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

From: "Rafael J. Wysocki" <rjw@rjwysocki.net>
To: Tejun Heo <tj@kernel.org>
Cc: Michal Hocko <mhocko@suse.cz>,
	Cong Wang <xiyou.wangcong@gmail.com>,
	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: Sun, 14 Sep 2014 18:43:31 +0200	[thread overview]
Message-ID: <1527959.PBej7RR7ig@vostro.rjw.lan> (raw)
In-Reply-To: <20140912235935.GB28183@mtj.dyndns.org>

On Saturday, September 13, 2014 08:59:35 AM Tejun Heo wrote:
> 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.

As Michal noted, we do oom_killer_disable() in freeze_processes(), so the
scenario above cannot actually happen to my eyes.  Or am I missing anything?

-- 
I speak only for myself.
Rafael J. Wysocki, Intel Open Source Technology Center.