false.  This
4156 * function can be called from any context but the caller is responsible
4157 * for synchronizing against on/offlining as necessary.
4158 */
4159bool css_has_online_children(struct cgroup_subsys_state *css)
4160{
4161	struct cgroup_subsys_state *child;
4162	bool ret = false;
4163
4164	rcu_read_lock();
4165	css_for_each_child(child, css) {
4166		if (child->flags & CSS_ONLINE) {
4167			ret = true;
4168			break;
4169		}
4170	}
4171	rcu_read_unlock();
4172	return ret;
4173}
4174
4175/**
4176 * css_task_iter_advance_css_set - advance a task itererator to the next css_set
4177 * @it: the iterator to advance
4178 *
4179 * Advance @it to the next css_set to walk.
4180 */
4181static void css_task_iter_advance_css_set(struct css_task_iter *it)
4182{
4183	struct list_head *l = it->cset_pos;
4184	struct cgrp_cset_link *link;
4185	struct css_set *cset;
4186
4187	lockdep_assert_held(&css_set_lock);
4188
4189	/* Advance to the next non-empty css_set */
4190	do {
4191		l = l->next;
4192		if (l == it->cset_head) {
4193			it->cset_pos = NULL;
4194			it->task_pos = NULL;
4195			return;
4196		}
4197
4198		if (it->ss) {
4199			cset = container_of(l, struct css_set,
4200					    e_cset_node[it->ss->id]);
4201		} else {
4202			link = list_entry(l, struct cgrp_cset_link, cset_link);
4203			cset = link->cset;
4204		}
4205	} while (!css_set_populated(cset));
4206
4207	it->cset_pos = l;
4208
4209	if (!list_empty(&cset->tasks))
4210		it->task_pos = cset->tasks.next;
4211	else
4212		it->task_pos = cset->mg_tasks.next;
4213
4214	it->tasks_head = &cset->tasks;
4215	it->mg_tasks_head = &cset->mg_tasks;
4216
4217	/*
4218	 * We don't keep css_sets locked across iteration steps and thus
4219	 * need to take steps to ensure that iteration can be resumed after
4220	 * the lock is re-acquired.  Iteration is performed at two levels -
4221	 * css_sets and tasks in them.
4222	 *
4223	 * Once created, a css_set never leaves its cgroup lists, so a
4224	 * pinned css_set is guaranteed to stay put and we can resume
4225	 * iteration afterwards.
4226	 *
4227	 * Tasks may leave @cset across iteration steps.  This is resolved
4228	 * by registering each iterator with the css_set currently being
4229	 * walked and making css_set_move_task() advance iterators whose
4230	 * next task is leaving.
4231	 */
4232	if (it->cur_cset) {
4233		list_del(&it->iters_node);
4234		put_css_set_locked(it->cur_cset);
4235	}
4236	get_css_set(cset);
4237	it->cur_cset = cset;
4238	list_add(&it->iters_node, &cset->task_iters);
4239}
4240
4241static void css_task_iter_advance(struct css_task_iter *it)
4242{
4243	struct list_head *l = it->task_pos;
4244
4245	lockdep_assert_held(&css_set_lock);
4246	WARN_ON_ONCE(!l);
4247
4248	/*
4249	 * Advance iterator to find next entry.  cset->tasks is consumed
4250	 * first and then ->mg_tasks.  After ->mg_tasks, we move onto the
4251	 * next cset.
4252	 */
4253	l = l->next;
4254
4255	if (l == it->tasks_head)
4256		l = it->mg_tasks_head->next;
4257
4258	if (l == it->mg_tasks_head)
4259		css_task_iter_advance_css_set(it);
4260	else
4261		it->task_pos = l;
4262}
4263
4264/**
4265 * css_task_iter_start - initiate task iteration
4266 * @css: the css to walk tasks of
4267 * @it: the task iterator to use
4268 *
4269 * Initiate iteration through the tasks of @css.  The caller can call
4270 * css_task_iter_next() to walk through the tasks until the function
4271 * returns NULL.  On completion of iteration, css_task_iter_end() must be
4272 * called.
4273 */
4274void css_task_iter_start(struct cgroup_subsys_state *css,
4275			 struct css_task_iter *it)
4276{
4277	/* no one should try to iterate before mounting cgroups */
4278	WARN_ON_ONCE(!use_task_css_set_links);
4279
4280	memset(it, 0, sizeof(*it));
4281
4282	spin_lock_irq(&css_set_lock);
4283
4284	it->ss = css->ss;
4285
4286	if (it->ss)
4287		it->cset_pos = &css->cgroup->e_csets[css->ss->id];
4288	else
4289		it->cset_pos = &css->cgroup->cset_links;
4290
4291	it->cset_head = it->cset_pos;
4292
4293	css_task_iter_advance_css_set(it);
4294
4295	spin_unlock_irq(&css_set_lock);
4296}
4297
4298/**
4299 * css_task_iter_next - return the next task for the iterator
4300 * @it: the task iterator being iterated
4301 *
4302 * The "next" function for task iteration.  @it should have been
4303 * initialized via css_task_iter_start().  Returns NULL when the iteration
4304 * reaches the end.
4305 */
4306struct task_struct *css_task_iter_next(struct css_task_iter *it)
4307{
4308	if (it->cur_task) {
4309		put_task_struct(it->cur_task);
4310		it->cur_task = NULL;
4311	}
4312
4313	spin_lock_irq(&css_set_lock);
4314
4315	if (it->task_pos) {
4316		it->cur_task = list_entry(it->task_pos, struct task_struct,
4317					  cg_list);
4318		get_task_struct(it->cur_task);
4319		css_task_iter_advance(it);
4320	}
4321
4322	spin_unlock_irq(&css_set_lock);
4323
4324	return it->cur_task;
4325}
4326
4327/**
4328 * css_task_iter_end - finish task iteration
4329 * @it: the task iterator to finish
4330 *
4331 * Finish task iteration started by css_task_iter_start().
4332 */
4333void css_task_iter_end(struct css_task_iter *it)
4334{
4335	if (it->cur_cset) {
4336		spin_lock_irq(&css_set_lock);
4337		list_del(&it->iters_node);
4338		put_css_set_locked(it->cur_cset);
4339		spin_unlock_irq(&css_set_lock);
4340	}
4341
4342	if (it->cur_task)
4343		put_task_struct(it->cur_task);
4344}
4345
4346/**
4347 * cgroup_trasnsfer_tasks - move tasks from one cgroup to another
4348 * @to: cgroup to which the tasks will be moved
4349 * @from: cgroup in which the tasks currently reside
4350 *
4351 * Locking rules between cgroup_post_fork() and the migration path
4352 * guarantee that, if a task is forking while being migrated, the new child
4353 * is guaranteed to be either visible in the source cgroup after the
4354 * parent's migration is complete or put into the target cgroup.  No task
4355 * can slip out of migration through forking.
4356 */
4357int cgroup_transfer_tasks(struct cgroup *to, struct cgroup *from)
4358{
4359	LIST_HEAD(preloaded_csets);
4360	struct cgrp_cset_link *link;
4361	struct css_task_iter it;
4362	struct task_struct *task;
4363	int ret;
4364
4365	if (!cgroup_may_migrate_to(to))
4366		return -EBUSY;
4367
4368	mutex_lock(&cgroup_mutex);
4369
4370	percpu_down_write(&cgroup_threadgroup_rwsem);
4371
4372	/* all tasks in @from are being moved, all csets are source */
4373	spin_lock_irq(&css_set_lock);
4374	list_for_each_entry(link, &from->cset_links, cset_link)
4375		cgroup_migrate_add_src(link->cset, to, &preloaded_csets);
4376	spin_unlock_irq(&css_set_lock);
4377
4378	ret = cgroup_migrate_prepare_dst(&preloaded_csets);
4379	if (ret)
4380		goto out_err;
4381
4382	/*
4383	 * Migrate tasks one-by-one until @from is empty.  This fails iff
4384	 * ->can_attach() fails.
4385	 */
4386	do {
4387		css_task_iter_start(&from->self, &it);
4388		task = css_task_iter_next(&it);
4389		if (task)
4390			get_task_struct(task);
4391		css_task_iter_end(&it);
4392
4393		if (task) {
4394			ret = cgroup_migrate(task, false, to->root);
4395			if (!ret)
4396				trace_cgroup_transfer_tasks(to, task, false);
4397			put_task_struct(task);
4398		}
4399	} while (task && !ret);
4400out_err:
4401	cgroup_migrate_finish(&preloaded_csets);
4402	percpu_up_write(&cgroup_threadgroup_rwsem);
4403	mutex_unlock(&cgroup_mutex);
4404	return ret;
4405}
4406
4407/*
4408 * Stuff for reading the 'tasks'/'procs' files.
4409 *
4410 * Reading this file can return large amounts of data if a cgroup has
4411 * *lots* of attached tasks. So it may need several calls to read(),
4412 * but we cannot guarantee that the information we produce is correct
4413 * unless we produce it entirely atomically.
4414 *
4415 */
4416
4417/* which pidlist file are we talking about? */
4418enum cgroup_filetype {
4419	CGROUP_FILE_PROCS,
4420	CGROUP_FILE_TASKS,
4421};
4422
4423/*
4424 * A pidlist is a list of pids that virtually represents the contents of one
4425 * of the cgroup files ("procs" or "tasks"). We keep a list of such pidlists,
4426 * a pair (one each for procs, tasks) for each pid namespace that's relevant
4427 * to the cgroup.
4428 */
4429struct cgroup_pidlist {
4430	/*
4431	 * used to find which pidlist is wanted. doesn't change as long as
4432	 * this particular list stays in the list.
4433	*/
4434	struct { enum cgroup_filetype type; struct pid_namespace *ns; } key;
4435	/* array of xids */
4436	pid_t *list;
4437	/* how many elements the above list has */
4438	int length;
4439	/* each of these stored in a list by its cgroup */
4440	struct list_head links;
4441	/* pointer to the cgroup we belong to, for list removal purposes */
4442	struct cgroup *owner;
4443	/* for delayed destruction */
4444	struct delayed_work destroy_dwork;
4445};
4446
4447/*
4448 * The following two functions "fix" the issue where there are more pids
4449 * than kmalloc will give memory for; in such cases, we use vmalloc/vfree.
4450 * TODO: replace with a kernel-wide solution to this problem
4451 */
4452#define PIDLIST_TOO_LARGE(c) ((c) * sizeof(pid_t) > (PAGE_SIZE * 2))
4453static void *pidlist_allocate(int count)
4454{
4455	if (PIDLIST_TOO_LARGE(count))
4456		return vmalloc(count * sizeof(pid_t));
4457	else
4458		return kmalloc(count * sizeof(pid_t), GFP_KERNEL);
4459}
4460
4461static void pidlist_free(void *p)
4462{
4463	kvfree(p);
4464}
4465
4466/*
4467 * Used to destroy all pidlists lingering waiting for destroy timer.  None
4468 * should be left afterwards.
4469 */
4470static void cgroup_pidlist_destroy_all(struct cgroup *cgrp)
4471{
4472	struct cgroup_pidlist *l, *tmp_l;
4473
4474	mutex_lock(&cgrp->pidlist_mutex);
4475	list_for_each_entry_safe(l, tmp_l, &cgrp->pidlists, links)
4476		mod_delayed_work(cgroup_pidlist_destroy_wq, &l->destroy_dwork, 0);
4477	mutex_unlock(&cgrp->pidlist_mutex);
4478
4479	flush_workqueue(cgroup_pidlist_destroy_wq);
4480	BUG_ON(!list_empty(&cgrp->pidlists));
4481}
4482
4483static void cgroup_pidlist_destroy_work_fn(struct work_struct *work)
4484{
4485	struct delayed_work *dwork = to_delayed_work(work);
4486	struct cgroup_pidlist *l = container_of(dwork, struct cgroup_pidlist,
4487						destroy_dwork);
4488	struct cgroup_pidlist *tofree = NULL;
4489
4490	mutex_lock(&l->owner->pidlist_mutex);
4491
4492	/*
4493	 * Destroy iff we didn't get queued again.  The state won't change
4494	 * as destroy_dwork can only be queued while locked.
