Home Home > GIT Browse
summaryrefslogtreecommitdiff
blob: 1dff0a478b45aace3903af82883cb3bf39194774 (plain)
1
2
3
4
5
6
7
8
9
10
11
12
13
14
15
16
17
18
19
20
21
22
23
24
25
26
27
28
29
30
31
32
33
34
35
36
37
38
39
40
41
42
43
44
45
46
47
48
49
50
51
52
53
54
55
56
57
58
59
60
61
62
63
64
65
66
67
68
69
70
71
72
73
74
75
76
77
78
79
80
81
82
83
84
85
86
87
88
89
90
91
92
93
94
95
96
97
98
99
100
101
102
103
104
105
106
107
108
109
110
111
112
113
114
115
116
117
118
119
120
121
122
123
124
125
126
127
128
129
130
131
132
133
134
135
136
137
138
139
140
141
142
143
144
145
146
147
148
149
150
151
152
153
154
155
156
157
158
159
160
161
162
163
164
165
166
167
168
169
170
171
172
173
174
175
176
177
178
179
180
181
182
183
184
185
186
187
188
189
190
191
192
193
194
195
196
197
198
199
200
201
202
203
204
205
206
207
208
209
210
211
212
213
214
215
216
217
218
219
220
221
222
223
224
225
226
227
228
229
230
231
232
233
234
235
236
237
238
239
240
241
242
243
244
245
246
247
248
249
250
251
252
253
254
255
256
257
258
259
260
261
262
263
264
265
266
267
268
269
270
271
272
273
274
275
276
277
278
279
280
281
282
283
284
285
286
287
288
289
290
291
292
293
294
295
296
297
298
299
300
301
302
303
304
305
306
307
308
309
310
311
312
313
314
315
316
317
318
319
320
321
322
323
324
325
326
327
328
329
330
331
332
333
334
335
336
337
338
339
340
341
342
343
344
345
346
347
348
349
350
351
352
353
354
355
356
357
358
359
360
361
362
363
364
365
366
367
368
369
370
371
372
373
374
375
376
377
378
379
380
381
382
383
384
385
386
387
388
389
390
391
392
393
394
395
396
397
398
399
400
401
402
403
404
405
406
407
408
409
410
411
412
413
414
415
416
417
418
419
420
421
422
423
424
425
426
427
428
429
430
431
432
433
434
435
436
437
438
439
440
441
442
443
444
445
446
447
448
449
450
451
452
453
454
455
456
457
458
459
460
461
462
463
464
465
466
467
468
469
470
471
472
473
474
475
476
477
478
479
480
481
482
483
484
485
486
487
488
489
490
491
492
493
494
495
496
497
498
499
500
501
502
503
504
505
506
507
508
509
510
511
512
513
514
515
516
517
518
519
520
521
522
523
524
525
526
527
528
529
530
531
532
533
534
535
536
537
538
539
540
541
542
543
544
545
546
547
548
549
550
551
552
553
554
555
556
557
558
559
560
561
562
563
564
565
566
567
568
569
570
571
572
573
574
575
576
577
578
579
580
581
582
583
584
585
586
587
588
589
590
591
592
593
594
595
596
597
598
599
600
601
602
603
604
605
606
607
608
609
610
611
612
613
614
615
616
617
618
619
620
621
622
623
624
625
626
627
628
629
630
631
632
633
634
635
636
637
638
639
640
641
642
643
644
645
646
647
648
649
650
651
652
653
654
655
656
657
658
659
660
661
662
663
664
665
666
667
668
669
670
671
672
673
674
675
676
677
678
679
680
681
682
683
684
685
686
687
688
689
690
691
692
693
694
695
696
697
698
699
700
701
702
703
704
705
706
707
708
709
710
711
712
713
714
715
716
717
718
719
720
721
722
723
724
725
726
727
728
729
730
731
732
733
734
735
736
737
738
739
740
741
742
743
744
745
746
747
748
749
750
751
752
753
754
755
756
/* SPDX-License-Identifier: GPL-2.0 */
/*
 * linux/cgroup-defs.h - basic definitions for cgroup
 *
 * This file provides basic type and interface.  Include this file directly
 * only if necessary to avoid cyclic dependencies.
 */
#ifndef _LINUX_CGROUP_DEFS_H
#define _LINUX_CGROUP_DEFS_H

