[PATCH] cgroup: use read lock to guard find_existing_css_set()

[Li Zefan <lizf@cn.fujitsu.com>]

The function does not modify anything (except the temporary
css template), so it's sufficient to hold read lock.

Signed-off-by: Li Zefan <lizf@cn.fujitsu.com>
---
 kernel/cgroup.c |    4 ++--
 1 files changed, 2 insertions(+), 2 deletions(-)

diff --git a/kernel/cgroup.c b/kernel/cgroup.c
index 2727f92..e9eb5da 100644
--- a/kernel/cgroup.c
+++ b/kernel/cgroup.c
@@ -406,11 +406,11 @@ static struct css_set *find_css_set(
 
 	/* First see if we already have a cgroup group that matches
 	 * the desired set */
-	write_lock(&css_set_lock);
+	read_lock(&css_set_lock);
 	res = find_existing_css_set(oldcg, cgrp, template);
 	if (res)
 		get_css_set(res);
-	write_unlock(&css_set_lock);
+	read_unlock(&css_set_lock);
 
 	if (res)
 		return res;
-- 1.5.4.rc3