include/linux/cgroup-defs.h

   1 /* SPDX-License-Identifier: GPL-2.0 */
   2 /*
   3  * linux/cgroup-defs.h - basic definitions for cgroup
   4  *
   5  * This file provides basic type and interface.  Include this file directly
   6  * only if necessary to avoid cyclic dependencies.
   7  */
   8 #ifndef _LINUX_CGROUP_DEFS_H
   9 #define _LINUX_CGROUP_DEFS_H
  10
  11 #include <linux/limits.h>
  12 #include <linux/list.h>
  13 #include <linux/idr.h>
  14 #include <linux/wait.h>
  15 #include <linux/mutex.h>
  16 #include <linux/rcupdate.h>
  17 #include <linux/refcount.h>
  18 #include <linux/percpu-refcount.h>
  19 #include <linux/percpu-rwsem.h>
  20 #include <linux/workqueue.h>
  21 #include <linux/bpf-cgroup.h>
  22
  23 #ifdef CONFIG_CGROUPS
  24
  25 struct cgroup;
  26 struct cgroup_root;
  27 struct cgroup_subsys;
  28 struct cgroup_taskset;
  29 struct kernfs_node;
  30 struct kernfs_ops;
  31 struct kernfs_open_file;
  32 struct seq_file;
  33
  34 #define MAX_CGROUP_TYPE_NAMELEN 32
  35 #define MAX_CGROUP_ROOT_NAMELEN 64
  36 #define MAX_CFTYPE_NAME         64
  37
  38 /* define the enumeration of all cgroup subsystems */
  39 #define SUBSYS(_x) _x ## _cgrp_id,
  40 enum cgroup_subsys_id {
  41 #include <linux/cgroup_subsys.h>
  42         CGROUP_SUBSYS_COUNT,
  43 };
  44 #undef SUBSYS
  45
  46 /* bits in struct cgroup_subsys_state flags field */
  47 enum {
  48         CSS_NO_REF      = (1 << 0), /* no reference counting for this css */
  49         CSS_ONLINE      = (1 << 1), /* between ->css_online() and ->css_offline() */
  50         CSS_RELEASED    = (1 << 2), /* refcnt reached zero, released */
  51         CSS_VISIBLE     = (1 << 3), /* css is visible to userland */
  52         CSS_DYING       = (1 << 4), /* css is dying */
  53 };
  54
  55 /* bits in struct cgroup flags field */
  56 enum {
  57         /* Control Group requires release notifications to userspace */
  58         CGRP_NOTIFY_ON_RELEASE,
  59         /*
  60          * Clone the parent's configuration when creating a new child
  61          * cpuset cgroup.  For historical reasons, this option can be
  62          * specified at mount time and thus is implemented here.
  63          */
  64         CGRP_CPUSET_CLONE_CHILDREN,
  65 };
  66
  67 /* cgroup_root->flags */
  68 enum {
  69         CGRP_ROOT_NOPREFIX      = (1 << 1), /* mounted subsystems have no named prefix */
  70         CGRP_ROOT_XATTR         = (1 << 2), /* supports extended attributes */
  71
  72         /*
  73          * Consider namespaces as delegation boundaries.  If this flag is
  74          * set, controller specific interface files in a namespace root
  75          * aren't writeable from inside the namespace.
  76          */
  77         CGRP_ROOT_NS_DELEGATE   = (1 << 3),
  78
  79         /*
  80          * Enable cpuset controller in v1 cgroup to use v2 behavior.
  81          */
  82         CGRP_ROOT_CPUSET_V2_MODE = (1 << 4),
  83 };
  84
  85 /* cftype->flags */
  86 enum {
  87         CFTYPE_ONLY_ON_ROOT     = (1 << 0),     /* only create on root cgrp */
  88         CFTYPE_NOT_ON_ROOT      = (1 << 1),     /* don't create on root cgrp */
  89         CFTYPE_NS_DELEGATABLE   = (1 << 2),     /* writeable beyond delegation boundaries */
  90
  91         CFTYPE_NO_PREFIX        = (1 << 3),     /* (DON'T USE FOR NEW FILES) no subsys prefix */
  92         CFTYPE_WORLD_WRITABLE   = (1 << 4),     /* (DON'T USE FOR NEW FILES) S_IWUGO */
  93
  94         /* internal flags, do not use outside cgroup core proper */
  95         __CFTYPE_ONLY_ON_DFL    = (1 << 16),    /* only on default hierarchy */
  96         __CFTYPE_NOT_ON_DFL     = (1 << 17),    /* not on default hierarchy */
  97 };
  98
  99 /*
 100  * cgroup_file is the handle for a file instance created in a cgroup which
 101  * is used, for example, to generate file changed notifications.  This can
 102  * be obtained by setting cftype->file_offset.
