/*
 *  Generic process-grouping system.
 *
 *  Based originally on the cpuset system, extracted by Paul Menage
 *  Copyright (C) 2006 Google, Inc
 *
 *  Notifications support
 *  Copyright (C) 2009 Nokia Corporation
 *  Author: Kirill A. Shutemov
 *
 *  Copyright notices from the original cpuset code:
 *  --------------------------------------------------
 *  Copyright (C) 2003 BULL SA.
 *  Copyright (C) 2004-2006 Silicon Graphics, Inc.
 *
 *  Portions derived from Patrick Mochel's sysfs code.
 *  sysfs is Copyright (c) 2001-3 Patrick Mochel
 *
 *  2003-10-10 Written by Simon Derr.
 *  2003-10-22 Updates by Stephen Hemminger.
 *  2004 May-July Rework by Paul Jackson.
 *  ---------------------------------------------------
 *
 *  This file is subject to the terms and conditions of the GNU General Public
 *  License.  See the file COPYING in the main directory of the Linux
 *  distribution for more details.
 */

#define pr_fmt(fmt) KBUILD_MODNAME ": " fmt

#include "cgroup-internal.h"

#include <linux/bpf-cgroup.h>
#include <linux/cred.h>
#include <linux/errno.h>
#include <linux/init_task.h>
#include <linux/kernel.h>
#include <linux/magic.h>
#include <linux/mutex.h>
#include <linux/mount.h>
#include <linux/pagemap.h>
#include <linux/proc_fs.h>
#include <linux/rcupdate.h>
#include <linux/sched.h>
#include <linux/sched/task.h>
#include <linux/slab.h>
#include <linux/spinlock.h>
#include <linux/percpu-rwsem.h>
#include <linux/string.h>
#include <linux/hashtable.h>
#include <linux/idr.h>
#include <linux/kthread.h>
#include <linux/atomic.h>
#include <linux/cpuset.h>
#include <linux/proc_ns.h>
#include <linux/nsproxy.h>
#include <linux/file.h>
#include <linux/fs_parser.h>
#include <linux/sched/cputime.h>
#include <linux/psi.h>
#include <net/sock.h>

#define CREATE_TRACE_POINTS
#include <trace/events/cgroup.h>

#define CGROUP_FILE_NAME_MAX            (MAX_CGROUP_TYPE_NAMELEN +      \
                                         MAX_CFTYPE_NAME + 2)
/* let's not notify more than 100 times per second */
#define CGROUP_FILE_NOTIFY_MIN_INTV     DIV_ROUND_UP(HZ, 100)

/*
 * To avoid confusing the compiler (and generating warnings) with code
 * that attempts to access what would be a 0-element array (i.e. sized
 * to a potentially empty array when CGROUP_SUBSYS_COUNT == 0), this
 * constant expression can be added.
 */
#define CGROUP_HAS_SUBSYS_CONFIG        (CGROUP_SUBSYS_COUNT > 0)

/*
 * cgroup_mutex is the master lock.  Any modification to cgroup or its
 * hierarchy must be performed while holding it.
 *
 * css_set_lock protects task->cgroups pointer, the list of css_set
 * objects, and the chain of tasks off each css_set.
 *
 * These locks are exported if CONFIG_PROVE_RCU so that accessors in
 * cgroup.h can use them for lockdep annotations.
 */
DEFINE_MUTEX(cgroup_mutex);
DEFINE_SPINLOCK(css_set_lock);

#ifdef CONFIG_PROVE_RCU
EXPORT_SYMBOL_GPL(cgroup_mutex);
EXPORT_SYMBOL_GPL(css_set_lock);
#endif

DEFINE_SPINLOCK(trace_cgroup_path_lock);
char trace_cgroup_path[TRACE_CGROUP_PATH_LEN];
static bool cgroup_debug __read_mostly;

/*
 * Protects cgroup_idr and css_idr so that IDs can be released without
 * grabbing cgroup_mutex.
 */
static DEFINE_SPINLOCK(cgroup_idr_lock);

/*
 * Protects cgroup_file->kn for !self csses.  It synchronizes notifications
 * against file removal/re-creation across css hiding.
 */
static DEFINE_SPINLOCK(cgroup_file_kn_lock);

DEFINE_PERCPU_RWSEM(cgroup_threadgroup_rwsem);

#define cgroup_assert_mutex_or_rcu_locked()                             \
        RCU_LOCKDEP_WARN(!rcu_read_lock_held() &&                       \
                           !lockdep_is_held(&cgroup_mutex),             \
                           "cgroup_mutex or RCU read lock required");

/*
 * cgroup destruction makes heavy use of work items and there can be a lot
 * of concurrent destructions.  Use a separate workqueue so that cgroup
 * destruction work items don't end up filling up max_active of system_wq
 * which may lead to deadlock.
 */
static struct workqueue_struct *cgroup_destroy_wq;

/* generate an array of cgroup subsystem pointers */
#define SUBSYS(_x) [_x ## _cgrp_id] = &_x ## _cgrp_subsys,
struct cgroup_subsys *cgroup_subsys[] = {
#include <linux/cgroup_subsys.h>
};
#undef SUBSYS

/* array of cgroup subsystem names */
#define SUBSYS(_x) [_x ## _cgrp_id] = #_x,
static const char *cgroup_subsys_name[] = {
#include <linux/cgroup_subsys.h>
};
#undef SUBSYS

/* array of static_keys for cgroup_subsys_enabled() and cgroup_subsys_on_dfl() */
#define SUBSYS(_x)                                                              \
        DEFINE_STATIC_KEY_TRUE(_x ## _cgrp_subsys_enabled_key);                 \
        DEFINE_STATIC_KEY_TRUE(_x ## _cgrp_subsys_on_dfl_key);                  \
        EXPORT_SYMBOL_GPL(_x ## _cgrp_subsys_enabled_key);                      \
        EXPORT_SYMBOL_GPL(_x ## _cgrp_subsys_on_dfl_key);
#include <linux/cgroup_subsys.h>
#undef SUBSYS

#define SUBSYS(_x) [_x ## _cgrp_id] = &_x ## _cgrp_subsys_enabled_key,
static struct static_key_true *cgroup_subsys_enabled_key[] = {
#include <linux/cgroup_subsys.h>
};
#undef SUBSYS

#define SUBSYS(_x) [_x ## _cgrp_id] = &_x ## _cgrp_subsys_on_dfl_key,
static struct static_key_true *cgroup_subsys_on_dfl_key[] = {
#include <linux/cgroup_subsys.h>
};
#undef SUBSYS

static DEFINE_PER_CPU(struct cgroup_rstat_cpu, cgrp_dfl_root_rstat_cpu);

/* the default hierarchy */
struct cgroup_root cgrp_dfl_root = { .cgrp.rstat_cpu = &cgrp_dfl_root_rstat_cpu };
EXPORT_SYMBOL_GPL(cgrp_dfl_root);

/*
 * The default hierarchy always exists but is hidden until mounted for the
 * first time.  This is for backward compatibility.
 */
static bool cgrp_dfl_visible;

/* some controllers are not supported in the default hierarchy */
static u16 cgrp_dfl_inhibit_ss_mask;

/* some controllers are implicitly enabled on the default hierarchy */
static u16 cgrp_dfl_implicit_ss_mask;

/* some controllers can be threaded on the default hierarchy */
static u16 cgrp_dfl_threaded_ss_mask;

/* The list of hierarchy roots */
LIST_HEAD(cgroup_roots);
static int cgroup_root_count;

/* hierarchy ID allocation and mapping, protected by cgroup_mutex */
static DEFINE_IDR(cgroup_hierarchy_idr);

/*
 * Assign a monotonically increasing serial number to csses.  It guarantees
 * cgroups with bigger numbers are newer than those with smaller numbers.
 * Also, as csses are always appended to the parent's ->children list, it
 * guarantees that sibling csses are always sorted in the ascending serial
 * number order on the list.  Protected by cgroup_mutex.
 */
static u64 css_serial_nr_next = 1;

/*
 * These bitmasks identify subsystems with specific features to avoid
 * having to do iterative checks repeatedly.
 */
static u16 have_fork_callback __read_mostly;
static u16 have_exit_callback __read_mostly;
static u16 have_release_callback __read_mostly;
static u16 have_canfork_callback __read_mostly;

/* cgroup namespace for init task */
struct cgroup_namespace init_cgroup_ns = {
        .ns.count       = REFCOUNT_INIT(2),
        .user_ns        = &init_user_ns,
        .ns.ops         = &cgroupns_operations,
        .ns.inum        = PROC_CGROUP_INIT_INO,
        .root_cset      = &init_css_set,
};

static struct file_system_type cgroup2_fs_type;
static struct cftype cgroup_base_files[];

