xref: /device/soc/rockchip/common/sdk_linux/kernel/cgroup/cgroup-v1.c (revision 3d0407ba)

// SPDX-License-Identifier: GPL-2.0-only
#include "cgroup-internal.h"

#include <linux/ctype.h>
#include <linux/kmod.h>
#include <linux/sort.h>
#include <linux/delay.h>
#include <linux/mm.h>
#include <linux/sched/signal.h>
#include <linux/sched/task.h>
#include <linux/magic.h>
#include <linux/slab.h>
#include <linux/vmalloc.h>
#include <linux/delayacct.h>
#include <linux/pid_namespace.h>
#include <linux/cgroupstats.h>
#include <linux/fs_parser.h>

#include <trace/events/cgroup.h>

/*
 * pidlists linger the following amount before being destroyed.  The goal
 * is avoiding frequent destruction in the middle of consecutive read calls
 * Expiring in the middle is a performance problem not a correctness one.
 * 1 sec should be enough.
 */
#define CGROUP_PIDLIST_DESTROY_DELAY HZ

#define CGROUP_ARRAY_INDEX_ZERO 0
#define CGROUP_ARRAY_INDEX_ONE 1
#define CGROUP_ARRAY_INDEX_TWO 2

/* Controllers blocked by the commandline in v1 */
static u16 cgroup_no_v1_mask;

/* disable named v1 mounts */
static bool cgroup_no_v1_named;

/*
 * pidlist destructions need to be flushed on cgroup destruction.  Use a
 * separate workqueue as flush domain.
 */
static struct workqueue_struct *cgroup_pidlist_destroy_wq;

/* protects cgroup_subsys->release_agent_path */
static DEFINE_SPINLOCK(release_agent_path_lock);

bool cgroup1_ssid_disabled(int ssid)
{
    return cgroup_no_v1_mask & (1 << ssid);
}

/**
 * cgroup_attach_task_all - attach task 'tsk' to all cgroups of task 'from'
 * @from: attach to all cgroups of a given task
 * @tsk: the task to be attached
 */
int cgroup_attach_task_all(struct task_struct *from, struct task_struct *tsk)
{
    struct cgroup_root *root;
    int retval = 0;

    mutex_lock(&cgroup_mutex);
    percpu_down_write(&cgroup_threadgroup_rwsem);
    for_each_root(root)
    {
        struct cgroup *from_cgrp;

        if (root == &cgrp_dfl_root) {
            continue;
        }

        spin_lock_irq(&css_set_lock);
        from_cgrp = task_cgroup_from_root(from, root);
        spin_unlock_irq(&css_set_lock);

        retval = cgroup_attach_task(from_cgrp, tsk, false);
        if (retval) {
            break;
        }
    }
    percpu_up_write(&cgroup_threadgroup_rwsem);
    mutex_unlock(&cgroup_mutex);

    return retval;
}
EXPORT_SYMBOL_GPL(cgroup_attach_task_all);

/**
 * cgroup_trasnsfer_tasks - move tasks from one cgroup to another
 * @to: cgroup to which the tasks will be moved
 * @from: cgroup in which the tasks currently reside
 *
 * Locking rules between cgroup_post_fork() and the migration path
 * guarantee that, if a task is forking while being migrated, the new child
 * is guaranteed to be either visible in the source cgroup after the
 * parent's migration is complete or put into the target cgroup.  No task
 * can slip out of migration through forking.
 */
int cgroup_transfer_tasks(struct cgroup *to, struct cgroup *from)
{
    DEFINE_CGROUP_MGCTX(mgctx);
    struct cgrp_cset_link *link;
    struct css_task_iter it;
    struct task_struct *task;
    int ret;

    if (cgroup_on_dfl(to)) {
        return -EINVAL;
    }

    ret = cgroup_migrate_vet_dst(to);
    if (ret) {
        return ret;
    }

    mutex_lock(&cgroup_mutex);

    percpu_down_write(&cgroup_threadgroup_rwsem);

    /* all tasks in @from are being moved, all csets are source */
    spin_lock_irq(&css_set_lock);
    list_for_each_entry(link, &from->cset_links, cset_link) cgroup_migrate_add_src(link->cset, to, &mgctx);
    spin_unlock_irq(&css_set_lock);

    ret = cgroup_migrate_prepare_dst(&mgctx);
    if (ret) {
        goto out_err;
    }

    /*
     * Migrate tasks one-by-one until @from is empty.  This fails iff
     * ->can_attach() fails.
     */
    do {
        css_task_iter_start(&from->self, 0, &it);

        do {
            task = css_task_iter_next(&it);
        } while (task && (task->flags & PF_EXITING));

        if (task) {
            get_task_struct(task);
        }
        css_task_iter_end(&it);

        if (task) {
            ret = cgroup_migrate(task, false, &mgctx);
            if (!ret) {
                TRACE_CGROUP_PATH(transfer_tasks, to, task, false);
            }
            put_task_struct(task);
        }
    } while (task && !ret);
out_err:
    cgroup_migrate_finish(&mgctx);
    percpu_up_write(&cgroup_threadgroup_rwsem);
    mutex_unlock(&cgroup_mutex);
    return ret;
}

/*
 * Stuff for reading the 'tasks'/'procs' files.
 *
 * Reading this file can return large amounts of data if a cgroup has
 * *lots* of attached tasks. So it may need several calls to read(),
 * but we cannot guarantee that the information we produce is correct
 * unless we produce it entirely atomically.
 *
 */

/* which pidlist file are we talking about? */
enum cgroup_filetype {
    CGROUP_FILE_PROCS,
    CGROUP_FILE_TASKS,
};