 103  */
 104 struct cgroup_file {
 105         /* do not access any fields from outside cgroup core */
 106         struct kernfs_node *kn;
 107 };
 108
 109 /*
 110  * Per-subsystem/per-cgroup state maintained by the system.  This is the
 111  * fundamental structural building block that controllers deal with.
 112  *
 113  * Fields marked with "PI:" are public and immutable and may be accessed
 114  * directly without synchronization.
 115  */
 116 struct cgroup_subsys_state {
 117         /* PI: the cgroup that this css is attached to */
 118         struct cgroup *cgroup;
 119
 120         /* PI: the cgroup subsystem that this css is attached to */
 121         struct cgroup_subsys *ss;
 122
 123         /* reference count - access via css_[try]get() and css_put() */
 124         struct percpu_ref refcnt;
 125
 126         /* siblings list anchored at the parent's ->children */
 127         struct list_head sibling;
 128         struct list_head children;
 129
 130         /*
 131          * PI: Subsys-unique ID.  0 is unused and root is always 1.  The
 132          * matching css can be looked up using css_from_id().
 133          */
 134         int id;
 135
 136         unsigned int flags;
 137
 138         /*
 139          * Monotonically increasing unique serial number which defines a
 140          * uniform order among all csses.  It's guaranteed that all
 141          * ->children lists are in the ascending order of ->serial_nr and
 142          * used to allow interrupting and resuming iterations.
 143          */
 144         u64 serial_nr;
 145
 146         /*
 147          * Incremented by online self and children.  Used to guarantee that
 148          * parents are not offlined before their children.
 149          */
 150         atomic_t online_cnt;
 151
 152         /* percpu_ref killing and RCU release */
 153         struct rcu_head rcu_head;
 154         struct work_struct destroy_work;
 155
 156         /*
 157          * PI: the parent css.  Placed here for cache proximity to following
 158          * fields of the containing structure.
 159          */
 160         struct cgroup_subsys_state *parent;
 161 };
 162
 163 /*
 164  * A css_set is a structure holding pointers to a set of
 165  * cgroup_subsys_state objects. This saves space in the task struct
 166  * object and speeds up fork()/exit(), since a single inc/dec and a
 167  * list_add()/del() can bump the reference count on the entire cgroup
 168  * set for a task.
 169  */
 170 struct css_set {
 171         /*
 172          * Set of subsystem states, one for each subsystem. This array is
 173          * immutable after creation apart from the init_css_set during
 174          * subsystem registration (at boot time).
 175          */
 176         struct cgroup_subsys_state *subsys[CGROUP_SUBSYS_COUNT];
 177
 178         /* reference count */
 179         refcount_t refcount;
 180
 181         /*
 182          * For a domain cgroup, the following points to self.  If threaded,
 183          * to the matching cset of the nearest domain ancestor.  The
 184          * dom_cset provides access to the domain cgroup and its csses to
 185          * which domain level resource consumptions should be charged.
 186          */
 187         struct css_set *dom_cset;
 188
 189         /* the default cgroup associated with this css_set */
 190         struct cgroup *dfl_cgrp;
 191
 192         /* internal task count, protected by css_set_lock */
 193         int nr_tasks;
 194
 195         /*
 196          * Lists running through all tasks using this cgroup group.
 197          * mg_tasks lists tasks which belong to this cset but are in the
 198          * process of being migrated out or in.  Protected by
 199          * css_set_rwsem, but, during migration, once tasks are moved to
 200          * mg_tasks, it can be read safely while holding cgroup_mutex.
 201          */
 202         struct list_head tasks;
 203         struct list_head mg_tasks;
 204
 205         /* all css_task_iters currently walking this cset */
 206         struct list_head task_iters;
 207
 208         /*
 209          * On the default hierarhcy, ->subsys[ssid] may point to a css
 210          * attached to an ancestor instead of the cgroup this css_set is
 211          * associated with.  The following node is anchored at
 212          * ->subsys[ssid]->cgroup->e_csets[ssid] and provides a way to
 213          * iterate through all css's attached to a given cgroup.