/* cgroup optional features */
enum cgroup_opt_features {
#ifdef CONFIG_PSI
        OPT_FEATURE_PRESSURE,
#endif
        OPT_FEATURE_COUNT
};

static const char *cgroup_opt_feature_names[OPT_FEATURE_COUNT] = {
#ifdef CONFIG_PSI
        "pressure",
#endif
};

static u16 cgroup_feature_disable_mask __read_mostly;

static int cgroup_apply_control(struct cgroup *cgrp);
static void cgroup_finalize_control(struct cgroup *cgrp, int ret);
static void css_task_iter_skip(struct css_task_iter *it,
                               struct task_struct *task);
static int cgroup_destroy_locked(struct cgroup *cgrp);
static struct cgroup_subsys_state *css_create(struct cgroup *cgrp,
                                              struct cgroup_subsys *ss);
static void css_release(struct percpu_ref *ref);
static void kill_css(struct cgroup_subsys_state *css);
static int cgroup_addrm_files(struct cgroup_subsys_state *css,
                              struct cgroup *cgrp, struct cftype cfts[],
                              bool is_add);

/**
 * cgroup_ssid_enabled - cgroup subsys enabled test by subsys ID
 * @ssid: subsys ID of interest
 *
 * cgroup_subsys_enabled() can only be used with literal subsys names which
 * is fine for individual subsystems but unsuitable for cgroup core.  This
 * is slower static_key_enabled() based test indexed by @ssid.
 */
bool cgroup_ssid_enabled(int ssid)
{
        if (!CGROUP_HAS_SUBSYS_CONFIG)
                return false;

        return static_key_enabled(cgroup_subsys_enabled_key[ssid]);
}

/**
 * cgroup_on_dfl - test whether a cgroup is on the default hierarchy
 * @cgrp: the cgroup of interest
 *
 * The default hierarchy is the v2 interface of cgroup and this function
 * can be used to test whether a cgroup is on the default hierarchy for
 * cases where a subsystem should behave differently depending on the
 * interface version.
 *
 * List of changed behaviors:
 *
 * - Mount options "noprefix", "xattr", "clone_children", "release_agent"
 *   and "name" are disallowed.
 *
 * - When mounting an existing superblock, mount options should match.
 *
 * - rename(2) is disallowed.
 *
 * - "tasks" is removed.  Everything should be at process granularity.  Use
 *   "cgroup.procs" instead.
 *
 * - "cgroup.procs" is not sorted.  pids will be unique unless they got
 *   recycled in-between reads.
 *
 * - "release_agent" and "notify_on_release" are removed.  Replacement
 *   notification mechanism will be implemented.
 *
 * - "cgroup.clone_children" is removed.
 *
 * - "cgroup.subtree_populated" is available.  Its value is 0 if the cgroup
 *   and its descendants contain no task; otherwise, 1.  The file also
 *   generates kernfs notification which can be monitored through poll and
 *   [di]notify when the value of the file changes.
 *
 * - cpuset: tasks will be kept in empty cpusets when hotplug happens and
 *   take masks of ancestors with non-empty cpus/mems, instead of being
 *   moved to an ancestor.
 *
 * - cpuset: a task can be moved into an empty cpuset, and again it takes
 *   masks of ancestors.
 *
 * - blkcg: blk-throttle becomes properly hierarchical.
 *
 * - debug: disallowed on the default hierarchy.
 */
bool cgroup_on_dfl(const struct cgroup *cgrp)
{
        return cgrp->root == &cgrp_dfl_root;
}

/* IDR wrappers which synchronize using cgroup_idr_lock */
static int cgroup_idr_alloc(struct idr *idr, void *ptr, int start, int end,
                            gfp_t gfp_mask)
{
        int ret;

        idr_preload(gfp_mask);
        spin_lock_bh(&cgroup_idr_lock);
        ret = idr_alloc(idr, ptr, start, end, gfp_mask & ~__GFP_DIRECT_RECLAIM);
        spin_unlock_bh(&cgroup_idr_lock);
        idr_preload_end();
        return ret;
}

static void *cgroup_idr_replace(struct idr *idr, void *ptr, int id)
{
        void *ret;

        spin_lock_bh(&cgroup_idr_lock);
        ret = idr_replace(idr, ptr, id);
        spin_unlock_bh(&cgroup_idr_lock);
        return ret;
}

static void cgroup_idr_remove(struct idr *idr, int id)
{
        spin_lock_bh(&cgroup_idr_lock);
        idr_remove(idr, id);
        spin_unlock_bh(&cgroup_idr_lock);
}

static bool cgroup_has_tasks(struct cgroup *cgrp)
{
        return cgrp->nr_populated_csets;
}

bool cgroup_is_threaded(struct cgroup *cgrp)
{
        return cgrp->dom_cgrp != cgrp;
}

/* can @cgrp host both domain and threaded children? */
static bool cgroup_is_mixable(struct cgroup *cgrp)
{
        /*
         * Root isn't under domain level resource control exempting it from
         * the no-internal-process constraint, so it can serve as a thread
         * root and a parent of resource domains at the same time.
         */
        return !cgroup_parent(cgrp);
}

/* can @cgrp become a thread root? Should always be true for a thread root */
static bool cgroup_can_be_thread_root(struct cgroup *cgrp)
{
        /* mixables don't care */
        if (cgroup_is_mixable(cgrp))
                return true;

        /* domain roots can't be nested under threaded */
        if (cgroup_is_threaded(cgrp))
                return false;

        /* can only have either domain or threaded children */
        if (cgrp->nr_populated_domain_children)
                return false;

        /* and no domain controllers can be enabled */
        if (cgrp->subtree_control & ~cgrp_dfl_threaded_ss_mask)
                return false;

        return true;
}

/* is @cgrp root of a threaded subtree? */
bool cgroup_is_thread_root(struct cgroup *cgrp)
{
        /* thread root should be a domain */
        if (cgroup_is_threaded(cgrp))
                return false;

        /* a domain w/ threaded children is a thread root */
        if (cgrp->nr_threaded_children)
                return true;

        /*
         * A domain which has tasks and explicit threaded controllers
         * enabled is a thread root.
         */
        if (cgroup_has_tasks(cgrp) &&
            (cgrp->subtree_control & cgrp_dfl_threaded_ss_mask))
                return true;

        return false;
}

/* a domain which isn't connected to the root w/o brekage can't be used */
static bool cgroup_is_valid_domain(struct cgroup *cgrp)
{
        /* the cgroup itself can be a thread root */
        if (cgroup_is_threaded(cgrp))
                return false;

        /* but the ancestors can't be unless mixable */
        while ((cgrp = cgroup_parent(cgrp))) {
                if (!cgroup_is_mixable(cgrp) && cgroup_is_thread_root(cgrp))
                        return false;
                if (cgroup_is_threaded(cgrp))
                        return false;
        }

        return true;
}

/* subsystems visibly enabled on a cgroup */
static u16 cgroup_control(struct cgroup *cgrp)
{
        struct cgroup *parent = cgroup_parent(cgrp);
        u16 root_ss_mask = cgrp->root->subsys_mask;

        if (parent) {
                u16 ss_mask = parent->subtree_control;

                /* threaded cgroups can only have threaded controllers */
                if (cgroup_is_threaded(cgrp))
                        ss_mask &= cgrp_dfl_threaded_ss_mask;
                return ss_mask;
        }

        if (cgroup_on_dfl(cgrp))
                root_ss_mask &= ~(cgrp_dfl_inhibit_ss_mask |
                                  cgrp_dfl_implicit_ss_mask);
        return root_ss_mask;
}

/* subsystems enabled on a cgroup */
static u16 cgroup_ss_mask(struct cgroup *cgrp)
{
        struct cgroup *parent = cgroup_parent(cgrp);

        if (parent) {
                u16 ss_mask = parent->subtree_ss_mask;

                /* threaded cgroups can only have threaded controllers */
                if (cgroup_is_threaded(cgrp))
                        ss_mask &= cgrp_dfl_threaded_ss_mask;
                return ss_mask;
        }

        return cgrp->root->subsys_mask;
}

/**
 * cgroup_css - obtain a cgroup's css for the specified subsystem
 * @cgrp: the cgroup of interest
 * @ss: the subsystem of interest (%NULL returns @cgrp->self)
 *
 * Return @cgrp's css (cgroup_subsys_state) associated with @ss.  This
 * function must be called either under cgroup_mutex or rcu_read_lock() and
 * the caller is responsible for pinning the returned css if it wants to
 * keep accessing it outside the said locks.  This function may return
 * %NULL if @cgrp doesn't have @subsys_id enabled.
 */
static struct cgroup_subsys_state *cgroup_css(struct cgroup *cgrp,
                                              struct cgroup_subsys *ss)
{
        if (CGROUP_HAS_SUBSYS_CONFIG && ss)
                return rcu_dereference_check(cgrp->subsys[ss->id],
                                        lockdep_is_held(&cgroup_mutex));
        else
                return &cgrp->self;
}