/*
 * A pidlist is a list of pids that virtually represents the contents of one
 * of the cgroup files ("procs" or "tasks"). We keep a list of such pidlists,
 * a pair (one each for procs, tasks) for each pid namespace that's relevant
 * to the cgroup.
 */
struct cgroup_pidlist {
    /*
     * used to find which pidlist is wanted. doesn't change as long as
     * this particular list stays in the list.
     */
    struct {
        enum cgroup_filetype type;
        struct pid_namespace *ns;
    } key;
    /* array of xids */
    pid_t *list;
    /* how many elements the above list has */
    int length;
    /* each of these stored in a list by its cgroup */
    struct list_head links;
    /* pointer to the cgroup we belong to, for list removal purposes */
    struct cgroup *owner;
    /* for delayed destruction */
    struct delayed_work destroy_dwork;
};

/*
 * Used to destroy all pidlists lingering waiting for destroy timer.  None
 * should be left afterwards.
 */
void cgroup1_pidlist_destroy_all(struct cgroup *cgrp)
{
    struct cgroup_pidlist *l, *tmp_l;

    mutex_lock(&cgrp->pidlist_mutex);
    list_for_each_entry_safe(l, tmp_l, &cgrp->pidlists, links)
        mod_delayed_work(cgroup_pidlist_destroy_wq, &l->destroy_dwork, 0);
    mutex_unlock(&cgrp->pidlist_mutex);

    flush_workqueue(cgroup_pidlist_destroy_wq);
    BUG_ON(!list_empty(&cgrp->pidlists));
}

static void cgroup_pidlist_destroy_work_fn(struct work_struct *work)
{
    struct delayed_work *dwork = to_delayed_work(work);
    struct cgroup_pidlist *l = container_of(dwork, struct cgroup_pidlist, destroy_dwork);
    struct cgroup_pidlist *tofree = NULL;

    mutex_lock(&l->owner->pidlist_mutex);

    /*
     * Destroy iff we didn't get queued again.  The state won't change
     * as destroy_dwork can only be queued while locked.
     */
    if (!delayed_work_pending(dwork)) {
        list_del(&l->links);
        kvfree(l->list);
        put_pid_ns(l->key.ns);
        tofree = l;
    }

    mutex_unlock(&l->owner->pidlist_mutex);
    kfree(tofree);
}

/*
 * pidlist_uniq - given a kmalloc()ed list, strip out all duplicate entries
 * Returns the number of unique elements.
 */
static int pidlist_uniq(pid_t *list, int length)
{
    int src, dest = 1;

    /*
     * we presume the 0th element is unique, so i starts at 1. trivial
     * edge cases first; no work needs to be done for either
     */
    if (length == 0 || length == 1) {
        return length;
    }
    /* src and dest walk down the list; dest counts unique elements */
    for (src = 1; src < length; src++) {
        /* find next unique element */
        while (list[src] == list[src - 1]) {
            src++;
            if (src == length) {
                goto after;
            }
        }
        /* dest always points to where the next unique element goes */
        list[dest] = list[src];
        dest++;
    }
after:
    return dest;
}

/*
 * The two pid files - task and cgroup.procs - guaranteed that the result
 * is sorted, which forced this whole pidlist fiasco.  As pid order is
 * different per namespace, each namespace needs differently sorted list,
 * making it impossible to use, for example, single rbtree of member tasks
 * sorted by task pointer.  As pidlists can be fairly large, allocating one
 * per open file is dangerous, so cgroup had to implement shared pool of
 * pidlists keyed by cgroup and namespace.
 */
static int cmppid(const void *a, const void *b)
{
    return *(pid_t *)a - *(pid_t *)b;
}

static struct cgroup_pidlist *cgroup_pidlist_find(struct cgroup *cgrp, enum cgroup_filetype type)
{
    struct cgroup_pidlist *l;
    /* don't need task_nsproxy() if we're looking at ourself */
    struct pid_namespace *ns = task_active_pid_ns(current);

    lockdep_assert_held(&cgrp->pidlist_mutex);

    list_for_each_entry(l, &cgrp->pidlists, links) if (l->key.type == type && l->key.ns == ns) return l;
    return NULL;
}

/*
 * find the appropriate pidlist for our purpose (given procs vs tasks)
 * returns with the lock on that pidlist already held, and takes care
 * of the use count, or returns NULL with no locks held if we're out of
 * memory.
 */
static struct cgroup_pidlist *cgroup_pidlist_find_create(struct cgroup *cgrp, enum cgroup_filetype type)
{
    struct cgroup_pidlist *l;

    lockdep_assert_held(&cgrp->pidlist_mutex);

    l = cgroup_pidlist_find(cgrp, type);
    if (l) {
        return l;
    }

    /* entry not found; create a new one */
    l = kzalloc(sizeof(struct cgroup_pidlist), GFP_KERNEL);
    if (!l) {
        return l;
    }

    INIT_DELAYED_WORK(&l->destroy_dwork, cgroup_pidlist_destroy_work_fn);
    l->key.type = type;
    /* don't need task_nsproxy() if we're looking at ourself */
    l->key.ns = get_pid_ns(task_active_pid_ns(current));
    l->owner = cgrp;
    list_add(&l->links, &cgrp->pidlists);
    return l;
}

/*
 * Load a cgroup's pidarray with either procs' tgids or tasks' pids
 */
static int pidlist_array_load(struct cgroup *cgrp, enum cgroup_filetype type, struct cgroup_pidlist **lp)
{
    pid_t *array;
    int length;
    int pid, n = 0; /* used for populating the array */
    struct css_task_iter it;
    struct task_struct *tsk;
    struct cgroup_pidlist *l;

    lockdep_assert_held(&cgrp->pidlist_mutex);

