SoftLimit tree 'find next one' loop uses next_mz to remember next one to

be visited if reclaimd==0.

But css'refcnt handling for next_mz is not enough and it makes css->refcnt
leak.
Signed-off-by: KAMEZAWA Hiroyuki <kamezawa.hiroyu@jp.fujitsu.com>
Cc: Balbir Singh <balbir@linux.vnet.ibm.com>
Cc: KAMEZAWA Hiroyuki <kamezawa.hiroyu@jp.fujitsu.com>
Cc: KOSAKI Motohiro <kosaki.motohiro@jp.fujitsu.com>
Cc: Li Zefan <lizf@cn.fujitsu.com>
Reviewed-by: Daisuke Nishimura <nishimura@mxp.nes.nec.co.jp>
Signed-off-by: Andrew Morton <akpm@linux-foundation.org>

mm/memcontrol.c

@@ -2226,6 +2226,8 @@ unsigned long mem_cgroup_soft_limit_reclaim(struct zone *zone, int order,
 		if (!reclaimed) {
 			do {
 				/*
+				 * Loop until we find yet another one.
+				 *
 				 * By the time we get the soft_limit lock
 				 * again, someone might have aded the
 				 * group back on the RB tree. Iterate to
@@ -2236,7 +2238,12 @@ unsigned long mem_cgroup_soft_limit_reclaim(struct zone *zone, int order,
 				 */
 				next_mz =
 				__mem_cgroup_largest_soft_limit_node(mctz);
-			} while (next_mz == mz);
+				if (next_mz == mz) {
+					css_put(&next_mz->mem->css);
+					next_mz = NULL;
+				} else /* next_mz == NULL or other memcg */
+					break;
+			} while (1);
 		}
 		mz->usage_in_excess =
 			res_counter_soft_limit_excess(&mz->mem->res);
@@ -2264,6 +2271,8 @@ unsigned long mem_cgroup_soft_limit_reclaim(struct zone *zone, int order,
 			loop > MEM_CGROUP_MAX_SOFT_LIMIT_RECLAIM_LOOPS))
 			break;
 	} while (!nr_reclaimed);
+	if (next_mz)
+		css_put(&next_mz->mem->css);
 	return nr_reclaimed;
 }