4495	 */
4496	if (!delayed_work_pending(dwork)) {
4497		list_del(&l->links);
4498		pidlist_free(l->list);
4499		put_pid_ns(l->key.ns);
4500		tofree = l;
4501	}
4502
4503	mutex_unlock(&l->owner->pidlist_mutex);
4504	kfree(tofree);
4505}
4506
4507/*
4508 * pidlist_uniq - given a kmalloc()ed list, strip out all duplicate entries
4509 * Returns the number of unique elements.
4510 */
4511static int pidlist_uniq(pid_t *list, int length)
4512{
4513	int src, dest = 1;
4514
4515	/*
4516	 * we presume the 0th element is unique, so i starts at 1. trivial
4517	 * edge cases first; no work needs to be done for either
4518	 */
4519	if (length == 0 || length == 1)
4520		return length;
4521	/* src and dest walk down the list; dest counts unique elements */
4522	for (src = 1; src < length; src++) {
4523		/* find next unique element */
4524		while (list[src] == list[src-1]) {
4525			src++;
4526			if (src == length)
4527				goto after;
4528		}
4529		/* dest always points to where the next unique element goes */
4530		list[dest] = list[src];
4531		dest++;
4532	}
4533after:
4534	return dest;
4535}
4536
4537/*
4538 * The two pid files - task and cgroup.procs - guaranteed that the result
4539 * is sorted, which forced this whole pidlist fiasco.  As pid order is
4540 * different per namespace, each namespace needs differently sorted list,
4541 * making it impossible to use, for example, single rbtree of member tasks
4542 * sorted by task pointer.  As pidlists can be fairly large, allocating one
4543 * per open file is dangerous, so cgroup had to implement shared pool of
4544 * pidlists keyed by cgroup and namespace.
4545 *
4546 * All this extra complexity was caused by the original implementation
4547 * committing to an entirely unnecessary property.  In the long term, we
4548 * want to do away with it.  Explicitly scramble sort order if on the
4549 * default hierarchy so that no such expectation exists in the new
4550 * interface.
4551 *
4552 * Scrambling is done by swapping every two consecutive bits, which is
4553 * non-identity one-to-one mapping which disturbs sort order sufficiently.
4554 */
4555static pid_t pid_fry(pid_t pid)
4556{
4557	unsigned a = pid & 0x55555555;
4558	unsigned b = pid & 0xAAAAAAAA;
4559
4560	return (a << 1) | (b >> 1);
4561}
4562
4563static pid_t cgroup_pid_fry(struct cgroup *cgrp, pid_t pid)
4564{
4565	if (cgroup_on_dfl(cgrp))
4566		return pid_fry(pid);
4567	else
4568		return pid;
4569}
4570
4571static int cmppid(const void *a, const void *b)
4572{
4573	return *(pid_t *)a - *(pid_t *)b;
4574}
4575
4576static int fried_cmppid(const void *a, const void *b)
4577{
4578	return pid_fry(*(pid_t *)a) - pid_fry(*(pid_t *)b);
4579}
4580
4581static struct cgroup_pidlist *cgroup_pidlist_find(struct cgroup *cgrp,
4582						  enum cgroup_filetype type)
4583{
4584	struct cgroup_pidlist *l;
4585	/* don't need task_nsproxy() if we're looking at ourself */
4586	struct pid_namespace *ns = task_active_pid_ns(current);
4587
4588	lockdep_assert_held(&cgrp->pidlist_mutex);
4589
4590	list_for_each_entry(l, &cgrp->pidlists, links)
4591		if (l->key.type == type && l->key.ns == ns)
4592			return l;
4593	return NULL;
4594}
4595
4596/*
4597 * find the appropriate pidlist for our purpose (given procs vs tasks)
4598 * returns with the lock on that pidlist already held, and takes care
4599 * of the use count, or returns NULL with no locks held if we're out of
4600 * memory.
4601 */
4602static struct cgroup_pidlist *cgroup_pidlist_find_create(struct cgroup *cgrp,
4603						enum cgroup_filetype type)
4604{
4605	struct cgroup_pidlist *l;
4606
4607	lockdep_assert_held(&cgrp->pidlist_mutex);
4608
4609	l = cgroup_pidlist_find(cgrp, type);
4610	if (l)
4611		return l;
4612
4613	/* entry not found; create a new one */
4614	l = kzalloc(sizeof(struct cgroup_pidlist), GFP_KERNEL);
4615	if (!l)
4616		return l;
4617
4618	INIT_DELAYED_WORK(&l->destroy_dwork, cgroup_pidlist_destroy_work_fn);
4619	l->key.type = type;
4620	/* don't need task_nsproxy() if we're looking at ourself */
4621	l->key.ns = get_pid_ns(task_active_pid_ns(current));
4622	l->owner = cgrp;
4623	list_add(&l->links, &cgrp->pidlists);
4624	return l;
4625}
4626
4627/*
4628 * Load a cgroup's pidarray with either procs' tgids or tasks' pids
4629 */
4630static int pidlist_array_load(struct cgroup *cgrp, enum cgroup_filetype type,
4631			      struct cgroup_pidlist **lp)
4632{
4633	pid_t *array;
4634	int length;
4635	int pid, n = 0; /* used for populating the array */
4636	struct css_task_iter it;
4637	struct task_struct *tsk;
4638	struct cgroup_pidlist *l;
4639
4640	lockdep_assert_held(&cgrp->pidlist_mutex);
4641
4642	/*
4643	 * If cgroup gets more users after we read count, we won't have
4644	 * enough space - tough.  This race is indistinguishable to the
4645	 * caller from the case that the additional cgroup users didn't
4646	 * show up until sometime later on.
4647	 */
4648	length = cgroup_task_count(cgrp);
4649	array = pidlist_allocate(length);
4650	if (!array)
4651		return -ENOMEM;
4652	/* now, populate the array */
4653	css_task_iter_start(&cgrp->self, &it);
4654	while ((tsk = css_task_iter_next(&it))) {
4655		if (unlikely(n == length))
4656			break;
4657		/* get tgid or pid for procs or tasks file respectively */
4658		if (type == CGROUP_FILE_PROCS)
4659			pid = task_tgid_vnr(tsk);
4660		else
4661			pid = task_pid_vnr(tsk);
4662		if (pid > 0) /* make sure to only use valid results */
4663			array[n++] = pid;
4664	}
4665	css_task_iter_end(&it);
4666	length = n;
4667	/* now sort & (if procs) strip out duplicates */
4668	if (cgroup_on_dfl(cgrp))
4669		sort(array, length, sizeof(pid_t), fried_cmppid, NULL);
4670	else
4671		sort(array, length, sizeof(pid_t), cmppid, NULL);
4672	if (type == CGROUP_FILE_PROCS)
4673		length = pidlist_uniq(array, length);
4674
4675	l = cgroup_pidlist_find_create(cgrp, type);
4676	if (!l) {
4677		pidlist_free(array);
4678		return -ENOMEM;
4679	}
4680
4681	/* store array, freeing old if necessary */
4682	pidlist_free(l->list);
4683	l->list = array;
4684	l->length = length;
4685	*lp = l;
4686	return 0;
4687}
4688
4689/**
4690 * cgroupstats_build - build and fill cgroupstats
4691 * @stats: cgroupstats to fill information into
4692 * @dentry: A dentry entry belonging to the cgroup for which stats have
4693 * been requested.
4694 *
4695 * Build and fill cgroupstats so that taskstats can export it to user
4696 * space.
4697 */
4698int cgroupstats_build(struct cgroupstats *stats, struct dentry *dentry)
4699{
4700	struct kernfs_node *kn = kernfs_node_from_dentry(dentry);
4701	struct cgroup *cgrp;
4702	struct css_task_iter it;
4703	struct task_struct *tsk;
4704
4705	/* it should be kernfs_node belonging to cgroupfs and is a directory */
4706	if (dentry->d_sb->s_type != &cgroup_fs_type || !kn ||
4707	    kernfs_type(kn) != KERNFS_DIR)
4708		return -EINVAL;
4709
4710	mutex_lock(&cgroup_mutex);
4711
4712	/*
4713	 * We aren't being called from kernfs and there's no guarantee on
4714	 * @kn->priv's validity.  For this and css_tryget_online_from_dir(),
4715	 * @kn->priv is RCU safe.  Let's do the RCU dancing.
4716	 */
4717	rcu_read_lock();
4718	cgrp = rcu_dereference(kn->priv);
4719	if (!cgrp || cgroup_is_dead(cgrp)) {
4720		rcu_read_unlock();
4721		mutex_unlock(&cgroup_mutex);
4722		return -ENOENT;
4723	}
4724	rcu_read_unlock();
4725
4726	css_task_iter_start(&cgrp->self, &it);
4727	while ((tsk = css_task_iter_next(&it))) {
4728		switch (tsk->state) {
4729		case TASK_RUNNING:
4730			stats->nr_running++;
4731			break;
4732		case TASK_INTERRUPTIBLE:
4733			stats->nr_sleeping++;
4734			break;
4735		case TASK_UNINTERRUPTIBLE:
4736			stats->nr_uninterruptible++;
4737			break;
4738		case TASK_STOPPED:
4739			stats->nr_stopped++;
4740			break;
4741		default:
4742			if (delayacct_is_task_waiting_on_io(tsk))
4743				stats->nr_io_wait++;
4744			break;
4745		}
4746	}
4747	css_task_iter_end(&it);
4748
4749	mutex_unlock(&cgroup_mutex);
4750	return 0;
4751}
4752
4753
4754/*
4755 * seq_file methods for the tasks/procs files. The seq_file position is the
4756 * next pid to display; the seq_file iterator is a pointer to the pid
4757 * in the cgroup->l->list array.
4758 */
4759
4760static void *cgroup_pidlist_start(struct seq_file *s, loff_t *pos)
4761{
4762	/*
4763	 * Initially we receive a position value that corresponds to
4764	 * one more than the last pid shown (or 0 on the first call or
4765	 * after a seek to the start). Use a binary-search to find the
4766	 * next pid to display, if any
4767	 */
4768	struct kernfs_open_file *of = s->private;
4769	struct cgroup *cgrp = seq_css(s)->cgroup;
4770	struct cgroup_pidlist *l;
4771	enum cgroup_filetype type = seq_cft(s)->private;
4772	int index = 0, pid = *pos;
4773	int *iter, ret;
4774
4775	mutex_lock(&cgrp->pidlist_mutex);
4776
4777	/*
4778	 * !NULL @of->priv indicates that this isn't the first start()
4779	 * after open.  If the matching pidlist is around, we can use that.
4780	 * Look for it.  Note that @of->priv can't be used directly.  It
4781	 * could already have been destroyed.
4782	 */
4783	if (of->priv)
4784		of->priv = cgroup_pidlist_find(cgrp, type);
4785
4786	/*
4787	 * Either this is the first start() after open or the matching
4788	 * pidlist has been destroyed inbetween.  Create a new one.