 214          */
 215         struct list_head e_cset_node[CGROUP_SUBSYS_COUNT];
 216
 217         /* all threaded csets whose ->dom_cset points to this cset */
 218         struct list_head threaded_csets;
 219         struct list_head threaded_csets_node;
 220
 221         /*
 222          * List running through all cgroup groups in the same hash
 223          * slot. Protected by css_set_lock
 224          */
 225         struct hlist_node hlist;
 226
 227         /*
 228          * List of cgrp_cset_links pointing at cgroups referenced from this
 229          * css_set.  Protected by css_set_lock.
 230          */
 231         struct list_head cgrp_links;
 232
 233         /*
 234          * List of csets participating in the on-going migration either as
 235          * source or destination.  Protected by cgroup_mutex.
 236          */
 237         struct list_head mg_preload_node;
 238         struct list_head mg_node;
 239
 240         /*
 241          * If this cset is acting as the source of migration the following
 242          * two fields are set.  mg_src_cgrp and mg_dst_cgrp are
 243          * respectively the source and destination cgroups of the on-going
 244          * migration.  mg_dst_cset is the destination cset the target tasks
 245          * on this cset should be migrated to.  Protected by cgroup_mutex.
 246          */
 247         struct cgroup *mg_src_cgrp;
 248         struct cgroup *mg_dst_cgrp;
 249         struct css_set *mg_dst_cset;
 250
 251         /* dead and being drained, ignore for migration */
 252         bool dead;
 253
 254         /* For RCU-protected deletion */
 255         struct rcu_head rcu_head;
 256 };
 257
 258 struct cgroup {
 259         /* self css with NULL ->ss, points back to this cgroup */
 260         struct cgroup_subsys_state self;
 261
 262         unsigned long flags;            /* "unsigned long" so bitops work */
 263
 264         /*
 265          * idr allocated in-hierarchy ID.
 266          *
 267          * ID 0 is not used, the ID of the root cgroup is always 1, and a
 268          * new cgroup will be assigned with a smallest available ID.
 269          *
 270          * Allocating/Removing ID must be protected by cgroup_mutex.
 271          */
 272         int id;
 273
 274         /*
 275          * The depth this cgroup is at.  The root is at depth zero and each
 276          * step down the hierarchy increments the level.  This along with
 277          * ancestor_ids[] can determine whether a given cgroup is a
 278          * descendant of another without traversing the hierarchy.
 279          */
 280         int level;
 281
 282         /* Maximum allowed descent tree depth */
 283         int max_depth;
 284
 285         /*
 286          * Keep track of total numbers of visible and dying descent cgroups.
 287          * Dying cgroups are cgroups which were deleted by a user,
 288          * but are still existing because someone else is holding a reference.
 289          * max_descendants is a maximum allowed number of descent cgroups.
 290          */
 291         int nr_descendants;
 292         int nr_dying_descendants;
 293         int max_descendants;
 294
 295         /*
 296          * Each non-empty css_set associated with this cgroup contributes
 297          * one to nr_populated_csets.  The counter is zero iff this cgroup
 298          * doesn't have any tasks.
 299          *
 300          * All children which have non-zero nr_populated_csets and/or
 301          * nr_populated_children of their own contribute one to either
 302          * nr_populated_domain_children or nr_populated_threaded_children
 303          * depending on their type.  Each counter is zero iff all cgroups
 304          * of the type in the subtree proper don't have any tasks.
 305          */
 306         int nr_populated_csets;
 307         int nr_populated_domain_children;
 308         int nr_populated_threaded_children;
 309
 310         int nr_threaded_children;       /* # of live threaded child cgroups */
 311
 312         struct kernfs_node *kn;         /* cgroup kernfs entry */
 313         struct cgroup_file procs_file;  /* handle for "cgroup.procs" */
 314         struct cgroup_file events_file; /* handle for "cgroup.events" */
 315
 316         /*
 317          * The bitmask of subsystems enabled on the child cgroups.
 318          * ->subtree_control is the one configured through
 319          * "cgroup.subtree_control" while ->child_ss_mask is the effective
 320          * one which may have more subsystems enabled.  Controller knobs
 321          * are made available iff it's enabled in ->subtree_control.
