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 /* 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/u64_stats_sync.h>
 #include <linux/workqueue.h>
 #include <linux/bpf-cgroup-defs.h>
 #include <linux/psi_types.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;
 struct poll_table_struct;
 
 #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,
 
     /* Control group has to be frozen. */
     CGRP_FREEZE,
 
     /* Cgroup is frozen. */
     CGRP_FROZEN,
 
     /* Control group has to be killed. */
     CGRP_KILL,
 };
 
 /* 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),
 
     /*
      * Reduce latencies on dynamic cgroup modifications such as task
      * migrations and controller on/offs by disabling percpu operation on
      * cgroup_threadgroup_rwsem. This makes hot path operations such as
      * forks and exits into the slow path and more expensive.
      *
      * The static usage pattern of creating a cgroup, enabling controllers,
      * and then seeding it with CLONE_INTO_CGROUP doesn't require write
      * locking cgroup_threadgroup_rwsem and thus doesn't benefit from
      * favordynmod.
      */
     CGRP_ROOT_FAVOR_DYNMODS = (1 << 4),
 
     /*
      * Enable cpuset controller in v1 cgroup to use v2 behavior.
      */
     CGRP_ROOT_CPUSET_V2_MODE = (1 << 16),
 
     /*
      * Enable legacy local memory.events.
      */
     CGRP_ROOT_MEMORY_LOCAL_EVENTS = (1 << 17),
 
     /*
      * Enable recursive subtree protection
      */
     CGRP_ROOT_MEMORY_RECURSIVE_PROT = (1 << 18),
 };
 
 /* 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 */
     CFTYPE_DEBUG        = (1 << 5), /* create when cgroup_debug */
     CFTYPE_PRESSURE     = (1 << 6), /* only if pressure feature is enabled */
 
     /* 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;
     unsigned long notified_at;
     struct timer_list notify_timer;
 };
 
 /*
  * 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;
 
     /* flush target list anchored at cgrp->rstat_css_list */
     struct list_head rstat_css_node;
 
     /*
      * 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 work_struct destroy_work;
     struct rcu_work destroy_rwork;
 
     /*
      * 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;
     struct list_head dying_tasks;
 
     /* all css_task_iters currently walking this cset */
     struct list_head task_iters;
 
     /*
      * On the default hierarchy, ->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_src_preload_node;
     struct list_head mg_dst_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_base_stat {
     struct task_cputime cputime;
 
 #ifdef CONFIG_SCHED_CORE
     u64 forceidle_sum;
 #endif
 };
 
 /*
  * rstat - cgroup scalable recursive statistics.  Accounting is done
  * per-cpu in cgroup_rstat_cpu which is then lazily propagated up the
  * hierarchy on reads.
  *
  * When a stat gets updated, the cgroup_rstat_cpu and its ancestors are
  * linked into the updated tree.  On the following read, propagation only
  * considers and consumes the updated tree.  This makes reading O(the
  * number of descendants which have been active since last read) instead of
  * O(the total number of descendants).
  *
  * This is important because there can be a lot of (draining) cgroups which
  * aren't active and stat may be read frequently.  The combination can
  * become very expensive.  By propagating selectively, increasing reading
  * frequency decreases the cost of each read.
  *
  * This struct hosts both the fields which implement the above -
  * updated_children and updated_next - and the fields which track basic
  * resource statistics on top of it - bsync, bstat and last_bstat.
  */
 struct cgroup_rstat_cpu {
     /*
      * ->bsync protects ->bstat.  These are the only fields which get
      * updated in the hot path.
      */
     struct u64_stats_sync bsync;
     struct cgroup_base_stat bstat;
 
     /*
      * Snapshots at the last reading.  These are used to calculate the
      * deltas to propagate to the global counters.
      */
     struct cgroup_base_stat last_bstat;
 
     /*
      * Child cgroups with stat updates on this cpu since the last read
      * are linked on the parent's ->updated_children through
      * ->updated_next.
      *
      * In addition to being more compact, singly-linked list pointing
      * to the cgroup makes it unnecessary for each per-cpu struct to
      * point back to the associated cgroup.
      *
      * Protected by per-cpu cgroup_rstat_cpu_lock.
      */
     struct cgroup *updated_children;    /* terminated by self cgroup */
     struct cgroup *updated_next;        /* NULL iff not on the list */
 };
 
 struct cgroup_freezer_state {
     /* Should the cgroup and its descendants be frozen. */
     bool freeze;
 
