cgroup: use negative bias on css->refcnt to block css_tryget()

[mirror_ubuntu-zesty-kernel.git] / include / linux / cgroup.h

#ifndef _LINUX_CGROUP_H
#define _LINUX_CGROUP_H
/*
 *  cgroup interface
 *
 *  Copyright (C) 2003 BULL SA
 *  Copyright (C) 2004-2006 Silicon Graphics, Inc.
 *
 */

#include <linux/sched.h>
#include <linux/cpumask.h>
#include <linux/nodemask.h>
#include <linux/rcupdate.h>
#include <linux/cgroupstats.h>
#include <linux/prio_heap.h>
#include <linux/rwsem.h>
#include <linux/idr.h>

#ifdef CONFIG_CGROUPS

struct cgroupfs_root;
struct cgroup_subsys;
struct inode;
struct cgroup;
struct css_id;

extern int cgroup_init_early(void);
extern int cgroup_init(void);
extern void cgroup_lock(void);
extern int cgroup_lock_is_held(void);
extern bool cgroup_lock_live_group(struct cgroup *cgrp);
extern void cgroup_unlock(void);
extern void cgroup_fork(struct task_struct *p);
extern void cgroup_fork_callbacks(struct task_struct *p);
extern void cgroup_post_fork(struct task_struct *p);
extern void cgroup_exit(struct task_struct *p, int run_callbacks);
extern int cgroupstats_build(struct cgroupstats *stats,
                                struct dentry *dentry);
extern int cgroup_load_subsys(struct cgroup_subsys *ss);
extern void cgroup_unload_subsys(struct cgroup_subsys *ss);

extern const struct file_operations proc_cgroup_operations;

/* Define the enumeration of all builtin cgroup subsystems */
#define SUBSYS(_x) _x ## _subsys_id,
enum cgroup_subsys_id {
#include <linux/cgroup_subsys.h>
        CGROUP_BUILTIN_SUBSYS_COUNT
};
#undef SUBSYS
/*
 * This define indicates the maximum number of subsystems that can be loaded
 * at once. We limit to this many since cgroupfs_root has subsys_bits to keep
 * track of all of them.
 */
#define CGROUP_SUBSYS_COUNT (BITS_PER_BYTE*sizeof(unsigned long))

/* Per-subsystem/per-cgroup state maintained by the system. */
struct cgroup_subsys_state {
        /*
         * The cgroup that this subsystem is attached to. Useful
         * for subsystems that want to know about the cgroup
         * hierarchy structure
         */
        struct cgroup *cgroup;

        /*
         * State maintained by the cgroup system to allow subsystems
         * to be "busy". Should be accessed via css_get(),
         * css_tryget() and and css_put().
         */

        atomic_t refcnt;

        unsigned long flags;
        /* ID for this css, if possible */
        struct css_id __rcu *id;
};

/* bits in struct cgroup_subsys_state flags field */
enum {
        CSS_ROOT, /* This CSS is the root of the subsystem */
        CSS_REMOVED, /* This CSS is dead */
};

/* Caller must verify that the css is not for root cgroup */
static inline void __css_get(struct cgroup_subsys_state *css, int count)
{
        atomic_add(count, &css->refcnt);
}

/*
 * Call css_get() to hold a reference on the css; it can be used
 * for a reference obtained via:
 * - an existing ref-counted reference to the css
 * - task->cgroups for a locked task
 */

static inline void css_get(struct cgroup_subsys_state *css)
{
        /* We don't need to reference count the root state */
        if (!test_bit(CSS_ROOT, &css->flags))
                __css_get(css, 1);
}

static inline bool css_is_removed(struct cgroup_subsys_state *css)
{
        return test_bit(CSS_REMOVED, &css->flags);
}

/*
 * Call css_tryget() to take a reference on a css if your existing
 * (known-valid) reference isn't already ref-counted. Returns false if
 * the css has been destroyed.
 */

extern bool __css_tryget(struct cgroup_subsys_state *css);
static inline bool css_tryget(struct cgroup_subsys_state *css)
{
        if (test_bit(CSS_ROOT, &css->flags))
                return true;
        return __css_tryget(css);
}