4789	 */
4790	if (!of->priv) {
4791		ret = pidlist_array_load(cgrp, type,
4792					 (struct cgroup_pidlist **)&of->priv);
4793		if (ret)
4794			return ERR_PTR(ret);
4795	}
4796	l = of->priv;
4797
4798	if (pid) {
4799		int end = l->length;
4800
4801		while (index < end) {
4802			int mid = (index + end) / 2;
4803			if (cgroup_pid_fry(cgrp, l->list[mid]) == pid) {
4804				index = mid;
4805				break;
4806			} else if (cgroup_pid_fry(cgrp, l->list[mid]) <= pid)
4807				index = mid + 1;
4808			else
4809				end = mid;
4810		}
4811	}
4812	/* If we're off the end of the array, we're done */
4813	if (index >= l->length)
4814		return NULL;
4815	/* Update the abstract position to be the actual pid that we found */
4816	iter = l->list + index;
4817	*pos = cgroup_pid_fry(cgrp, *iter);
4818	return iter;
4819}
4820
4821static void cgroup_pidlist_stop(struct seq_file *s, void *v)
4822{
4823	struct kernfs_open_file *of = s->private;
4824	struct cgroup_pidlist *l = of->priv;
4825
4826	if (l)
4827		mod_delayed_work(cgroup_pidlist_destroy_wq, &l->destroy_dwork,
4828				 CGROUP_PIDLIST_DESTROY_DELAY);
4829	mutex_unlock(&seq_css(s)->cgroup->pidlist_mutex);
4830}
4831
4832static void *cgroup_pidlist_next(struct seq_file *s, void *v, loff_t *pos)
4833{
4834	struct kernfs_open_file *of = s->private;
4835	struct cgroup_pidlist *l = of->priv;
4836	pid_t *p = v;
4837	pid_t *end = l->list + l->length;
4838	/*
4839	 * Advance to the next pid in the array. If this goes off the
4840	 * end, we're done
4841	 */
4842	p++;
4843	if (p >= end) {
4844		return NULL;
4845	} else {
4846		*pos = cgroup_pid_fry(seq_css(s)->cgroup, *p);
4847		return p;
4848	}
4849}
4850
4851static int cgroup_pidlist_show(struct seq_file *s, void *v)
4852{
4853	seq_printf(s, "%d\n", *(int *)v);
4854
4855	return 0;
4856}
4857
4858static u64 cgroup_read_notify_on_release(struct cgroup_subsys_state *css,
4859					 struct cftype *cft)
4860{
4861	return notify_on_release(css->cgroup);
4862}
4863
4864static int cgroup_write_notify_on_release(struct cgroup_subsys_state *css,
4865					  struct cftype *cft, u64 val)
4866{
4867	if (val)
4868		set_bit(CGRP_NOTIFY_ON_RELEASE, &css->cgroup->flags);
4869	else
4870		clear_bit(CGRP_NOTIFY_ON_RELEASE, &css->cgroup->flags);
4871	return 0;
4872}
4873
4874static u64 cgroup_clone_children_read(struct cgroup_subsys_state *css,
4875				      struct cftype *cft)
4876{
4877	return test_bit(CGRP_CPUSET_CLONE_CHILDREN, &css->cgroup->flags);
4878}
4879
4880static int cgroup_clone_children_write(struct cgroup_subsys_state *css,
4881				       struct cftype *cft, u64 val)
4882{
4883	if (val)
4884		set_bit(CGRP_CPUSET_CLONE_CHILDREN, &css->cgroup->flags);
4885	else
4886		clear_bit(CGRP_CPUSET_CLONE_CHILDREN, &css->cgroup->flags);
4887	return 0;
4888}
4889
4890/* cgroup core interface files for the default hierarchy */
4891static struct cftype cgroup_dfl_base_files[] = {
4892	{
4893		.name = "cgroup.procs",
4894		.file_offset = offsetof(struct cgroup, procs_file),
4895		.seq_start = cgroup_pidlist_start,
4896		.seq_next = cgroup_pidlist_next,
4897		.seq_stop = cgroup_pidlist_stop,
4898		.seq_show = cgroup_pidlist_show,
4899		.private = CGROUP_FILE_PROCS,
4900		.write = cgroup_procs_write,
4901	},
4902	{
4903		.name = "cgroup.controllers",
4904		.seq_show = cgroup_controllers_show,
4905	},
4906	{
4907		.name = "cgroup.subtree_control",
4908		.seq_show = cgroup_subtree_control_show,
4909		.write = cgroup_subtree_control_write,
4910	},
4911	{
4912		.name = "cgroup.events",
4913		.flags = CFTYPE_NOT_ON_ROOT,
4914		.file_offset = offsetof(struct cgroup, events_file),
4915		.seq_show = cgroup_events_show,
4916	},
4917	{ }	/* terminate */
4918};
4919
4920/* cgroup core interface files for the legacy hierarchies */
4921static struct cftype cgroup_legacy_base_files[] = {
4922	{
4923		.name = "cgroup.procs",
4924		.seq_start = cgroup_pidlist_start,
4925		.seq_next = cgroup_pidlist_next,
4926		.seq_stop = cgroup_pidlist_stop,
4927		.seq_show = cgroup_pidlist_show,
4928		.private = CGROUP_FILE_PROCS,
4929		.write = cgroup_procs_write,
4930	},
4931	{
4932		.name = "cgroup.clone_children",
4933		.read_u64 = cgroup_clone_children_read,
4934		.write_u64 = cgroup_clone_children_write,
4935	},
4936	{
4937		.name = "cgroup.sane_behavior",
4938		.flags = CFTYPE_ONLY_ON_ROOT,
4939		.seq_show = cgroup_sane_behavior_show,
4940	},
4941	{
4942		.name = "tasks",
4943		.seq_start = cgroup_pidlist_start,
4944		.seq_next = cgroup_pidlist_next,
4945		.seq_stop = cgroup_pidlist_stop,
4946		.seq_show = cgroup_pidlist_show,
4947		.private = CGROUP_FILE_TASKS,
4948		.write = cgroup_tasks_write,
4949	},
4950	{
4951		.name = "notify_on_release",
4952		.read_u64 = cgroup_read_notify_on_release,
4953		.write_u64 = cgroup_write_notify_on_release,
4954	},
4955	{
4956		.name = "release_agent",
4957		.flags = CFTYPE_ONLY_ON_ROOT,
4958		.seq_show = cgroup_release_agent_show,
4959		.write = cgroup_release_agent_write,
4960		.max_write_len = PATH_MAX - 1,
4961	},
4962	{ }	/* terminate */
4963};
4964
4965/*
4966 * css destruction is four-stage process.
4967 *
4968 * 1. Destruction starts.  Killing of the percpu_ref is initiated.
4969 *    Implemented in kill_css().
4970 *
4971 * 2. When the percpu_ref is confirmed to be visible as killed on all CPUs
4972 *    and thus css_tryget_online() is guaranteed to fail, the css can be
4973 *    offlined by invoking offline_css().  After offlining, the base ref is
4974 *    put.  Implemented in css_killed_work_fn().
4975 *
4976 * 3. When the percpu_ref reaches zero, the only possible remaining
4977 *    accessors are inside RCU read sections.  css_release() schedules the
4978 *    RCU callback.
4979 *
4980 * 4. After the grace period, the css can be freed.  Implemented in
4981 *    css_free_work_fn().
4982 *
4983 * It is actually hairier because both step 2 and 4 require process context
4984 * and thus involve punting to css->destroy_work adding two additional
4985 * steps to the already complex sequence.
4986 */
4987static void css_free_work_fn(struct work_struct *work)
4988{
4989	struct cgroup_subsys_state *css =
4990		container_of(work, struct cgroup_subsys_state, destroy_work);
4991	struct cgroup_subsys *ss = css->ss;
4992	struct cgroup *cgrp = css->cgroup;
4993
4994	percpu_ref_exit(&css->refcnt);
4995
4996	if (ss) {
4997		/* css free path */
4998		struct cgroup_subsys_state *parent = css->parent;
4999		int id = css->id;
5000
5001		ss->css_free(css);
5002		cgroup_idr_remove(&ss->css_idr, id);
5003		cgroup_put(cgrp);
5004
5005		if (parent)
5006			css_put(parent);
5007	} else {
5008		/* cgroup free path */
5009		atomic_dec(&cgrp->root->nr_cgrps);
5010		cgroup_pidlist_destroy_all(cgrp);
5011		cancel_work_sync(&cgrp->release_agent_work);
5012
5013		if (cgroup_parent(cgrp)) {
5014			/*
5015			 * We get a ref to the parent, and put the ref when
5016			 * this cgroup is being freed, so it's guaranteed
5017			 * that the parent won't be destroyed before its
5018			 * children.
5019			 */
5020			cgroup_put(cgroup_parent(cgrp));
5021			kernfs_put(cgrp->kn);
5022			kfree(cgrp);
5023		} else {
5024			/*
5025			 * This is root cgroup's refcnt reaching zero,
5026			 * which indicates that the root should be
5027			 * released.
5028			 */
5029			cgroup_destroy_root(cgrp->root);
5030		}
5031	}
5032}
5033
5034static void css_free_rcu_fn(struct rcu_head *rcu_head)
5035{
5036	struct cgroup_subsys_state *css =
5037		container_of(rcu_head, struct cgroup_subsys_state, rcu_head);
5038
5039	INIT_WORK(&css->destroy_work, css_free_work_fn);
5040	queue_work(cgroup_destroy_wq, &css->destroy_work);
5041}
5042
5043static void css_release_work_fn(struct work_struct *work)
5044{
5045	struct cgroup_subsys_state *css =
5046		container_of(work, struct cgroup_subsys_state, destroy_work);
5047	struct cgroup_subsys *ss = css->ss;
5048	struct cgroup *cgrp = css->cgroup;
5049
5050	mutex_lock(&cgroup_mutex);
5051
5052	css->flags |= CSS_RELEASED;
5053	list_del_rcu(&css->sibling);
5054
5055	if (ss) {
5056		/* css release path */
5057		cgroup_idr_replace(&ss->css_idr, NULL, css->id);
5058		if (ss->css_released)
5059			ss->css_released(css);
5060	} else {
5061		/* cgroup release path */
5062		trace_cgroup_release(cgrp);
5063
5064		cgroup_idr_remove(&cgrp->root->cgroup_idr, cgrp->id);
5065		cgrp->id = -1;
5066
5067		/*
5068		 * There are two control paths which try to determine
5069		 * cgroup from dentry without going through kernfs -
5070		 * cgroupstats_build() and css_tryget_online_from_dir().
5071		 * Those are supported by RCU protecting clearing of
5072		 * cgrp->kn->priv backpointer.
