linux-kernel - Re: [PATCH] cgroup: fix top cgroup refcnt leak

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Message-ID: <20140214160225.GD31544@htj.dyndns.org>
Date:	Fri, 14 Feb 2014 11:02:25 -0500
From:	Tejun Heo <tj@...nel.org>
To:	Li Zefan <lizf.kern@...il.com>
Cc:	Li Zefan <lizefan@...wei.com>, LKML <linux-kernel@...r.kernel.org>,
	Cgroups <cgroups@...r.kernel.org>
Subject: Re: [PATCH] cgroup: fix top cgroup refcnt leak

On Fri, Feb 14, 2014 at 07:15:18PM +0800, Li Zefan wrote:
> >  		/*
> > +		 * A root's lifetime is governed by its top cgroup.  Zero
> > +		 * ref indicate that the root is being destroyed.  Wait for
> > +		 * destruction to complete so that the subsystems are free.
> > +		 * We can use wait_queue for the wait but this path is
> > +		 * super cold.  Let's just sleep for a bit and retry.
> > +		 */
> > +		if (!atomic_read(&root->top_cgroup.refcnt)) {
> 
> oops, this fix is wrong. We call kernfs_mount() without cgroup locks and it
> drops cgroup refcnt if failed.
> 
> I guess we need to bump the refcnt and then drop it after kernfs_mount().

Alright, will wait for the updated fix.

Thanks!

-- 
tejun
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