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From: Michal Hocko <mhocko@kernel.org>
To: Tetsuo Handa <penguin-kernel@I-love.SAKURA.ne.jp>
Cc: linux-mm@kvack.org, rientjes@google.com, oleg@redhat.com,
	vdavydov@parallels.com, mgorman@techsingularity.net,
	hughd@google.com, riel@redhat.com, akpm@linux-foundation.org,
	linux-kernel@vger.kernel.org
Subject: Re: mm, oom_reaper: How to handle race with oom_killer_disable() ?
Date: Wed, 22 Jun 2016 08:50:16 +0200	[thread overview]
Message-ID: <20160622065016.GD7520@dhcp22.suse.cz> (raw)
In-Reply-To: <20160622064015.GB7520@dhcp22.suse.cz>

On Wed 22-06-16 08:40:15, Michal Hocko wrote:
> On Wed 22-06-16 06:47:48, Tetsuo Handa wrote:
> > Michal Hocko wrote:
> > > On Wed 22-06-16 00:32:29, Tetsuo Handa wrote:
> > > > Michal Hocko wrote:
> > > [...]
> > > > > Hmm, what about the following instead. It is rather a workaround than a
> > > > > full flaged fix but it seems much more easier and shouldn't introduce
> > > > > new issues.
> > > > 
> > > > Yes, I think that will work. But I think below patch (marking signal_struct
> > > > to ignore TIF_MEMDIE instead of clearing TIF_MEMDIE from task_struct) on top of
> > > > current linux.git will implement no-lockup requirement. No race is possible unlike
> > > > "[PATCH 10/10] mm, oom: hide mm which is shared with kthread or global init".
> > > 
> > > Not really. Because without the exit_oom_victim from oom_reaper you have
> > > no guarantee that the oom_killer_disable will ever return. I have
> > > mentioned that in the changelog. There is simply no guarantee the oom
> > > victim will ever reach exit_mm->exit_oom_victim.
> > 
> > Why? Since any allocation after setting oom_killer_disabled = true will be
> > forced to fail, nobody will be blocked on waiting for memory allocation. Thus,
> > the TIF_MEMDIE tasks will eventually reach exit_mm->exit_oom_victim, won't it?
> 
> What if it gets blocked waiting for an operation which cannot make any
> forward progress because it cannot proceed with an allocation (e.g.
> an open coded allocation retry loop - not that uncommon when sending
> a bio)? I mean if we want to guarantee a forward progress then there has
> to be something to clear the flag no matter in what state the oom victim
> is or give up on oom_killer_disable.

That being said I guess the patch to try_to_freeze_tasks after
oom_killer_disable should be simple enough to go for now and stable
trees and we can come up with something less hackish later. I do not
like the fact that oom_killer_disable doesn't act as a full "barrier"
anymore.

What do you think?
-- 
Michal Hocko
SUSE Labs

  reply	other threads:[~2016-06-22  6:57 UTC|newest]

Thread overview: 14+ messages / expand[flat|nested]  mbox.gz  Atom feed  top
2016-06-10 14:23 Tetsuo Handa
2016-06-13 11:19 ` Michal Hocko
2016-06-21  8:31   ` Michal Hocko
2016-06-21 11:03     ` Tetsuo Handa
2016-06-21 11:46       ` Michal Hocko
2016-06-21 13:27         ` Michal Hocko
2016-06-21 15:32           ` Tetsuo Handa
2016-06-21 17:46             ` Michal Hocko
2016-06-21 21:47               ` Tetsuo Handa
2016-06-22  6:40                 ` Michal Hocko
2016-06-22  6:50                   ` Michal Hocko [this message]
2016-06-22 10:57                     ` Tetsuo Handa
2016-06-22 12:08                       ` Michal Hocko
2016-06-22 12:15                         ` Michal Hocko

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