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

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Message-ID: <20100603142717.GC3548@redhat.com>
Date:	Thu, 3 Jun 2010 16:27:17 +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, Oleg Nesterov wrote:
>
> > > 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.
>
> It's a problem that would probably never happen in practice because

No need to convince me this bug is minor. I repeated this every time.
I only argued with the "isn't a bugfix, no side effects".

> considered the ideal task to kill.  If you think this is rc material, then
> push it to Andrew and say that.

No, I don't think it is strictly necessary to push this fix into rc.
But I don't understand why this matters. And in any case, when it comes
to oom, I am in no position to make any authoritative decisions.


David, I don't understand why do you refuse to re-diff your changes
on top of Kosaki's work. If nothing else, this will help to review
your changes.

Oleg.

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