    /*
     * If cgroup gets more users after we read count, we won't have
     * enough space - tough.  This race is indistinguishable to the
     * caller from the case that the additional cgroup users didn't
     * show up until sometime later on.
     */
    length = cgroup_task_count(cgrp);
    array = kvmalloc_array(length, sizeof(pid_t), GFP_KERNEL);
    if (!array) {
        return -ENOMEM;
    }
    /* now, populate the array */
    css_task_iter_start(&cgrp->self, 0, &it);
    while ((tsk = css_task_iter_next(&it))) {
        if (unlikely(n == length)) {
            break;
        }
        /* get tgid or pid for procs or tasks file respectively */
        if (type == CGROUP_FILE_PROCS) {
            pid = task_tgid_vnr(tsk);
        } else {
            pid = task_pid_vnr(tsk);
        }
        if (pid > 0) { /* make sure to only use valid results */
            array[n++] = pid;
        }
    }
    css_task_iter_end(&it);
    length = n;
    /* now sort & (if procs) strip out duplicates */
    sort(array, length, sizeof(pid_t), cmppid, NULL);
    if (type == CGROUP_FILE_PROCS) {
        length = pidlist_uniq(array, length);
    }

    l = cgroup_pidlist_find_create(cgrp, type);
    if (!l) {
        kvfree(array);
        return -ENOMEM;
    }

    /* store array, freeing old if necessary */
    kvfree(l->list);
    l->list = array;
    l->length = length;
    *lp = l;
    return 0;
}

/*
 * seq_file methods for the tasks/procs files. The seq_file position is the
 * next pid to display; the seq_file iterator is a pointer to the pid
 * in the cgroup->l->list array.
 */

static void *cgroup_pidlist_start(struct seq_file *s, loff_t *pos)
{
    /*
     * Initially we receive a position value that corresponds to
     * one more than the last pid shown (or 0 on the first call or
     * after a seek to the start). Use a binary-search to find the
     * next pid to display, if any
     */
    struct kernfs_open_file *of = s->private;
    struct cgroup_file_ctx *ctx = of->priv;
    struct cgroup *cgrp = seq_css(s)->cgroup;
    struct cgroup_pidlist *l;
    enum cgroup_filetype type = seq_cft(s)->private;
    int index = 0, pid = *pos;
    int *iter, ret;

    mutex_lock(&cgrp->pidlist_mutex);

    /*
     * !NULL @ctx->procs1.pidlist indicates that this isn't the first
     * start() after open. If the matching pidlist is around, we can use
     * that. Look for it. Note that @ctx->procs1.pidlist can't be used
     * directly. It could already have been destroyed.
     */
    if (ctx->procs1.pidlist) {
        ctx->procs1.pidlist = cgroup_pidlist_find(cgrp, type);
    }

    /*
     * Either this is the first start() after open or the matching
     * pidlist has been destroyed inbetween.  Create a new one.
     */
    if (!ctx->procs1.pidlist) {
        ret = pidlist_array_load(cgrp, type, &ctx->procs1.pidlist);
        if (ret) {
            return ERR_PTR(ret);
        }
    }
    l = ctx->procs1.pidlist;

    if (pid) {
        int end = l->length;

        while (index < end) {
            int mid = (index + end) / 2;
            if (l->list[mid] == pid) {
                index = mid;
                break;
            } else if (l->list[mid] <= pid) {
                index = mid + 1;
            } else {
                end = mid;
            }
        }
    }
    /* If we're off the end of the array, we're done */
    if (index >= l->length) {
        return NULL;
    }
    /* Update the abstract position to be the actual pid that we found */
    iter = l->list + index;
    *pos = *iter;
    return iter;
}

static void cgroup_pidlist_stop(struct seq_file *s, void *v)
{
    struct kernfs_open_file *of = s->private;
    struct cgroup_file_ctx *ctx = of->priv;
    struct cgroup_pidlist *l = ctx->procs1.pidlist;

    if (l) {
        mod_delayed_work(cgroup_pidlist_destroy_wq, &l->destroy_dwork, CGROUP_PIDLIST_DESTROY_DELAY);
    }
    mutex_unlock(&seq_css(s)->cgroup->pidlist_mutex);
}

static void *cgroup_pidlist_next(struct seq_file *s, void *v, loff_t *pos)
{
    struct kernfs_open_file *of = s->private;
    struct cgroup_file_ctx *ctx = of->priv;
    struct cgroup_pidlist *l = ctx->procs1.pidlist;
    pid_t *p = v;
    pid_t *end = l->list + l->length;
    /*
     * Advance to the next pid in the array. If this goes off the
     * end, we're done
     */
    p++;
    if (p >= end) {
        (*pos)++;
        return NULL;
    } else {
        *pos = *p;
        return p;
    }
}

static int cgroup_pidlist_show(struct seq_file *s, void *v)
{
    seq_printf(s, "%d\n", *(int *)v);

    return 0;
}

static ssize_t cgroup1_procs_write_func(struct kernfs_open_file *of, char *buf, size_t nbytes, loff_t off,
                                        bool threadgroup)
{
    struct cgroup *cgrp;
    struct task_struct *task;
    const struct cred *cred, *tcred;
    ssize_t ret;
    bool locked;

    cgrp = cgroup_kn_lock_live(of->kn, false);
    if (!cgrp) {
        return -ENODEV;
    }

    task = cgroup_procs_write_start(buf, threadgroup, &locked);
    ret = PTR_ERR_OR_ZERO(task);
    if (ret) {
        goto out_unlock;
    }