/**
 * cgroup_tryget_css - try to get a cgroup's css for the specified subsystem
 * @cgrp: the cgroup of interest
 * @ss: the subsystem of interest
 *
 * Find and get @cgrp's css associated with @ss.  If the css doesn't exist
 * or is offline, %NULL is returned.
 */
static struct cgroup_subsys_state *cgroup_tryget_css(struct cgroup *cgrp,
                                                     struct cgroup_subsys *ss)
{
        struct cgroup_subsys_state *css;

        rcu_read_lock();
        css = cgroup_css(cgrp, ss);
        if (css && !css_tryget_online(css))
                css = NULL;
        rcu_read_unlock();

        return css;
}

/**
 * cgroup_e_css_by_mask - obtain a cgroup's effective css for the specified ss
 * @cgrp: the cgroup of interest
 * @ss: the subsystem of interest (%NULL returns @cgrp->self)
 *
 * Similar to cgroup_css() but returns the effective css, which is defined
 * as the matching css of the nearest ancestor including self which has @ss
 * enabled.  If @ss is associated with the hierarchy @cgrp is on, this
 * function is guaranteed to return non-NULL css.
 */
static struct cgroup_subsys_state *cgroup_e_css_by_mask(struct cgroup *cgrp,
                                                        struct cgroup_subsys *ss)
{
        lockdep_assert_held(&cgroup_mutex);

        if (!ss)
                return &cgrp->self;

        /*
         * This function is used while updating css associations and thus
         * can't test the csses directly.  Test ss_mask.
         */
        while (!(cgroup_ss_mask(cgrp) & (1 << ss->id))) {
                cgrp = cgroup_parent(cgrp);
                if (!cgrp)
                        return NULL;
        }

        return cgroup_css(cgrp, ss);
}

/**
 * cgroup_e_css - obtain a cgroup's effective css for the specified subsystem
 * @cgrp: the cgroup of interest
 * @ss: the subsystem of interest
 *
 * Find and get the effective css of @cgrp for @ss.  The effective css is
 * defined as the matching css of the nearest ancestor including self which
 * has @ss enabled.  If @ss is not mounted on the hierarchy @cgrp is on,
 * the root css is returned, so this function always returns a valid css.
 *
 * The returned css is not guaranteed to be online, and therefore it is the
 * callers responsibility to try get a reference for it.
 */
struct cgroup_subsys_state *cgroup_e_css(struct cgroup *cgrp,
                                         struct cgroup_subsys *ss)
{
        struct cgroup_subsys_state *css;

        if (!CGROUP_HAS_SUBSYS_CONFIG)
                return NULL;

        do {
                css = cgroup_css(cgrp, ss);

                if (css)
                        return css;
                cgrp = cgroup_parent(cgrp);
        } while (cgrp);

        return init_css_set.subsys[ss->id];
}

/**
 * cgroup_get_e_css - get a cgroup's effective css for the specified subsystem
 * @cgrp: the cgroup of interest
 * @ss: the subsystem of interest
 *
 * Find and get the effective css of @cgrp for @ss.  The effective css is
 * defined as the matching css of the nearest ancestor including self which
 * has @ss enabled.  If @ss is not mounted on the hierarchy @cgrp is on,
 * the root css is returned, so this function always returns a valid css.
 * The returned css must be put using css_put().
 */
struct cgroup_subsys_state *cgroup_get_e_css(struct cgroup *cgrp,
                                             struct cgroup_subsys *ss)
{
        struct cgroup_subsys_state *css;

        if (!CGROUP_HAS_SUBSYS_CONFIG)
                return NULL;

        rcu_read_lock();

        do {
                css = cgroup_css(cgrp, ss);

                if (css && css_tryget_online(css))
                        goto out_unlock;
                cgrp = cgroup_parent(cgrp);
        } while (cgrp);

        css = init_css_set.subsys[ss->id];
        css_get(css);
out_unlock:
        rcu_read_unlock();
        return css;
}
EXPORT_SYMBOL_GPL(cgroup_get_e_css);

static void cgroup_get_live(struct cgroup *cgrp)
{
        WARN_ON_ONCE(cgroup_is_dead(cgrp));
        css_get(&cgrp->self);
}

/**
 * __cgroup_task_count - count the number of tasks in a cgroup. The caller
 * is responsible for taking the css_set_lock.
 * @cgrp: the cgroup in question
 */
int __cgroup_task_count(const struct cgroup *cgrp)
{
        int count = 0;
        struct cgrp_cset_link *link;

        lockdep_assert_held(&css_set_lock);

        list_for_each_entry(link, &cgrp->cset_links, cset_link)
                count += link->cset->nr_tasks;

        return count;
}

/**
 * cgroup_task_count - count the number of tasks in a cgroup.
 * @cgrp: the cgroup in question
 */
int cgroup_task_count(const struct cgroup *cgrp)
{
        int count;

        spin_lock_irq(&css_set_lock);
        count = __cgroup_task_count(cgrp);
        spin_unlock_irq(&css_set_lock);

        return count;
}

struct cgroup_subsys_state *of_css(struct kernfs_open_file *of)
{
        struct cgroup *cgrp = of->kn->parent->priv;
        struct cftype *cft = of_cft(of);

        /*
         * This is open and unprotected implementation of cgroup_css().
         * seq_css() is only called from a kernfs file operation which has
         * an active reference on the file.  Because all the subsystem
         * files are drained before a css is disassociated with a cgroup,
         * the matching css from the cgroup's subsys table is guaranteed to
         * be and stay valid until the enclosing operation is complete.
         */
        if (CGROUP_HAS_SUBSYS_CONFIG && cft->ss)
                return rcu_dereference_raw(cgrp->subsys[cft->ss->id]);
        else
                return &cgrp->self;
}
EXPORT_SYMBOL_GPL(of_css);

/**
 * for_each_css - iterate all css's of a cgroup
 * @css: the iteration cursor
 * @ssid: the index of the subsystem, CGROUP_SUBSYS_COUNT after reaching the end
 * @cgrp: the target cgroup to iterate css's of
 *
 * Should be called under cgroup_[tree_]mutex.
 */
#define for_each_css(css, ssid, cgrp)                                   \
        for ((ssid) = 0; (ssid) < CGROUP_SUBSYS_COUNT; (ssid)++)        \
                if (!((css) = rcu_dereference_check(                    \
                                (cgrp)->subsys[(ssid)],                 \
                                lockdep_is_held(&cgroup_mutex)))) { }   \
                else

/**
 * for_each_e_css - iterate all effective css's of a cgroup
 * @css: the iteration cursor
 * @ssid: the index of the subsystem, CGROUP_SUBSYS_COUNT after reaching the end
 * @cgrp: the target cgroup to iterate css's of
 *
 * Should be called under cgroup_[tree_]mutex.
 */
#define for_each_e_css(css, ssid, cgrp)                                     \
        for ((ssid) = 0; (ssid) < CGROUP_SUBSYS_COUNT; (ssid)++)            \
                if (!((css) = cgroup_e_css_by_mask(cgrp,                    \
                                                   cgroup_subsys[(ssid)]))) \
                        ;                                                   \
                else

/**
 * do_each_subsys_mask - filter for_each_subsys with a bitmask
 * @ss: the iteration cursor
 * @ssid: the index of @ss, CGROUP_SUBSYS_COUNT after reaching the end
 * @ss_mask: the bitmask
 *
 * The block will only run for cases where the ssid-th bit (1 << ssid) of
 * @ss_mask is set.
 */
#define do_each_subsys_mask(ss, ssid, ss_mask) do {                     \
        unsigned long __ss_mask = (ss_mask);                            \
        if (!CGROUP_HAS_SUBSYS_CONFIG) {                                \
                (ssid) = 0;                                             \
                break;                                                  \
        }                                                               \
        for_each_set_bit(ssid, &__ss_mask, CGROUP_SUBSYS_COUNT) {       \
                (ss) = cgroup_subsys[ssid];                             \
                {

#define while_each_subsys_mask()                                        \
                }                                                       \
        }                                                               \
} while (false)

/* iterate over child cgrps, lock should be held throughout iteration */
#define cgroup_for_each_live_child(child, cgrp)                         \
        list_for_each_entry((child), &(cgrp)->self.children, self.sibling) \
                if (({ lockdep_assert_held(&cgroup_mutex);              \
                       cgroup_is_dead(child); }))                       \
                        ;                                               \
                else

