linux-kernel - Re: [BUG] sched: leaf_cfs_rq

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Date:	Wed, 16 Mar 2016 10:49:12 -0700
From:	Tejun Heo <tj@...nel.org>
To:	Peter Zijlstra <peterz@...radead.org>
Cc:	Kazuki Yamaguchi <k@....jp>,
	Niklas Cassel <niklas.cassel@...s.com>,
	linux-kernel@...r.kernel.org
Subject: Re: [BUG] sched: leaf_cfs_rq_list use after free

On Wed, Mar 16, 2016 at 06:04:56PM +0100, Peter Zijlstra wrote:
> > Hmmm... I don't think it'd be safe to merge the two ops.  Nothing
> > guarantees that the RCU callback of cpu controller is called after the
> > cgroup core one and cgroup core one would do use-after-free.  Just
> > changing offline to released should do.
> 
> I'm confused, the code looks like:
> 
> static void cpu_cgroup_css_released(struct cgroup_subsys_state *css)
> {
> 	struct task_group *tg = css_tg(css);
> 
> 	sched_offline_group(tg);
> }
> 
> static void cpu_cgroup_css_free(struct cgroup_subsys_state *css)
> {
> 	struct task_group *tg = css_tg(css);
> 
> 	/*
> 	 * Relies on the RCU grace period between css_release() and this.
> 	 */
> 	sched_free_group(tg);
> }

Oops, misread the two functions swapping positions as getting merged.
Yes, that is correct.  Sorry about the confusion.  Please feel free to
add

 Acked-by: Tejun Heo <tj@...nel.org>

Thanks.

-- 
tejun