linux-kernel - Re: [Patch v4 1/2] freezer: check OOM kill while being frozen

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Date:	Sat, 13 Sep 2014 08:59:35 +0900
From:	Tejun Heo <tj@...nel.org>
To:	Michal Hocko <mhocko@...e.cz>
Cc:	Cong Wang <xiyou.wangcong@...il.com>,
	"Rafael J. Wysocki" <rjw@...ysocki.net>,
	LKML <linux-kernel@...r.kernel.org>,
	David Rientjes <rientjes@...gle.com>,
	Andrew Morton <akpm@...ux-foundation.org>
Subject: Re: [Patch v4 1/2] freezer: check OOM kill while being frozen

On Thu, Sep 11, 2014 at 06:30:04PM +0200, Michal Hocko wrote:
> > I am wondering if the folllowing check makes any sense with regarding
> > to rule out PM freeze:
> > 
> >         if ((!pm_nosig_freezing && !pm_freezing) &&
> >             cgroup_freezing(current) && test_thread_flag(TIF_MEMDIE))
> >                 return true;

Doesn't this mean that if PM freezing and OOM killing race each other,
the system may hang?  Driver PM operation may try to allocate memory
-> triggers OOM -> OOM killer selects an already frozen task ->
nothing happens.  I wonder whether OOM killing and PM operations
should be mutually exclusive at a higher level.  e.g. make OOM killing
always override freezing but let hibernation abort operation before
taking snapshot if OOM killing has happened since the beginning of the
PM operation.

Thanks.

-- 
tejun
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