5073		 */
5074		if (cgrp->kn)
5075			RCU_INIT_POINTER(*(void __rcu __force **)&cgrp->kn->priv,
5076					 NULL);
5077
5078		cgroup_bpf_put(cgrp);
5079	}
5080
5081	mutex_unlock(&cgroup_mutex);
5082
5083	call_rcu(&css->rcu_head, css_free_rcu_fn);
5084}
5085
5086static void css_release(struct percpu_ref *ref)
5087{
5088	struct cgroup_subsys_state *css =
5089		container_of(ref, struct cgroup_subsys_state, refcnt);
5090
5091	INIT_WORK(&css->destroy_work, css_release_work_fn);
5092	queue_work(cgroup_destroy_wq, &css->destroy_work);
5093}
5094
5095static void init_and_link_css(struct cgroup_subsys_state *css,
5096			      struct cgroup_subsys *ss, struct cgroup *cgrp)
5097{
5098	lockdep_assert_held(&cgroup_mutex);
5099
5100	cgroup_get(cgrp);
5101
5102	memset(css, 0, sizeof(*css));
5103	css->cgroup = cgrp;
5104	css->ss = ss;
5105	css->id = -1;
5106	INIT_LIST_HEAD(&css->sibling);
5107	INIT_LIST_HEAD(&css->children);
5108	css->serial_nr = css_serial_nr_next++;
5109	atomic_set(&css->online_cnt, 0);
5110
5111	if (cgroup_parent(cgrp)) {
5112		css->parent = cgroup_css(cgroup_parent(cgrp), ss);
5113		css_get(css->parent);
5114	}
5115
5116	BUG_ON(cgroup_css(cgrp, ss));
5117}
5118
5119/* invoke ->css_online() on a new CSS and mark it online if successful */
5120static int online_css(struct cgroup_subsys_state *css)
5121{
5122	struct cgroup_subsys *ss = css->ss;
5123	int ret = 0;
5124
5125	lockdep_assert_held(&cgroup_mutex);
5126
5127	if (ss->css_online)
5128		ret = ss->css_online(css);
5129	if (!ret) {
5130		css->flags |= CSS_ONLINE;
5131		rcu_assign_pointer(css->cgroup->subsys[ss->id], css);
5132
5133		atomic_inc(&css->online_cnt);
5134		if (css->parent)
5135			atomic_inc(&css->parent->online_cnt);
5136	}
5137	return ret;
5138}
5139
5140/* if the CSS is online, invoke ->css_offline() on it and mark it offline */
5141static void offline_css(struct cgroup_subsys_state *css)
5142{
5143	struct cgroup_subsys *ss = css->ss;
5144
5145	lockdep_assert_held(&cgroup_mutex);
5146
5147	if (!(css->flags & CSS_ONLINE))
5148		return;
5149
5150	if (ss->css_reset)
5151		ss->css_reset(css);
5152
5153	if (ss->css_offline)
5154		ss->css_offline(css);
5155
5156	css->flags &= ~CSS_ONLINE;
5157	RCU_INIT_POINTER(css->cgroup->subsys[ss->id], NULL);
5158
5159	wake_up_all(&css->cgroup->offline_waitq);
5160}
5161
5162/**
5163 * css_create - create a cgroup_subsys_state
5164 * @cgrp: the cgroup new css will be associated with
5165 * @ss: the subsys of new css
5166 *
5167 * Create a new css associated with @cgrp - @ss pair.  On success, the new
5168 * css is online and installed in @cgrp.  This function doesn't create the
5169 * interface files.  Returns 0 on success, -errno on failure.
5170 */
5171static struct cgroup_subsys_state *css_create(struct cgroup *cgrp,
5172					      struct cgroup_subsys *ss)
5173{
5174	struct cgroup *parent = cgroup_parent(cgrp);
5175	struct cgroup_subsys_state *parent_css = cgroup_css(parent, ss);
5176	struct cgroup_subsys_state *css;
5177	int err;
5178
5179	lockdep_assert_held(&cgroup_mutex);
5180
5181	css = ss->css_alloc(parent_css);
5182	if (!css)
5183		css = ERR_PTR(-ENOMEM);
5184	if (IS_ERR(css))
5185		return css;
5186
5187	init_and_link_css(css, ss, cgrp);
5188
5189	err = percpu_ref_init(&css->refcnt, css_release, 0, GFP_KERNEL);
5190	if (err)
5191		goto err_free_css;
5192
5193	err = cgroup_idr_alloc(&ss->css_idr, NULL, 2, 0, GFP_KERNEL);
5194	if (err < 0)
5195		goto err_free_css;
5196	css->id = err;
5197
5198	/* @css is ready to be brought online now, make it visible */
5199	list_add_tail_rcu(&css->sibling, &parent_css->children);
5200	cgroup_idr_replace(&ss->css_idr, css, css->id);
5201
5202	err = online_css(css);
5203	if (err)
5204		goto err_list_del;
5205
5206	if (ss->broken_hierarchy && !ss->warned_broken_hierarchy &&
5207	    cgroup_parent(parent)) {
5208		pr_warn("%s (%d) created nested cgroup for controller \"%s\" which has incomplete hierarchy support. Nested cgroups may change behavior in the future.\n",
5209			current->comm, current->pid, ss->name);
5210		if (!strcmp(ss->name, "memory"))
5211			pr_warn("\"memory\" requires setting use_hierarchy to 1 on the root\n");
5212		ss->warned_broken_hierarchy = true;
5213	}
5214
5215	return css;
5216
5217err_list_del:
5218	list_del_rcu(&css->sibling);
 
 
 
5219err_free_css:
5220	call_rcu(&css->rcu_head, css_free_rcu_fn);
5221	return ERR_PTR(err);
5222}
5223
5224/*
5225 * The returned cgroup is fully initialized including its control mask, but
5226 * it isn't associated with its kernfs_node and doesn't have the control
5227 * mask applied.
5228 */
5229static struct cgroup *cgroup_create(struct cgroup *parent)
5230{
5231	struct cgroup_root *root = parent->root;
5232	struct cgroup *cgrp, *tcgrp;
5233	int level = parent->level + 1;
5234	int ret;
5235
5236	/* allocate the cgroup and its ID, 0 is reserved for the root */
5237	cgrp = kzalloc(sizeof(*cgrp) +
5238		       sizeof(cgrp->ancestor_ids[0]) * (level + 1), GFP_KERNEL);
5239	if (!cgrp)
5240		return ERR_PTR(-ENOMEM);
5241
5242	ret = percpu_ref_init(&cgrp->self.refcnt, css_release, 0, GFP_KERNEL);
5243	if (ret)
5244		goto out_free_cgrp;
5245
5246	/*
5247	 * Temporarily set the pointer to NULL, so idr_find() won't return
5248	 * a half-baked cgroup.
5249	 */
5250	cgrp->id = cgroup_idr_alloc(&root->cgroup_idr, NULL, 2, 0, GFP_KERNEL);
5251	if (cgrp->id < 0) {
5252		ret = -ENOMEM;
5253		goto out_cancel_ref;
5254	}
5255
5256	init_cgroup_housekeeping(cgrp);
5257
5258	cgrp->self.parent = &parent->self;
5259	cgrp->root = root;
5260	cgrp->level = level;
5261
5262	for (tcgrp = cgrp; tcgrp; tcgrp = cgroup_parent(tcgrp))
5263		cgrp->ancestor_ids[tcgrp->level] = tcgrp->id;
5264
5265	if (notify_on_release(parent))
5266		set_bit(CGRP_NOTIFY_ON_RELEASE, &cgrp->flags);
5267
5268	if (test_bit(CGRP_CPUSET_CLONE_CHILDREN, &parent->flags))
5269		set_bit(CGRP_CPUSET_CLONE_CHILDREN, &cgrp->flags);
5270
5271	cgrp->self.serial_nr = css_serial_nr_next++;
5272
5273	/* allocation complete, commit to creation */
5274	list_add_tail_rcu(&cgrp->self.sibling, &cgroup_parent(cgrp)->self.children);
5275	atomic_inc(&root->nr_cgrps);
5276	cgroup_get(parent);
5277
5278	/*
5279	 * @cgrp is now fully operational.  If something fails after this
5280	 * point, it'll be released via the normal destruction path.
5281	 */
5282	cgroup_idr_replace(&root->cgroup_idr, cgrp, cgrp->id);
5283
5284	/*
5285	 * On the default hierarchy, a child doesn't automatically inherit
5286	 * subtree_control from the parent.  Each is configured manually.
5287	 */
5288	if (!cgroup_on_dfl(cgrp))
5289		cgrp->subtree_control = cgroup_control(cgrp);
5290
5291	if (parent)
5292		cgroup_bpf_inherit(cgrp, parent);
5293
5294	cgroup_propagate_control(cgrp);
5295
 
 
 
 
 
5296	return cgrp;
5297
5298out_cancel_ref:
5299	percpu_ref_exit(&cgrp->self.refcnt);
5300out_free_cgrp:
5301	kfree(cgrp);
5302	return ERR_PTR(ret);
 
 
 
5303}
5304
5305static int cgroup_mkdir(struct kernfs_node *parent_kn, const char *name,
5306			umode_t mode)
5307{
5308	struct cgroup *parent, *cgrp;
5309	struct kernfs_node *kn;
5310	int ret;
5311
5312	/* do not accept '\n' to prevent making /proc/<pid>/cgroup unparsable */
5313	if (strchr(name, '\n'))
5314		return -EINVAL;
5315
5316	parent = cgroup_kn_lock_live(parent_kn, false);
5317	if (!parent)
5318		return -ENODEV;
5319
5320	cgrp = cgroup_create(parent);
5321	if (IS_ERR(cgrp)) {
5322		ret = PTR_ERR(cgrp);
5323		goto out_unlock;
5324	}
5325
5326	/* create the directory */
5327	kn = kernfs_create_dir(parent->kn, name, mode, cgrp);
5328	if (IS_ERR(kn)) {
5329		ret = PTR_ERR(kn);
5330		goto out_destroy;
5331	}
5332	cgrp->kn = kn;
5333
5334	/*
5335	 * This extra ref will be put in cgroup_free_fn() and guarantees
5336	 * that @cgrp->kn is always accessible.
5337	 */
5338	kernfs_get(kn);
5339
5340	ret = cgroup_kn_set_ugid(kn);
5341	if (ret)
5342		goto out_destroy;
5343
5344	ret = css_populate_dir(&cgrp->self);
5345	if (ret)
5346		goto out_destroy;
5347
5348	ret = cgroup_apply_control_enable(cgrp);
5349	if (ret)
5350		goto out_destroy;
5351
5352	trace_cgroup_mkdir(cgrp);
5353
5354	/* let's create and online css's */
5355	kernfs_activate(kn);
5356
5357	ret = 0;
5358	goto out_unlock;
5359
5360out_destroy:
5361	cgroup_destroy_locked(cgrp);
5362out_unlock:
5363	cgroup_kn_unlock(parent_kn);
5364	return ret;
5365}
5366
5367/*
5368 * This is called when the refcnt of a css is confirmed to be killed.
5369 * css_tryget_online() is now guaranteed to fail.  Tell the subsystem to
5370 * initate destruction and put the css ref from kill_css().
5371 */
5372static void css_killed_work_fn(struct work_struct *work)
5373{
5374	struct cgroup_subsys_state *css =
5375		container_of(work, struct cgroup_subsys_state, destroy_work);
5376
5377	mutex_lock(&cgroup_mutex);
5378
5379	do {
5380		offline_css(css);
5381		css_put(css);
5382		/* @css can't go away while we're holding cgroup_mutex */
5383		css = css->parent;
5384	} while (css && atomic_dec_and_test(&css->online_cnt));
5385
5386	mutex_unlock(&cgroup_mutex);
5387}
5388
5389/* css kill confirmation processing requires process context, bounce */
5390static void css_killed_ref_fn(struct percpu_ref *ref)
5391{
5392	struct cgroup_subsys_state *css =
5393		container_of(ref, struct cgroup_subsys_state, refcnt);
5394
5395	if (atomic_dec_and_test(&css->online_cnt)) {
5396		INIT_WORK(&css->destroy_work, css_killed_work_fn);
5397		queue_work(cgroup_destroy_wq, &css->destroy_work);
5398	}
5399}
5400
5401/**
5402 * kill_css - destroy a css
5403 * @css: css to destroy
5404 *
5405 * This function initiates destruction of @css by removing cgroup interface
5406 * files and putting its base reference.  ->css_offline() will be invoked
5407 * asynchronously once css_tryget_online() is guaranteed to fail and when
5408 * the reference count reaches zero, @css will be released.
5409 */
5410static void kill_css(struct cgroup_subsys_state *css)
5411{
5412	lockdep_assert_held(&cgroup_mutex);
5413
5414	/*
5415	 * This must happen before css is disassociated with its cgroup.
5416	 * See seq_css() for details.
5417	 */
5418	css_clear_dir(css);
5419
5420	/*
5421	 * Killing would put the base ref, but we need to keep it alive
5422	 * until after ->css_offline().