 322          */
 323         u16 subtree_control;
 324         u16 subtree_ss_mask;
 325         u16 old_subtree_control;
 326         u16 old_subtree_ss_mask;
 327
 328         /* Private pointers for each registered subsystem */
 329         struct cgroup_subsys_state __rcu *subsys[CGROUP_SUBSYS_COUNT];
 330
 331         struct cgroup_root *root;
 332
 333         /*
 334          * List of cgrp_cset_links pointing at css_sets with tasks in this
 335          * cgroup.  Protected by css_set_lock.
 336          */
 337         struct list_head cset_links;
 338
 339         /*
 340          * On the default hierarchy, a css_set for a cgroup with some
 341          * susbsys disabled will point to css's which are associated with
 342          * the closest ancestor which has the subsys enabled.  The
 343          * following lists all css_sets which point to this cgroup's css
 344          * for the given subsystem.
 345          */
 346         struct list_head e_csets[CGROUP_SUBSYS_COUNT];
 347
 348         /*
 349          * If !threaded, self.  If threaded, it points to the nearest
 350          * domain ancestor.  Inside a threaded subtree, cgroups are exempt
 351          * from process granularity and no-internal-task constraint.
 352          * Domain level resource consumptions which aren't tied to a
 353          * specific task are charged to the dom_cgrp.
 354          */
 355         struct cgroup *dom_cgrp;
 356
 357         /*
 358          * list of pidlists, up to two for each namespace (one for procs, one
 359          * for tasks); created on demand.
 360          */
 361         struct list_head pidlists;
 362         struct mutex pidlist_mutex;
 363
 364         /* used to wait for offlining of csses */
 365         wait_queue_head_t offline_waitq;
 366
 367         /* used to schedule release agent */
 368         struct work_struct release_agent_work;
 369
 370         /* used to store eBPF programs */
 371         struct cgroup_bpf bpf;
 372
 373         /* ids of the ancestors at each level including self */
 374         int ancestor_ids[];
 375 };
 376
 377 /*
 378  * A cgroup_root represents the root of a cgroup hierarchy, and may be
 379  * associated with a kernfs_root to form an active hierarchy.  This is
 380  * internal to cgroup core.  Don't access directly from controllers.
 381  */
 382 struct cgroup_root {
 383         struct kernfs_root *kf_root;
 384
 385         /* The bitmask of subsystems attached to this hierarchy */
 386         unsigned int subsys_mask;
 387
 388         /* Unique id for this hierarchy. */
 389         int hierarchy_id;
 390
 391         /* The root cgroup.  Root is destroyed on its release. */
 392         struct cgroup cgrp;
 393
 394         /* for cgrp->ancestor_ids[0] */
 395         int cgrp_ancestor_id_storage;
 396
 397         /* Number of cgroups in the hierarchy, used only for /proc/cgroups */
 398         atomic_t nr_cgrps;
 399
 400         /* A list running through the active hierarchies */
 401         struct list_head root_list;
 402
 403         /* Hierarchy-specific flags */
 404         unsigned int flags;
 405
 406         /* IDs for cgroups in this hierarchy */
 407         struct idr cgroup_idr;
 408
 409         /* The path to use for release notifications. */
 410         char release_agent_path[PATH_MAX];
 411
 412         /* The name for this hierarchy - may be empty */
 413         char name[MAX_CGROUP_ROOT_NAMELEN];
 414 };
 415
 416 /*
 417  * struct cftype: handler definitions for cgroup control files
 418  *
 419  * When reading/writing to a file:
 420  *      - the cgroup to use is file->f_path.dentry->d_parent->d_fsdata
 421  *      - the 'cftype' of the file is file->f_path.dentry->d_fsdata
 422  */
 423 struct cftype {
 424         /*
 425          * By convention, the name should begin with the name of the
 426          * subsystem, followed by a period.  Zero length string indicates
 427          * end of cftype array.
 428          */
 429         char name[MAX_CFTYPE_NAME];
 430         unsigned long private;
 431
 432         /*
 433          * The maximum length of string, excluding trailing nul, that can
 434          * be passed to write.  If < PAGE_SIZE-1, PAGE_SIZE-1 is assumed.