    /*
     * Even if we're attaching all tasks in the thread group, we only need
     * to check permissions on one of them. Check permissions using the
     * credentials from file open to protect against inherited fd attacks.
     */
    cred = of->file->f_cred;
    tcred = get_task_cred(task);
#ifdef CONFIG_HYPERHOLD
    if (!uid_eq(cred->euid, GLOBAL_MEMMGR_UID) && !uid_eq(cred->euid, GLOBAL_ROOT_UID) &&
#else
    if (!uid_eq(cred->euid, GLOBAL_ROOT_UID) &&
#endif
        !uid_eq(cred->euid, tcred->uid) && !uid_eq(cred->euid, tcred->suid) &&
        !ns_capable(tcred->user_ns, CAP_SYS_NICE))
        ret = -EACCES;
    put_cred(tcred);
    if (ret) {
        goto out_finish;
    }

    ret = cgroup_attach_task(cgrp, task, threadgroup);

out_finish:
    cgroup_procs_write_finish(task, locked);
out_unlock:
    cgroup_kn_unlock(of->kn);

    return ret ?: nbytes;
}

static ssize_t cgroup1_procs_write(struct kernfs_open_file *of, char *buf, size_t nbytes, loff_t off)
{
    return cgroup1_procs_write_func(of, buf, nbytes, off, true);
}

static ssize_t cgroup1_tasks_write(struct kernfs_open_file *of, char *buf, size_t nbytes, loff_t off)
{
    return cgroup1_procs_write_func(of, buf, nbytes, off, false);
}

static ssize_t cgroup_release_agent_write(struct kernfs_open_file *of, char *buf, size_t nbytes, loff_t off)
{
    struct cgroup *cgrp;
    struct cgroup_file_ctx *ctx;

    BUILD_BUG_ON(sizeof(cgrp->root->release_agent_path) < PATH_MAX);

    /*
     * Release agent gets called with all capabilities,
     * require capabilities to set release agent.
     */
    ctx = of->priv;
    if ((ctx->ns->user_ns != &init_user_ns) ||
        !file_ns_capable(of->file, &init_user_ns, CAP_SYS_ADMIN))
        return -EPERM;

    cgrp = cgroup_kn_lock_live(of->kn, false);
    if (!cgrp) {
        return -ENODEV;
    }
    spin_lock(&release_agent_path_lock);
    strlcpy(cgrp->root->release_agent_path, strstrip(buf), sizeof(cgrp->root->release_agent_path));
    spin_unlock(&release_agent_path_lock);
    cgroup_kn_unlock(of->kn);
    return nbytes;
}

static int cgroup_release_agent_show(struct seq_file *seq, void *v)
{
    struct cgroup *cgrp = seq_css(seq)->cgroup;

    spin_lock(&release_agent_path_lock);
    seq_puts(seq, cgrp->root->release_agent_path);
    spin_unlock(&release_agent_path_lock);
    seq_putc(seq, '\n');
    return 0;
}

static int cgroup_sane_behavior_show(struct seq_file *seq, void *v)
{
    seq_puts(seq, "0\n");
    return 0;
}

static u64 cgroup_read_notify_on_release(struct cgroup_subsys_state *css, struct cftype *cft)
{
    return notify_on_release(css->cgroup);
}

static int cgroup_write_notify_on_release(struct cgroup_subsys_state *css, struct cftype *cft, u64 val)
{
    if (val) {
        set_bit(CGRP_NOTIFY_ON_RELEASE, &css->cgroup->flags);
    } else {
        clear_bit(CGRP_NOTIFY_ON_RELEASE, &css->cgroup->flags);
    }
    return 0;
}

static u64 cgroup_clone_children_read(struct cgroup_subsys_state *css, struct cftype *cft)
{
    return test_bit(CGRP_CPUSET_CLONE_CHILDREN, &css->cgroup->flags);
}

static int cgroup_clone_children_write(struct cgroup_subsys_state *css, struct cftype *cft, u64 val)
{
    if (val) {
        set_bit(CGRP_CPUSET_CLONE_CHILDREN, &css->cgroup->flags);
    } else {
        clear_bit(CGRP_CPUSET_CLONE_CHILDREN, &css->cgroup->flags);
    }
    return 0;
}

/* cgroup core interface files for the legacy hierarchies */
struct cftype cgroup1_base_files[] = {
    {
        .name = "cgroup.procs",
        .seq_start = cgroup_pidlist_start,
        .seq_next = cgroup_pidlist_next,
        .seq_stop = cgroup_pidlist_stop,
        .seq_show = cgroup_pidlist_show,
        .private = CGROUP_FILE_PROCS,
        .write = cgroup1_procs_write,
    },
    {
        .name = "cgroup.clone_children",
        .read_u64 = cgroup_clone_children_read,
        .write_u64 = cgroup_clone_children_write,
    },
    {
        .name = "cgroup.sane_behavior",
        .flags = CFTYPE_ONLY_ON_ROOT,
        .seq_show = cgroup_sane_behavior_show,
    },
    {
        .name = "tasks",
        .seq_start = cgroup_pidlist_start,
        .seq_next = cgroup_pidlist_next,
        .seq_stop = cgroup_pidlist_stop,
        .seq_show = cgroup_pidlist_show,
        .private = CGROUP_FILE_TASKS,
        .write = cgroup1_tasks_write,
    },
    {
        .name = "notify_on_release",
        .read_u64 = cgroup_read_notify_on_release,
        .write_u64 = cgroup_write_notify_on_release,
    },
    {
        .name = "release_agent",
        .flags = CFTYPE_ONLY_ON_ROOT,
        .seq_show = cgroup_release_agent_show,
        .write = cgroup_release_agent_write,
        .max_write_len = PATH_MAX - 1,
    },
    {} /* terminate */
};