#include <linux/limits.h>
#include <linux/list.h>
#include <linux/idr.h>
#include <linux/wait.h>
#include <linux/mutex.h>
#include <linux/rcupdate.h>
#include <linux/refcount.h>
#include <linux/percpu-refcount.h>
#include <linux/percpu-rwsem.h>
#include <linux/workqueue.h>
#include <linux/bpf-cgroup.h>

#ifdef CONFIG_CGROUPS

struct cgroup;
struct cgroup_root;
struct cgroup_subsys;
struct cgroup_taskset;
struct kernfs_node;
struct kernfs_ops;
struct kernfs_open_file;
struct seq_file;

#define MAX_CGROUP_TYPE_NAMELEN 32
#define MAX_CGROUP_ROOT_NAMELEN 64
#define MAX_CFTYPE_NAME		64

/* define the enumeration of all cgroup subsystems */
#define SUBSYS(_x) _x ## _cgrp_id,
enum cgroup_subsys_id {
#include <linux/cgroup_subsys.h>
	CGROUP_SUBSYS_COUNT,
};
#undef SUBSYS

/* bits in struct cgroup_subsys_state flags field */
enum {
	CSS_NO_REF	= (1 << 0), /* no reference counting for this css */
	CSS_ONLINE	= (1 << 1), /* between ->css_online() and ->css_offline() */
	CSS_RELEASED	= (1 << 2), /* refcnt reached zero, released */
	CSS_VISIBLE	= (1 << 3), /* css is visible to userland */
	CSS_DYING	= (1 << 4), /* css is dying */
};

/* bits in struct cgroup flags field */
enum {
	/* Control Group requires release notifications to userspace */
	CGRP_NOTIFY_ON_RELEASE,
	/*
	 * Clone the parent's configuration when creating a new child
	 * cpuset cgroup.  For historical reasons, this option can be
	 * specified at mount time and thus is implemented here.
	 */
	CGRP_CPUSET_CLONE_CHILDREN,
};

/* cgroup_root->flags */
enum {
	CGRP_ROOT_NOPREFIX	= (1 << 1), /* mounted subsystems have no named prefix */
	CGRP_ROOT_XATTR		= (1 << 2), /* supports extended attributes */

	/*
	 * Consider namespaces as delegation boundaries.  If this flag is
	 * set, controller specific interface files in a namespace root
	 * aren't writeable from inside the namespace.
	 */
	CGRP_ROOT_NS_DELEGATE	= (1 << 3),

	/*
	 * Enable cpuset controller in v1 cgroup to use v2 behavior.
	 */
	CGRP_ROOT_CPUSET_V2_MODE = (1 << 4),
};

/* cftype->flags */
enum {
	CFTYPE_ONLY_ON_ROOT	= (1 << 0),	/* only create on root cgrp */
	CFTYPE_NOT_ON_ROOT	= (1 << 1),	/* don't create on root cgrp */
	CFTYPE_NS_DELEGATABLE	= (1 << 2),	/* writeable beyond delegation boundaries */

	CFTYPE_NO_PREFIX	= (1 << 3),	/* (DON'T USE FOR NEW FILES) no subsys prefix */
	CFTYPE_WORLD_WRITABLE	= (1 << 4),	/* (DON'T USE FOR NEW FILES) S_IWUGO */

	/* internal flags, do not use outside cgroup core proper */
	__CFTYPE_ONLY_ON_DFL	= (1 << 16),	/* only on default hierarchy */
	__CFTYPE_NOT_ON_DFL	= (1 << 17),	/* not on default hierarchy */
};

/*
 * cgroup_file is the handle for a file instance created in a cgroup which
 * is used, for example, to generate file changed notifications.  This can
 * be obtained by setting cftype->file_offset.
 */
struct cgroup_file {
	/* do not access any fields from outside cgroup core */
	struct kernfs_node *kn;
};

/*
 * Per-subsystem/per-cgroup state maintained by the system.  This is the
 * fundamental structural building block that controllers deal with.
 *
 * Fields marked with "PI:" are public and immutable and may be accessed
 * directly without synchronization.
 */
struct cgroup_subsys_state {
	/* PI: the cgroup that this css is attached to */
	struct cgroup *cgroup;

	/* PI: the cgroup subsystem that this css is attached to */
	struct cgroup_subsys *ss;