5423	 */
5424	css_get(css);
5425
5426	/*
5427	 * cgroup core guarantees that, by the time ->css_offline() is
5428	 * invoked, no new css reference will be given out via
5429	 * css_tryget_online().  We can't simply call percpu_ref_kill() and
5430	 * proceed to offlining css's because percpu_ref_kill() doesn't
5431	 * guarantee that the ref is seen as killed on all CPUs on return.
5432	 *
5433	 * Use percpu_ref_kill_and_confirm() to get notifications as each
5434	 * css is confirmed to be seen as killed on all CPUs.
5435	 */
5436	percpu_ref_kill_and_confirm(&css->refcnt, css_killed_ref_fn);
5437}
5438
5439/**
5440 * cgroup_destroy_locked - the first stage of cgroup destruction
5441 * @cgrp: cgroup to be destroyed
5442 *
5443 * css's make use of percpu refcnts whose killing latency shouldn't be
5444 * exposed to userland and are RCU protected.  Also, cgroup core needs to
5445 * guarantee that css_tryget_online() won't succeed by the time
5446 * ->css_offline() is invoked.  To satisfy all the requirements,
5447 * destruction is implemented in the following two steps.
5448 *
5449 * s1. Verify @cgrp can be destroyed and mark it dying.  Remove all
5450 *     userland visible parts and start killing the percpu refcnts of
5451 *     css's.  Set up so that the next stage will be kicked off once all
5452 *     the percpu refcnts are confirmed to be killed.
5453 *
5454 * s2. Invoke ->css_offline(), mark the cgroup dead and proceed with the
5455 *     rest of destruction.  Once all cgroup references are gone, the
5456 *     cgroup is RCU-freed.
5457 *
5458 * This function implements s1.  After this step, @cgrp is gone as far as
5459 * the userland is concerned and a new cgroup with the same name may be
5460 * created.  As cgroup doesn't care about the names internally, this
5461 * doesn't cause any problem.
5462 */
5463static int cgroup_destroy_locked(struct cgroup *cgrp)
5464	__releases(&cgroup_mutex) __acquires(&cgroup_mutex)
5465{
5466	struct cgroup_subsys_state *css;
5467	struct cgrp_cset_link *link;
5468	int ssid;
5469
5470	lockdep_assert_held(&cgroup_mutex);
5471
5472	/*
5473	 * Only migration can raise populated from zero and we're already
5474	 * holding cgroup_mutex.
5475	 */
5476	if (cgroup_is_populated(cgrp))
5477		return -EBUSY;
5478
5479	/*
5480	 * Make sure there's no live children.  We can't test emptiness of
5481	 * ->self.children as dead children linger on it while being
5482	 * drained; otherwise, "rmdir parent/child parent" may fail.
5483	 */
5484	if (css_has_online_children(&cgrp->self))
5485		return -EBUSY;
5486
5487	/*
5488	 * Mark @cgrp and the associated csets dead.  The former prevents
5489	 * further task migration and child creation by disabling
5490	 * cgroup_lock_live_group().  The latter makes the csets ignored by
5491	 * the migration path.
5492	 */
5493	cgrp->self.flags &= ~CSS_ONLINE;
5494
5495	spin_lock_irq(&css_set_lock);
5496	list_for_each_entry(link, &cgrp->cset_links, cset_link)
5497		link->cset->dead = true;
5498	spin_unlock_irq(&css_set_lock);
5499
5500	/* initiate massacre of all css's */
5501	for_each_css(css, ssid, cgrp)
5502		kill_css(css);
5503
5504	/*
5505	 * Remove @cgrp directory along with the base files.  @cgrp has an
5506	 * extra ref on its kn.
5507	 */
5508	kernfs_remove(cgrp->kn);
5509
5510	check_for_release(cgroup_parent(cgrp));
5511
5512	/* put the base reference */
5513	percpu_ref_kill(&cgrp->self.refcnt);
5514
5515	return 0;
5516};
5517
5518static int cgroup_rmdir(struct kernfs_node *kn)
5519{
5520	struct cgroup *cgrp;
5521	int ret = 0;
5522
5523	cgrp = cgroup_kn_lock_live(kn, false);
5524	if (!cgrp)
5525		return 0;
5526
5527	ret = cgroup_destroy_locked(cgrp);
5528
5529	if (!ret)
5530		trace_cgroup_rmdir(cgrp);
5531
5532	cgroup_kn_unlock(kn);
5533	return ret;
5534}
5535
5536static struct kernfs_syscall_ops cgroup_kf_syscall_ops = {
5537	.remount_fs		= cgroup_remount,
5538	.show_options		= cgroup_show_options,
5539	.mkdir			= cgroup_mkdir,
5540	.rmdir			= cgroup_rmdir,
5541	.rename			= cgroup_rename,
5542	.show_path		= cgroup_show_path,
5543};
5544
5545static void __init cgroup_init_subsys(struct cgroup_subsys *ss, bool early)
5546{
5547	struct cgroup_subsys_state *css;
5548
5549	pr_debug("Initializing cgroup subsys %s\n", ss->name);
5550
5551	mutex_lock(&cgroup_mutex);
5552
5553	idr_init(&ss->css_idr);
5554	INIT_LIST_HEAD(&ss->cfts);
5555
5556	/* Create the root cgroup state for this subsystem */
5557	ss->root = &cgrp_dfl_root;
5558	css = ss->css_alloc(cgroup_css(&cgrp_dfl_root.cgrp, ss));
5559	/* We don't handle early failures gracefully */
5560	BUG_ON(IS_ERR(css));
5561	init_and_link_css(css, ss, &cgrp_dfl_root.cgrp);
5562
5563	/*
5564	 * Root csses are never destroyed and we can't initialize
5565	 * percpu_ref during early init.  Disable refcnting.
5566	 */
5567	css->flags |= CSS_NO_REF;
5568
5569	if (early) {
5570		/* allocation can't be done safely during early init */
5571		css->id = 1;
5572	} else {
5573		css->id = cgroup_idr_alloc(&ss->css_idr, css, 1, 2, GFP_KERNEL);
5574		BUG_ON(css->id < 0);
5575	}
5576
5577	/* Update the init_css_set to contain a subsys
5578	 * pointer to this state - since the subsystem is
5579	 * newly registered, all tasks and hence the
5580	 * init_css_set is in the subsystem's root cgroup. */
5581	init_css_set.subsys[ss->id] = css;
5582
5583	have_fork_callback |= (bool)ss->fork << ss->id;
5584	have_exit_callback |= (bool)ss->exit << ss->id;
5585	have_free_callback |= (bool)ss->free << ss->id;
5586	have_canfork_callback |= (bool)ss->can_fork << ss->id;
5587
5588	/* At system boot, before all subsystems have been
5589	 * registered, no tasks have been forked, so we don't
5590	 * need to invoke fork callbacks here. */
5591	BUG_ON(!list_empty(&init_task.tasks));
5592
5593	BUG_ON(online_css(css));
5594
5595	mutex_unlock(&cgroup_mutex);
5596}
5597
5598/**
5599 * cgroup_init_early - cgroup initialization at system boot
5600 *
5601 * Initialize cgroups at system boot, and initialize any
5602 * subsystems that request early init.
5603 */
5604int __init cgroup_init_early(void)
5605{
5606	static struct cgroup_sb_opts __initdata opts;
5607	struct cgroup_subsys *ss;
5608	int i;
5609
5610	init_cgroup_root(&cgrp_dfl_root, &opts);
5611	cgrp_dfl_root.cgrp.self.flags |= CSS_NO_REF;
5612
5613	RCU_INIT_POINTER(init_task.cgroups, &init_css_set);
5614
5615	for_each_subsys(ss, i) {
5616		WARN(!ss->css_alloc || !ss->css_free || ss->name || ss->id,
5617		     "invalid cgroup_subsys %d:%s css_alloc=%p css_free=%p id:name=%d:%s\n",
5618		     i, cgroup_subsys_name[i], ss->css_alloc, ss->css_free,
5619		     ss->id, ss->name);
5620		WARN(strlen(cgroup_subsys_name[i]) > MAX_CGROUP_TYPE_NAMELEN,
5621		     "cgroup_subsys_name %s too long\n", cgroup_subsys_name[i]);
5622
5623		ss->id = i;
5624		ss->name = cgroup_subsys_name[i];
5625		if (!ss->legacy_name)
5626			ss->legacy_name = cgroup_subsys_name[i];
5627
5628		if (ss->early_init)
5629			cgroup_init_subsys(ss, true);
5630	}
5631	return 0;
5632}
5633
5634static u16 cgroup_disable_mask __initdata;
5635
5636/**
5637 * cgroup_init - cgroup initialization
5638 *
5639 * Register cgroup filesystem and /proc file, and initialize
5640 * any subsystems that didn't request early init.
5641 */
5642int __init cgroup_init(void)
5643{
5644	struct cgroup_subsys *ss;
5645	int ssid;
5646
5647	BUILD_BUG_ON(CGROUP_SUBSYS_COUNT > 16);
5648	BUG_ON(percpu_init_rwsem(&cgroup_threadgroup_rwsem));
5649	BUG_ON(cgroup_init_cftypes(NULL, cgroup_dfl_base_files));
5650	BUG_ON(cgroup_init_cftypes(NULL, cgroup_legacy_base_files));
5651
5652	/*
5653	 * The latency of the synchronize_sched() is too high for cgroups,
5654	 * avoid it at the cost of forcing all readers into the slow path.
5655	 */
5656	rcu_sync_enter_start(&cgroup_threadgroup_rwsem.rss);
5657
5658	get_user_ns(init_cgroup_ns.user_ns);
5659
5660	mutex_lock(&cgroup_mutex);
5661
5662	/*
5663	 * Add init_css_set to the hash table so that dfl_root can link to
5664	 * it during init.
5665	 */
5666	hash_add(css_set_table, &init_css_set.hlist,
5667		 css_set_hash(init_css_set.subsys));
5668
5669	BUG_ON(cgroup_setup_root(&cgrp_dfl_root, 0));
5670
5671	mutex_unlock(&cgroup_mutex);
5672
5673	for_each_subsys(ss, ssid) {
5674		if (ss->early_init) {
5675			struct cgroup_subsys_state *css =
5676				init_css_set.subsys[ss->id];
5677
5678			css->id = cgroup_idr_alloc(&ss->css_idr, css, 1, 2,
5679						   GFP_KERNEL);
5680			BUG_ON(css->id < 0);
5681		} else {
5682			cgroup_init_subsys(ss, false);
5683		}
5684
5685		list_add_tail(&init_css_set.e_cset_node[ssid],
5686			      &cgrp_dfl_root.cgrp.e_csets[ssid]);
5687
5688		/*
5689		 * Setting dfl_root subsys_mask needs to consider the
5690		 * disabled flag and cftype registration needs kmalloc,
5691		 * both of which aren't available during early_init.