/* Display information about each subsystem and each hierarchy */
int proc_cgroupstats_show(struct seq_file *m, void *v)
{
    struct cgroup_subsys *ss;
    int i;
    bool dead;

    seq_puts(m, "#subsys_name\thierarchy\tnum_cgroups\tenabled\n");
    /*
     * ideally we don't want subsystems moving around while we do this.
     * cgroup_mutex is also necessary to guarantee an atomic snapshot of
     * subsys/hierarchy state.
     */
    mutex_lock(&cgroup_mutex);

    for_each_subsys(ss, i) for_each_subsys(ss, i)
    {
        dead = percpu_ref_is_dying(&ss->root->cgrp.self.refcnt);
        seq_printf(m, "%s\t%d\t%d\t%d\n", ss->legacy_name, dead ? 0 : ss->root->hierarchy_id,
                   dead ? 0 : atomic_read(&ss->root->nr_cgrps), cgroup_ssid_enabled(i));
    }

    mutex_unlock(&cgroup_mutex);
    return 0;
}

/**
 * cgroupstats_build - build and fill cgroupstats
 * @stats: cgroupstats to fill information into
 * @dentry: A dentry entry belonging to the cgroup for which stats have
 * been requested.
 *
 * Build and fill cgroupstats so that taskstats can export it to user
 * space.
 */
int cgroupstats_build(struct cgroupstats *stats, struct dentry *dentry)
{
    struct kernfs_node *kn = kernfs_node_from_dentry(dentry);
    struct cgroup *cgrp;
    struct css_task_iter it;
    struct task_struct *tsk;

    /* it should be kernfs_node belonging to cgroupfs and is a directory */
    if (dentry->d_sb->s_type != &cgroup_fs_type || !kn || kernfs_type(kn) != KERNFS_DIR) {
        return -EINVAL;
    }

    mutex_lock(&cgroup_mutex);

    /*
     * We aren't being called from kernfs and there's no guarantee on
     * @kn->priv's validity.  For this and css_tryget_online_from_dir(),
     * @kn->priv is RCU safe.  Let's do the RCU dancing.
     */
    rcu_read_lock();
    cgrp = rcu_dereference(*(void __rcu __force **)&kn->priv);
    if (!cgrp || cgroup_is_dead(cgrp)) {
        rcu_read_unlock();
        mutex_unlock(&cgroup_mutex);
        return -ENOENT;
    }
    rcu_read_unlock();

    css_task_iter_start(&cgrp->self, 0, &it);
    while ((tsk = css_task_iter_next(&it))) {
        switch (tsk->state) {
            case TASK_RUNNING:
                stats->nr_running++;
                break;
            case TASK_INTERRUPTIBLE:
                stats->nr_sleeping++;
                break;
            case TASK_UNINTERRUPTIBLE:
                stats->nr_uninterruptible++;
                break;
            case TASK_STOPPED:
                stats->nr_stopped++;
                break;
            default:
                if (delayacct_is_task_waiting_on_io(tsk)) {
                    stats->nr_io_wait++;
                }
                break;
        }
    }
    css_task_iter_end(&it);

    mutex_unlock(&cgroup_mutex);
    return 0;
}

void cgroup1_check_for_release(struct cgroup *cgrp)
{
    if (notify_on_release(cgrp) && !cgroup_is_populated(cgrp) && !css_has_online_children(&cgrp->self) &&
        !cgroup_is_dead(cgrp)) {
        schedule_work(&cgrp->release_agent_work);
    }
}

/*
 * Notify userspace when a cgroup is released, by running the
 * configured release agent with the name of the cgroup (path
 * relative to the root of cgroup file system) as the argument.
 *
 * Most likely, this user command will try to rmdir this cgroup.
 *
 * This races with the possibility that some other task will be
 * attached to this cgroup before it is removed, or that some other
 * user task will 'mkdir' a child cgroup of this cgroup.  That's ok.
 * The presumed 'rmdir' will fail quietly if this cgroup is no longer
 * unused, and this cgroup will be reprieved from its death sentence,
 * to continue to serve a useful existence.  Next time it's released,
 * we will get notified again, if it still has 'notify_on_release' set.
 *
 * The final arg to call_usermodehelper() is UMH_WAIT_EXEC, which
 * means only wait until the task is successfully execve()'d.  The
 * separate release agent task is forked by call_usermodehelper(),
 * then control in this thread returns here, without waiting for the
 * release agent task.  We don't bother to wait because the caller of
 * this routine has no use for the exit status of the release agent
 * task, so no sense holding our caller up for that.
 */
void cgroup1_release_agent(struct work_struct *work)
{
    struct cgroup *cgrp = container_of(work, struct cgroup, release_agent_work);
    char *pathbuf, *agentbuf;
    char *argv[3], *envp[3];
    int ret;

    /* snoop agent path and exit early if empty */
    if (!cgrp->root->release_agent_path[0]) {
        return;
    }

    /* prepare argument buffers */
    pathbuf = kmalloc(PATH_MAX, GFP_KERNEL);
    agentbuf = kmalloc(PATH_MAX, GFP_KERNEL);
    if (!pathbuf || !agentbuf) {
        goto out_free;
    }

    spin_lock(&release_agent_path_lock);
    strlcpy(agentbuf, cgrp->root->release_agent_path, PATH_MAX);
    spin_unlock(&release_agent_path_lock);
    if (!agentbuf[0]) {
        goto out_free;
    }

    ret = cgroup_path_ns(cgrp, pathbuf, PATH_MAX, &init_cgroup_ns);
    if (ret < 0 || ret >= PATH_MAX) {
        goto out_free;
    }

    argv[CGROUP_ARRAY_INDEX_ZERO] = agentbuf;
    argv[CGROUP_ARRAY_INDEX_ONE] = pathbuf;
    argv[CGROUP_ARRAY_INDEX_TWO] = NULL;

