[PATCH] cgroup: Fix uninitialized variable warning

[Ross Zwisler <ross.zwisler-VuQAYsv1563Yd54FQh9/CA@public.gmane.org>]

Commit 1f7dd3e5a6e4 ("cgroup: fix handling of multi-destination migration
from subtree_control enabling") introduced the following compiler warning:

mm/memcontrol.c: In function ‘mem_cgroup_can_attach’:
mm/memcontrol.c:4790:9: warning: ‘memcg’ may be used uninitialized in this function [-Wmaybe-uninitialized]
   mc.to = memcg;
         ^

Fix this by initializing 'memcg' to NULL.

This was found using gcc (GCC) 4.9.2 20150212 (Red Hat 4.9.2-6).

Signed-off-by: Ross Zwisler <ross.zwisler-VuQAYsv1563Yd54FQh9/CA@public.gmane.org>
---
 mm/memcontrol.c | 2 +-
 1 file changed, 1 insertion(+), 1 deletion(-)

diff --git a/mm/memcontrol.c b/mm/memcontrol.c
index 48b22c3..ffd9750 100644
--- a/mm/memcontrol.c
+++ b/mm/memcontrol.c
@@ -4735,7 +4735,7 @@ static void mem_cgroup_clear_mc(void)
 static int mem_cgroup_can_attach(struct cgroup_taskset *tset)
 {
 	struct cgroup_subsys_state *css;
-	struct mem_cgroup *memcg;
+	struct mem_cgroup *memcg = NULL; /* unneeded init to make gcc happy */
 	struct mem_cgroup *from;
 	struct task_struct *leader, *p;
 	struct mm_struct *mm;
-- 
2.6.3