	/* reference count - access via css_[try]get() and css_put() */
	struct percpu_ref refcnt;

	/* siblings list anchored at the parent's ->children */
	struct list_head sibling;
	struct list_head children;

	/*
	 * PI: Subsys-unique ID.  0 is unused and root is always 1.  The
	 * matching css can be looked up using css_from_id().
	 */
	int id;

	unsigned int flags;

	/*
	 * Monotonically increasing unique serial number which defines a
	 * uniform order among all csses.  It's guaranteed that all
	 * ->children lists are in the ascending order of ->serial_nr and
	 * used to allow interrupting and resuming iterations.
	 */
	u64 serial_nr;

	/*
	 * Incremented by online self and children.  Used to guarantee that
	 * parents are not offlined before their children.
	 */
	atomic_t online_cnt;

	/* percpu_ref killing and RCU release */
	struct rcu_head rcu_head;
	struct work_struct destroy_work;

	/*
	 * PI: the parent css.	Placed here for cache proximity to following
	 * fields of the containing structure.
	 */
	struct cgroup_subsys_state *parent;
};

/*
 * A css_set is a structure holding pointers to a set of
 * cgroup_subsys_state objects. This saves space in the task struct
 * object and speeds up fork()/exit(), since a single inc/dec and a
 * list_add()/del() can bump the reference count on the entire cgroup
 * set for a task.
 */
struct css_set {
	/*
	 * Set of subsystem states, one for each subsystem. This array is
	 * immutable after creation apart from the init_css_set during
	 * subsystem registration (at boot time).
	 */
	struct cgroup_subsys_state *subsys[CGROUP_SUBSYS_COUNT];

	/* reference count */
	refcount_t refcount;

	/*
	 * For a domain cgroup, the following points to self.  If threaded,
	 * to the matching cset of the nearest domain ancestor.  The
	 * dom_cset provides access to the domain cgroup and its csses to
	 * which domain level resource consumptions should be charged.
	 */
	struct css_set *dom_cset;

	/* the default cgroup associated with this css_set */
	struct cgroup *dfl_cgrp;

	/* internal task count, protected by css_set_lock */
	int nr_tasks;

	/*
	 * Lists running through all tasks using this cgroup group.
	 * mg_tasks lists tasks which belong to this cset but are in the
	 * process of being migrated out or in.  Protected by
	 * css_set_rwsem, but, during migration, once tasks are moved to
	 * mg_tasks, it can be read safely while holding cgroup_mutex.
	 */
	struct list_head tasks;
	struct list_head mg_tasks;

	/* all css_task_iters currently walking this cset */
	struct list_head task_iters;

	/*
	 * On the default hierarhcy, ->subsys[ssid] may point to a css
	 * attached to an ancestor instead of the cgroup this css_set is
	 * associated with.  The following node is anchored at
	 * ->subsys[ssid]->cgroup->e_csets[ssid] and provides a way to
	 * iterate through all css's attached to a given cgroup.
	 */
	struct list_head e_cset_node[CGROUP_SUBSYS_COUNT];

	/* all threaded csets whose ->dom_cset points to this cset */
	struct list_head threaded_csets;
	struct list_head threaded_csets_node;

	/*
	 * List running through all cgroup groups in the same hash
	 * slot. Protected by css_set_lock
	 */
	struct hlist_node hlist;

	/*
	 * List of cgrp_cset_links pointing at cgroups referenced from this
	 * css_set.  Protected by css_set_lock.
	 */
	struct list_head cgrp_links;

	/*
	 * List of csets participating in the on-going migration either as
	 * source or destination.  Protected by cgroup_mutex.
	 */
	struct list_head mg_preload_node;
	struct list_head mg_node;

	/*
	 * If this cset is acting as the source of migration the following
	 * two fields are set.  mg_src_cgrp and mg_dst_cgrp are
	 * respectively the source and destination cgroups of the on-going
	 * migration.  mg_dst_cset is the destination cset the target tasks
	 * on this cset should be migrated to.  Protected by cgroup_mutex.
	 */
	struct cgroup *mg_src_cgrp;
	struct cgroup *mg_dst_cgrp;
	struct css_set *mg_dst_cset;

	/* dead and being drained, ignore for migration */
	bool dead;

