linux-kernel - Re: + freezer-check-oom-kill-while-being-frozen.patch added to -mm tree

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Message-ID: <20141016213512.GA28099@redhat.com>
Date:	Thu, 16 Oct 2014 23:35:12 +0200
From:	Oleg Nesterov <oleg@...hat.com>
To:	Cong Wang <xiyou.wangcong@...il.com>
Cc:	Michal Hocko <mhocko@...e.cz>,
	David Rientjes <rientjes@...gle.com>,
	"Rafael J. Wysocki" <rjw@...ysocki.net>, Tejun Heo <tj@...nel.org>,
	Andrew Morton <akpm@...ux-foundation.org>,
	LKML <linux-kernel@...r.kernel.org>
Subject: Re: + freezer-check-oom-kill-while-being-frozen.patch added to -mm
	tree

On 10/16, Cong Wang wrote:
>
> On Thu, Oct 16, 2014 at 2:11 PM, Oleg Nesterov <oleg@...hat.com> wrote:
> >
> > But also I can't understand why this patch helps. The changelog says:
> >
> >         do_send_sig_info will wake up the thread
> >
> > why?
> >
>
> This is a question for Michal who rewrites my changelog:
>
> http://marc.info/?l=linux-kernel&m=140986986423092&w=2
>
> :)

OK, I hope Michal can answer my question if you do not want to
do this ;) So far I think this patch is not right.

If a task B is already frozen, it sleeps in D state.

If OOM selects B as a victim after that, it won't be woken by
SIGKILL, thus it obviously can't call should_thaw_current() and
notice TIF_MEMDIE.

Btw, I also do not understand the cgroup_freezing() check in
should_thaw_current(), but this is another story.

Oleg.	

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