linux-kernel - Re: [PATCH 1/3] cgroup: fix umount vs cgroup_cfs

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Message-ID: <20130618160507.GG2767@htj.dyndns.org>
Date:	Tue, 18 Jun 2013 09:05:07 -0700
From:	Tejun Heo <tj@...nel.org>
To:	Li Zefan <lizefan@...wei.com>
Cc:	LKML <linux-kernel@...r.kernel.org>,
	Cgroups <cgroups@...r.kernel.org>
Subject: Re: [PATCH 1/3] cgroup: fix umount vs cgroup_cfs_commit() race

On Tue, Jun 18, 2013 at 06:40:19PM +0800, Li Zefan wrote:
> cgroup_cfs_commit() uses dget() to keep cgroup alive after cgroup_mutex
> is dropped, but dget() won't prevent cgroupfs from being umounted. When
> the race happens, vfs will see some dentries with non-zero refcnt while
> umount is in process.
> 
> Keep running this:
>   mount -t cgroup -o blkio xxx /cgroup
>   umount /cgroup
> 
> And this:
>   modprobe cfq-iosched
>   rmmod cfs-iosched
> 
> After a while, the BUG() in shrink_dcache_for_umount_subtree() may
> be triggered:
> 
>   BUG: Dentry xxx{i=0,n=blkio.yyy} still in use (1) [umount of cgroup cgroup]
> 
> Signed-off-by: Li Zefan <lizefan@...wei.com>

Applied 1-3 to cgroup/for-3.11 w/ stable cc'd on 1 and 2.

Thanks!

-- 
tejun
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