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Date: Wed, 21 Mar 2007 19:55:34 +0300
From: Oleg Nesterov <oleg@tv-sign.ru>
To: Andrew Morton <akpm@linux-foundation.org>
Cc: "Rafael J. Wysocki" <rjw@sisk.pl>,
       Nigel Cunningham <nigel@nigel.suspend2.net>,
       "Eric W. Biederman" <ebiederm@xmission.com>,
       Sukadev Bhattiprolu <sukadev@us.ibm.com>,
       Jiri Slaby <jirislaby@gmail.com>, Pavel Machek <pavel@ucw.cz>,
       linux-pm@lists.osdl.org, linux-kernel@vger.kernel.org
Subject: Re: [linux-pm] 2.6.21-rc4-mm1: freezing of processes broken
Message-ID: <20070321165534.GA476@tv-sign.ru>
References: <20070319205623.299d0378.akpm@linux-foundation.org> <1174446834.6665.3.camel@nigel.suspend2.net> <20070321142350.GB78@tv-sign.ru> <200703211545.17919.rjw@sisk.pl> <20070321082029.2a38e09f.akpm@linux-foundation.org>
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On 03/21, Andrew Morton wrote:
>
> On Wed, 21 Mar 2007 15:45:16 +0100 "Rafael J. Wysocki" <rjw@sisk.pl> wrote:
> 
> > On Wednesday, 21 March 2007 15:23, Oleg Nesterov wrote:
> > > > 
> > > > Could the freezer code be trying to freeze the idle thread as a result?
> > > 
> > > Yes. remove-the-likelypid-check-in-copy_process.patch make idle threads
> > > visible to for_each_process/do_each_thread. Note also that idle threads
> > > have ->mm != NULL. freezer, oom_kill, move_task_off_dead_cpu, etc, should
> > > not see idle threads, but they do now.
> > 
> > Well, I think this is a good enough reason for asking Andrew to drop this
> > patch.
> 
> Or we change the freezer to skip pid==0 tasks.

I strongly disagree. In that case we should audit all users of for_each_process.
Imho, this change is too dangerous. Actually, I personally think it is very good
that idle threads are special and not visible, imho we should not change this.

Btw. Rafael, Andrew, what about

	[PATCH] Make XFS workqueues nonfreezable
	http://marc.info/?l=linux-kernel&m=117270675922229

, don't you think this should go to 2.6.21 ?

Oleg.