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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.
#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.h>
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_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>
#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 */
* 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.
/* 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.
* Enable cpuset controller in v1 cgroup to use v2 behavior.
/* 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 */
/* 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;
/* 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_base_stat {
struct task_cputime cputime;
* 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 {
/* 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 "" */
* 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;
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 pending_bstat; /* pending from children */
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 store eBPF programs */
struct cgroup_bpf bpf;
/* If there is block congestion on this cgroup. */
atomic_t congestion_count;
/* 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 */
* 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);
struct lock_class_key lockdep_key;
* Control Group subsystem type.
* See Documentation/cgroup-v1/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);
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);
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)
* 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)
#else /* CONFIG_CGROUPS */
static inline void cgroup_threadgroup_change_begin(struct task_struct *tsk)
static inline void cgroup_threadgroup_change_end(struct task_struct *tsk) {}
#endif /* CONFIG_CGROUPS */
* 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 {
struct {
u8 is_data;
u8 padding;
u16 prioidx;
u32 classid;
} __packed;
struct {
u32 classid;
u16 prioidx;
u8 padding;
u8 is_data;
} __packed;
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(const 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(const 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)
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)
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() */
struct sock_cgroup_data {
#endif /* _LINUX_CGROUP_DEFS_H */