	/* For RCU-protected deletion */
	struct rcu_head rcu_head;
};

struct cgroup {
	/* self css with NULL ->ss, points back to this cgroup */
	struct cgroup_subsys_state self;

	unsigned long flags;		/* "unsigned long" so bitops work */

	/*
	 * idr allocated in-hierarchy ID.
	 *
	 * ID 0 is not used, the ID of the root cgroup is always 1, and a
	 * new cgroup will be assigned with a smallest available ID.
	 *
	 * Allocating/Removing ID must be protected by cgroup_mutex.
	 */
	int id;

	/*
	 * The depth this cgroup is at.  The root is at depth zero and each
	 * step down the hierarchy increments the level.  This along with
	 * ancestor_ids[] can determine whether a given cgroup is a
	 * descendant of another without traversing the hierarchy.
	 */
	int level;

	/* Maximum allowed descent tree depth */
	int max_depth;

	/*
	 * Keep track of total numbers of visible and dying descent cgroups.
	 * Dying cgroups are cgroups which were deleted by a user,
	 * but are still existing because someone else is holding a reference.
	 * max_descendants is a maximum allowed number of descent cgroups.
	 */
	int nr_descendants;
	int nr_dying_descendants;
	int max_descendants;

	/*
	 * Each non-empty css_set associated with this cgroup contributes
	 * one to nr_populated_csets.  The counter is zero iff this cgroup
	 * doesn't have any tasks.
	 *
	 * All children which have non-zero nr_populated_csets and/or
	 * nr_populated_children of their own contribute one to either
	 * nr_populated_domain_children or nr_populated_threaded_children
	 * depending on their type.  Each counter is zero iff all cgroups
	 * of the type in the subtree proper don't have any tasks.
	 */
	int nr_populated_csets;
	int nr_populated_domain_children;
	int nr_populated_threaded_children;

	int nr_threaded_children;	/* # of live threaded child cgroups */

	struct kernfs_node *kn;		/* cgroup kernfs entry */
	struct cgroup_file procs_file;	/* handle for "cgroup.procs" */
	struct cgroup_file events_file;	/* handle for "cgroup.events" */

	/*
	 * The bitmask of subsystems enabled on the child cgroups.
	 * ->subtree_control is the one configured through
	 * "cgroup.subtree_control" while ->child_ss_mask is the effective
	 * one which may have more subsystems enabled.  Controller knobs
	 * are made available iff it's enabled in ->subtree_control.
	 */
	u16 subtree_control;
	u16 subtree_ss_mask;
	u16 old_subtree_control;
	u16 old_subtree_ss_mask;

	/* Private pointers for each registered subsystem */
	struct cgroup_subsys_state __rcu *subsys[CGROUP_SUBSYS_COUNT];

	struct cgroup_root *root;

	/*
	 * List of cgrp_cset_links pointing at css_sets with tasks in this
	 * cgroup.  Protected by css_set_lock.
	 */
	struct list_head cset_links;

	/*
	 * On the default hierarchy, a css_set for a cgroup with some
	 * susbsys disabled will point to css's which are associated with
	 * the closest ancestor which has the subsys enabled.  The
	 * following lists all css_sets which point to this cgroup's css
	 * for the given subsystem.
	 */
	struct list_head e_csets[CGROUP_SUBSYS_COUNT];

	/*
	 * If !threaded, self.  If threaded, it points to the nearest
	 * domain ancestor.  Inside a threaded subtree, cgroups are exempt
	 * from process granularity and no-internal-task constraint.
	 * Domain level resource consumptions which aren't tied to a
	 * specific task are charged to the dom_cgrp.
	 */
	struct cgroup *dom_cgrp;

	/*
	 * list of pidlists, up to two for each namespace (one for procs, one
	 * for tasks); created on demand.
	 */
	struct list_head pidlists;
	struct mutex pidlist_mutex;

	/* used to wait for offlining of csses */
	wait_queue_head_t offline_waitq;

	/* used to schedule release agent */
	struct work_struct release_agent_work;

	/* used to store eBPF programs */
	struct cgroup_bpf bpf;

	/* ids of the ancestors at each level including self */
	int ancestor_ids[];
};

/*
 * A cgroup_root represents the root of a cgroup hierarchy, and may be
 * associated with a kernfs_root to form an active hierarchy.  This is
 * internal to cgroup core.  Don't access directly from controllers.
 */
struct cgroup_root {
	struct kernfs_root *kf_root;