     /* Should the cgroup actually be frozen? */
     int e_freeze;
 
     /* Fields below are protected by css_set_lock */
 
     /* Number of frozen descendant cgroups */
     int nr_frozen_descendants;
 
     /*
      * Number of tasks, which are counted as frozen:
      * frozen, SIGSTOPped, and PTRACEd.
      */
     int nr_frozen_tasks;
 };
 
 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 */
 
     /*
      * 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.
      *
      * nr_descendants and nr_dying_descendants are protected
      * by cgroup_mutex and css_set_lock. It's fine to read them holding
      * any of cgroup_mutex and css_set_lock; for writing both locks
      * should be held.
      */
     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 ->subtree_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;
     struct cgroup *old_dom_cgrp;        /* used while enabling threaded */
 
     /* per-cpu recursive resource statistics */
     struct cgroup_rstat_cpu __percpu *rstat_cpu;
     struct list_head rstat_css_list;
 
     /* cgroup basic resource statistics */
     struct cgroup_base_stat last_bstat;
     struct cgroup_base_stat bstat;
     struct prev_cputime prev_cputime;   /* for printing out cputime */
 
     /*
      * 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 track pressure stalls */
     struct psi_group *psi;
 
     /* used to store eBPF programs */
     struct cgroup_bpf bpf;
 
     /* If there is block congestion on this cgroup. */
     atomic_t congestion_count;
 
     /* Used to store internal freezer state */
     struct cgroup_freezer_state freezer;
 
     /* ids of the ancestors at each level including self */
     u64 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] */
     u64 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;
 
     /* 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);
 
     __poll_t (*poll)(struct kernfs_open_file *of,
              struct poll_table_struct *pt);
 
 #ifdef CONFIG_DEBUG_LOCK_ALLOC
     struct lock_class_key   lockdep_key;
 #endif
 };
 
 /*
  * Control Group subsystem type.
  * See Documentation/admin-guide/cgroup-v1/cgroups.rst 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);
     void (*css_rstat_flush)(struct cgroup_subsys_state *css, int cpu);
     int (*css_extra_stat_show)(struct seq_file *seq,
                    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,
             struct css_set *cset);
     void (*cancel_fork)(struct task_struct *task, struct css_set *cset);
     void (*fork)(struct task_struct *task);
     void (*exit)(struct task_struct *task);
     void (*release)(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;
 
     /* the following two fields are initialized automatically 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.
  */
 struct sock_cgroup_data {
     struct cgroup   *cgroup; /* v2 */
 #ifdef CONFIG_CGROUP_NET_CLASSID
     u32     classid; /* v1 */
 #endif
 #ifdef CONFIG_CGROUP_NET_PRIO
     u16     prioidx; /* v1 */
 #endif
 };
 
 static inline u16 sock_cgroup_prioidx(const struct sock_cgroup_data *skcd)
 {
 #ifdef CONFIG_CGROUP_NET_PRIO
     return READ_ONCE(skcd->prioidx);
 #else
     return 1;
 #endif
 }
 
 static inline u32 sock_cgroup_classid(const struct sock_cgroup_data *skcd)
 {
 #ifdef CONFIG_CGROUP_NET_CLASSID
     return READ_ONCE(skcd->classid);
 #else
     return 0;
 #endif
 }
 
 static inline void sock_cgroup_set_prioidx(struct sock_cgroup_data *skcd,
                        u16 prioidx)
 {
 #ifdef CONFIG_CGROUP_NET_PRIO
     WRITE_ONCE(skcd->prioidx, prioidx);
 #endif
 }
 
 static inline void sock_cgroup_set_classid(struct sock_cgroup_data *skcd,
                        u32 classid)
 {
 #ifdef CONFIG_CGROUP_NET_CLASSID
     WRITE_ONCE(skcd->classid, classid);
 #endif
 }
 
 #else   /* CONFIG_SOCK_CGROUP_DATA */
 
 struct sock_cgroup_data {
 };
 
 #endif  /* CONFIG_SOCK_CGROUP_DATA */
 
 #endif  /* _LINUX_CGROUP_DEFS_H */

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