/*
 * css_put() should be called to release a reference taken by
 * css_get() or css_tryget()
 */

extern void __css_put(struct cgroup_subsys_state *css);
static inline void css_put(struct cgroup_subsys_state *css)
{
        if (!test_bit(CSS_ROOT, &css->flags))
                __css_put(css);
}

/* bits in struct cgroup flags field */
enum {
        /* Control Group is dead */
        CGRP_REMOVED,
        /*
         * Control Group has previously had a child cgroup or a task,
         * but no longer (only if CGRP_NOTIFY_ON_RELEASE is set)
         */
        CGRP_RELEASABLE,
        /* Control Group requires release notifications to userspace */
        CGRP_NOTIFY_ON_RELEASE,
        /*
         * A thread in rmdir() is wating for this cgroup.
         */
        CGRP_WAIT_ON_RMDIR,
        /*
         * Clone cgroup values when creating a new child cgroup
         */
        CGRP_CLONE_CHILDREN,
};

struct cgroup {
        unsigned long flags;            /* "unsigned long" so bitops work */

        /*
         * count users of this cgroup. >0 means busy, but doesn't
         * necessarily indicate the number of tasks in the cgroup
         */
        atomic_t count;

        /*
         * We link our 'sibling' struct into our parent's 'children'.
         * Our children link their 'sibling' into our 'children'.
         */
        struct list_head sibling;       /* my parent's children */
        struct list_head children;      /* my children */
        struct list_head files;         /* my files */

        struct cgroup *parent;          /* my parent */
        struct dentry __rcu *dentry;    /* cgroup fs entry, RCU protected */

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

        struct cgroupfs_root *root;
        struct cgroup *top_cgroup;

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

        struct list_head allcg_node;    /* cgroupfs_root->allcg_list */
        struct list_head cft_q_node;    /* used during cftype add/rm */

        /*
         * Linked list running through all cgroups that can
         * potentially be reaped by the release agent. Protected by
         * release_list_lock
         */
        struct list_head release_list;

        /*
         * 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;

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

        /* List of events which userspace want to receive */
        struct list_head event_list;
        spinlock_t event_list_lock;
};

/*
 * 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 {

        /* Reference count */
        atomic_t refcount;

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

        /*
         * List running through all tasks using this cgroup
         * group. Protected by css_set_lock
         */
        struct list_head tasks;

        /*
         * List of cg_cgroup_link objects on link chains from
         * cgroups referenced from this css_set. Protected by
         * css_set_lock
         */
        struct list_head cg_links;

        /*
         * 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) and modular subsystem
         * loading/unloading.
         */
        struct cgroup_subsys_state *subsys[CGROUP_SUBSYS_COUNT];

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

/*
 * cgroup_map_cb is an abstract callback API for reporting map-valued
 * control files
 */

struct cgroup_map_cb {
        int (*fill)(struct cgroup_map_cb *cb, const char *key, u64 value);
        void *state;
};

/*
 * struct cftype: handler definitions for cgroup control files
 *
 * When reading/writing to a file:
 *      - the cgroup to use is file->f_dentry->d_parent->d_fsdata
 *      - the 'cftype' of the file is file->f_dentry->d_fsdata
 */

/* cftype->flags */
#define CFTYPE_ONLY_ON_ROOT     (1U << 0)       /* only create on root cg */
#define CFTYPE_NOT_ON_ROOT      (1U << 1)       /* don't create onp root cg */

#define MAX_CFTYPE_NAME         64

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];
        int private;
        /*
         * If not 0, file mode is set to this value, otherwise it will
         * be figured out automatically
         */
        umode_t mode;

        /*
         * If non-zero, defines the maximum length of string that can
         * be passed to write_string; defaults to 64
         */
        size_t max_write_len;

