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

From: Tejun Heo <tj@kernel.org>
To: Michal Hocko <mhocko@suse.cz>
Cc: Cong Wang <xiyou.wangcong@gmail.com>,
	"Rafael J. Wysocki" <rjw@rjwysocki.net>,
	LKML <linux-kernel@vger.kernel.org>,
	David Rientjes <rientjes@google.com>,
	Andrew Morton <akpm@linux-foundation.org>
Subject: Re: [Patch v4 1/2] freezer: check OOM kill while being frozen
Date: Sat, 13 Sep 2014 08:59:35 +0900	[thread overview]
Message-ID: <20140912235935.GB28183@mtj.dyndns.org> (raw)
In-Reply-To: <20140911163004.GN22042@dhcp22.suse.cz>

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