 435          */
 436         size_t max_write_len;
 437
 438         /* CFTYPE_* flags */
 439         unsigned int flags;
 440
 441         /*
 442          * If non-zero, should contain the offset from the start of css to
 443          * a struct cgroup_file field.  cgroup will record the handle of
 444          * the created file into it.  The recorded handle can be used as
 445          * long as the containing css remains accessible.
 446          */
 447         unsigned int file_offset;
 448
 449         /*
 450          * Fields used for internal bookkeeping.  Initialized automatically
 451          * during registration.
 452          */
 453         struct cgroup_subsys *ss;       /* NULL for cgroup core files */
 454         struct list_head node;          /* anchored at ss->cfts */
 455         struct kernfs_ops *kf_ops;
 456
 457         int (*open)(struct kernfs_open_file *of);
 458         void (*release)(struct kernfs_open_file *of);
 459
 460         /*
 461          * read_u64() is a shortcut for the common case of returning a
 462          * single integer. Use it in place of read()
 463          */
 464         u64 (*read_u64)(struct cgroup_subsys_state *css, struct cftype *cft);
 465         /*
 466          * read_s64() is a signed version of read_u64()
 467          */
 468         s64 (*read_s64)(struct cgroup_subsys_state *css, struct cftype *cft);
 469
 470         /* generic seq_file read interface */
 471         int (*seq_show)(struct seq_file *sf, void *v);
 472
 473         /* optional ops, implement all or none */
 474         void *(*seq_start)(struct seq_file *sf, loff_t *ppos);
 475         void *(*seq_next)(struct seq_file *sf, void *v, loff_t *ppos);
 476         void (*seq_stop)(struct seq_file *sf, void *v);
 477
 478         /*
 479          * write_u64() is a shortcut for the common case of accepting
 480          * a single integer (as parsed by simple_strtoull) from
 481          * userspace. Use in place of write(); return 0 or error.
 482          */
 483         int (*write_u64)(struct cgroup_subsys_state *css, struct cftype *cft,
 484                          u64 val);
 485         /*
 486          * write_s64() is a signed version of write_u64()
 487          */
 488         int (*write_s64)(struct cgroup_subsys_state *css, struct cftype *cft,
 489                          s64 val);
 490
 491         /*
 492          * write() is the generic write callback which maps directly to
 493          * kernfs write operation and overrides all other operations.
 494          * Maximum write size is determined by ->max_write_len.  Use
 495          * of_css/cft() to access the associated css and cft.
 496          */
 497         ssize_t (*write)(struct kernfs_open_file *of,
 498                          char *buf, size_t nbytes, loff_t off);
 499
 500 #ifdef CONFIG_DEBUG_LOCK_ALLOC
 501         struct lock_class_key   lockdep_key;
 502 #endif
 503 };
 504
 505 /*
 506  * Control Group subsystem type.
 507  * See Documentation/cgroups/cgroups.txt for details
 508  */
 509 struct cgroup_subsys {
 510         struct cgroup_subsys_state *(*css_alloc)(struct cgroup_subsys_state *parent_css);
 511         int (*css_online)(struct cgroup_subsys_state *css);
 512         void (*css_offline)(struct cgroup_subsys_state *css);
 513         void (*css_released)(struct cgroup_subsys_state *css);
 514         void (*css_free)(struct cgroup_subsys_state *css);
 515         void (*css_reset)(struct cgroup_subsys_state *css);
 516
 517         int (*can_attach)(struct cgroup_taskset *tset);
 518         void (*cancel_attach)(struct cgroup_taskset *tset);
 519         void (*attach)(struct cgroup_taskset *tset);
 520         void (*post_attach)(void);
 521         int (*can_fork)(struct task_struct *task);
 522         void (*cancel_fork)(struct task_struct *task);
 523         void (*fork)(struct task_struct *task);
 524         void (*exit)(struct task_struct *task);
 525         void (*free)(struct task_struct *task);
 526         void (*bind)(struct cgroup_subsys_state *root_css);
 527
 528         bool early_init:1;
 529
 530         /*
 531          * If %true, the controller, on the default hierarchy, doesn't show
 532          * up in "cgroup.controllers" or "cgroup.subtree_control", is
 533          * implicitly enabled on all cgroups on the default hierarchy, and
 534          * bypasses the "no internal process" constraint.  This is for
 535          * utility type controllers which is transparent to userland.
 536          *
 537          * An implicit controller can be stolen from the default hierarchy
 538          * anytime and thus must be okay with offline csses from previous
 539          * hierarchies coexisting with csses for the current one.
