From 3dece8347df6a16239fab10dadb370854f1c969c Mon Sep 17 00:00:00 2001
From: KAMEZAWA Hiroyuki <kamezawa.hiroyu@jp.fujitsu.com>
Date: Thu, 1 Oct 2009 15:44:09 -0700
Subject: [PATCH] cgroup: catch bad css refcnt at css_put

__css_put() doesn't check a bug as refcnt goes to minus.
I think it should be caught. This patch adds a check for it.

Signed-off-by: KAMEZAWA Hiroyuki <kamezawa.hiroyu@jp.fujitsu.com>
Cc: Paul Menage <menage@google.com>
Cc: Li Zefan <lizf@cn.fujitsu.com>
Cc: Balbir Singh <balbir@in.ibm.com>
Cc: Daisuke Nishimura <nishimura@mxp.nes.nec.co.jp>
Signed-off-by: Andrew Morton <akpm@linux-foundation.org>
Signed-off-by: Linus Torvalds <torvalds@linux-foundation.org>
---
 kernel/cgroup.c | 5 ++++-
 1 file changed, 4 insertions(+), 1 deletion(-)

diff --git a/kernel/cgroup.c b/kernel/cgroup.c
index d2b88596efd..ca83b73fba1 100644
--- a/kernel/cgroup.c
+++ b/kernel/cgroup.c
@@ -3708,8 +3708,10 @@ static void check_for_release(struct cgroup *cgrp)
 void __css_put(struct cgroup_subsys_state *css)
 {
 	struct cgroup *cgrp = css->cgroup;
+	int val;
 	rcu_read_lock();
-	if (atomic_dec_return(&css->refcnt) == 1) {
+	val = atomic_dec_return(&css->refcnt);
+	if (val == 1) {
 		if (notify_on_release(cgrp)) {
 			set_bit(CGRP_RELEASABLE, &cgrp->flags);
 			check_for_release(cgrp);
@@ -3717,6 +3719,7 @@ void __css_put(struct cgroup_subsys_state *css)
 		cgroup_wakeup_rmdir_waiter(cgrp);
 	}
 	rcu_read_unlock();
+	WARN_ON_ONCE(val < 1);
 }
 
 /*