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

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Date:	Wed, 21 Mar 2007 19:55:34 +0300
From:	Oleg Nesterov <oleg@...sign.ru>
To:	Andrew Morton <akpm@...ux-foundation.org>
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 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.

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.

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