The patch titled
Subject: memcg: do not report racy no-eligible OOM tasks
has been added to the -mm tree. Its filename is
memcg-do-not-report-racy-no-eligible-oom-tasks.patch
This patch should soon appear at
http://ozlabs.org/~akpm/mmots/broken-out/memcg-do-not-report-racy-no-eligible-oom-tasks.patch
and later at
http://ozlabs.org/~akpm/mmotm/broken-out/memcg-do-not-report-racy-no-eligible-oom-tasks.patch
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------------------------------------------------------
From: Michal Hocko <mhocko@xxxxxxxx>
Subject: memcg: do not report racy no-eligible OOM tasks
Tetsuo has reported [1] that a single process group memcg might easily
swamp the log with no-eligible oom victim reports due to race between the
memcg charge and oom_reaper
Thread 1 Thread2 oom_reaper
try_charge try_charge
mem_cgroup_out_of_memory
mutex_lock(oom_lock)
mem_cgroup_out_of_memory
mutex_lock(oom_lock)
out_of_memory
select_bad_process
oom_kill_process(current)
wake_oom_reaper
oom_reap_task
MMF_OOM_SKIP->victim
mutex_unlock(oom_lock)
out_of_memory
select_bad_process # no task
If Thread1 didn't race it would bail out from try_charge and force the
charge. We can achieve the same by checking tsk_is_oom_victim inside the
oom_lock and therefore close the race.
[1] http://lkml.kernel.org/r/bb2074c0-34fe-8c2c-1c7d-db71338f1e7f@xxxxxxxxxxxxxxxxxxx
Link: http://lkml.kernel.org/r/20190107143802.16847-3-mhocko@xxxxxxxxxx
Signed-off-by: Michal Hocko <mhocko@xxxxxxxx>
Cc: Tetsuo Handa <penguin-kernel@xxxxxxxxxxxxxxxxxxx>
Cc: Johannes Weiner <hannes@xxxxxxxxxxx>
Signed-off-by: Andrew Morton <akpm@xxxxxxxxxxxxxxxxxxxx>
---
mm/memcontrol.c | 14 +++++++++++++-
1 file changed, 13 insertions(+), 1 deletion(-)
--- a/mm/memcontrol.c~memcg-do-not-report-racy-no-eligible-oom-tasks
+++ a/mm/memcontrol.c
@@ -1387,10 +1387,22 @@ static bool mem_cgroup_out_of_memory(str
.gfp_mask = gfp_mask,
.order = order,
};
- bool ret;
+ bool ret = true;
mutex_lock(&oom_lock);
+
+ /*
+ * multi-threaded tasks might race with oom_reaper and gain
+ * MMF_OOM_SKIP before reaching out_of_memory which can lead
+ * to out_of_memory failure if the task is the last one in
+ * memcg which would be a false possitive failure reported
+ */
+ if (tsk_is_oom_victim(current))
+ goto unlock;
+
ret = out_of_memory(&oc);
+
+unlock:
mutex_unlock(&oom_lock);
return ret;
}
_
Patches currently in -mm which might be from mhocko@xxxxxxxx are
mm-oom-marks-all-killed-tasks-as-oom-victims.patch
memcg-do-not-report-racy-no-eligible-oom-tasks.patch
