linux-kernel - Re: [PATCH 1/5] oom: select_bad_process: check PF

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Date:	Wed, 2 Jun 2010 23:33:32 +0200
From:	Oleg Nesterov <oleg@...hat.com>
To:	David Rientjes <rientjes@...gle.com>
Cc:	KOSAKI Motohiro <kosaki.motohiro@...fujitsu.com>,
	LKML <linux-kernel@...r.kernel.org>,
	linux-mm <linux-mm@...ck.org>,
	Andrew Morton <akpm@...ux-foundation.org>,
	KAMEZAWA Hiroyuki <kamezawa.hiroyu@...fujitsu.com>,
	Nick Piggin <npiggin@...e.de>
Subject: Re: [PATCH 1/5] oom: select_bad_process: check PF_KTHREAD instead
	of !mm to skip kthreads

On 06/02, David Rientjes wrote:
>
> On Wed, 2 Jun 2010, KOSAKI Motohiro wrote:
>
> > > Again, the question is whether or not the fix is rc material or not,
> > > otherwise there's no difference in the route that it gets upstream: the
> > > patch is duplicated in both series.  If you feel that this minor issue
> > > (which has never been reported in at least the last three years and
> > > doesn't have any side effects other than a couple of millisecond delay
> > > until unuse_mm() when the oom killer will kill something else) should be
> > > addressed in 2.6.35-rc2, then that's a conversation to be had with Andrew.
> >
> > Well, we have bugfix-at-first development rule. Why do you refuse our
> > development process?
>
> This isn't a bugfix, it simply prevents a recall to the oom killer after
> the kthread has called unuse_mm().  Please show where any side effects of
> oom killing a kthread, which cannot exit, as a result of use_mm() causes a
> problem _anywhere_.

I already showed you the side effects, but you removed this part in your
reply.

>From http://marc.info/?l=linux-kernel&m=127542732121077

	It can't die but force_sig() does bad things which shouldn't be done
	with workqueue thread. Note that it removes SIG_IGN, sets
	SIGNAL_GROUP_EXIT, makes signal_pending/fatal_signal_pedning true, etc.

A workqueue thread must not run with SIGNAL_GROUP_EXIT set, SIGKILL
must be ignored, signal_pending() must not be true.

This is bug. It is minor, agreed, currently use_mm() is only used by aio.

Oleg.

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