Commit 3fa59dfb authored by KAMEZAWA Hiroyuki's avatar KAMEZAWA Hiroyuki Committed by Linus Torvalds
Browse files

cgroup: fix potential deadlock in pre_destroy



As Balbir pointed out, memcg's pre_destroy handler has potential deadlock.

It has following lock sequence.

	cgroup_mutex (cgroup_rmdir)
	    -> pre_destroy -> mem_cgroup_pre_destroy-> force_empty
		-> cpu_hotplug.lock. (lru_add_drain_all->
				      schedule_work->
                                      get_online_cpus)

But, cpuset has following.
	cpu_hotplug.lock (call notifier)
		-> cgroup_mutex. (within notifier)

Then, this lock sequence should be fixed.

Considering how pre_destroy works, it's not necessary to holding
cgroup_mutex() while calling it.

As a side effect, we don't have to wait at this mutex while memcg's
force_empty works.(it can be long when there are tons of pages.)
Signed-off-by: default avatarKAMEZAWA Hiroyuki <kamezawa.hiroyu@jp.fujitsu.com>
Acked-by: default avatarBalbir Singh <balbir@linux.vnet.ibm.com>
Cc: Li Zefan <lizf@cn.fujitsu.com>
Cc: Paul Menage <menage@google.com>
Cc: Daisuke Nishimura <nishimura@mxp.nes.nec.co.jp>
Signed-off-by: default avatarAndrew Morton <akpm@linux-foundation.org>
Signed-off-by: default avatarLinus Torvalds <torvalds@linux-foundation.org>
parent 0ae15132
......@@ -2472,10 +2472,7 @@ static int cgroup_rmdir(struct inode *unused_dir, struct dentry *dentry)
mutex_unlock(&cgroup_mutex);
return -EBUSY;
}
parent = cgrp->parent;
root = cgrp->root;
sb = root->sb;
mutex_unlock(&cgroup_mutex);
/*
* Call pre_destroy handlers of subsys. Notify subsystems
......@@ -2483,7 +2480,14 @@ static int cgroup_rmdir(struct inode *unused_dir, struct dentry *dentry)
*/
cgroup_call_pre_destroy(cgrp);
if (cgroup_has_css_refs(cgrp)) {
mutex_lock(&cgroup_mutex);
parent = cgrp->parent;
root = cgrp->root;
sb = root->sb;
if (atomic_read(&cgrp->count)
|| !list_empty(&cgrp->children)
|| cgroup_has_css_refs(cgrp)) {
mutex_unlock(&cgroup_mutex);
return -EBUSY;
}
......
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