From: Tetsuo Handa <penguin-kernel@i-love.sakura.ne.jp>
To: Michal Hocko <mhocko@kernel.org>, linux-mm@kvack.org
Cc: Johannes Weiner <hannes@cmpxchg.org>,
David Rientjes <rientjes@google.com>,
Andrew Morton <akpm@linux-foundation.org>,
LKML <linux-kernel@vger.kernel.org>,
Michal Hocko <mhocko@suse.com>
Subject: Re: [RFC PATCH 2/2] memcg: do not report racy no-eligible OOM tasks
Date: Mon, 22 Oct 2018 20:45:17 +0900 [thread overview]
Message-ID: <f9a8079f-55b0-301e-9b3d-a5250bd7d277@i-love.sakura.ne.jp> (raw)
In-Reply-To: <20181022071323.9550-3-mhocko@kernel.org>
On 2018/10/22 16:13, Michal Hocko wrote:
> From: Michal Hocko <mhocko@suse.com>
>
> 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@i-love.sakura.ne.jp
> Signed-off-by: Michal Hocko <mhocko@suse.com>
> ---
> mm/memcontrol.c | 14 +++++++++++++-
> 1 file changed, 13 insertions(+), 1 deletion(-)
>
> diff --git a/mm/memcontrol.c b/mm/memcontrol.c
> index e79cb59552d9..a9dfed29967b 100644
> --- a/mm/memcontrol.c
> +++ b/mm/memcontrol.c
> @@ -1380,10 +1380,22 @@ static bool mem_cgroup_out_of_memory(struct mem_cgroup *memcg, gfp_t gfp_mask,
> .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;
> +
This is not wrong but is strange. We can use mutex_lock_killable(&oom_lock)
so that any killed threads no longer wait for oom_lock.
Also, closing this race for only memcg OOM path is strange. Global OOM path
(which are CLONE_VM without CLONE_THREAD) is still suffering this race
(though frequency is lower than memcg OOM due to use of mutex_trylock()). Either
checking before calling out_of_memory() or checking task_will_free_mem(current)
inside out_of_memory() will close this race for both paths.
> ret = out_of_memory(&oc);
> +
> +unlock:
> mutex_unlock(&oom_lock);
> return ret;
> }
>
next prev parent reply other threads:[~2018-10-22 11:45 UTC|newest]
Thread overview: 30+ messages / expand[flat|nested] mbox.gz Atom feed top
2018-10-22 7:13 [RFC PATCH 0/2] oom, memcg: do not report racy no-eligible OOM Michal Hocko
2018-10-22 7:13 ` [RFC PATCH 1/2] mm, oom: marks all killed tasks as oom victims Michal Hocko
2018-10-22 7:58 ` Tetsuo Handa
2018-10-22 8:48 ` Michal Hocko
2018-10-22 9:42 ` Tetsuo Handa
2018-10-22 10:43 ` Michal Hocko
2018-10-22 10:56 ` Tetsuo Handa
2018-10-22 11:12 ` Michal Hocko
2018-10-22 11:16 ` [RFC PATCH v2 " Michal Hocko
2018-10-22 7:13 ` [RFC PATCH 2/2] memcg: do not report racy no-eligible OOM tasks Michal Hocko
2018-10-22 11:45 ` Tetsuo Handa [this message]
2018-10-22 12:03 ` Michal Hocko
2018-10-22 13:20 ` Tetsuo Handa
2018-10-22 13:43 ` Michal Hocko
2018-10-22 15:12 ` Tetsuo Handa
2018-10-23 1:01 ` Tetsuo Handa
2018-10-23 11:42 ` Michal Hocko
2018-10-23 12:10 ` Michal Hocko
2018-10-23 12:33 ` Tetsuo Handa
2018-10-23 12:48 ` Michal Hocko
2018-10-26 14:25 ` Johannes Weiner
2018-10-26 19:25 ` Michal Hocko
2018-10-26 19:33 ` Michal Hocko
2018-10-27 1:10 ` Tetsuo Handa
2018-11-06 9:44 ` Tetsuo Handa
2018-11-06 12:42 ` Michal Hocko
2018-11-07 9:45 ` Tetsuo Handa
2018-11-07 10:08 ` Michal Hocko
2018-12-07 12:43 ` Tetsuo Handa
2018-12-12 10:23 ` Tetsuo Handa
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