    /* minimal command environment */
    envp[CGROUP_ARRAY_INDEX_ZERO] = "HOME=/";
    envp[CGROUP_ARRAY_INDEX_ONE] = "PATH=/sbin:/bin:/usr/sbin:/usr/bin";
    envp[CGROUP_ARRAY_INDEX_TWO] = NULL;

    call_usermodehelper(argv[0], argv, envp, UMH_WAIT_EXEC);
out_free:
    kfree(agentbuf);
    kfree(pathbuf);
}

/*
 * cgroup_rename - Only allow simple rename of directories in place.
 */
static int cgroup1_rename(struct kernfs_node *kn, struct kernfs_node *new_parent, const char *new_name_str)
{
    struct cgroup *cgrp = kn->priv;
    int ret;

    /* do not accept '\n' to prevent making /proc/<pid>/cgroup unparsable */
    if (strchr(new_name_str, '\n')) {
        return -EINVAL;
    }

    if (kernfs_type(kn) != KERNFS_DIR) {
        return -ENOTDIR;
    }
    if (kn->parent != new_parent) {
        return -EIO;
    }

    /*
     * We're gonna grab cgroup_mutex which nests outside kernfs
     * active_ref.  kernfs_rename() doesn't require active_ref
     * protection.  Break them before grabbing cgroup_mutex.
     */
    kernfs_break_active_protection(new_parent);
    kernfs_break_active_protection(kn);

    mutex_lock(&cgroup_mutex);

    ret = kernfs_rename(kn, new_parent, new_name_str);
    if (!ret) {
        TRACE_CGROUP_PATH(rename, cgrp);
    }

    mutex_unlock(&cgroup_mutex);

    kernfs_unbreak_active_protection(kn);
    kernfs_unbreak_active_protection(new_parent);
    return ret;
}

static int cgroup1_show_options(struct seq_file *seq, struct kernfs_root *kf_root)
{
    struct cgroup_root *root = cgroup_root_from_kf(kf_root);
    struct cgroup_subsys *ss;
    int ssid;

    for_each_subsys(ss, ssid) if (root->subsys_mask & (1 << ssid)) seq_show_option(seq, ss->legacy_name, NULL);
    if (root->flags & CGRP_ROOT_NOPREFIX) {
        seq_puts(seq, ",noprefix");
    }
    if (root->flags & CGRP_ROOT_XATTR) {
        seq_puts(seq, ",xattr");
    }
    if (root->flags & CGRP_ROOT_CPUSET_V2_MODE) {
        seq_puts(seq, ",cpuset_v2_mode");
    }

    spin_lock(&release_agent_path_lock);
    if (strlen(root->release_agent_path)) {
        seq_show_option(seq, "release_agent", root->release_agent_path);
    }
    spin_unlock(&release_agent_path_lock);

    if (test_bit(CGRP_CPUSET_CLONE_CHILDREN, &root->cgrp.flags)) {
        seq_puts(seq, ",clone_children");
    }
    if (strlen(root->name)) {
        seq_show_option(seq, "name", root->name);
    }
    return 0;
}

enum cgroup1_param {
    Opt_all,
    Opt_clone_children,
    Opt_cpuset_v2_mode,
    Opt_name,
    Opt_none,
    Opt_noprefix,
    Opt_release_agent,
    Opt_xattr,
};

const struct fs_parameter_spec cgroup1_fs_parameters[] = {fsparam_flag("all", Opt_all),
                                                          fsparam_flag("clone_children", Opt_clone_children),
                                                          fsparam_flag("cpuset_v2_mode", Opt_cpuset_v2_mode),
                                                          fsparam_string("name", Opt_name),
                                                          fsparam_flag("none", Opt_none),
                                                          fsparam_flag("noprefix", Opt_noprefix),
                                                          fsparam_string("release_agent", Opt_release_agent),
                                                          fsparam_flag("xattr", Opt_xattr),
                                                          {}};

int cgroup1_parse_param(struct fs_context *fc, struct fs_parameter *param)
{
    struct cgroup_fs_context *ctx = cgroup_fc2context(fc);
    struct cgroup_subsys *ss;
    struct fs_parse_result result;
    int opt, i;

    opt = fs_parse(fc, cgroup1_fs_parameters, param, &result);
    if (opt == -ENOPARAM) {
        int ret;

        ret = vfs_parse_fs_param_source(fc, param);
        if (ret != -ENOPARAM) {
            return ret;
        }
        for_each_subsys(ss, i)
        {
            if (strcmp(param->key, ss->legacy_name)) {
                continue;
            }
            if (!cgroup_ssid_enabled(i) || cgroup1_ssid_disabled(i)) {
                return invalfc(fc, "Disabled controller '%s'", param->key);
            }
            ctx->subsys_mask |= (1 << i);
            return 0;
        }
        return invalfc(fc, "Unknown subsys name '%s'", param->key);
    }
    if (opt < 0) {
        return opt;
    }