 540          */
 541         bool implicit_on_dfl:1;
 542
 543         /*
 544          * If %true, the controller, supports threaded mode on the default
 545          * hierarchy.  In a threaded subtree, both process granularity and
 546          * no-internal-process constraint are ignored and a threaded
 547          * controllers should be able to handle that.
 548          *
 549          * Note that as an implicit controller is automatically enabled on
 550          * all cgroups on the default hierarchy, it should also be
 551          * threaded.  implicit && !threaded is not supported.
 552          */
 553         bool threaded:1;
 554
 555         /*
 556          * If %false, this subsystem is properly hierarchical -
 557          * configuration, resource accounting and restriction on a parent
 558          * cgroup cover those of its children.  If %true, hierarchy support
 559          * is broken in some ways - some subsystems ignore hierarchy
 560          * completely while others are only implemented half-way.
 561          *
 562          * It's now disallowed to create nested cgroups if the subsystem is
 563          * broken and cgroup core will emit a warning message on such
 564          * cases.  Eventually, all subsystems will be made properly
 565          * hierarchical and this will go away.
 566          */
 567         bool broken_hierarchy:1;
 568         bool warned_broken_hierarchy:1;
 569
 570         /* the following two fields are initialized automtically during boot */
 571         int id;
 572         const char *name;
 573
 574         /* optional, initialized automatically during boot if not set */
 575         const char *legacy_name;
 576
 577         /* link to parent, protected by cgroup_lock() */
 578         struct cgroup_root *root;
 579
 580         /* idr for css->id */
 581         struct idr css_idr;
 582
 583         /*
 584          * List of cftypes.  Each entry is the first entry of an array
 585          * terminated by zero length name.
 586          */
 587         struct list_head cfts;
 588
 589         /*
 590          * Base cftypes which are automatically registered.  The two can
 591          * point to the same array.
 592          */
 593         struct cftype *dfl_cftypes;     /* for the default hierarchy */
 594         struct cftype *legacy_cftypes;  /* for the legacy hierarchies */
 595
 596         /*
 597          * A subsystem may depend on other subsystems.  When such subsystem
 598          * is enabled on a cgroup, the depended-upon subsystems are enabled
 599          * together if available.  Subsystems enabled due to dependency are
 600          * not visible to userland until explicitly enabled.  The following
 601          * specifies the mask of subsystems that this one depends on.
 602          */
 603         unsigned int depends_on;
 604 };
 605
 606 extern struct percpu_rw_semaphore cgroup_threadgroup_rwsem;
 607
 608 /**
 609  * cgroup_threadgroup_change_begin - threadgroup exclusion for cgroups
 610  * @tsk: target task
 611  *
 612  * Allows cgroup operations to synchronize against threadgroup changes
 613  * using a percpu_rw_semaphore.
 614  */
 615 static inline void cgroup_threadgroup_change_begin(struct task_struct *tsk)
 616 {
 617         percpu_down_read(&cgroup_threadgroup_rwsem);
 618 }
 619
 620 /**
 621  * cgroup_threadgroup_change_end - threadgroup exclusion for cgroups
 622  * @tsk: target task
 623  *
 624  * Counterpart of cgroup_threadcgroup_change_begin().
 625  */
 626 static inline void cgroup_threadgroup_change_end(struct task_struct *tsk)
 627 {
 628         percpu_up_read(&cgroup_threadgroup_rwsem);
 629 }
 630
 631 #else   /* CONFIG_CGROUPS */
 632
 633 #define CGROUP_SUBSYS_COUNT 0
 634
 635 static inline void cgroup_threadgroup_change_begin(struct task_struct *tsk)
 636 {
 637         might_sleep();
 638 }
 639
 640 static inline void cgroup_threadgroup_change_end(struct task_struct *tsk) {}
 641
 642 #endif  /* CONFIG_CGROUPS */
 643
 644 #ifdef CONFIG_SOCK_CGROUP_DATA
 645
 646 /*
 647  * sock_cgroup_data is embedded at sock->sk_cgrp_data and contains
 648  * per-socket cgroup information except for memcg association.
 649  *
 650  * On legacy hierarchies, net_prio and net_cls controllers directly set
 651  * attributes on each sock which can then be tested by the network layer.
