linux-kernel - Re: [PATCH 0/2] oom, memcg: do not report racy no-eligible OOM

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Date:   Fri, 11 Jan 2019 14:34:01 +0100
From:   Michal Hocko <mhocko@...nel.org>
To:     Tetsuo Handa <penguin-kernel@...ove.sakura.ne.jp>
Cc:     Andrew Morton <akpm@...ux-foundation.org>, linux-mm@...ck.org,
        Johannes Weiner <hannes@...xchg.org>,
        LKML <linux-kernel@...r.kernel.org>
Subject: Re: [PATCH 0/2] oom, memcg: do not report racy no-eligible OOM

On Fri 11-01-19 21:40:52, Tetsuo Handa wrote:
[...]
> Did you notice that there is no
> 
>   "Killed process %d (%s) total-vm:%lukB, anon-rss:%lukB, file-rss:%lukB, shmem-rss:%lukB\n"
> 
> line between
> 
>   [   71.304703][ T9694] Memory cgroup out of memory: Kill process 9692 (a.out) score 904 or sacrifice child
> 
> and
> 
>   [   71.309149][   T54] oom_reaper: reaped process 9750 (a.out), now anon-rss:0kB, file-rss:0kB, shmem-rss:185532kB
> 
> ? Then, you will find that [ T9694] failed to reach for_each_process(p) loop inside
> __oom_kill_process() in the first round of out_of_memory() call because
> find_lock_task_mm() == NULL at __oom_kill_process() because Ctrl-C made that victim
> complete exit_mm() before find_lock_task_mm() is called.

OK, so we haven't killed anything because the victim has exited by the
time we wanted to do so. We still have other tasks sharing that mm
pending and not killed because nothing has killed them yet, right?

How come the oom reaper could act on this oom event at all then?

What am I missing?
-- 
Michal Hocko
SUSE Labs