/* walk live descendants in pre order */
#define cgroup_for_each_live_descendant_pre(dsct, d_css, cgrp)          \
        css_for_each_descendant_pre((d_css), cgroup_css((cgrp), NULL))  \
                if (({ lockdep_assert_held(&cgroup_mutex);              \
                       (dsct) = (d_css)->cgroup;                        \
                       cgroup_is_dead(dsct); }))                        \
                        ;                                               \
                else

/* walk live descendants in postorder */
#define cgroup_for_each_live_descendant_post(dsct, d_css, cgrp)         \
        css_for_each_descendant_post((d_css), cgroup_css((cgrp), NULL)) \
                if (({ lockdep_assert_held(&cgroup_mutex);              \
                       (dsct) = (d_css)->cgroup;                        \
                       cgroup_is_dead(dsct); }))                        \
                        ;                                               \
                else

/*
 * The default css_set - used by init and its children prior to any
 * hierarchies being mounted. It contains a pointer to the root state
 * for each subsystem. Also used to anchor the list of css_sets. Not
 * reference-counted, to improve performance when child cgroups
 * haven't been created.
 */
struct css_set init_css_set = {
        .refcount               = REFCOUNT_INIT(1),
        .dom_cset               = &init_css_set,
        .tasks                  = LIST_HEAD_INIT(init_css_set.tasks),
        .mg_tasks               = LIST_HEAD_INIT(init_css_set.mg_tasks),
        .dying_tasks            = LIST_HEAD_INIT(init_css_set.dying_tasks),
        .task_iters             = LIST_HEAD_INIT(init_css_set.task_iters),
        .threaded_csets         = LIST_HEAD_INIT(init_css_set.threaded_csets),
        .cgrp_links             = LIST_HEAD_INIT(init_css_set.cgrp_links),
        .mg_src_preload_node    = LIST_HEAD_INIT(init_css_set.mg_src_preload_node),
        .mg_dst_preload_node    = LIST_HEAD_INIT(init_css_set.mg_dst_preload_node),
        .mg_node                = LIST_HEAD_INIT(init_css_set.mg_node),

        /*
         * The following field is re-initialized when this cset gets linked
         * in cgroup_init().  However, let's initialize the field
         * statically too so that the default cgroup can be accessed safely
         * early during boot.
         */
        .dfl_cgrp               = &cgrp_dfl_root.cgrp,
};

static int css_set_count        = 1;    /* 1 for init_css_set */

static bool css_set_threaded(struct css_set *cset)
{
        return cset->dom_cset != cset;
}

/**
 * css_set_populated - does a css_set contain any tasks?
 * @cset: target css_set
 *
 * css_set_populated() should be the same as !!cset->nr_tasks at steady
 * state. However, css_set_populated() can be called while a task is being
 * added to or removed from the linked list before the nr_tasks is
 * properly updated. Hence, we can't just look at ->nr_tasks here.
 */
static bool css_set_populated(struct css_set *cset)
{
        lockdep_assert_held(&css_set_lock);

        return !list_empty(&cset->tasks) || !list_empty(&cset->mg_tasks);
}

/**
 * cgroup_update_populated - update the populated count of a cgroup
 * @cgrp: the target cgroup
 * @populated: inc or dec populated count
 *
 * One of the css_sets associated with @cgrp is either getting its first
 * task or losing the last.  Update @cgrp->nr_populated_* accordingly.  The
 * count is propagated towards root so that a given cgroup's
 * nr_populated_children is zero iff none of its descendants contain any
 * tasks.
 *
 * @cgrp's interface file "cgroup.populated" is zero if both
 * @cgrp->nr_populated_csets and @cgrp->nr_populated_children are zero and
 * 1 otherwise.  When the sum changes from or to zero, userland is notified
 * that the content of the interface file has changed.  This can be used to
 * detect when @cgrp and its descendants become populated or empty.
 */
static void cgroup_update_populated(struct cgroup *cgrp, bool populated)
{
        struct cgroup *child = NULL;
        int adj = populated ? 1 : -1;

        lockdep_assert_held(&css_set_lock);

        do {
                bool was_populated = cgroup_is_populated(cgrp);

                if (!child) {
                        cgrp->nr_populated_csets += adj;
                } else {
                        if (cgroup_is_threaded(child))
                                cgrp->nr_populated_threaded_children += adj;
                        else
                                cgrp->nr_populated_domain_children += adj;
                }

                if (was_populated == cgroup_is_populated(cgrp))
                        break;

                cgroup1_check_for_release(cgrp);
                TRACE_CGROUP_PATH(notify_populated, cgrp,
                                  cgroup_is_populated(cgrp));
                cgroup_file_notify(&cgrp->events_file);

                child = cgrp;
                cgrp = cgroup_parent(cgrp);
        } while (cgrp);
}

/**
 * css_set_update_populated - update populated state of a css_set
 * @cset: target css_set
 * @populated: whether @cset is populated or depopulated
 *
 * @cset is either getting the first task or losing the last.  Update the
 * populated counters of all associated cgroups accordingly.
 */
static void css_set_update_populated(struct css_set *cset, bool populated)
{
        struct cgrp_cset_link *link;

        lockdep_assert_held(&css_set_lock);

        list_for_each_entry(link, &cset->cgrp_links, cgrp_link)
                cgroup_update_populated(link->cgrp, populated);
}

/*
 * @task is leaving, advance task iterators which are pointing to it so
 * that they can resume at the next position.  Advancing an iterator might
 * remove it from the list, use safe walk.  See css_task_iter_skip() for
 * details.
 */
static void css_set_skip_task_iters(struct css_set *cset,
                                    struct task_struct *task)
{
        struct css_task_iter *it, *pos;

        list_for_each_entry_safe(it, pos, &cset->task_iters, iters_node)
                css_task_iter_skip(it, task);
}

/**
 * css_set_move_task - move a task from one css_set to another
 * @task: task being moved
 * @from_cset: css_set @task currently belongs to (may be NULL)
 * @to_cset: new css_set @task is being moved to (may be NULL)
 * @use_mg_tasks: move to @to_cset->mg_tasks instead of ->tasks
 *
 * Move @task from @from_cset to @to_cset.  If @task didn't belong to any
 * css_set, @from_cset can be NULL.  If @task is being disassociated
 * instead of moved, @to_cset can be NULL.
 *
 * This function automatically handles populated counter updates and
 * css_task_iter adjustments but the caller is responsible for managing
 * @from_cset and @to_cset's reference counts.
 */
static void css_set_move_task(struct task_struct *task,
                              struct css_set *from_cset, struct css_set *to_cset,
                              bool use_mg_tasks)
{
        lockdep_assert_held(&css_set_lock);

        if (to_cset && !css_set_populated(to_cset))
                css_set_update_populated(to_cset, true);

        if (from_cset) {
                WARN_ON_ONCE(list_empty(&task->cg_list));

                css_set_skip_task_iters(from_cset, task);
                list_del_init(&task->cg_list);
                if (!css_set_populated(from_cset))
                        css_set_update_populated(from_cset, false);
        } else {
                WARN_ON_ONCE(!list_empty(&task->cg_list));
        }

        if (to_cset) {
                /*
                 * We are synchronized through cgroup_threadgroup_rwsem
                 * against PF_EXITING setting such that we can't race
                 * against cgroup_exit()/cgroup_free() dropping the css_set.
                 */
                WARN_ON_ONCE(task->flags & PF_EXITING);

                cgroup_move_task(task, to_cset);
                list_add_tail(&task->cg_list, use_mg_tasks ? &to_cset->mg_tasks :
                                                             &to_cset->tasks);
        }
}

/*
 * hash table for cgroup groups. This improves the performance to find
 * an existing css_set. This hash doesn't (currently) take into
 * account cgroups in empty hierarchies.
 */
#define CSS_SET_HASH_BITS       7
static DEFINE_HASHTABLE(css_set_table, CSS_SET_HASH_BITS);

static unsigned long css_set_hash(struct cgroup_subsys_state *css[])
{
        unsigned long key = 0UL;
        struct cgroup_subsys *ss;
        int i;

        for_each_subsys(ss, i)
                key += (unsigned long)css[i];
        key = (key >> 16) ^ key;

        return key;
}

void put_css_set_locked(struct css_set *cset)
{
        struct cgrp_cset_link *link, *tmp_link;
        struct cgroup_subsys *ss;
        int ssid;

        lockdep_assert_held(&css_set_lock);

        if (!refcount_dec_and_test(&cset->refcount))
                return;

        WARN_ON_ONCE(!list_empty(&cset->threaded_csets));