    switch (opt) {
        case Opt_none:
            /* Explicitly have no subsystems */
            ctx->none = true;
            break;
        case Opt_all:
            ctx->all_ss = true;
            break;
        case Opt_noprefix:
            ctx->flags |= CGRP_ROOT_NOPREFIX;
            break;
        case Opt_clone_children:
            ctx->cpuset_clone_children = true;
            break;
        case Opt_cpuset_v2_mode:
            ctx->flags |= CGRP_ROOT_CPUSET_V2_MODE;
            break;
        case Opt_xattr:
            ctx->flags |= CGRP_ROOT_XATTR;
            break;
        case Opt_release_agent:
            /* Specifying two release agents is forbidden */
            if (ctx->release_agent) {
                return invalfc(fc, "release_agent respecified");
            }
            /*
             * Release agent gets called with all capabilities,
             * require capabilities to set release agent.
             */
            if ((fc->user_ns != &init_user_ns) || !capable(CAP_SYS_ADMIN)) {
                return invalfc(fc, "Setting release_agent not allowed");
            }
            ctx->release_agent = param->string;
            param->string = NULL;
            break;
        case Opt_name:
            /* blocked by boot param? */
            if (cgroup_no_v1_named) {
                return -ENOENT;
            }
            /* Can't specify an empty name */
            if (!param->size) {
                return invalfc(fc, "Empty name");
            }
            if (param->size > MAX_CGROUP_ROOT_NAMELEN - 1) {
                return invalfc(fc, "Name too long");
            }
            /* Must match [\w.-]+ */
            for (i = 0; i < param->size; i++) {
                char c = param->string[i];
                if (isalnum(c)) {
                    continue;
                }
                if ((c == '.') || (c == '-') || (c == '_')) {
                    continue;
                }
                return invalfc(fc, "Invalid name");
            }
            /* Specifying two names is forbidden */
            if (ctx->name) {
                return invalfc(fc, "name respecified");
            }
            ctx->name = param->string;
            param->string = NULL;
            break;
        default:
            break;
    }
    return 0;
}

static int check_cgroupfs_options(struct fs_context *fc)
{
    struct cgroup_fs_context *ctx = cgroup_fc2context(fc);
    u16 mask = U16_MAX;
    u16 enabled = 0;
    struct cgroup_subsys *ss;
    int i;

#ifdef CONFIG_CPUSETS
    mask = ~((u16)1 << cpuset_cgrp_id);
#endif
    for_each_subsys(ss, i) if (cgroup_ssid_enabled(i) && !cgroup1_ssid_disabled(i)) enabled |= 1 << i;

    ctx->subsys_mask &= enabled;

    /*
     * In absense of 'none', 'name=' or subsystem name options,
     * let's default to 'all'.
     */
    if (!ctx->subsys_mask && !ctx->none && !ctx->name) {
        ctx->all_ss = true;
    }

    if (ctx->all_ss) {
        /* Mutually exclusive option 'all' + subsystem name */
        if (ctx->subsys_mask) {
            return invalfc(fc, "subsys name conflicts with all");
        }
        /* 'all' => select all the subsystems */
        ctx->subsys_mask = enabled;
    }

    /*
     * We either have to specify by name or by subsystems. (So all
     * empty hierarchies must have a name).
     */
    if (!ctx->subsys_mask && !ctx->name) {
        return invalfc(fc, "Need name or subsystem set");
    }

    /*
     * Option noprefix was introduced just for backward compatibility
     * with the old cpuset, so we allow noprefix only if mounting just
     * the cpuset subsystem.
     */
    if ((ctx->flags & CGRP_ROOT_NOPREFIX) && (ctx->subsys_mask & mask)) {
        return invalfc(fc, "noprefix used incorrectly");
    }

    /* Can't specify "none" and some subsystems */
    if (ctx->subsys_mask && ctx->none) {
        return invalfc(fc, "none used incorrectly");
    }

    return 0;
}

int cgroup1_reconfigure(struct fs_context *fc)
{
    struct cgroup_fs_context *ctx = cgroup_fc2context(fc);
    struct kernfs_root *kf_root = kernfs_root_from_sb(fc->root->d_sb);
    struct cgroup_root *root = cgroup_root_from_kf(kf_root);
    int ret = 0;
    u16 added_mask, removed_mask;

    cgroup_lock_and_drain_offline(&cgrp_dfl_root.cgrp);

    /* See what subsystems are wanted */
    ret = check_cgroupfs_options(fc);
    if (ret) {
        goto out_unlock;
    }

    if (ctx->subsys_mask != root->subsys_mask || ctx->release_agent) {
        pr_warn("option changes via remount are deprecated (pid=%d comm=%s)\n", task_tgid_nr(current), current->comm);
    }

    added_mask = ctx->subsys_mask & ~root->subsys_mask;
    removed_mask = root->subsys_mask & ~ctx->subsys_mask;

    /* Don't allow flags or name to change at remount */
    if ((ctx->flags ^ root->flags) || (ctx->name && strcmp(ctx->name, root->name))) {
        errorfc(fc, "option or name mismatch, new: 0x%x \"%s\", old: 0x%x \"%s\"", ctx->flags, ctx->name ?: "",
                root->flags, root->name);
        ret = -EINVAL;
        goto out_unlock;
    }

    /* remounting is not allowed for populated hierarchies */
    if (!list_empty(&root->cgrp.self.children)) {
        ret = -EBUSY;
        goto out_unlock;
    }

    ret = rebind_subsystems(root, added_mask);
    if (ret) {
        goto out_unlock;
    }

