linux-kernel - Re: [PATCH 3/4] OOM, PM: OOM killed task shouldn't escape PM suspend

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Date:	Thu, 6 Nov 2014 17:31:24 +0100
From:	Michal Hocko <mhocko@...e.cz>
To:	Tejun Heo <tj@...nel.org>
Cc:	"Rafael J. Wysocki" <rjw@...ysocki.net>,
	Andrew Morton <akpm@...ux-foundation.org>,
	Cong Wang <xiyou.wangcong@...il.com>,
	David Rientjes <rientjes@...gle.com>,
	Oleg Nesterov <oleg@...hat.com>,
	LKML <linux-kernel@...r.kernel.org>, linux-mm@...ck.org,
	Linux PM list <linux-pm@...r.kernel.org>
Subject: Re: [PATCH 3/4] OOM, PM: OOM killed task shouldn't escape PM suspend

On Thu 06-11-14 11:12:11, Tejun Heo wrote:
> On Thu, Nov 06, 2014 at 05:01:58PM +0100, Michal Hocko wrote:
> > Yes, OOM killer simply kicks the process sets TIF_MEMDIE and terminates.
> > That will release the read_lock, allow this to take the write lock and
> > check whether it the current has been killed without any races.
> > OOM killer doesn't wait for the killed task. The allocation is retried.
> > 
> > Does this explain your concern?
> 
> Draining oom killer then doesn't mean anything, no?  OOM killer may
> have been disabled and drained but the killed tasks might wake up
> after the PM freezer considers them to be frozen, right?  What am I
> missing?

The mutual exclusion between OOM and the freezer will cause that the
victim will have TIF_MEMDIE already set when try_to_freeze_tasks even
starts. Then freezing_slow_path wouldn't allow the task to enter the
fridge so the wake up moment is not really that important.

-- 
Michal Hocko
SUSE Labs
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