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

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Date:	Wed, 21 Mar 2007 17:23:50 +0300
From:	Oleg Nesterov <oleg@...sign.ru>
To:	Nigel Cunningham <nigel@...el.suspend2.net>
Cc:	"Eric W. Biederman" <ebiederm@...ssion.com>,
	"Rafael J. Wysocki" <rjw@...k.pl>,
	Sukadev Bhattiprolu <sukadev@...ibm.com>,
	Jiri Slaby <jirislaby@...il.com>, Pavel Machek <pavel@....cz>,
	Andrew Morton <akpm@...ux-foundation.org>,
	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, Nigel Cunningham wrote:
> 
> On Tue, 2007-03-20 at 19:23 -0600, Eric W. Biederman wrote:
> > >> > Rafael J. Wysocki napsal(a):
> > >
> > > Bisection shows that the freezing of processes has been broken by one of the
> > > patches:
> > >
> > > remove-the-likelypid-check-in-copy_process.patch
> > 
> > Grr.  Oleg's review of remove-the-likelypid-check-in-copy-process
> > showed it to be questionable (and it was just an optimization)
> > so we can get rid of that one easily. 
> > 
> > Although all it did that was really questionable was add
> > the idle process to the global process list and bump a process
> > count when we forked the idle process.  Not dramatically dangerous
> > things.
> 
> 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.

Oleg.

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