        /* CFTYPE_* flags */
        unsigned int flags;

        int (*open)(struct inode *inode, struct file *file);
        ssize_t (*read)(struct cgroup *cgrp, struct cftype *cft,
                        struct file *file,
                        char __user *buf, size_t nbytes, loff_t *ppos);
        /*
         * 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 *cgrp, struct cftype *cft);
        /*
         * read_s64() is a signed version of read_u64()
         */
        s64 (*read_s64)(struct cgroup *cgrp, struct cftype *cft);
        /*
         * read_map() is used for defining a map of key/value
         * pairs. It should call cb->fill(cb, key, value) for each
         * entry. The key/value pairs (and their ordering) should not
         * change between reboots.
         */
        int (*read_map)(struct cgroup *cont, struct cftype *cft,
                        struct cgroup_map_cb *cb);
        /*
         * read_seq_string() is used for outputting a simple sequence
         * using seqfile.
         */
        int (*read_seq_string)(struct cgroup *cont, struct cftype *cft,
                               struct seq_file *m);

        ssize_t (*write)(struct cgroup *cgrp, struct cftype *cft,
                         struct file *file,
                         const char __user *buf, size_t nbytes, loff_t *ppos);

        /*
         * 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 *cgrp, struct cftype *cft, u64 val);
        /*
         * write_s64() is a signed version of write_u64()
         */
        int (*write_s64)(struct cgroup *cgrp, struct cftype *cft, s64 val);

        /*
         * write_string() is passed a nul-terminated kernelspace
         * buffer of maximum length determined by max_write_len.
         * Returns 0 or -ve error code.
         */
        int (*write_string)(struct cgroup *cgrp, struct cftype *cft,
                            const char *buffer);
        /*
         * trigger() callback can be used to get some kick from the
         * userspace, when the actual string written is not important
         * at all. The private field can be used to determine the
         * kick type for multiplexing.
         */
        int (*trigger)(struct cgroup *cgrp, unsigned int event);

        int (*release)(struct inode *inode, struct file *file);

        /*
         * register_event() callback will be used to add new userspace
         * waiter for changes related to the cftype. Implement it if
         * you want to provide this functionality. Use eventfd_signal()
         * on eventfd to send notification to userspace.
         */
        int (*register_event)(struct cgroup *cgrp, struct cftype *cft,
                        struct eventfd_ctx *eventfd, const char *args);
        /*
         * unregister_event() callback will be called when userspace
         * closes the eventfd or on cgroup removing.
         * This callback must be implemented, if you want provide
         * notification functionality.
         */
        void (*unregister_event)(struct cgroup *cgrp, struct cftype *cft,
                        struct eventfd_ctx *eventfd);
};

/*
 * cftype_sets describe cftypes belonging to a subsystem and are chained at
 * cgroup_subsys->cftsets.  Each cftset points to an array of cftypes
 * terminated by zero length name.
 */
struct cftype_set {
        struct list_head                node;   /* chained at subsys->cftsets */
        const struct cftype             *cfts;
};

struct cgroup_scanner {
        struct cgroup *cg;
        int (*test_task)(struct task_struct *p, struct cgroup_scanner *scan);
        void (*process_task)(struct task_struct *p,
                        struct cgroup_scanner *scan);
        struct ptr_heap *heap;
        void *data;
};

int cgroup_add_cftypes(struct cgroup_subsys *ss, const struct cftype *cfts);
int cgroup_rm_cftypes(struct cgroup_subsys *ss, const struct cftype *cfts);

int cgroup_is_removed(const struct cgroup *cgrp);

int cgroup_path(const struct cgroup *cgrp, char *buf, int buflen);

int cgroup_task_count(const struct cgroup *cgrp);

/* Return true if cgrp is a descendant of the task's cgroup */
int cgroup_is_descendant(const struct cgroup *cgrp, struct task_struct *task);

/*
 * When the subsys has to access css and may add permanent refcnt to css,
 * it should take care of racy conditions with rmdir(). Following set of
 * functions, is for stop/restart rmdir if necessary.
 * Because these will call css_get/put, "css" should be alive css.
 *
 *  cgroup_exclude_rmdir();
 *  ...do some jobs which may access arbitrary empty cgroup
 *  cgroup_release_and_wakeup_rmdir();
 *
 *  When someone removes a cgroup while cgroup_exclude_rmdir() holds it,
 *  it sleeps and cgroup_release_and_wakeup_rmdir() will wake him up.
 */

void cgroup_exclude_rmdir(struct cgroup_subsys_state *css);
void cgroup_release_and_wakeup_rmdir(struct cgroup_subsys_state *css);

