linux-kernel - Re: [linux-pm] 2.6.21-rc4-mm1: freezing of processes broken

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Message-Id: <20070321090824.38d67ce3.akpm@linux-foundation.org>
Date:	Wed, 21 Mar 2007 09:08:24 -0800
From:	Andrew Morton <akpm@...ux-foundation.org>
To:	Oleg Nesterov <oleg@...sign.ru>, David Chinner <dgc@....com>
Cc:	"Rafael J. Wysocki" <rjw@...k.pl>,
	Nigel Cunningham <nigel@...el.suspend2.net>,
	"Eric W. Biederman" <ebiederm@...ssion.com>,
	Sukadev Bhattiprolu <sukadev@...ibm.com>,
	Jiri Slaby <jirislaby@...il.com>, Pavel Machek <pavel@....cz>,
	linux-pm@...ts.osdl.org, linux-kernel@...r.kernel.org
Subject: Re: [linux-pm] 2.6.21-rc4-mm1: freezing of processes broken

On Wed, 21 Mar 2007 19:55:34 +0300 Oleg Nesterov <oleg@...sign.ru> wrote:

> On 03/21, Andrew Morton wrote:
> >
> > On Wed, 21 Mar 2007 15:45:16 +0100 "Rafael J. Wysocki" <rjw@...k.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.

OK, I'll tentatively drop remove-the-likelypid-check-in-copy_process.patch

> 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 ?
> 

I've sent it to the XFS guys a couple of times, but their black hole is one
of the deeper ones.

David?
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