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SubjectRe: + memcg-do-not-report-racy-no-eligible-oom-tasks.patch added to -mm tree
On Fri 25-01-19 11:56:24, Johannes Weiner wrote:
> On Wed, Jan 09, 2019 at 11:03:06AM -0800, akpm@linux-foundation.org wrote:
> >
> > 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
> >
> > Before you just go and hit "reply", please:
> > a) Consider who else should be cc'ed
> > b) Prefer to cc a suitable mailing list as well
> > c) Ideally: find the original patch on the mailing list and do a
> > reply-to-all to that, adding suitable additional cc's
> >
> > *** Remember to use Documentation/process/submit-checklist.rst when testing your code ***
> >
> > The -mm tree is included into linux-next and is updated
> > there every 3-4 working days
> >
> > ------------------------------------------------------
> > From: Michal Hocko <mhocko@suse.com>
> > 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@i-love.sakura.ne.jp
> > Link: http://lkml.kernel.org/r/20190107143802.16847-3-mhocko@kernel.org
> > Signed-off-by: Michal Hocko <mhocko@suse.com>
> > Cc: Tetsuo Handa <penguin-kernel@I-love.SAKURA.ne.jp>
> > Cc: Johannes Weiner <hannes@cmpxchg.org>
> > Signed-off-by: Andrew Morton <akpm@linux-foundation.org>
>
> It looks like this problem is happening in production systems:
>
> https://www.spinics.net/lists/cgroups/msg21268.html
>
> where the threads don't exit because they are trapped writing out the
> oom messages to a slow console (running the reproducer from this email
> thread triggers the oom flooding).
>
> So IMO we should put this into 5.0 and add:

Please note that Tetsuo has found out that this will not work with the
CLONE_VM without CLONE_SIGHAND cases and his http://lkml.kernel.org/r/01370f70-e1f6-ebe4-b95e-0df21a0bc15e@i-love.sakura.ne.jp
should handle this case as well. I've only had objections to the
changelog but other than that the patch looked sensible to me.
--
Michal Hocko
SUSE Labs

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