        /* This css_set is dead. Unlink it and release cgroup and css refs */
        for_each_subsys(ss, ssid) {
                list_del(&cset->e_cset_node[ssid]);
                css_put(cset->subsys[ssid]);
        }
        hash_del(&cset->hlist);
        css_set_count--;

        list_for_each_entry_safe(link, tmp_link, &cset->cgrp_links, cgrp_link) {
                list_del(&link->cset_link);
                list_del(&link->cgrp_link);
                if (cgroup_parent(link->cgrp))
                        cgroup_put(link->cgrp);
                kfree(link);
        }

        if (css_set_threaded(cset)) {
                list_del(&cset->threaded_csets_node);
                put_css_set_locked(cset->dom_cset);
        }

        kfree_rcu(cset, rcu_head);
}

/**
 * compare_css_sets - helper function for find_existing_css_set().
 * @cset: candidate css_set being tested
 * @old_cset: existing css_set for a task
 * @new_cgrp: cgroup that's being entered by the task
 * @template: desired set of css pointers in css_set (pre-calculated)
 *
 * Returns true if "cset" matches "old_cset" except for the hierarchy
 * which "new_cgrp" belongs to, for which it should match "new_cgrp".
 */

static bool compare_css_sets(struct css_set *cset,
                             struct css_set *old_cset,
                             struct cgroup *new_cgrp,
                             struct cgroup_subsys_state *template[])
{
        struct cgroup *new_dfl_cgrp;
        struct list_head *l1, *l2;

        /*
         * On the default hierarchy, there can be csets which are
         * associated with the same set of cgroups but different csses.
         * Let's first ensure that csses match.
         */
        if (memcmp(template, cset->subsys, sizeof(cset->subsys)))
                return false;


        /* @cset's domain should match the default cgroup's */
        if (cgroup_on_dfl(new_cgrp))
                new_dfl_cgrp = new_cgrp;
        else
                new_dfl_cgrp = old_cset->dfl_cgrp;

        if (new_dfl_cgrp->dom_cgrp != cset->dom_cset->dfl_cgrp)
                return false;

        /*
         * Compare cgroup pointers in order to distinguish between
         * different cgroups in hierarchies.  As different cgroups may
         * share the same effective css, this comparison is always
         * necessary.
         */
        l1 = &cset->cgrp_links;
        l2 = &old_cset->cgrp_links;
        while (1) {
                struct cgrp_cset_link *link1, *link2;
                struct cgroup *cgrp1, *cgrp2;

                l1 = l1->next;
                l2 = l2->next;
                /* See if we reached the end - both lists are equal length. */
                if (l1 == &cset->cgrp_links) {
                        BUG_ON(l2 != &old_cset->cgrp_links);
                        break;
                } else {
                        BUG_ON(l2 == &old_cset->cgrp_links);
                }
                /* Locate the cgroups associated with these links. */
                link1 = list_entry(l1, struct cgrp_cset_link, cgrp_link);
                link2 = list_entry(l2, struct cgrp_cset_link, cgrp_link);
                cgrp1 = link1->cgrp;
                cgrp2 = link2->cgrp;
                /* Hierarchies should be linked in the same order. */
                BUG_ON(cgrp1->root != cgrp2->root);

                /*
                 * If this hierarchy is the hierarchy of the cgroup
                 * that's changing, then we need to check that this
                 * css_set points to the new cgroup; if it's any other
                 * hierarchy, then this css_set should point to the
                 * same cgroup as the old css_set.
                 */
                if (cgrp1->root == new_cgrp->root) {
                        if (cgrp1 != new_cgrp)
                                return false;
                } else {
                        if (cgrp1 != cgrp2)
                                return false;
                }
        }
        return true;
}

/**
 * find_existing_css_set - init css array and find the matching css_set
 * @old_cset: the css_set that we're using before the cgroup transition
 * @cgrp: the cgroup that we're moving into
 * @template: out param for the new set of csses, should be clear on entry
 */
static struct css_set *find_existing_css_set(struct css_set *old_cset,
                                        struct cgroup *cgrp,
                                        struct cgroup_subsys_state *template[])
{
        struct cgroup_root *root = cgrp->root;
        struct cgroup_subsys *ss;
        struct css_set *cset;
        unsigned long key;
        int i;

        /*
         * Build the set of subsystem state objects that we want to see in the
         * new css_set. While subsystems can change globally, the entries here
         * won't change, so no need for locking.
         */
        for_each_subsys(ss, i) {
                if (root->subsys_mask & (1UL << i)) {
                        /*
                         * @ss is in this hierarchy, so we want the
                         * effective css from @cgrp.
                         */
                        template[i] = cgroup_e_css_by_mask(cgrp, ss);
                } else {
                        /*
                         * @ss is not in this hierarchy, so we don't want
                         * to change the css.
                         */
                        template[i] = old_cset->subsys[i];
                }
        }

        key = css_set_hash(template);
        hash_for_each_possible(css_set_table, cset, hlist, key) {
                if (!compare_css_sets(cset, old_cset, cgrp, template))
                        continue;

                /* This css_set matches what we need */
                return cset;
        }

        /* No existing cgroup group matched */
        return NULL;
}

static void free_cgrp_cset_links(struct list_head *links_to_free)
{
        struct cgrp_cset_link *link, *tmp_link;

        list_for_each_entry_safe(link, tmp_link, links_to_free, cset_link) {
                list_del(&link->cset_link);
                kfree(link);
        }
}

/**
 * allocate_cgrp_cset_links - allocate cgrp_cset_links
 * @count: the number of links to allocate
 * @tmp_links: list_head the allocated links are put on
 *
 * Allocate @count cgrp_cset_link structures and chain them on @tmp_links
 * through ->cset_link.  Returns 0 on success or -errno.
 */
static int allocate_cgrp_cset_links(int count, struct list_head *tmp_links)
{
        struct cgrp_cset_link *link;
        int i;

        INIT_LIST_HEAD(tmp_links);

        for (i = 0; i < count; i++) {
                link = kzalloc(sizeof(*link), GFP_KERNEL);
                if (!link) {
                        free_cgrp_cset_links(tmp_links);
                        return -ENOMEM;
                }
                list_add(&link->cset_link, tmp_links);
        }
        return 0;
}

/**
 * link_css_set - a helper function to link a css_set to a cgroup
 * @tmp_links: cgrp_cset_link objects allocated by allocate_cgrp_cset_links()
 * @cset: the css_set to be linked
 * @cgrp: the destination cgroup
 */
static void link_css_set(struct list_head *tmp_links, struct css_set *cset,
                         struct cgroup *cgrp)
{
        struct cgrp_cset_link *link;

        BUG_ON(list_empty(tmp_links));

        if (cgroup_on_dfl(cgrp))
                cset->dfl_cgrp = cgrp;

        link = list_first_entry(tmp_links, struct cgrp_cset_link, cset_link);
        link->cset = cset;
        link->cgrp = cgrp;

        /*
         * Always add links to the tail of the lists so that the lists are
         * in chronological order.
         */
        list_move_tail(&link->cset_link, &cgrp->cset_links);
        list_add_tail(&link->cgrp_link, &cset->cgrp_links);

        if (cgroup_parent(cgrp))
                cgroup_get_live(cgrp);
}

/**
 * find_css_set - return a new css_set with one cgroup updated
 * @old_cset: the baseline css_set
 * @cgrp: the cgroup to be updated
 *
 * Return a new css_set that's equivalent to @old_cset, but with @cgrp
 * substituted into the appropriate hierarchy.
 */
static struct css_set *find_css_set(struct css_set *old_cset,
                                    struct cgroup *cgrp)
{
        struct cgroup_subsys_state *template[CGROUP_SUBSYS_COUNT] = { };
        struct css_set *cset;
        struct list_head tmp_links;
        struct cgrp_cset_link *link;
        struct cgroup_subsys *ss;
        unsigned long key;
        int ssid;

        lockdep_assert_held(&cgroup_mutex);

        /* First see if we already have a cgroup group that matches
         * the desired set */
        spin_lock_irq(&css_set_lock);
        cset = find_existing_css_set(old_cset, cgrp, template);
        if (cset)
                get_css_set(cset);
        spin_unlock_irq(&css_set_lock);

        if (cset)
                return cset;

        cset = kzalloc(sizeof(*cset), GFP_KERNEL);
        if (!cset)
                return NULL;

        /* Allocate all the cgrp_cset_link objects that we'll need */
        if (allocate_cgrp_cset_links(cgroup_root_count, &tmp_links) < 0) {
                kfree(cset);
                return NULL;
        }

        refcount_set(&cset->refcount, 1);
        cset->dom_cset = cset;
        INIT_LIST_HEAD(&cset->tasks);
        INIT_LIST_HEAD(&cset->mg_tasks);
        INIT_LIST_HEAD(&cset->dying_tasks);
        INIT_LIST_HEAD(&cset->task_iters);
        INIT_LIST_HEAD(&cset->threaded_csets);
        INIT_HLIST_NODE(&cset->hlist);
        INIT_LIST_HEAD(&cset->cgrp_links);
        INIT_LIST_HEAD(&cset->mg_src_preload_node);
        INIT_LIST_HEAD(&cset->mg_dst_preload_node);
        INIT_LIST_HEAD(&cset->mg_node);

