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

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Message-ID: <20121022192506.GA27163@redhat.com>
Date:	Mon, 22 Oct 2012 21:25:06 +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

Tha last question ;)

On 10/16, Tejun Heo 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?

IOW,

> Test
> +	 * equality with THAWED.  Read the comment in freezer_attach().
> +	 */
> +	if (freezer->state != CGROUP_THAWED)
>  		freeze_task(task);
> -

This can only happen in the "normal" case, when a CGROUP_FREEZING task
forks the new child. So we could even do BUG_ON(state = CGROUP_FROZEN).

Or there could be another reason?

Oleg.

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