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

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Date:	Tue, 23 Oct 2012 18:14:14 +0200
From:	Oleg Nesterov <oleg@...hat.com>
To:	Tejun Heo <tj@...nel.org>
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

On 10/22, Tejun Heo wrote:
>
> 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.

Yes, I see.

Indeed, cgroup_task_migrate() is called before ->attach().

Thanks!

Oleg.

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