Commit 53e871a3 authored by Zefan Li's avatar Zefan Li Committed by yanhaitao
Browse files

cgroup: wait for cgroup destruction to complete when umount 

hulk inclusion
category: bugfix
bugzilla: https://gitee.com/openeuler/kernel/issues/I8QLND


CVE: N/A

-------------------------------------------------

Since commit 3c606d35 ("cgroup: prevent mount hang due to memory
controller lifetime"), a cgroup root won't be destroyed if there are any
child cgroups, dead or alive.

This introduced a small regression.

    # cat test.sh
    mount -t cgroup -o cpuset xxx /cgroup
    mkdir /cgroup/tmp
    rmdir /cgroup/tmp
    umount /cgroup

After running this script, you'll probably find the cgroup hierarchy
is still active.

    # cat /proc/cgroups | grep cpuset
    #subsys_name    hierarchy       num_cgroups     enabled
    cpuset  1       1       1
    ...

Fix this by waiting for a while when umount. Now run the script again
and you'll see:

    # cat /proc/cgroups | grep cpuset
    #subsys_name    hierarchy       num_cgroups     enabled
    cpuset  0       1       1
    ...

Cc: stable@vger.kernel.org # 3.19+
Signed-off-by: default avatarZefan Li <lizefan@huawei.com>
Signed-off-by: default avatarchenridong <chenridong@huawei.com>
parent 5204214f

include/linux/cgroup-defs.h

+3 −0
Original line number Diff line number Diff line
@@ -556,6 +556,9 @@ struct cgroup_root { 
	/* Number of cgroups in the hierarchy, used only for /proc/cgroups */

	atomic_t nr_cgrps;



	/* Wait while cgroups are being destroyed */

	wait_queue_head_t wait;



	/* A list running through the active hierarchies */

	struct list_head root_list;

kernel/cgroup/cgroup.c

+15 −0
Original line number Diff line number Diff line
@@ -2018,6 +2018,7 @@ void init_cgroup_root(struct cgroup_fs_context *ctx) 
	atomic_set(&root->nr_cgrps, 1);

	cgrp->root = root;

	init_cgroup_housekeeping(cgrp);

	init_waitqueue_head(&root->wait);



	/* DYNMODS must be modified through cgroup_favor_dynmods() */

	root->flags = ctx->flags & ~CGRP_ROOT_FAVOR_DYNMODS;
@@ -2254,6 +2255,17 @@ static void cgroup_kill_sb(struct super_block *sb) 
	struct kernfs_root *kf_root = kernfs_root_from_sb(sb);

	struct cgroup_root *root = cgroup_root_from_kf(kf_root);



	/*

	* Wait if there are cgroups being destroyed, because the destruction

	* is asynchronous. On the other hand some controllers like memcg

	* may pin cgroups for a very long time, so don't wait forever.

	*/

	if (root != &cgrp_dfl_root) {

		wait_event_timeout(root->wait,

				   list_empty(&root->cgrp.self.children),

				   msecs_to_jiffies(500));

	}



	/*

	 * If @root doesn't have any children, start killing it.

	 * This prevents new mounts by disabling percpu_ref_tryget_live().
@@ -5445,6 +5457,9 @@ static void css_release_work_fn(struct work_struct *work) 
		if (cgrp->kn)

			RCU_INIT_POINTER(*(void __rcu __force **)&cgrp->kn->priv,

					 NULL);

		if (css->parent && !css->parent->parent &&

		    list_empty(&css->parent->children))

			wake_up(&cgrp->root->wait);

	}



	cgroup_unlock();