        /* Copy the set of subsystem state objects generated in
         * find_existing_css_set() */
        memcpy(cset->subsys, template, sizeof(cset->subsys));

        spin_lock_irq(&css_set_lock);
        /* Add reference counts and links from the new css_set. */
        list_for_each_entry(link, &old_cset->cgrp_links, cgrp_link) {
                struct cgroup *c = link->cgrp;

                if (c->root == cgrp->root)
                        c = cgrp;
                link_css_set(&tmp_links, cset, c);
        }

        BUG_ON(!list_empty(&tmp_links));

        css_set_count++;

        /* Add @cset to the hash table */
        key = css_set_hash(cset->subsys);
        hash_add(css_set_table, &cset->hlist, key);

        for_each_subsys(ss, ssid) {
                struct cgroup_subsys_state *css = cset->subsys[ssid];

                list_add_tail(&cset->e_cset_node[ssid],
                              &css->cgroup->e_csets[ssid]);
                css_get(css);
        }

        spin_unlock_irq(&css_set_lock);

        /*
         * If @cset should be threaded, look up the matching dom_cset and
         * link them up.  We first fully initialize @cset then look for the
         * dom_cset.  It's simpler this way and safe as @cset is guaranteed
         * to stay empty until we return.
         */
        if (cgroup_is_threaded(cset->dfl_cgrp)) {
                struct css_set *dcset;

                dcset = find_css_set(cset, cset->dfl_cgrp->dom_cgrp);
                if (!dcset) {
                        put_css_set(cset);
                        return NULL;
                }

                spin_lock_irq(&css_set_lock);
                cset->dom_cset = dcset;
                list_add_tail(&cset->threaded_csets_node,
                              &dcset->threaded_csets);
                spin_unlock_irq(&css_set_lock);
        }

        return cset;
}

struct cgroup_root *cgroup_root_from_kf(struct kernfs_root *kf_root)
{
        struct cgroup *root_cgrp = kernfs_root_to_node(kf_root)->priv;

        return root_cgrp->root;
}

void cgroup_favor_dynmods(struct cgroup_root *root, bool favor)
{
        bool favoring = root->flags & CGRP_ROOT_FAVOR_DYNMODS;

        /* see the comment above CGRP_ROOT_FAVOR_DYNMODS definition */
        if (favor && !favoring) {
                rcu_sync_enter(&cgroup_threadgroup_rwsem.rss);
                root->flags |= CGRP_ROOT_FAVOR_DYNMODS;
        } else if (!favor && favoring) {
                rcu_sync_exit(&cgroup_threadgroup_rwsem.rss);
                root->flags &= ~CGRP_ROOT_FAVOR_DYNMODS;
        }
}

static int cgroup_init_root_id(struct cgroup_root *root)
{
        int id;

        lockdep_assert_held(&cgroup_mutex);

        id = idr_alloc_cyclic(&cgroup_hierarchy_idr, root, 0, 0, GFP_KERNEL);
        if (id < 0)
                return id;

        root->hierarchy_id = id;
        return 0;
}

static void cgroup_exit_root_id(struct cgroup_root *root)
{
        lockdep_assert_held(&cgroup_mutex);

        idr_remove(&cgroup_hierarchy_idr, root->hierarchy_id);
}

void cgroup_free_root(struct cgroup_root *root)
{
        kfree(root);
}

static void cgroup_destroy_root(struct cgroup_root *root)
{
        struct cgroup *cgrp = &root->cgrp;
        struct cgrp_cset_link *link, *tmp_link;

        trace_cgroup_destroy_root(root);

        cgroup_lock_and_drain_offline(&cgrp_dfl_root.cgrp);

        BUG_ON(atomic_read(&root->nr_cgrps));
        BUG_ON(!list_empty(&cgrp->self.children));

        /* Rebind all subsystems back to the default hierarchy */
        WARN_ON(rebind_subsystems(&cgrp_dfl_root, root->subsys_mask));

        /*
         * Release all the links from cset_links to this hierarchy's
         * root cgroup
         */
        spin_lock_irq(&css_set_lock);

        list_for_each_entry_safe(link, tmp_link, &cgrp->cset_links, cset_link) {
                list_del(&link->cset_link);
                list_del(&link->cgrp_link);
                kfree(link);
        }

        spin_unlock_irq(&css_set_lock);

        if (!list_empty(&root->root_list)) {
                list_del(&root->root_list);
                cgroup_root_count--;
        }

        cgroup_favor_dynmods(root, false);
        cgroup_exit_root_id(root);

        mutex_unlock(&cgroup_mutex);

        cgroup_rstat_exit(cgrp);
        kernfs_destroy_root(root->kf_root);
        cgroup_free_root(root);
}

static inline struct cgroup *__cset_cgroup_from_root(struct css_set *cset,
                                            struct cgroup_root *root)
{
        struct cgroup *res_cgroup = NULL;

        if (cset == &init_css_set) {
                res_cgroup = &root->cgrp;
        } else if (root == &cgrp_dfl_root) {
                res_cgroup = cset->dfl_cgrp;
        } else {
                struct cgrp_cset_link *link;

                list_for_each_entry(link, &cset->cgrp_links, cgrp_link) {
                        struct cgroup *c = link->cgrp;

                        if (c->root == root) {
                                res_cgroup = c;
                                break;
                        }
                }
        }

        return res_cgroup;
}

/*
 * look up cgroup associated with current task's cgroup namespace on the
 * specified hierarchy
 */
static struct cgroup *
current_cgns_cgroup_from_root(struct cgroup_root *root)
{
        struct cgroup *res = NULL;
        struct css_set *cset;

        lockdep_assert_held(&css_set_lock);

        rcu_read_lock();

        cset = current->nsproxy->cgroup_ns->root_cset;
        res = __cset_cgroup_from_root(cset, root);

        rcu_read_unlock();

        BUG_ON(!res);
        return res;
}

/* look up cgroup associated with given css_set on the specified hierarchy */
static struct cgroup *cset_cgroup_from_root(struct css_set *cset,
                                            struct cgroup_root *root)
{
        struct cgroup *res = NULL;

        lockdep_assert_held(&cgroup_mutex);
        lockdep_assert_held(&css_set_lock);

        res = __cset_cgroup_from_root(cset, root);

        BUG_ON(!res);
        return res;
}

/*
 * Return the cgroup for "task" from the given hierarchy. Must be
 * called with cgroup_mutex and css_set_lock held.
 */
struct cgroup *task_cgroup_from_root(struct task_struct *task,
                                     struct cgroup_root *root)
{
        /*
         * No need to lock the task - since we hold css_set_lock the
         * task can't change groups.
         */
        return cset_cgroup_from_root(task_css_set(task), root);
}

/*
 * A task must hold cgroup_mutex to modify cgroups.
 *
 * Any task can increment and decrement the count field without lock.
 * So in general, code holding cgroup_mutex can't rely on the count
 * field not changing.  However, if the count goes to zero, then only
 * cgroup_attach_task() can increment it again.  Because a count of zero
 * means that no tasks are currently attached, therefore there is no
 * way a task attached to that cgroup can fork (the other way to
 * increment the count).  So code holding cgroup_mutex can safely
 * assume that if the count is zero, it will stay zero. Similarly, if
 * a task holds cgroup_mutex on a cgroup with zero count, it
 * knows that the cgroup won't be removed, as cgroup_rmdir()
 * needs that mutex.
 *
 * A cgroup can only be deleted if both its 'count' of using tasks
 * is zero, and its list of 'children' cgroups is empty.  Since all
 * tasks in the system use _some_ cgroup, and since there is always at
 * least one task in the system (init, pid == 1), therefore, root cgroup
 * always has either children cgroups and/or using tasks.  So we don't
 * need a special hack to ensure that root cgroup cannot be deleted.
 *
 * P.S.  One more locking exception.  RCU is used to guard the
 * update of a tasks cgroup pointer by cgroup_attach_task()
 */

static struct kernfs_syscall_ops cgroup_kf_syscall_ops;

static char *cgroup_file_name(struct cgroup *cgrp, const struct cftype *cft,
                              char *buf)
{
        struct cgroup_subsys *ss = cft->ss;

        if (cft->ss && !(cft->flags & CFTYPE_NO_PREFIX) &&
            !(cgrp->root->flags & CGRP_ROOT_NOPREFIX)) {
                const char *dbg = (cft->flags & CFTYPE_DEBUG) ? ".__DEBUG__." : "";

                snprintf(buf, CGROUP_FILE_NAME_MAX, "%s%s.%s",
                         dbg, cgroup_on_dfl(cgrp) ? ss->name : ss->legacy_name,
                         cft->name);
        } else {
                strscpy(buf, cft->name, CGROUP_FILE_NAME_MAX);
        }
        return buf;
}

