linux-kernel - Re: [PATCH 5/7] cgroup_freezer: allow moving tasks in and out of a frozen cgroup

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Message-ID: <20121022212505.GG5951@atj.dyndns.org>
Date:	Mon, 22 Oct 2012 17:25:05 -0400
From:	Tejun Heo <tj@...nel.org>
To:	Oleg Nesterov <oleg@...hat.com>
Cc:	rjw@...k.pl, linux-kernel@...r.kernel.org, lizefan@...wei.com,
	containers@...ts.linux-foundation.org, cgroups@...r.kernel.org
Subject: Re: [PATCH 5/7] cgroup_freezer: allow moving tasks in and out of a
 frozen cgroup

Hello,

On Mon, Oct 22, 2012 at 09:25:06PM +0200, Oleg Nesterov wrote:
> > @@ -190,12 +201,12 @@ static void freezer_fork(struct task_struct *task)
> >  		goto out;
> >
> >  	spin_lock_irq(&freezer->lock);
> > -	BUG_ON(freezer->state == CGROUP_FROZEN);
> > -
> > -	/* Locking avoids race with FREEZING -> THAWED transitions. */
> > -	if (freezer->state == CGROUP_FREEZING)
> > +	/*
> > +	 * @task might have been just migrated into a FROZEN cgroup.
> 
> Confused. If it was migrated, then freezer_attach() should take care
> do freeze_task?

Hmmm... there's a window where a task is migrated but ->attach()
hasn't completed yet, so freezer_attach() might not have kicked in
yet.  It might not be strictly necessary but I think it's more
consistent this way.  No?

Thanks.

--
tejun
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