	/* The bitmask of subsystems attached to this hierarchy */
	unsigned int subsys_mask;

	/* Unique id for this hierarchy. */
	int hierarchy_id;

	/* The root cgroup.  Root is destroyed on its release. */
	struct cgroup cgrp;

	/* for cgrp->ancestor_ids[0] */
	int cgrp_ancestor_id_storage;

	/* Number of cgroups in the hierarchy, used only for /proc/cgroups */
	atomic_t nr_cgrps;

	/* A list running through the active hierarchies */
	struct list_head root_list;

	/* Hierarchy-specific flags */
	unsigned int flags;

	/* IDs for cgroups in this hierarchy */
	struct idr cgroup_idr;

	/* The path to use for release notifications. */
	char release_agent_path[PATH_MAX];

	/* The name for this hierarchy - may be empty */
	char name[MAX_CGROUP_ROOT_NAMELEN];
};

/*
 * struct cftype: handler definitions for cgroup control files
 *
 * When reading/writing to a file:
 *	- the cgroup to use is file->f_path.dentry->d_parent->d_fsdata
 *	- the 'cftype' of the file is file->f_path.dentry->d_fsdata
 */
struct cftype {
	/*
	 * By convention, the name should begin with the name of the
	 * subsystem, followed by a period.  Zero length string indicates
	 * end of cftype array.
	 */
	char name[MAX_CFTYPE_NAME];
	unsigned long private;

	/*
	 * The maximum length of string, excluding trailing nul, that can
	 * be passed to write.  If < PAGE_SIZE-1, PAGE_SIZE-1 is assumed.
	 */
	size_t max_write_len;

	/* CFTYPE_* flags */
	unsigned int flags;

	/*
	 * If non-zero, should contain the offset from the start of css to
	 * a struct cgroup_file field.  cgroup will record the handle of
	 * the created file into it.  The recorded handle can be used as
	 * long as the containing css remains accessible.
	 */
	unsigned int file_offset;

	/*
	 * Fields used for internal bookkeeping.  Initialized automatically
	 * during registration.
	 */
	struct cgroup_subsys *ss;	/* NULL for cgroup core files */
	struct list_head node;		/* anchored at ss->cfts */
	struct kernfs_ops *kf_ops;

	int (*open)(struct kernfs_open_file *of);
	void (*release)(struct kernfs_open_file *of);

	/*
	 * read_u64() is a shortcut for the common case of returning a
	 * single integer. Use it in place of read()
	 */
	u64 (*read_u64)(struct cgroup_subsys_state *css, struct cftype *cft);
	/*
	 * read_s64() is a signed version of read_u64()
	 */
	s64 (*read_s64)(struct cgroup_subsys_state *css, struct cftype *cft);

	/* generic seq_file read interface */
	int (*seq_show)(struct seq_file *sf, void *v);

	/* optional ops, implement all or none */
	void *(*seq_start)(struct seq_file *sf, loff_t *ppos);
	void *(*seq_next)(struct seq_file *sf, void *v, loff_t *ppos);
	void (*seq_stop)(struct seq_file *sf, void *v);

	/*
	 * write_u64() is a shortcut for the common case of accepting
	 * a single integer (as parsed by simple_strtoull) from
	 * userspace. Use in place of write(); return 0 or error.
	 */
	int (*write_u64)(struct cgroup_subsys_state *css, struct cftype *cft,
			 u64 val);
	/*
	 * write_s64() is a signed version of write_u64()
	 */
	int (*write_s64)(struct cgroup_subsys_state *css, struct cftype *cft,
			 s64 val);

	/*
	 * write() is the generic write callback which maps directly to
	 * kernfs write operation and overrides all other operations.
	 * Maximum write size is determined by ->max_write_len.  Use
	 * of_css/cft() to access the associated css and cft.
	 */
	ssize_t (*write)(struct kernfs_open_file *of,
			 char *buf, size_t nbytes, loff_t off);

#ifdef CONFIG_DEBUG_LOCK_ALLOC
	struct lock_class_key	lockdep_key;
#endif
};