/**
 * cgroup_file_mode - deduce file mode of a control file
 * @cft: the control file in question
 *
 * S_IRUGO for read, S_IWUSR for write.
 */
static umode_t cgroup_file_mode(const struct cftype *cft)
{
        umode_t mode = 0;

        if (cft->read_u64 || cft->read_s64 || cft->seq_show)
                mode |= S_IRUGO;

        if (cft->write_u64 || cft->write_s64 || cft->write) {
                if (cft->flags & CFTYPE_WORLD_WRITABLE)
                        mode |= S_IWUGO;
                else
                        mode |= S_IWUSR;
        }

        return mode;
}

/**
 * cgroup_calc_subtree_ss_mask - calculate subtree_ss_mask
 * @subtree_control: the new subtree_control mask to consider
 * @this_ss_mask: available subsystems
 *
 * On the default hierarchy, a subsystem may request other subsystems to be
 * enabled together through its ->depends_on mask.  In such cases, more
 * subsystems than specified in "cgroup.subtree_control" may be enabled.
 *
 * This function calculates which subsystems need to be enabled if
 * @subtree_control is to be applied while restricted to @this_ss_mask.
 */
static u16 cgroup_calc_subtree_ss_mask(u16 subtree_control, u16 this_ss_mask)
{
        u16 cur_ss_mask = subtree_control;
        struct cgroup_subsys *ss;
        int ssid;

        lockdep_assert_held(&cgroup_mutex);

        cur_ss_mask |= cgrp_dfl_implicit_ss_mask;

        while (true) {
                u16 new_ss_mask = cur_ss_mask;

                do_each_subsys_mask(ss, ssid, cur_ss_mask) {
                        new_ss_mask |= ss->depends_on;
                } while_each_subsys_mask();

                /*
                 * Mask out subsystems which aren't available.  This can
                 * happen only if some depended-upon subsystems were bound
                 * to non-default hierarchies.
                 */
                new_ss_mask &= this_ss_mask;

                if (new_ss_mask == cur_ss_mask)
                        break;
                cur_ss_mask = new_ss_mask;
        }

        return cur_ss_mask;
}

/**
 * cgroup_kn_unlock - unlocking helper for cgroup kernfs methods
 * @kn: the kernfs_node being serviced
 *
 * This helper undoes cgroup_kn_lock_live() and should be invoked before
 * the method finishes if locking succeeded.  Note that once this function
 * returns the cgroup returned by cgroup_kn_lock_live() may become
 * inaccessible any time.  If the caller intends to continue to access the
 * cgroup, it should pin it before invoking this function.
 */
void cgroup_kn_unlock(struct kernfs_node *kn)
{
        struct cgroup *cgrp;

        if (kernfs_type(kn) == KERNFS_DIR)
                cgrp = kn->priv;
        else
                cgrp = kn->parent->priv;

        mutex_unlock(&cgroup_mutex);

        kernfs_unbreak_active_protection(kn);
        cgroup_put(cgrp);
}

/**
 * cgroup_kn_lock_live - locking helper for cgroup kernfs methods
 * @kn: the kernfs_node being serviced
 * @drain_offline: perform offline draining on the cgroup
 *
 * This helper is to be used by a cgroup kernfs method currently servicing
 * @kn.  It breaks the active protection, performs cgroup locking and
 * verifies that the associated cgroup is alive.  Returns the cgroup if
 * alive; otherwise, %NULL.  A successful return should be undone by a
 * matching cgroup_kn_unlock() invocation.  If @drain_offline is %true, the
 * cgroup is drained of offlining csses before return.
 *
 * Any cgroup kernfs method implementation which requires locking the
 * associated cgroup should use this helper.  It avoids nesting cgroup
 * locking under kernfs active protection and allows all kernfs operations
 * including self-removal.
 */
struct cgroup *cgroup_kn_lock_live(struct kernfs_node *kn, bool drain_offline)
{
        struct cgroup *cgrp;

        if (kernfs_type(kn) == KERNFS_DIR)
                cgrp = kn->priv;
        else
                cgrp = kn->parent->priv;

        /*
         * We're gonna grab cgroup_mutex which nests outside kernfs
         * active_ref.  cgroup liveliness check alone provides enough
         * protection against removal.  Ensure @cgrp stays accessible and
         * break the active_ref protection.
         */
        if (!cgroup_tryget(cgrp))
                return NULL;
        kernfs_break_active_protection(kn);

        if (drain_offline)
                cgroup_lock_and_drain_offline(cgrp);
        else
                mutex_lock(&cgroup_mutex);

        if (!cgroup_is_dead(cgrp))
                return cgrp;

        cgroup_kn_unlock(kn);
        return NULL;
}

static void cgroup_rm_file(struct cgroup *cgrp, const struct cftype *cft)
{
        char name[CGROUP_FILE_NAME_MAX];

        lockdep_assert_held(&cgroup_mutex);

        if (cft->file_offset) {
                struct cgroup_subsys_state *css = cgroup_css(cgrp, cft->ss);
                struct cgroup_file *cfile = (void *)css + cft->file_offset;

                spin_lock_irq(&cgroup_file_kn_lock);
                cfile->kn = NULL;
                spin_unlock_irq(&cgroup_file_kn_lock);

                del_timer_sync(&cfile->notify_timer);
        }

        kernfs_remove_by_name(cgrp->kn, cgroup_file_name(cgrp, cft, name));
}

/**
 * css_clear_dir - remove subsys files in a cgroup directory
 * @css: target css
 */
static void css_clear_dir(struct cgroup_subsys_state *css)
{
        struct cgroup *cgrp = css->cgroup;
        struct cftype *cfts;

        if (!(css->flags & CSS_VISIBLE))
                return;

        css->flags &= ~CSS_VISIBLE;

        if (!css->ss) {
                if (cgroup_on_dfl(cgrp))
                        cfts = cgroup_base_files;
                else
                        cfts = cgroup1_base_files;

                cgroup_addrm_files(css, cgrp, cfts, false);
        } else {
                list_for_each_entry(cfts, &css->ss->cfts, node)
                        cgroup_addrm_files(css, cgrp, cfts, false);
        }
}

/**
 * css_populate_dir - create subsys files in a cgroup directory
 * @css: target css
 *
 * On failure, no file is added.
 */
static int css_populate_dir(struct cgroup_subsys_state *css)
{
        struct cgroup *cgrp = css->cgroup;
        struct cftype *cfts, *failed_cfts;
        int ret;

        if ((css->flags & CSS_VISIBLE) || !cgrp->kn)
                return 0;

        if (!css->ss) {
                if (cgroup_on_dfl(cgrp))
                        cfts = cgroup_base_files;
                else
                        cfts = cgroup1_base_files;

                ret = cgroup_addrm_files(&cgrp->self, cgrp, cfts, true);
                if (ret < 0)
                        return ret;
        } else {
                list_for_each_entry(cfts, &css->ss->cfts, node) {
                        ret = cgroup_addrm_files(css, cgrp, cfts, true);
                        if (ret < 0) {
                                failed_cfts = cfts;
                                goto err;
                        }
                }
        }

        css->flags |= CSS_VISIBLE;

        return 0;
err:
        list_for_each_entry(cfts, &css->ss->cfts, node) {
                if (cfts == failed_cfts)
                        break;
                cgroup_addrm_files(css, cgrp, cfts, false);
        }
        return ret;
}

int rebind_subsystems(struct cgroup_root *dst_root, u16 ss_mask)
{
        struct cgroup *dcgrp = &dst_root->cgrp;
        struct cgroup_subsys *ss;
        int ssid, i, ret;
        u16 dfl_disable_ss_mask = 0;

        lockdep_assert_held(&cgroup_mutex);

        do_each_subsys_mask(ss, ssid, ss_mask) {
                /*
                 * If @ss has non-root csses attached to it, can't move.
                 * If @ss is an implicit controller, it is exempt from this
                 * rule and can be stolen.
                 */
                if (css_next_child(NULL, cgroup_css(&ss->root->cgrp, ss)) &&
                    !ss->implicit_on_dfl)
                        return -EBUSY;

                /* can't move between two non-dummy roots either */
                if (ss->root != &cgrp_dfl_root && dst_root != &cgrp_dfl_root)
                        return -EBUSY;

                /*
                 * Collect ssid's that need to be disabled from default
                 * hierarchy.
                 */
                if (ss->root == &cgrp_dfl_root)
                        dfl_disable_ss_mask |= 1 << ssid;

        } while_each_subsys_mask();

        if (dfl_disable_ss_mask) {
                struct cgroup *scgrp = &cgrp_dfl_root.cgrp;

