linux-kernel - Re: [PATCH 1/4] freezer_cg: fix improper BUG

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Message-ID: <48FD81CD.7080103@fr.ibm.com>
Date:	Tue, 21 Oct 2008 09:16:29 +0200
From:	Cedric Le Goater <clg@...ibm.com>
To:	Li Zefan <lizf@...fujitsu.com>
CC:	Andrew Morton <akpm@...ux-foundation.org>,
	Linux Containers <containers@...ts.linux-foundation.org>,
	LKML <linux-kernel@...r.kernel.org>
Subject: Re: [PATCH 1/4] freezer_cg: fix improper BUG_ON() causing oops

Li Zefan wrote:
> The BUG_ON() should be protected by freezer->lock, otherwise it
> can be triggered easily when a task has been unfreezed but the
> corresponding cgroup hasn't been changed to FROZEN state.

yes. thanks,

Acked-by: Cedric Le Goater <clg@...ibm.com>

> Signed-off-by: Li Zefan <lizf@...fujitsu.com>
> ---
>  kernel/cgroup_freezer.c |    3 ++-
>  1 files changed, 2 insertions(+), 1 deletions(-)
> 
> diff --git a/kernel/cgroup_freezer.c b/kernel/cgroup_freezer.c
> index e950569..7f54d1c 100644
> --- a/kernel/cgroup_freezer.c
> +++ b/kernel/cgroup_freezer.c
> @@ -190,8 +190,9 @@ static void freezer_fork(struct cgroup_subsys *ss, struct task_struct *task)
>  	freezer = task_freezer(task);
>  	task_unlock(task);
>  
> -	BUG_ON(freezer->state == CGROUP_FROZEN);
>  	spin_lock_irq(&freezer->lock);
> +	BUG_ON(freezer->state == CGROUP_FROZEN);
> +
>  	/* Locking avoids race with FREEZING -> THAWED transitions. */
>  	if (freezer->state == CGROUP_FREEZING)
>  		freeze_task(task, true);

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