/*
 * Control Group taskset, used to pass around set of tasks to cgroup_subsys
 * methods.
 */
struct cgroup_taskset;
struct task_struct *cgroup_taskset_first(struct cgroup_taskset *tset);
struct task_struct *cgroup_taskset_next(struct cgroup_taskset *tset);
struct cgroup *cgroup_taskset_cur_cgroup(struct cgroup_taskset *tset);
int cgroup_taskset_size(struct cgroup_taskset *tset);

/**
 * cgroup_taskset_for_each - iterate cgroup_taskset
 * @task: the loop cursor
 * @skip_cgrp: skip if task's cgroup matches this, %NULL to iterate through all
 * @tset: taskset to iterate
 */
#define cgroup_taskset_for_each(task, skip_cgrp, tset)                  \
        for ((task) = cgroup_taskset_first((tset)); (task);             \
             (task) = cgroup_taskset_next((tset)))                      \
                if (!(skip_cgrp) ||                                     \
                    cgroup_taskset_cur_cgroup((tset)) != (skip_cgrp))

/*
 * Control Group subsystem type.
 * See Documentation/cgroups/cgroups.txt for details
 */

struct cgroup_subsys {
        struct cgroup_subsys_state *(*create)(struct cgroup *cgrp);
        int (*pre_destroy)(struct cgroup *cgrp);
        void (*destroy)(struct cgroup *cgrp);
        int (*can_attach)(struct cgroup *cgrp, struct cgroup_taskset *tset);
        void (*cancel_attach)(struct cgroup *cgrp, struct cgroup_taskset *tset);
        void (*attach)(struct cgroup *cgrp, struct cgroup_taskset *tset);
        void (*fork)(struct task_struct *task);
        void (*exit)(struct cgroup *cgrp, struct cgroup *old_cgrp,
                     struct task_struct *task);
        int (*populate)(struct cgroup_subsys *ss, struct cgroup *cgrp);
        void (*post_clone)(struct cgroup *cgrp);
        void (*bind)(struct cgroup *root);

        int subsys_id;
        int active;
        int disabled;
        int early_init;
        /*
         * True if this subsys uses ID. ID is not available before cgroup_init()
         * (not available in early_init time.)
         */
        bool use_id;
#define MAX_CGROUP_TYPE_NAMELEN 32
        const char *name;

        /*
         * Protects sibling/children links of cgroups in this
         * hierarchy, plus protects which hierarchy (or none) the
         * subsystem is a part of (i.e. root/sibling).  To avoid
         * potential deadlocks, the following operations should not be
         * undertaken while holding any hierarchy_mutex:
         *
         * - allocating memory
         * - initiating hotplug events
         */
        struct mutex hierarchy_mutex;
        struct lock_class_key subsys_key;

        /*
         * Link to parent, and list entry in parent's children.
         * Protected by this->hierarchy_mutex and cgroup_lock()
         */
        struct cgroupfs_root *root;
        struct list_head sibling;
        /* used when use_id == true */
        struct idr idr;
        spinlock_t id_lock;

        /* list of cftype_sets */
        struct list_head cftsets;

        /* base cftypes, automatically [de]registered with subsys itself */
        struct cftype *base_cftypes;
        struct cftype_set base_cftset;

        /* should be defined only by modular subsystems */
        struct module *module;
};

#define SUBSYS(_x) extern struct cgroup_subsys _x ## _subsys;
#include <linux/cgroup_subsys.h>
#undef SUBSYS

static inline struct cgroup_subsys_state *cgroup_subsys_state(
        struct cgroup *cgrp, int subsys_id)
{
        return cgrp->subsys[subsys_id];
}

/*
 * function to get the cgroup_subsys_state which allows for extra
 * rcu_dereference_check() conditions, such as locks used during the
 * cgroup_subsys::attach() methods.
 */
#define task_subsys_state_check(task, subsys_id, __c)                   \
        rcu_dereference_check(task->cgroups->subsys[subsys_id],         \
                              lockdep_is_held(&task->alloc_lock) ||     \
                              cgroup_lock_is_held() || (__c))

static inline struct cgroup_subsys_state *
task_subsys_state(struct task_struct *task, int subsys_id)
{
        return task_subsys_state_check(task, subsys_id, false);
}

static inline struct cgroup* task_cgroup(struct task_struct *task,
                                               int subsys_id)
{
        return task_subsys_state(task, subsys_id)->cgroup;
}

