[PATCH 2/2] memcg, oom: do not wake up memcg_oom_waitq if waitqueue is empty

[Haifeng Xu <haifeng.xu@shopee.com>]

Only when memcg oom killer is disabled, the task which triggers memecg
oom handling will sleep on a waitqueue. Except this case, the waitqueue
is empty though under_oom is true. There is no need to step into wake
up path when resolve the oom situation. So add a check that whether the
waitqueue is empty.

Signed-off-by: Haifeng Xu <haifeng.xu@shopee.com>
---
 mm/memcontrol.c | 2 +-
 1 file changed, 1 insertion(+), 1 deletion(-)

diff --git a/mm/memcontrol.c b/mm/memcontrol.c
index 0b6ed63504ca..2bb98ff5be3d 100644
--- a/mm/memcontrol.c
+++ b/mm/memcontrol.c
@@ -1918,7 +1918,7 @@ static void memcg_oom_recover(struct mem_cgroup *memcg)
 	 * achieved by invoking mem_cgroup_mark_under_oom() before
 	 * triggering notification.
 	 */
-	if (memcg && memcg->under_oom)
+	if (memcg && memcg->under_oom && !list_empty(&memcg_oom_waitq.head))
 		__wake_up(&memcg_oom_waitq, TASK_NORMAL, 0, memcg);
 }
 
-- 
2.25.1