linux-kernel - Re: [PATCH 08/16] freezer: use dedicated lock instead of task

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Message-ID: <20110829072054.GB16431@mtj.dyndns.org>
Date:	Mon, 29 Aug 2011 09:20:54 +0200
From:	Tejun Heo <tj@...nel.org>
To:	Oleg Nesterov <oleg@...hat.com>
Cc:	rjw@...k.pl, paul@...lmenage.org, linux-kernel@...r.kernel.org,
	arnd@...db.de
Subject: Re: [PATCH 08/16] freezer: use dedicated lock instead of task_lock()
 + memory barrier

Hello,

On Sun, Aug 28, 2011 at 07:51:16PM +0200, Oleg Nesterov wrote:
> On 08/19, Tejun Heo wrote:
> >
> > it's by no means a
> > hot path and the priority is staying unintrusive and safe.  This patch
> > makes it simply use a dedicated lock
> 
> Agreed. but could you explain why it should be irq-safe? This is not
> clear from the changelog.

It doesn't need to be.  cgroup_freezer assumes irq-safety so I didn't
want to change it.  I was thinking about dropping irq-safety from all
of them later on.

> Off-topic, but fake_signal_wake_up() is not safe if the caller
> try_to_freeze_cgroup(). Unlike try_to_freeze_tasks() (which holds
> tasklist) we can race with the exiting thread, ->sighand can be
> NULL.

Indeed, guess we'll need to grab tasklist_lock around
try_to_freeze_cgroup() too.

Thanks.

-- 
tejun
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