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Date: Sun, 7 Dec 2014 11:45:39 +0100
From: Michal Hocko <mhocko@suse.cz>
Subject: Re: [PATCH -v2 2/5] OOM: thaw the OOM victim if it is frozen
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To: Tejun Heo <tj@kernel.org>
Cc: linux-mm@kvack.org, Andrew Morton <akpm@linux-foundation.org>, "\\\"Rafael J. Wysocki\\\"" <rjw@rjwysocki.net>, David Rientjes <rientjes@google.com>, Johannes Weiner <hannes@cmpxchg.org>, Oleg Nesterov <oleg@redhat.com>, Cong Wang <xiyou.wangcong@gmail.com>, LKML <linux-kernel@vger.kernel.org>, linux-pm@vger.kernel.org

On Sun 07-12-14 11:24:30, Michal Hocko wrote:
> On Sat 06-12-14 08:06:57, Tejun Heo wrote:
> > Hello,
> > 
> > On Fri, Dec 05, 2014 at 05:41:44PM +0100, Michal Hocko wrote:
> > > oom_kill_process only sets TIF_MEMDIE flag and sends a signal to the
> > > victim. This is basically noop when the task is frozen though because
> > > the task sleeps in uninterruptible sleep. The victim is eventually
> > > thawed later when oom_scan_process_thread meets the task again in a
> > > later OOM invocation so the OOM killer doesn't live lock. But this is
> > > less than optimal. Let's add the frozen check and thaw the task right
> > > before we send SIGKILL to the victim.
> > > 
> > > The check and thawing in oom_scan_process_thread has to stay because the
> > > task might got access to memory reserves even without an explicit
> > > SIGKILL from oom_kill_process (e.g. it already has fatal signal pending
> > > or it is exiting already).
> > 
> > How else would a task get TIF_MEMDIE?  If there are other paths which
> > set TIF_MEMDIE, the right thing to do is creating a function which
> > thaws / wakes up the target task and use it there too.  Please
> > interlock these things properly from the get-go instead of scattering
> > these things around.
> 
> See __out_of_memory which sets TIF_MEMDIE on current when it is exiting
> or has fatal signals pending. This task cannot be frozen obviously.

On the other hand we are doing the same early in oom_kill_process which
doesn't work on the current. I've moved the __thaw_task
into mark_tsk_oom_victim so it catches all instances now.
oom_scan_process_thread doesn't need to thaw anymore.
---