/*
 * Control Group subsystem type.
 * See Documentation/cgroups/cgroups.txt for details
 */
struct cgroup_subsys {
	struct cgroup_subsys_state *(*css_alloc)(struct cgroup_subsys_state *parent_css);
	int (*css_online)(struct cgroup_subsys_state *css);
	void (*css_offline)(struct cgroup_subsys_state *css);
	void (*css_released)(struct cgroup_subsys_state *css);
	void (*css_free)(struct cgroup_subsys_state *css);
	void (*css_reset)(struct cgroup_subsys_state *css);

	int (*can_attach)(struct cgroup_taskset *tset);
	void (*cancel_attach)(struct cgroup_taskset *tset);
	void (*attach)(struct cgroup_taskset *tset);
	void (*post_attach)(void);
	int (*can_fork)(struct task_struct *task);
	void (*cancel_fork)(struct task_struct *task);
	void (*fork)(struct task_struct *task);
	void (*exit)(struct task_struct *task);
	void (*free)(struct task_struct *task);
	void (*bind)(struct cgroup_subsys_state *root_css);

	bool early_init:1;

	/*
	 * If %true, the controller, on the default hierarchy, doesn't show
	 * up in "cgroup.controllers" or "cgroup.subtree_control", is
	 * implicitly enabled on all cgroups on the default hierarchy, and
	 * bypasses the "no internal process" constraint.  This is for
	 * utility type controllers which is transparent to userland.
	 *
	 * An implicit controller can be stolen from the default hierarchy
	 * anytime and thus must be okay with offline csses from previous
	 * hierarchies coexisting with csses for the current one.
	 */
	bool implicit_on_dfl:1;

	/*
	 * If %true, the controller, supports threaded mode on the default
	 * hierarchy.  In a threaded subtree, both process granularity and
	 * no-internal-process constraint are ignored and a threaded
	 * controllers should be able to handle that.
	 *
	 * Note that as an implicit controller is automatically enabled on
	 * all cgroups on the default hierarchy, it should also be
	 * threaded.  implicit && !threaded is not supported.
	 */
	bool threaded:1;

	/*
	 * If %false, this subsystem is properly hierarchical -
	 * configuration, resource accounting and restriction on a parent
	 * cgroup cover those of its children.  If %true, hierarchy support
	 * is broken in some ways - some subsystems ignore hierarchy
	 * completely while others are only implemented half-way.
	 *
	 * It's now disallowed to create nested cgroups if the subsystem is
	 * broken and cgroup core will emit a warning message on such
	 * cases.  Eventually, all subsystems will be made properly
	 * hierarchical and this will go away.
	 */
	bool broken_hierarchy:1;
	bool warned_broken_hierarchy:1;

	/* the following two fields are initialized automtically during boot */
	int id;
	const char *name;

	/* optional, initialized automatically during boot if not set */
	const char *legacy_name;

	/* link to parent, protected by cgroup_lock() */
	struct cgroup_root *root;

	/* idr for css->id */
	struct idr css_idr;

	/*
	 * List of cftypes.  Each entry is the first entry of an array
	 * terminated by zero length name.
	 */
	struct list_head cfts;

	/*
	 * Base cftypes which are automatically registered.  The two can
	 * point to the same array.
	 */
	struct cftype *dfl_cftypes;	/* for the default hierarchy */
	struct cftype *legacy_cftypes;	/* for the legacy hierarchies */

	/*
	 * A subsystem may depend on other subsystems.  When such subsystem
	 * is enabled on a cgroup, the depended-upon subsystems are enabled
	 * together if available.  Subsystems enabled due to dependency are
	 * not visible to userland until explicitly enabled.  The following
	 * specifies the mask of subsystems that this one depends on.
	 */
	unsigned int depends_on;
};

extern struct percpu_rw_semaphore cgroup_threadgroup_rwsem;

/**
 * cgroup_threadgroup_change_begin - threadgroup exclusion for cgroups
 * @tsk: target task
 *
 * Allows cgroup operations to synchronize against threadgroup changes
 * using a percpu_rw_semaphore.
 */
static inline void cgroup_threadgroup_change_begin(struct task_struct *tsk)
{
	percpu_down_read(&cgroup_threadgroup_rwsem);
}

/**
 * cgroup_threadgroup_change_end - threadgroup exclusion for cgroups
 * @tsk: target task
 *
 * Counterpart of cgroup_threadcgroup_change_begin().
 */
static inline void cgroup_threadgroup_change_end(struct task_struct *tsk)
{
	percpu_up_read(&cgroup_threadgroup_rwsem);
}