5692		 */
5693		if (cgroup_disable_mask & (1 << ssid)) {
5694			static_branch_disable(cgroup_subsys_enabled_key[ssid]);
5695			printk(KERN_INFO "Disabling %s control group subsystem\n",
5696			       ss->name);
5697			continue;
5698		}
5699
5700		if (cgroup_ssid_no_v1(ssid))
5701			printk(KERN_INFO "Disabling %s control group subsystem in v1 mounts\n",
5702			       ss->name);
5703
5704		cgrp_dfl_root.subsys_mask |= 1 << ss->id;
5705
5706		if (ss->implicit_on_dfl)
5707			cgrp_dfl_implicit_ss_mask |= 1 << ss->id;
5708		else if (!ss->dfl_cftypes)
5709			cgrp_dfl_inhibit_ss_mask |= 1 << ss->id;
5710
5711		if (ss->dfl_cftypes == ss->legacy_cftypes) {
5712			WARN_ON(cgroup_add_cftypes(ss, ss->dfl_cftypes));
5713		} else {
5714			WARN_ON(cgroup_add_dfl_cftypes(ss, ss->dfl_cftypes));
5715			WARN_ON(cgroup_add_legacy_cftypes(ss, ss->legacy_cftypes));
5716		}
5717
5718		if (ss->bind)
5719			ss->bind(init_css_set.subsys[ssid]);
5720	}
5721
5722	/* init_css_set.subsys[] has been updated, re-hash */
5723	hash_del(&init_css_set.hlist);
5724	hash_add(css_set_table, &init_css_set.hlist,
5725		 css_set_hash(init_css_set.subsys));
5726
5727	WARN_ON(sysfs_create_mount_point(fs_kobj, "cgroup"));
5728	WARN_ON(register_filesystem(&cgroup_fs_type));
5729	WARN_ON(register_filesystem(&cgroup2_fs_type));
5730	WARN_ON(!proc_create("cgroups", 0, NULL, &proc_cgroupstats_operations));
5731
5732	return 0;
5733}
5734
5735static int __init cgroup_wq_init(void)
5736{
5737	/*
5738	 * There isn't much point in executing destruction path in
5739	 * parallel.  Good chunk is serialized with cgroup_mutex anyway.
5740	 * Use 1 for @max_active.
5741	 *
5742	 * We would prefer to do this in cgroup_init() above, but that
5743	 * is called before init_workqueues(): so leave this until after.
5744	 */
5745	cgroup_destroy_wq = alloc_workqueue("cgroup_destroy", 0, 1);
5746	BUG_ON(!cgroup_destroy_wq);
5747
5748	/*
5749	 * Used to destroy pidlists and separate to serve as flush domain.
5750	 * Cap @max_active to 1 too.
5751	 */
5752	cgroup_pidlist_destroy_wq = alloc_workqueue("cgroup_pidlist_destroy",
5753						    0, 1);
5754	BUG_ON(!cgroup_pidlist_destroy_wq);
5755
5756	return 0;
5757}
5758core_initcall(cgroup_wq_init);
5759
5760/*
5761 * proc_cgroup_show()
5762 *  - Print task's cgroup paths into seq_file, one line for each hierarchy
5763 *  - Used for /proc/<pid>/cgroup.
5764 */
5765int proc_cgroup_show(struct seq_file *m, struct pid_namespace *ns,
5766		     struct pid *pid, struct task_struct *tsk)
5767{
5768	char *buf;
5769	int retval;
5770	struct cgroup_root *root;
5771
5772	retval = -ENOMEM;
5773	buf = kmalloc(PATH_MAX, GFP_KERNEL);
5774	if (!buf)
5775		goto out;
5776
5777	mutex_lock(&cgroup_mutex);
5778	spin_lock_irq(&css_set_lock);
5779
5780	for_each_root(root) {
5781		struct cgroup_subsys *ss;
5782		struct cgroup *cgrp;
5783		int ssid, count = 0;
5784
5785		if (root == &cgrp_dfl_root && !cgrp_dfl_visible)
5786			continue;
5787
5788		seq_printf(m, "%d:", root->hierarchy_id);
5789		if (root != &cgrp_dfl_root)
5790			for_each_subsys(ss, ssid)
5791				if (root->subsys_mask & (1 << ssid))
5792					seq_printf(m, "%s%s", count++ ? "," : "",
5793						   ss->legacy_name);
5794		if (strlen(root->name))
5795			seq_printf(m, "%sname=%s", count ? "," : "",
5796				   root->name);
5797		seq_putc(m, ':');
5798
5799		cgrp = task_cgroup_from_root(tsk, root);
5800
5801		/*
5802		 * On traditional hierarchies, all zombie tasks show up as
5803		 * belonging to the root cgroup.  On the default hierarchy,
5804		 * while a zombie doesn't show up in "cgroup.procs" and
5805		 * thus can't be migrated, its /proc/PID/cgroup keeps
5806		 * reporting the cgroup it belonged to before exiting.  If
5807		 * the cgroup is removed before the zombie is reaped,
5808		 * " (deleted)" is appended to the cgroup path.
5809		 */
5810		if (cgroup_on_dfl(cgrp) || !(tsk->flags & PF_EXITING)) {
5811			retval = cgroup_path_ns_locked(cgrp, buf, PATH_MAX,
5812						current->nsproxy->cgroup_ns);
5813			if (retval >= PATH_MAX)
5814				retval = -ENAMETOOLONG;
5815			if (retval < 0)
5816				goto out_unlock;
5817
5818			seq_puts(m, buf);
5819		} else {
5820			seq_puts(m, "/");
5821		}
5822
 
 
5823		if (cgroup_on_dfl(cgrp) && cgroup_is_dead(cgrp))
5824			seq_puts(m, " (deleted)\n");
5825		else
5826			seq_putc(m, '\n');
5827	}
5828
5829	retval = 0;
5830out_unlock:
5831	spin_unlock_irq(&css_set_lock);
5832	mutex_unlock(&cgroup_mutex);
5833	kfree(buf);
5834out:
5835	return retval;
5836}
5837
5838/* Display information about each subsystem and each hierarchy */
5839static int proc_cgroupstats_show(struct seq_file *m, void *v)
5840{
5841	struct cgroup_subsys *ss;
5842	int i;
5843
5844	seq_puts(m, "#subsys_name\thierarchy\tnum_cgroups\tenabled\n");
5845	/*
5846	 * ideally we don't want subsystems moving around while we do this.
5847	 * cgroup_mutex is also necessary to guarantee an atomic snapshot of
5848	 * subsys/hierarchy state.
5849	 */
5850	mutex_lock(&cgroup_mutex);
5851
5852	for_each_subsys(ss, i)
5853		seq_printf(m, "%s\t%d\t%d\t%d\n",
5854			   ss->legacy_name, ss->root->hierarchy_id,
5855			   atomic_read(&ss->root->nr_cgrps),
5856			   cgroup_ssid_enabled(i));
5857
5858	mutex_unlock(&cgroup_mutex);
5859	return 0;
5860}
5861
5862static int cgroupstats_open(struct inode *inode, struct file *file)
5863{
5864	return single_open(file, proc_cgroupstats_show, NULL);
5865}
5866
5867static const struct file_operations proc_cgroupstats_operations = {
5868	.open = cgroupstats_open,
5869	.read = seq_read,
5870	.llseek = seq_lseek,
5871	.release = single_release,
5872};
5873
5874/**
5875 * cgroup_fork - initialize cgroup related fields during copy_process()
5876 * @child: pointer to task_struct of forking parent process.
5877 *
5878 * A task is associated with the init_css_set until cgroup_post_fork()
5879 * attaches it to the parent's css_set.  Empty cg_list indicates that
5880 * @child isn't holding reference to its css_set.
5881 */
5882void cgroup_fork(struct task_struct *child)
5883{
5884	RCU_INIT_POINTER(child->cgroups, &init_css_set);
5885	INIT_LIST_HEAD(&child->cg_list);
5886}
5887
5888/**
5889 * cgroup_can_fork - called on a new task before the process is exposed
5890 * @child: the task in question.
5891 *
5892 * This calls the subsystem can_fork() callbacks. If the can_fork() callback
5893 * returns an error, the fork aborts with that error code. This allows for
5894 * a cgroup subsystem to conditionally allow or deny new forks.
5895 */
5896int cgroup_can_fork(struct task_struct *child)
5897{
5898	struct cgroup_subsys *ss;
5899	int i, j, ret;
5900
5901	do_each_subsys_mask(ss, i, have_canfork_callback) {
5902		ret = ss->can_fork(child);
5903		if (ret)
5904			goto out_revert;
5905	} while_each_subsys_mask();
5906
5907	return 0;
5908
5909out_revert:
5910	for_each_subsys(ss, j) {
5911		if (j >= i)
5912			break;
5913		if (ss->cancel_fork)
5914			ss->cancel_fork(child);
5915	}
5916
5917	return ret;
5918}
5919
5920/**
5921 * cgroup_cancel_fork - called if a fork failed after cgroup_can_fork()
5922 * @child: the task in question
5923 *
5924 * This calls the cancel_fork() callbacks if a fork failed *after*
5925 * cgroup_can_fork() succeded.
5926 */
5927void cgroup_cancel_fork(struct task_struct *child)
5928{
5929	struct cgroup_subsys *ss;
5930	int i;
5931
5932	for_each_subsys(ss, i)
5933		if (ss->cancel_fork)
5934			ss->cancel_fork(child);
5935}
5936
5937/**
5938 * cgroup_post_fork - called on a new task after adding it to the task list
5939 * @child: the task in question
5940 *
5941 * Adds the task to the list running through its css_set if necessary and
5942 * call the subsystem fork() callbacks.  Has to be after the task is
5943 * visible on the task list in case we race with the first call to
5944 * cgroup_task_iter_start() - to guarantee that the new task ends up on its
5945 * list.
5946 */
5947void cgroup_post_fork(struct task_struct *child)
5948{
5949	struct cgroup_subsys *ss;
5950	int i;
5951
5952	/*
5953	 * This may race against cgroup_enable_task_cg_lists().  As that
5954	 * function sets use_task_css_set_links before grabbing
5955	 * tasklist_lock and we just went through tasklist_lock to add
5956	 * @child, it's guaranteed that either we see the set
5957	 * use_task_css_set_links or cgroup_enable_task_cg_lists() sees
5958	 * @child during its iteration.
5959	 *
5960	 * If we won the race, @child is associated with %current's
5961	 * css_set.  Grabbing css_set_lock guarantees both that the
5962	 * association is stable, and, on completion of the parent's
5963	 * migration, @child is visible in the source of migration or
5964	 * already in the destination cgroup.  This guarantee is necessary
5965	 * when implementing operations which need to migrate all tasks of
5966	 * a cgroup to another.
5967	 *
5968	 * Note that if we lose to cgroup_enable_task_cg_lists(), @child
5969	 * will remain in init_css_set.  This is safe because all tasks are
5970	 * in the init_css_set before cg_links is enabled and there's no
5971	 * operation which transfers all tasks out of init_css_set.
5972	 */
5973	if (use_task_css_set_links) {
5974		struct css_set *cset;
5975
5976		spin_lock_irq(&css_set_lock);
5977		cset = task_css_set(current);
5978		if (list_empty(&child->cg_list)) {
5979			get_css_set(cset);
5980			css_set_move_task(child, NULL, cset, false);
5981		}
5982		spin_unlock_irq(&css_set_lock);
5983	}
5984
5985	/*
5986	 * Call ss->fork().  This must happen after @child is linked on
5987	 * css_set; otherwise, @child might change state between ->fork()
5988	 * and addition to css_set.
5989	 */
5990	do_each_subsys_mask(ss, i, have_fork_callback) {
5991		ss->fork(child);
5992	} while_each_subsys_mask();
5993}
5994
5995/**
5996 * cgroup_exit - detach cgroup from exiting task
5997 * @tsk: pointer to task_struct of exiting process
5998 *
5999 * Description: Detach cgroup from @tsk and release it.
6000 *
6001 * Note that cgroups marked notify_on_release force every task in
6002 * them to take the global cgroup_mutex mutex when exiting.
6003 * This could impact scaling on very large systems.  Be reluctant to
6004 * use notify_on_release cgroups where very high task exit scaling
6005 * is required on large systems.
6006 *
6007 * We set the exiting tasks cgroup to the root cgroup (top_cgroup).  We
6008 * call cgroup_exit() while the task is still competent to handle
6009 * notify_on_release(), then leave the task attached to the root cgroup in
6010 * each hierarchy for the remainder of its exit.  No need to bother with
6011 * init_css_set refcnting.  init_css_set never goes away and we can't race
6012 * with migration path - PF_EXITING is visible to migration path.