 652  * On the default hierarchy, each sock is associated with the cgroup it was
 653  * created in and the networking layer can match the cgroup directly.
 654  *
 655  * To avoid carrying all three cgroup related fields separately in sock,
 656  * sock_cgroup_data overloads (prioidx, classid) and the cgroup pointer.
 657  * On boot, sock_cgroup_data records the cgroup that the sock was created
 658  * in so that cgroup2 matches can be made; however, once either net_prio or
 659  * net_cls starts being used, the area is overriden to carry prioidx and/or
 660  * classid.  The two modes are distinguished by whether the lowest bit is
 661  * set.  Clear bit indicates cgroup pointer while set bit prioidx and
 662  * classid.
 663  *
 664  * While userland may start using net_prio or net_cls at any time, once
 665  * either is used, cgroup2 matching no longer works.  There is no reason to
 666  * mix the two and this is in line with how legacy and v2 compatibility is
 667  * handled.  On mode switch, cgroup references which are already being
 668  * pointed to by socks may be leaked.  While this can be remedied by adding
 669  * synchronization around sock_cgroup_data, given that the number of leaked
 670  * cgroups is bound and highly unlikely to be high, this seems to be the
 671  * better trade-off.
 672  */
 673 struct sock_cgroup_data {
 674         union {
 675 #ifdef __LITTLE_ENDIAN
 676                 struct {
 677                         u8      is_data;
 678                         u8      padding;
 679                         u16     prioidx;
 680                         u32     classid;
 681                 } __packed;
 682 #else
 683                 struct {
 684                         u32     classid;
 685                         u16     prioidx;
 686                         u8      padding;
 687                         u8      is_data;
 688                 } __packed;
 689 #endif
 690                 u64             val;
 691         };
 692 };
 693
 694 /*
 695  * There's a theoretical window where the following accessors race with
 696  * updaters and return part of the previous pointer as the prioidx or
 697  * classid.  Such races are short-lived and the result isn't critical.
 698  */
 699 static inline u16 sock_cgroup_prioidx(struct sock_cgroup_data *skcd)
 700 {
 701         /* fallback to 1 which is always the ID of the root cgroup */
 702         return (skcd->is_data & 1) ? skcd->prioidx : 1;
 703 }
 704
 705 static inline u32 sock_cgroup_classid(struct sock_cgroup_data *skcd)
 706 {
 707         /* fallback to 0 which is the unconfigured default classid */
 708         return (skcd->is_data & 1) ? skcd->classid : 0;
 709 }
 710
 711 /*
 712  * If invoked concurrently, the updaters may clobber each other.  The
 713  * caller is responsible for synchronization.
 714  */
 715 static inline void sock_cgroup_set_prioidx(struct sock_cgroup_data *skcd,
 716                                            u16 prioidx)
 717 {
 718         struct sock_cgroup_data skcd_buf = {{ .val = READ_ONCE(skcd->val) }};
 719
 720         if (sock_cgroup_prioidx(&skcd_buf) == prioidx)
 721                 return;
 722
 723         if (!(skcd_buf.is_data & 1)) {
 724                 skcd_buf.val = 0;
 725                 skcd_buf.is_data = 1;
 726         }
 727
 728         skcd_buf.prioidx = prioidx;
 729         WRITE_ONCE(skcd->val, skcd_buf.val);    /* see sock_cgroup_ptr() */
 730 }
 731
 732 static inline void sock_cgroup_set_classid(struct sock_cgroup_data *skcd,
 733                                            u32 classid)
 734 {
 735         struct sock_cgroup_data skcd_buf = {{ .val = READ_ONCE(skcd->val) }};
 736
 737         if (sock_cgroup_classid(&skcd_buf) == classid)
 738                 return;
 739
 740         if (!(skcd_buf.is_data & 1)) {
 741                 skcd_buf.val = 0;
 742                 skcd_buf.is_data = 1;
 743         }
 744
 745         skcd_buf.classid = classid;
 746         WRITE_ONCE(skcd->val, skcd_buf.val);    /* see sock_cgroup_ptr() */
 747 }
 748
 749 #else   /* CONFIG_SOCK_CGROUP_DATA */
 750
 751 struct sock_cgroup_data {
 752 };
 753
 754 #endif  /* CONFIG_SOCK_CGROUP_DATA */
 755
 756 #endif  /* _LINUX_CGROUP_DEFS_H */