Re: + memcg-do-not-report-racy-no-eligible-oom-tasks.patch added to -mm tree

Re: + memcg-do-not-report-racy-no-eligible-oom-tasks.patch added to -mm tree

[Johannes Weiner]

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:

Fixes: 29ef680ae7c2 ("memcg, oom: move out_of_memory back to the charge path")
Fixes: 3100dab2aa09 ("mm: memcontrol: print proper OOM header when no eligible victim left")
Cc: stable@kernel.org # 4.19+

> --- 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;

Should this be false if skip the oom kill, btw? Either will result in
a forced charge - false will do so right away, true will retry once
and then trigger the victim check in try_charge().

It's just weird to return true when we didn't do what the caller asked
us to do.

>  	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;

Re: + memcg-do-not-report-racy-no-eligible-oom-tasks.patch added to -mm tree

[Michal Hocko]

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

Re: + memcg-do-not-report-racy-no-eligible-oom-tasks.patch added to -mm tree

[Johannes Weiner]

On Fri, Jan 25, 2019 at 06:24:16PM +0100, Michal Hocko wrote:
> 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.

I see. Yeah that looks reasonable to me too.

Tetsuo, could you include the Fixes: and CC: stable in your patch?

Re: + memcg-do-not-report-racy-no-eligible-oom-tasks.patch added to -mm tree

[Tetsuo Handa]

On 2019/01/26 3:33, Johannes Weiner wrote:
> On Fri, Jan 25, 2019 at 06:24:16PM +0100, Michal Hocko wrote:
>> On Fri 25-01-19 11:56:24, Johannes Weiner wrote:
>>> 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.
> 
> I see. Yeah that looks reasonable to me too.
> 
> Tetsuo, could you include the Fixes: and CC: stable in your patch?
> 

Andrew Morton is still offline. Do we want to ask Linus Torvalds?

Re: + memcg-do-not-report-racy-no-eligible-oom-tasks.patch added to -mm tree

[Andrew Morton]

On Fri, 25 Jan 2019 18:24:16 +0100 Michal Hocko <mhocko@kernel.org> wrote:

> > >     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.

So I think you're saying that 

mm-oom-marks-all-killed-tasks-as-oom-victims.patch
and
memcg-do-not-report-racy-no-eligible-oom-tasks.patch

should be dropped and that "[PATCH v2] memcg: killed threads should not
invoke memcg OOM killer" should be redone with some changelog
alterations and should be merged instead?

Re: + memcg-do-not-report-racy-no-eligible-oom-tasks.patch added to -mm tree

[Michal Hocko]

On Mon 28-01-19 10:26:16, Andrew Morton wrote:
> On Fri, 25 Jan 2019 18:24:16 +0100 Michal Hocko <mhocko@kernel.org> wrote:
> 
> > > >     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.
> 
> So I think you're saying that 
> 
> mm-oom-marks-all-killed-tasks-as-oom-victims.patch
> and
> memcg-do-not-report-racy-no-eligible-oom-tasks.patch
> 
> should be dropped and that "[PATCH v2] memcg: killed threads should not
> invoke memcg OOM killer" should be redone with some changelog
> alterations and should be merged instead?

Yup.

-- 
Michal Hocko
SUSE Labs