6013 */
6014void cgroup_exit(struct task_struct *tsk)
6015{
6016	struct cgroup_subsys *ss;
6017	struct css_set *cset;
6018	int i;
6019
6020	/*
6021	 * Unlink from @tsk from its css_set.  As migration path can't race
6022	 * with us, we can check css_set and cg_list without synchronization.
6023	 */
6024	cset = task_css_set(tsk);
6025
6026	if (!list_empty(&tsk->cg_list)) {
6027		spin_lock_irq(&css_set_lock);
6028		css_set_move_task(tsk, cset, NULL, false);
6029		spin_unlock_irq(&css_set_lock);
6030	} else {
6031		get_css_set(cset);
6032	}
6033
6034	/* see cgroup_post_fork() for details */
6035	do_each_subsys_mask(ss, i, have_exit_callback) {
6036		ss->exit(tsk);
6037	} while_each_subsys_mask();
6038}
6039
6040void cgroup_free(struct task_struct *task)
6041{
6042	struct css_set *cset = task_css_set(task);
6043	struct cgroup_subsys *ss;
6044	int ssid;
6045
6046	do_each_subsys_mask(ss, ssid, have_free_callback) {
6047		ss->free(task);
6048	} while_each_subsys_mask();
6049
6050	put_css_set(cset);
6051}
6052
6053static void check_for_release(struct cgroup *cgrp)
6054{
6055	if (notify_on_release(cgrp) && !cgroup_is_populated(cgrp) &&
6056	    !css_has_online_children(&cgrp->self) && !cgroup_is_dead(cgrp))
6057		schedule_work(&cgrp->release_agent_work);
6058}
6059
6060/*
6061 * Notify userspace when a cgroup is released, by running the
6062 * configured release agent with the name of the cgroup (path
6063 * relative to the root of cgroup file system) as the argument.
6064 *
6065 * Most likely, this user command will try to rmdir this cgroup.
6066 *
6067 * This races with the possibility that some other task will be
6068 * attached to this cgroup before it is removed, or that some other
6069 * user task will 'mkdir' a child cgroup of this cgroup.  That's ok.
6070 * The presumed 'rmdir' will fail quietly if this cgroup is no longer
6071 * unused, and this cgroup will be reprieved from its death sentence,
6072 * to continue to serve a useful existence.  Next time it's released,
6073 * we will get notified again, if it still has 'notify_on_release' set.
6074 *
6075 * The final arg to call_usermodehelper() is UMH_WAIT_EXEC, which
6076 * means only wait until the task is successfully execve()'d.  The
6077 * separate release agent task is forked by call_usermodehelper(),
6078 * then control in this thread returns here, without waiting for the
6079 * release agent task.  We don't bother to wait because the caller of
6080 * this routine has no use for the exit status of the release agent
6081 * task, so no sense holding our caller up for that.
6082 */
6083static void cgroup_release_agent(struct work_struct *work)
6084{
6085	struct cgroup *cgrp =
6086		container_of(work, struct cgroup, release_agent_work);
6087	char *pathbuf = NULL, *agentbuf = NULL;
6088	char *argv[3], *envp[3];
6089	int ret;
6090
6091	mutex_lock(&cgroup_mutex);
6092
6093	pathbuf = kmalloc(PATH_MAX, GFP_KERNEL);
6094	agentbuf = kstrdup(cgrp->root->release_agent_path, GFP_KERNEL);
6095	if (!pathbuf || !agentbuf)
6096		goto out;
6097
6098	spin_lock_irq(&css_set_lock);
6099	ret = cgroup_path_ns_locked(cgrp, pathbuf, PATH_MAX, &init_cgroup_ns);
6100	spin_unlock_irq(&css_set_lock);
6101	if (ret < 0 || ret >= PATH_MAX)
6102		goto out;
6103
6104	argv[0] = agentbuf;
6105	argv[1] = pathbuf;
6106	argv[2] = NULL;
6107
6108	/* minimal command environment */
6109	envp[0] = "HOME=/";
6110	envp[1] = "PATH=/sbin:/bin:/usr/sbin:/usr/bin";
6111	envp[2] = NULL;
6112
6113	mutex_unlock(&cgroup_mutex);
6114	call_usermodehelper(argv[0], argv, envp, UMH_WAIT_EXEC);
6115	goto out_free;
6116out:
6117	mutex_unlock(&cgroup_mutex);
6118out_free:
6119	kfree(agentbuf);
6120	kfree(pathbuf);
6121}
6122
6123static int __init cgroup_disable(char *str)
6124{
6125	struct cgroup_subsys *ss;
6126	char *token;
6127	int i;
6128
6129	while ((token = strsep(&str, ",")) != NULL) {
6130		if (!*token)
6131			continue;
6132
6133		for_each_subsys(ss, i) {
6134			if (strcmp(token, ss->name) &&
6135			    strcmp(token, ss->legacy_name))
6136				continue;
6137			cgroup_disable_mask |= 1 << i;
6138		}
6139	}
6140	return 1;
6141}
6142__setup("cgroup_disable=", cgroup_disable);
6143
6144static int __init cgroup_no_v1(char *str)
6145{
6146	struct cgroup_subsys *ss;
6147	char *token;
6148	int i;
6149
6150	while ((token = strsep(&str, ",")) != NULL) {
6151		if (!*token)
6152			continue;
6153
6154		if (!strcmp(token, "all")) {
6155			cgroup_no_v1_mask = U16_MAX;
6156			break;
6157		}
6158
6159		for_each_subsys(ss, i) {
6160			if (strcmp(token, ss->name) &&
6161			    strcmp(token, ss->legacy_name))
6162				continue;
6163
6164			cgroup_no_v1_mask |= 1 << i;
6165		}
6166	}
6167	return 1;
6168}
6169__setup("cgroup_no_v1=", cgroup_no_v1);
6170
6171/**
6172 * css_tryget_online_from_dir - get corresponding css from a cgroup dentry
6173 * @dentry: directory dentry of interest
6174 * @ss: subsystem of interest
6175 *
6176 * If @dentry is a directory for a cgroup which has @ss enabled on it, try
6177 * to get the corresponding css and return it.  If such css doesn't exist
6178 * or can't be pinned, an ERR_PTR value is returned.
6179 */
6180struct cgroup_subsys_state *css_tryget_online_from_dir(struct dentry *dentry,
6181						       struct cgroup_subsys *ss)
6182{
6183	struct kernfs_node *kn = kernfs_node_from_dentry(dentry);
6184	struct file_system_type *s_type = dentry->d_sb->s_type;
6185	struct cgroup_subsys_state *css = NULL;
6186	struct cgroup *cgrp;
6187
6188	/* is @dentry a cgroup dir? */
6189	if ((s_type != &cgroup_fs_type && s_type != &cgroup2_fs_type) ||
6190	    !kn || kernfs_type(kn) != KERNFS_DIR)
6191		return ERR_PTR(-EBADF);
6192
6193	rcu_read_lock();
6194
6195	/*
6196	 * This path doesn't originate from kernfs and @kn could already
6197	 * have been or be removed at any point.  @kn->priv is RCU
6198	 * protected for this access.  See css_release_work_fn() for details.
6199	 */
6200	cgrp = rcu_dereference(kn->priv);
6201	if (cgrp)
6202		css = cgroup_css(cgrp, ss);
6203
6204	if (!css || !css_tryget_online(css))
6205		css = ERR_PTR(-ENOENT);
6206
6207	rcu_read_unlock();
6208	return css;
6209}
6210
6211/**
6212 * css_from_id - lookup css by id
6213 * @id: the cgroup id
6214 * @ss: cgroup subsys to be looked into
6215 *
6216 * Returns the css if there's valid one with @id, otherwise returns NULL.
6217 * Should be called under rcu_read_lock().
6218 */
6219struct cgroup_subsys_state *css_from_id(int id, struct cgroup_subsys *ss)
6220{
6221	WARN_ON_ONCE(!rcu_read_lock_held());
6222	return idr_find(&ss->css_idr, id);
6223}
6224
6225/**
6226 * cgroup_get_from_path - lookup and get a cgroup from its default hierarchy path
6227 * @path: path on the default hierarchy
6228 *
6229 * Find the cgroup at @path on the default hierarchy, increment its
6230 * reference count and return it.  Returns pointer to the found cgroup on
6231 * success, ERR_PTR(-ENOENT) if @path doens't exist and ERR_PTR(-ENOTDIR)
6232 * if @path points to a non-directory.
6233 */
6234struct cgroup *cgroup_get_from_path(const char *path)
6235{
6236	struct kernfs_node *kn;
6237	struct cgroup *cgrp;
6238
6239	mutex_lock(&cgroup_mutex);
6240
6241	kn = kernfs_walk_and_get(cgrp_dfl_root.cgrp.kn, path);
6242	if (kn) {
6243		if (kernfs_type(kn) == KERNFS_DIR) {
6244			cgrp = kn->priv;
6245			cgroup_get(cgrp);
6246		} else {
6247			cgrp = ERR_PTR(-ENOTDIR);
6248		}
6249		kernfs_put(kn);
6250	} else {
6251		cgrp = ERR_PTR(-ENOENT);
6252	}
6253
6254	mutex_unlock(&cgroup_mutex);
6255	return cgrp;
6256}
6257EXPORT_SYMBOL_GPL(cgroup_get_from_path);
6258
6259/**
6260 * cgroup_get_from_fd - get a cgroup pointer from a fd
6261 * @fd: fd obtained by open(cgroup2_dir)
6262 *
6263 * Find the cgroup from a fd which should be obtained
6264 * by opening a cgroup directory.  Returns a pointer to the
6265 * cgroup on success. ERR_PTR is returned if the cgroup
6266 * cannot be found.
6267 */
6268struct cgroup *cgroup_get_from_fd(int fd)
6269{
6270	struct cgroup_subsys_state *css;
6271	struct cgroup *cgrp;
6272	struct file *f;
6273
6274	f = fget_raw(fd);
6275	if (!f)
6276		return ERR_PTR(-EBADF);
6277
6278	css = css_tryget_online_from_dir(f->f_path.dentry, NULL);
6279	fput(f);
6280	if (IS_ERR(css))
6281		return ERR_CAST(css);
6282
6283	cgrp = css->cgroup;
6284	if (!cgroup_on_dfl(cgrp)) {
6285		cgroup_put(cgrp);
6286		return ERR_PTR(-EBADF);
6287	}
6288
6289	return cgrp;
6290}
6291EXPORT_SYMBOL_GPL(cgroup_get_from_fd);
6292
6293/*
6294 * sock->sk_cgrp_data handling.  For more info, see sock_cgroup_data
6295 * definition in cgroup-defs.h.