                /*
                 * Controllers from default hierarchy that need to be rebound
                 * are all disabled together in one go.
                 */
                cgrp_dfl_root.subsys_mask &= ~dfl_disable_ss_mask;
                WARN_ON(cgroup_apply_control(scgrp));
                cgroup_finalize_control(scgrp, 0);
        }

        do_each_subsys_mask(ss, ssid, ss_mask) {
                struct cgroup_root *src_root = ss->root;
                struct cgroup *scgrp = &src_root->cgrp;
                struct cgroup_subsys_state *css = cgroup_css(scgrp, ss);
                struct css_set *cset;

                WARN_ON(!css || cgroup_css(dcgrp, ss));

                if (src_root != &cgrp_dfl_root) {
                        /* disable from the source */
                        src_root->subsys_mask &= ~(1 << ssid);
                        WARN_ON(cgroup_apply_control(scgrp));
                        cgroup_finalize_control(scgrp, 0);
                }

                /* rebind */
                RCU_INIT_POINTER(scgrp->subsys[ssid], NULL);
                rcu_assign_pointer(dcgrp->subsys[ssid], css);
                ss->root = dst_root;
                css->cgroup = dcgrp;

                spin_lock_irq(&css_set_lock);
                hash_for_each(css_set_table, i, cset, hlist)
                        list_move_tail(&cset->e_cset_node[ss->id],
                                       &dcgrp->e_csets[ss->id]);
                spin_unlock_irq(&css_set_lock);

                if (ss->css_rstat_flush) {
                        list_del_rcu(&css->rstat_css_node);
                        synchronize_rcu();
                        list_add_rcu(&css->rstat_css_node,
                                     &dcgrp->rstat_css_list);
                }

                /* default hierarchy doesn't enable controllers by default */
                dst_root->subsys_mask |= 1 << ssid;
                if (dst_root == &cgrp_dfl_root) {
                        static_branch_enable(cgroup_subsys_on_dfl_key[ssid]);
                } else {
                        dcgrp->subtree_control |= 1 << ssid;
                        static_branch_disable(cgroup_subsys_on_dfl_key[ssid]);
                }

                ret = cgroup_apply_control(dcgrp);
                if (ret)
                        pr_warn("partial failure to rebind %s controller (err=%d)\n",
                                ss->name, ret);

                if (ss->bind)
                        ss->bind(css);
        } while_each_subsys_mask();

        kernfs_activate(dcgrp->kn);
        return 0;
}

int cgroup_show_path(struct seq_file *sf, struct kernfs_node *kf_node,
                     struct kernfs_root *kf_root)
{
        int len = 0;
        char *buf = NULL;
        struct cgroup_root *kf_cgroot = cgroup_root_from_kf(kf_root);
        struct cgroup *ns_cgroup;

        buf = kmalloc(PATH_MAX, GFP_KERNEL);
        if (!buf)
                return -ENOMEM;

        spin_lock_irq(&css_set_lock);
        ns_cgroup = current_cgns_cgroup_from_root(kf_cgroot);
        len = kernfs_path_from_node(kf_node, ns_cgroup->kn, buf, PATH_MAX);
        spin_unlock_irq(&css_set_lock);

        if (len >= PATH_MAX)
                len = -ERANGE;
        else if (len > 0) {
                seq_escape(sf, buf, " \t\n\\");
                len = 0;
        }
        kfree(buf);
        return len;
}

enum cgroup2_param {
        Opt_nsdelegate,
        Opt_favordynmods,
        Opt_memory_localevents,
        Opt_memory_recursiveprot,
        nr__cgroup2_params
};

static const struct fs_parameter_spec cgroup2_fs_parameters[] = {
        fsparam_flag("nsdelegate",              Opt_nsdelegate),
        fsparam_flag("favordynmods",            Opt_favordynmods),
        fsparam_flag("memory_localevents",      Opt_memory_localevents),
        fsparam_flag("memory_recursiveprot",    Opt_memory_recursiveprot),
        {}
};

static int cgroup2_parse_param(struct fs_context *fc, struct fs_parameter *param)
{
        struct cgroup_fs_context *ctx = cgroup_fc2context(fc);
        struct fs_parse_result result;
        int opt;

        opt = fs_parse(fc, cgroup2_fs_parameters, param, &result);
        if (opt < 0)
                return opt;

        switch (opt) {
        case Opt_nsdelegate:
                ctx->flags |= CGRP_ROOT_NS_DELEGATE;
                return 0;
        case Opt_favordynmods:
                ctx->flags |= CGRP_ROOT_FAVOR_DYNMODS;
                return 0;
        case Opt_memory_localevents:
                ctx->flags |= CGRP_ROOT_MEMORY_LOCAL_EVENTS;
                return 0;
        case Opt_memory_recursiveprot:
                ctx->flags |= CGRP_ROOT_MEMORY_RECURSIVE_PROT;
                return 0;
        }
        return -EINVAL;
}

static void apply_cgroup_root_flags(unsigned int root_flags)
{
        if (current->nsproxy->cgroup_ns == &init_cgroup_ns) {
                if (root_flags & CGRP_ROOT_NS_DELEGATE)
                        cgrp_dfl_root.flags |= CGRP_ROOT_NS_DELEGATE;
                else
                        cgrp_dfl_root.flags &= ~CGRP_ROOT_NS_DELEGATE;

                cgroup_favor_dynmods(&cgrp_dfl_root,
                                     root_flags & CGRP_ROOT_FAVOR_DYNMODS);

                if (root_flags & CGRP_ROOT_MEMORY_LOCAL_EVENTS)
                        cgrp_dfl_root.flags |= CGRP_ROOT_MEMORY_LOCAL_EVENTS;
                else
                        cgrp_dfl_root.flags &= ~CGRP_ROOT_MEMORY_LOCAL_EVENTS;

                if (root_flags & CGRP_ROOT_MEMORY_RECURSIVE_PROT)
                        cgrp_dfl_root.flags |= CGRP_ROOT_MEMORY_RECURSIVE_PROT;
                else
                        cgrp_dfl_root.flags &= ~CGRP_ROOT_MEMORY_RECURSIVE_PROT;
        }
}

static int cgroup_show_options(struct seq_file *seq, struct kernfs_root *kf_root)
{
        if (cgrp_dfl_root.flags & CGRP_ROOT_NS_DELEGATE)
                seq_puts(seq, ",nsdelegate");
        if (cgrp_dfl_root.flags & CGRP_ROOT_FAVOR_DYNMODS)
                seq_puts(seq, ",favordynmods");
        if (cgrp_dfl_root.flags & CGRP_ROOT_MEMORY_LOCAL_EVENTS)
                seq_puts(seq, ",memory_localevents");
        if (cgrp_dfl_root.flags & CGRP_ROOT_MEMORY_RECURSIVE_PROT)
                seq_puts(seq, ",memory_recursiveprot");
        return 0;
}

static int cgroup_reconfigure(struct fs_context *fc)
{
        struct cgroup_fs_context *ctx = cgroup_fc2context(fc);

        apply_cgroup_root_flags(ctx->flags);
        return 0;
}

static void init_cgroup_housekeeping(struct cgroup *cgrp)
{
        struct cgroup_subsys *ss;
        int ssid;

        INIT_LIST_HEAD(&cgrp->self.sibling);
        INIT_LIST_HEAD(&cgrp->self.children);
        INIT_LIST_HEAD(&cgrp->cset_links);
        INIT_LIST_HEAD(&cgrp->pidlists);
        mutex_init(&cgrp->pidlist_mutex);
        cgrp->self.cgroup = cgrp;
        cgrp->self.flags |= CSS_ONLINE;
        cgrp->dom_cgrp = cgrp;
        cgrp->max_descendants = INT_MAX;
        cgrp->max_depth = INT_MAX;
        INIT_LIST_HEAD(&cgrp->rstat_css_list);
        prev_cputime_init(&cgrp->prev_cputime);

        for_each_subsys(ss, ssid)
                INIT_LIST_HEAD(&cgrp->e_csets[ssid]);

        init_waitqueue_head(&cgrp->offline_waitq);
        INIT_WORK(&cgrp->release_agent_work, cgroup1_release_agent);
}

void init_cgroup_root(struct cgroup_fs_context *ctx)
{
        struct cgroup_root *root = ctx->root;
        struct cgroup *cgrp = &root->cgrp;

        INIT_LIST_HEAD(&root->root_list);
        atomic_set(&root->nr_cgrps, 1);
        cgrp->root = root;
        init_cgroup_housekeeping(cgrp);

        /* DYNMODS must be modified through cgroup_favor_dynmods() */
        root->flags = ctx->flags & ~CGRP_ROOT_FAVOR_DYNMODS;