    WARN_ON(rebind_subsystems(&cgrp_dfl_root, removed_mask));

    if (ctx->release_agent) {
        spin_lock(&release_agent_path_lock);
        strcpy(root->release_agent_path, ctx->release_agent);
        spin_unlock(&release_agent_path_lock);
    }

    trace_cgroup_remount(root);

out_unlock:
    mutex_unlock(&cgroup_mutex);
    return ret;
}

struct kernfs_syscall_ops cgroup1_kf_syscall_ops = {
    .rename = cgroup1_rename,
    .show_options = cgroup1_show_options,
    .mkdir = cgroup_mkdir,
    .rmdir = cgroup_rmdir,
    .show_path = cgroup_show_path,
};

/*
 * The guts of cgroup1 mount - find or create cgroup_root to use.
 * Called with cgroup_mutex held; returns 0 on success, -E... on
 * error and positive - in case when the candidate is busy dying.
 * On success it stashes a reference to cgroup_root into given
 * cgroup_fs_context; that reference is *NOT* counting towards the
 * cgroup_root refcount.
 */
static int cgroup1_root_to_use(struct fs_context *fc)
{
    struct cgroup_fs_context *ctx = cgroup_fc2context(fc);
    struct cgroup_root *root;
    struct cgroup_subsys *ss;
    int i, ret;

    /* First find the desired set of subsystems */
    ret = check_cgroupfs_options(fc);
    if (ret) {
        return ret;
    }

    /*
     * Destruction of cgroup root is asynchronous, so subsystems may
     * still be dying after the previous unmount.  Let's drain the
     * dying subsystems.  We just need to ensure that the ones
     * unmounted previously finish dying and don't care about new ones
     * starting.  Testing ref liveliness is good enough.
     */
    for_each_subsys(ss, i)
    {
        if (!(ctx->subsys_mask & (1 << i)) || ss->root == &cgrp_dfl_root) {
            continue;
        }

        if (!percpu_ref_tryget_live(&ss->root->cgrp.self.refcnt)) {
            return 1; /* restart */
        }
        cgroup_put(&ss->root->cgrp);
    }

    for_each_root(root)
    {
        bool name_match = false;

        if (root == &cgrp_dfl_root) {
            continue;
        }

        /*
         * If we asked for a name then it must match.  Also, if
         * name matches but sybsys_mask doesn't, we should fail.
         * Remember whether name matched.
         */
        if (ctx->name) {
            if (strcmp(ctx->name, root->name)) {
                continue;
            }
            name_match = true;
        }

        /*
         * If we asked for subsystems (or explicitly for no
         * subsystems) then they must match.
         */
        if ((ctx->subsys_mask || ctx->none) && (ctx->subsys_mask != root->subsys_mask)) {
            if (!name_match) {
                continue;
            }
            return -EBUSY;
        }

        if (root->flags ^ ctx->flags) {
            pr_warn("new mount options do not match the existing superblock, will be ignored\n");
        }

        ctx->root = root;
        return 0;
    }

    /*
     * No such thing, create a new one.  name= matching without subsys
     * specification is allowed for already existing hierarchies but we
     * can't create new one without subsys specification.
     */
    if (!ctx->subsys_mask && !ctx->none) {
        return invalfc(fc, "No subsys list or none specified");
    }

    /* Hierarchies may only be created in the initial cgroup namespace. */
    if (ctx->ns != &init_cgroup_ns) {
        return -EPERM;
    }

    root = kzalloc(sizeof(*root), GFP_KERNEL);
    if (!root) {
        return -ENOMEM;
    }

    ctx->root = root;
    init_cgroup_root(ctx);

    ret = cgroup_setup_root(root, ctx->subsys_mask);
    if (ret) {
        cgroup_free_root(root);
    }
    return ret;
}

int cgroup1_get_tree(struct fs_context *fc)
{
    struct cgroup_fs_context *ctx = cgroup_fc2context(fc);
    int ret;

    /* Check if the caller has permission to mount. */
    if (!ns_capable(ctx->ns->user_ns, CAP_SYS_ADMIN)) {
        return -EPERM;
    }

    cgroup_lock_and_drain_offline(&cgrp_dfl_root.cgrp);

    ret = cgroup1_root_to_use(fc);
    if (!ret && !percpu_ref_tryget_live(&ctx->root->cgrp.self.refcnt)) {
        ret = 1; /* restart */
    }

    mutex_unlock(&cgroup_mutex);

    if (!ret) {
        ret = cgroup_do_get_tree(fc);
    }

    if (!ret && percpu_ref_is_dying(&ctx->root->cgrp.self.refcnt)) {
        fc_drop_locked(fc);
        ret = 1;
    }

    if (unlikely(ret > 0)) {
        msleep(0xa);
        return restart_syscall();
    }
    return ret;
}

static int __init cgroup1_wq_init(void)
{
    /*
     * Used to destroy pidlists and separate to serve as flush domain.
     * Cap @max_active to 1 too.
     */
    cgroup_pidlist_destroy_wq = alloc_workqueue("cgroup_pidlist_destroy", 0, 1);
    BUG_ON(!cgroup_pidlist_destroy_wq);
    return 0;
}
core_initcall(cgroup1_wq_init);

static int __init cgroup_no_v1(char *str)
{
    struct cgroup_subsys *ss;
    char *token;
    int i;

    while ((token = strsep(&str, ",")) != NULL) {
        if (!*token) {
            continue;
        }

        if (!strcmp(token, "all")) {
            cgroup_no_v1_mask = U16_MAX;
            continue;
        }

        if (!strcmp(token, "named")) {
            cgroup_no_v1_named = true;
            continue;
        }

        for_each_subsys(ss, i)
        {
            if (strcmp(token, ss->name) && strcmp(token, ss->legacy_name)) {
                continue;
            }

            cgroup_no_v1_mask |= 1 << i;
        }
    }
    return 1;
}
__setup("cgroup_no_v1=", cgroup_no_v1);