/* A cgroup_iter should be treated as an opaque object */
struct cgroup_iter {
        struct list_head *cg_link;
        struct list_head *task;
};

/*
 * To iterate across the tasks in a cgroup:
 *
 * 1) call cgroup_iter_start to initialize an iterator
 *
 * 2) call cgroup_iter_next() to retrieve member tasks until it
 *    returns NULL or until you want to end the iteration
 *
 * 3) call cgroup_iter_end() to destroy the iterator.
 *
 * Or, call cgroup_scan_tasks() to iterate through every task in a
 * cgroup - cgroup_scan_tasks() holds the css_set_lock when calling
 * the test_task() callback, but not while calling the process_task()
 * callback.
 */
void cgroup_iter_start(struct cgroup *cgrp, struct cgroup_iter *it);
struct task_struct *cgroup_iter_next(struct cgroup *cgrp,
                                        struct cgroup_iter *it);
void cgroup_iter_end(struct cgroup *cgrp, struct cgroup_iter *it);
int cgroup_scan_tasks(struct cgroup_scanner *scan);
int cgroup_attach_task(struct cgroup *, struct task_struct *);
int cgroup_attach_task_all(struct task_struct *from, struct task_struct *);

/*
 * CSS ID is ID for cgroup_subsys_state structs under subsys. This only works
 * if cgroup_subsys.use_id == true. It can be used for looking up and scanning.
 * CSS ID is assigned at cgroup allocation (create) automatically
 * and removed when subsys calls free_css_id() function. This is because
 * the lifetime of cgroup_subsys_state is subsys's matter.
 *
 * Looking up and scanning function should be called under rcu_read_lock().
 * Taking cgroup_mutex()/hierarchy_mutex() is not necessary for following calls.
 * But the css returned by this routine can be "not populated yet" or "being
 * destroyed". The caller should check css and cgroup's status.
 */

/*
 * Typically Called at ->destroy(), or somewhere the subsys frees
 * cgroup_subsys_state.
 */
void free_css_id(struct cgroup_subsys *ss, struct cgroup_subsys_state *css);

/* Find a cgroup_subsys_state which has given ID */

struct cgroup_subsys_state *css_lookup(struct cgroup_subsys *ss, int id);

/*
 * Get a cgroup whose id is greater than or equal to id under tree of root.
 * Returning a cgroup_subsys_state or NULL.
 */
struct cgroup_subsys_state *css_get_next(struct cgroup_subsys *ss, int id,
                struct cgroup_subsys_state *root, int *foundid);

/* Returns true if root is ancestor of cg */
bool css_is_ancestor(struct cgroup_subsys_state *cg,
                     const struct cgroup_subsys_state *root);

/* Get id and depth of css */
unsigned short css_id(struct cgroup_subsys_state *css);
unsigned short css_depth(struct cgroup_subsys_state *css);
struct cgroup_subsys_state *cgroup_css_from_dir(struct file *f, int id);

#else /* !CONFIG_CGROUPS */

static inline int cgroup_init_early(void) { return 0; }
static inline int cgroup_init(void) { return 0; }
static inline void cgroup_fork(struct task_struct *p) {}
static inline void cgroup_fork_callbacks(struct task_struct *p) {}
static inline void cgroup_post_fork(struct task_struct *p) {}
static inline void cgroup_exit(struct task_struct *p, int callbacks) {}

static inline void cgroup_lock(void) {}
static inline void cgroup_unlock(void) {}
static inline int cgroupstats_build(struct cgroupstats *stats,
                                        struct dentry *dentry)
{
        return -EINVAL;
}

/* No cgroups - nothing to do */
static inline int cgroup_attach_task_all(struct task_struct *from,
                                         struct task_struct *t)
{
        return 0;
}

#endif /* !CONFIG_CGROUPS */

#endif /* _LINUX_CGROUP_H */