[PATCH 7/6] mm, oom: task_will_free_mem should skip oom_reaped tasks

[Michal Hocko]

From: Michal Hocko <mhocko@xxxxxxxx>

0-day robot has encountered the following:
[   82.694232] Out of memory: Kill process 3914 (trinity-c0) score 167 or sacrifice child
[   82.695110] Killed process 3914 (trinity-c0) total-vm:55864kB, anon-rss:1512kB, file-rss:1088kB, shmem-rss:25616kB
[   82.706724] oom_reaper: reaped process 3914 (trinity-c0), now anon-rss:0kB, file-rss:0kB, shmem-rss:26488kB
[   82.715540] oom_reaper: reaped process 3914 (trinity-c0), now anon-rss:0kB, file-rss:0kB, shmem-rss:26900kB
[   82.717662] oom_reaper: reaped process 3914 (trinity-c0), now anon-rss:0kB, file-rss:0kB, shmem-rss:26900kB
[   82.725804] oom_reaper: reaped process 3914 (trinity-c0), now anon-rss:0kB, file-rss:0kB, shmem-rss:27296kB
[   82.739091] oom_reaper: reaped process 3914 (trinity-c0), now anon-rss:0kB, file-rss:0kB, shmem-rss:28148kB

oom_reaper is trying to reap the same task again and again. This
is possible only when the oom killer is bypassed because of
task_will_free_mem because we skip over tasks with MMF_OOM_REAPED
already set during select_bad_process. Teach task_will_free_mem to skip
over MMF_OOM_REAPED tasks as well because they will be unlikely to free
anything more.

Analyzed-by: Tetsuo Handa <penguin-kernel@xxxxxxxxxxxxxxxxxxx>
Signed-off-by: Michal Hocko <mhocko@xxxxxxxx>
---
 mm/oom_kill.c | 9 +++++++++
 1 file changed, 9 insertions(+)

diff --git a/mm/oom_kill.c b/mm/oom_kill.c
index dacfb6ab7b04..d6e121decb1a 100644
--- a/mm/oom_kill.c
+++ b/mm/oom_kill.c
@@ -766,6 +766,15 @@ bool task_will_free_mem(struct task_struct *task)
 		return true;
 	}
 
+	/*
+	 * This task has already been drained by the oom reaper so there are
+	 * only small chances it will free some more
+	 */
+	if (test_bit(MMF_OOM_REAPED, &mm->flags)) {
+		task_unlock(p);
+		return false;
+	}
+
 	/* pin the mm to not get freed and reused */
 	atomic_inc(&mm->mm_count);
 	task_unlock(p);
-- 
2.8.1