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

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Message-Id: <200703211308.33295.rjw@sisk.pl>
Date:	Wed, 21 Mar 2007 13:08:32 +0100
From:	"Rafael J. Wysocki" <rjw@...k.pl>
To:	"Eric W. Biederman" <ebiederm@...ssion.com>
Cc:	Jiri Slaby <jirislaby@...il.com>,
	Andrew Morton <akpm@...ux-foundation.org>,
	Pavel Machek <pavel@....cz>, linux-pm@...ts.osdl.org,
	linux-kernel@...r.kernel.org,
	Sukadev Bhattiprolu <sukadev@...ibm.com>,
	Oleg Nesterov <oleg@...sign.ru>,
	Nigel Cunningham <ncunningham@...uxmail.org>
Subject: Re: [linux-pm] 2.6.21-rc4-mm1: freezing of processes broken

On Wednesday, 21 March 2007 02:23, Eric W. Biederman wrote:
> "Rafael J. Wysocki" <rjw@...k.pl> writes:
> 
> > On Tuesday, 20 March 2007 22:06, Rafael J. Wysocki wrote:
> >> On Tuesday, 20 March 2007 21:58, Jiri Slaby wrote:
> >> > Rafael J. Wysocki napsal(a):
> >> > > Actually, the problem is 100% reproducible on my system too and I doubt
> > it's
> >> > > caused by the recent freezer patches.
> >> > 
> >> > I don't know what exactly do you mean by recent, but 2.6.21-rc3-mm2 works
> >> > for me.
> >> 
> >> Thanks for the confirmation.
> >> 
> >> The patches I was talking about had already been in 2.6.21-rc3-mm2, so the
> >> reason of this failure must be different.
> >
> > 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.

I think this patch is the culprit, though, as it seems that the freezer tries
to freeze the idle process and fails.  Yesterday I didn't have the time to
figure out the exact reason, I'll try to look at it later today.

> > use-task_pgrp-task_session-in-copy_process.patch
> 
> As I recall that patch was pretty trivial, and shouldn't have
> anything to do with the freezer.   The process freezer doesn't care
> about pids does it?

No, it doesn't, at least not directly.  I'll try to run the kernel with this
change and without remove-the-likelypid-check-in-copy_process.patch .

Greetings,
Rafael
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