6296 */
6297#ifdef CONFIG_SOCK_CGROUP_DATA
6298
6299#if defined(CONFIG_CGROUP_NET_PRIO) || defined(CONFIG_CGROUP_NET_CLASSID)
6300
6301DEFINE_SPINLOCK(cgroup_sk_update_lock);
6302static bool cgroup_sk_alloc_disabled __read_mostly;
6303
6304void cgroup_sk_alloc_disable(void)
6305{
6306	if (cgroup_sk_alloc_disabled)
6307		return;
6308	pr_info("cgroup: disabling cgroup2 socket matching due to net_prio or net_cls activation\n");
6309	cgroup_sk_alloc_disabled = true;
6310}
6311
6312#else
6313
6314#define cgroup_sk_alloc_disabled	false
6315
6316#endif
6317
6318void cgroup_sk_alloc(struct sock_cgroup_data *skcd)
6319{
6320	if (cgroup_sk_alloc_disabled)
6321		return;
6322
6323	/* Socket clone path */
6324	if (skcd->val) {
6325		cgroup_get(sock_cgroup_ptr(skcd));
6326		return;
6327	}
6328
6329	rcu_read_lock();
6330
6331	while (true) {
6332		struct css_set *cset;
6333
6334		cset = task_css_set(current);
6335		if (likely(cgroup_tryget(cset->dfl_cgrp))) {
6336			skcd->val = (unsigned long)cset->dfl_cgrp;
6337			break;
6338		}
6339		cpu_relax();
6340	}
6341
6342	rcu_read_unlock();
6343}
6344
6345void cgroup_sk_free(struct sock_cgroup_data *skcd)
6346{
6347	cgroup_put(sock_cgroup_ptr(skcd));
6348}
6349
6350#endif	/* CONFIG_SOCK_CGROUP_DATA */
6351
6352/* cgroup namespaces */
6353
6354static struct ucounts *inc_cgroup_namespaces(struct user_namespace *ns)
6355{
6356	return inc_ucount(ns, current_euid(), UCOUNT_CGROUP_NAMESPACES);
6357}
6358
6359static void dec_cgroup_namespaces(struct ucounts *ucounts)
6360{
6361	dec_ucount(ucounts, UCOUNT_CGROUP_NAMESPACES);
6362}
6363
6364static struct cgroup_namespace *alloc_cgroup_ns(void)
6365{
6366	struct cgroup_namespace *new_ns;
6367	int ret;
6368
6369	new_ns = kzalloc(sizeof(struct cgroup_namespace), GFP_KERNEL);
6370	if (!new_ns)
6371		return ERR_PTR(-ENOMEM);
6372	ret = ns_alloc_inum(&new_ns->ns);
6373	if (ret) {
6374		kfree(new_ns);
6375		return ERR_PTR(ret);
6376	}
6377	atomic_set(&new_ns->count, 1);
6378	new_ns->ns.ops = &cgroupns_operations;
6379	return new_ns;
6380}
6381
6382void free_cgroup_ns(struct cgroup_namespace *ns)
6383{
6384	put_css_set(ns->root_cset);
6385	dec_cgroup_namespaces(ns->ucounts);
6386	put_user_ns(ns->user_ns);
6387	ns_free_inum(&ns->ns);
6388	kfree(ns);
6389}
6390EXPORT_SYMBOL(free_cgroup_ns);
6391
6392struct cgroup_namespace *copy_cgroup_ns(unsigned long flags,
6393					struct user_namespace *user_ns,
6394					struct cgroup_namespace *old_ns)
6395{
6396	struct cgroup_namespace *new_ns;
6397	struct ucounts *ucounts;
6398	struct css_set *cset;
6399
6400	BUG_ON(!old_ns);
6401
6402	if (!(flags & CLONE_NEWCGROUP)) {
6403		get_cgroup_ns(old_ns);
6404		return old_ns;
6405	}
6406
6407	/* Allow only sysadmin to create cgroup namespace. */
6408	if (!ns_capable(user_ns, CAP_SYS_ADMIN))
6409		return ERR_PTR(-EPERM);
6410
6411	ucounts = inc_cgroup_namespaces(user_ns);
6412	if (!ucounts)
6413		return ERR_PTR(-ENOSPC);
6414
6415	/* It is not safe to take cgroup_mutex here */
6416	spin_lock_irq(&css_set_lock);
6417	cset = task_css_set(current);
6418	get_css_set(cset);
6419	spin_unlock_irq(&css_set_lock);
 
 
6420
6421	new_ns = alloc_cgroup_ns();
6422	if (IS_ERR(new_ns)) {
6423		put_css_set(cset);
6424		dec_cgroup_namespaces(ucounts);
6425		return new_ns;
6426	}
6427
6428	new_ns->user_ns = get_user_ns(user_ns);
6429	new_ns->ucounts = ucounts;
6430	new_ns->root_cset = cset;
6431
6432	return new_ns;
6433}
6434
6435static inline struct cgroup_namespace *to_cg_ns(struct ns_common *ns)
6436{
6437	return container_of(ns, struct cgroup_namespace, ns);
6438}
6439
6440static int cgroupns_install(struct nsproxy *nsproxy, struct ns_common *ns)
6441{
6442	struct cgroup_namespace *cgroup_ns = to_cg_ns(ns);
6443
6444	if (!ns_capable(current_user_ns(), CAP_SYS_ADMIN) ||
6445	    !ns_capable(cgroup_ns->user_ns, CAP_SYS_ADMIN))
6446		return -EPERM;
6447
6448	/* Don't need to do anything if we are attaching to our own cgroupns. */
6449	if (cgroup_ns == nsproxy->cgroup_ns)
6450		return 0;
6451
6452	get_cgroup_ns(cgroup_ns);
6453	put_cgroup_ns(nsproxy->cgroup_ns);
6454	nsproxy->cgroup_ns = cgroup_ns;
6455
6456	return 0;
6457}
6458
6459static struct ns_common *cgroupns_get(struct task_struct *task)
6460{
6461	struct cgroup_namespace *ns = NULL;
6462	struct nsproxy *nsproxy;
6463
6464	task_lock(task);
6465	nsproxy = task->nsproxy;
6466	if (nsproxy) {
6467		ns = nsproxy->cgroup_ns;
6468		get_cgroup_ns(ns);
6469	}
6470	task_unlock(task);
6471
6472	return ns ? &ns->ns : NULL;
6473}
6474
6475static void cgroupns_put(struct ns_common *ns)
6476{
6477	put_cgroup_ns(to_cg_ns(ns));
6478}
6479
6480static struct user_namespace *cgroupns_owner(struct ns_common *ns)
6481{
6482	return to_cg_ns(ns)->user_ns;
6483}
6484
6485const struct proc_ns_operations cgroupns_operations = {
6486	.name		= "cgroup",
6487	.type		= CLONE_NEWCGROUP,
6488	.get		= cgroupns_get,
6489	.put		= cgroupns_put,
6490	.install	= cgroupns_install,
6491	.owner		= cgroupns_owner,
6492};
6493
6494static __init int cgroup_namespaces_init(void)
6495{
6496	return 0;
6497}
6498subsys_initcall(cgroup_namespaces_init);
6499
6500#ifdef CONFIG_CGROUP_BPF
6501int cgroup_bpf_update(struct cgroup *cgrp, struct bpf_prog *prog,
6502		      enum bpf_attach_type type, bool overridable)
6503{
6504	struct cgroup *parent = cgroup_parent(cgrp);
6505	int ret;
6506
6507	mutex_lock(&cgroup_mutex);
6508	ret = __cgroup_bpf_update(cgrp, parent, prog, type, overridable);
6509	mutex_unlock(&cgroup_mutex);
6510	return ret;
6511}
6512#endif /* CONFIG_CGROUP_BPF */
6513
6514#ifdef CONFIG_CGROUP_DEBUG
6515static struct cgroup_subsys_state *
6516debug_css_alloc(struct cgroup_subsys_state *parent_css)
6517{
6518	struct cgroup_subsys_state *css = kzalloc(sizeof(*css), GFP_KERNEL);
6519
6520	if (!css)
6521		return ERR_PTR(-ENOMEM);
6522
6523	return css;
6524}
6525
6526static void debug_css_free(struct cgroup_subsys_state *css)
6527{
6528	kfree(css);
6529}
6530
6531static u64 debug_taskcount_read(struct cgroup_subsys_state *css,
6532				struct cftype *cft)
6533{
6534	return cgroup_task_count(css->cgroup);
6535}
6536
6537static u64 current_css_set_read(struct cgroup_subsys_state *css,
6538				struct cftype *cft)
6539{
6540	return (u64)(unsigned long)current->cgroups;
6541}
6542
6543static u64 current_css_set_refcount_read(struct cgroup_subsys_state *css,
6544					 struct cftype *cft)
6545{
6546	u64 count;
6547
6548	rcu_read_lock();
6549	count = atomic_read(&task_css_set(current)->refcount);
6550	rcu_read_unlock();
6551	return count;
6552}
6553
6554static int current_css_set_cg_links_read(struct seq_file *seq, void *v)
6555{
6556	struct cgrp_cset_link *link;
6557	struct css_set *cset;
6558	char *name_buf;
6559
6560	name_buf = kmalloc(NAME_MAX + 1, GFP_KERNEL);
6561	if (!name_buf)
6562		return -ENOMEM;
6563
6564	spin_lock_irq(&css_set_lock);
6565	rcu_read_lock();
6566	cset = rcu_dereference(current->cgroups);
6567	list_for_each_entry(link, &cset->cgrp_links, cgrp_link) {
6568		struct cgroup *c = link->cgrp;
6569
6570		cgroup_name(c, name_buf, NAME_MAX + 1);
6571		seq_printf(seq, "Root %d group %s\n",
6572			   c->root->hierarchy_id, name_buf);
6573	}
6574	rcu_read_unlock();
6575	spin_unlock_irq(&css_set_lock);
6576	kfree(name_buf);
6577	return 0;
6578}
6579
6580#define MAX_TASKS_SHOWN_PER_CSS 25
6581static int cgroup_css_links_read(struct seq_file *seq, void *v)
6582{
6583	struct cgroup_subsys_state *css = seq_css(seq);
6584	struct cgrp_cset_link *link;
6585
6586	spin_lock_irq(&css_set_lock);
6587	list_for_each_entry(link, &css->cgroup->cset_links, cset_link) {
6588		struct css_set *cset = link->cset;
6589		struct task_struct *task;
6590		int count = 0;
6591
6592		seq_printf(seq, "css_set %p\n", cset);
6593
6594		list_for_each_entry(task, &cset->tasks, cg_list) {
6595			if (count++ > MAX_TASKS_SHOWN_PER_CSS)
6596				goto overflow;
6597			seq_printf(seq, "  task %d\n", task_pid_vnr(task));
6598		}
6599
6600		list_for_each_entry(task, &cset->mg_tasks, cg_list) {
6601			if (count++ > MAX_TASKS_SHOWN_PER_CSS)
6602				goto overflow;
6603			seq_printf(seq, "  task %d\n", task_pid_vnr(task));
6604		}
6605		continue;
6606	overflow:
6607		seq_puts(seq, "  ...\n");
6608	}
6609	spin_unlock_irq(&css_set_lock);
6610	return 0;
6611}
6612
6613static u64 releasable_read(struct cgroup_subsys_state *css, struct cftype *cft)
6614{
6615	return (!cgroup_is_populated(css->cgroup) &&
6616		!css_has_online_children(&css->cgroup->self));
6617}
6618
6619static struct cftype debug_files[] =  {
6620	{
6621		.name = "taskcount",
6622		.read_u64 = debug_taskcount_read,
6623	},
6624
6625	{
6626		.name = "current_css_set",
6627		.read_u64 = current_css_set_read,
6628	},
6629
6630	{
6631		.name = "current_css_set_refcount",
6632		.read_u64 = current_css_set_refcount_read,
6633	},
6634
6635	{
6636		.name = "current_css_set_cg_links",
6637		.seq_show = current_css_set_cg_links_read,
6638	},
6639
6640	{
6641		.name = "cgroup_css_links",
6642		.seq_show = cgroup_css_links_read,
6643	},
6644
6645	{
6646		.name = "releasable",
6647		.read_u64 = releasable_read,
6648	},
6649
6650	{ }	/* terminate */
6651};
6652
6653struct cgroup_subsys debug_cgrp_subsys = {
6654	.css_alloc = debug_css_alloc,
6655	.css_free = debug_css_free,
6656	.legacy_cftypes = debug_files,
6657};
6658#endif /* CONFIG_CGROUP_DEBUG */