#else	/* CONFIG_CGROUPS */

#define CGROUP_SUBSYS_COUNT 0

static inline void cgroup_threadgroup_change_begin(struct task_struct *tsk)
{
	might_sleep();
}

static inline void cgroup_threadgroup_change_end(struct task_struct *tsk) {}

#endif	/* CONFIG_CGROUPS */

#ifdef CONFIG_SOCK_CGROUP_DATA

/*
 * sock_cgroup_data is embedded at sock->sk_cgrp_data and contains
 * per-socket cgroup information except for memcg association.
 *
 * On legacy hierarchies, net_prio and net_cls controllers directly set
 * attributes on each sock which can then be tested by the network layer.
 * On the default hierarchy, each sock is associated with the cgroup it was
 * created in and the networking layer can match the cgroup directly.
 *
 * To avoid carrying all three cgroup related fields separately in sock,
 * sock_cgroup_data overloads (prioidx, classid) and the cgroup pointer.
 * On boot, sock_cgroup_data records the cgroup that the sock was created
 * in so that cgroup2 matches can be made; however, once either net_prio or
 * net_cls starts being used, the area is overriden to carry prioidx and/or
 * classid.  The two modes are distinguished by whether the lowest bit is
 * set.  Clear bit indicates cgroup pointer while set bit prioidx and
 * classid.
 *
 * While userland may start using net_prio or net_cls at any time, once
 * either is used, cgroup2 matching no longer works.  There is no reason to
 * mix the two and this is in line with how legacy and v2 compatibility is
 * handled.  On mode switch, cgroup references which are already being
 * pointed to by socks may be leaked.  While this can be remedied by adding
 * synchronization around sock_cgroup_data, given that the number of leaked
 * cgroups is bound and highly unlikely to be high, this seems to be the
 * better trade-off.
 */
struct sock_cgroup_data {
	union {
#ifdef __LITTLE_ENDIAN
		struct {
			u8	is_data;
			u8	padding;
			u16	prioidx;
			u32	classid;
		} __packed;
#else
		struct {
			u32	classid;
			u16	prioidx;
			u8	padding;
			u8	is_data;
		} __packed;
#endif
		u64		val;
	};
};

/*
 * There's a theoretical window where the following accessors race with
 * updaters and return part of the previous pointer as the prioidx or
 * classid.  Such races are short-lived and the result isn't critical.
 */
static inline u16 sock_cgroup_prioidx(struct sock_cgroup_data *skcd)
{
	/* fallback to 1 which is always the ID of the root cgroup */
	return (skcd->is_data & 1) ? skcd->prioidx : 1;
}

static inline u32 sock_cgroup_classid(struct sock_cgroup_data *skcd)
{
	/* fallback to 0 which is the unconfigured default classid */
	return (skcd->is_data & 1) ? skcd->classid : 0;
}

/*
 * If invoked concurrently, the updaters may clobber each other.  The
 * caller is responsible for synchronization.
 */
static inline void sock_cgroup_set_prioidx(struct sock_cgroup_data *skcd,
					   u16 prioidx)
{
	struct sock_cgroup_data skcd_buf = {{ .val = READ_ONCE(skcd->val) }};

	if (sock_cgroup_prioidx(&skcd_buf) == prioidx)
		return;

	if (!(skcd_buf.is_data & 1)) {
		skcd_buf.val = 0;
		skcd_buf.is_data = 1;
	}

	skcd_buf.prioidx = prioidx;
	WRITE_ONCE(skcd->val, skcd_buf.val);	/* see sock_cgroup_ptr() */
}

static inline void sock_cgroup_set_classid(struct sock_cgroup_data *skcd,
					   u32 classid)
{
	struct sock_cgroup_data skcd_buf = {{ .val = READ_ONCE(skcd->val) }};

	if (sock_cgroup_classid(&skcd_buf) == classid)
		return;

	if (!(skcd_buf.is_data & 1)) {
		skcd_buf.val = 0;
		skcd_buf.is_data = 1;
	}

	skcd_buf.classid = classid;
	WRITE_ONCE(skcd->val, skcd_buf.val);	/* see sock_cgroup_ptr() */
}

#else	/* CONFIG_SOCK_CGROUP_DATA */

struct sock_cgroup_data {
};

#endif	/* CONFIG_SOCK_CGROUP_DATA */

#endif	/* _LINUX_CGROUP_DEFS_H */