From 839ec5452ebfd5905b9c69b20ceb640903a8ea1a Mon Sep 17 00:00:00 2001
From: Paul Menage <menage@google.com>
Date: Thu, 29 Jan 2009 14:25:22 -0800
Subject: [PATCH] cgroup: fix root_count when mount fails due to busy subsystem

root_count was being incremented in cgroup_get_sb() after all error
checking was complete, but decremented in cgroup_kill_sb(), which can be
called on a superblock that we gave up on due to an error.  This patch
changes cgroup_kill_sb() to only decrement root_count if the root was
previously linked into the list of roots.

Signed-off-by: Paul Menage <menage@google.com>
Tested-by: Serge Hallyn <serue@us.ibm.com>
Cc: Ingo Molnar <mingo@elte.hu>
Signed-off-by: Andrew Morton <akpm@linux-foundation.org>
Signed-off-by: Linus Torvalds <torvalds@linux-foundation.org>
---
 kernel/cgroup.c | 6 ++++--
 1 file changed, 4 insertions(+), 2 deletions(-)

diff --git a/kernel/cgroup.c b/kernel/cgroup.c
index 492215d67fa5..5a54ff42874e 100644
--- a/kernel/cgroup.c
+++ b/kernel/cgroup.c
@@ -1115,8 +1115,10 @@ static void cgroup_kill_sb(struct super_block *sb) {
 	}
 	write_unlock(&css_set_lock);
 
-	list_del(&root->root_list);
-	root_count--;
+	if (!list_empty(&root->root_list)) {
+		list_del(&root->root_list);
+		root_count--;
+	}
 
 	mutex_unlock(&cgroup_mutex);