linux-kernel - Re: 3.5-rc3: BUG: Dentry still in use (1) [unmount of cgroup cgroup]

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Date:	Thu, 28 Jun 2012 11:07:12 -0700
From:	"tj@...nel.org" <tj@...nel.org>
To:	Li Zefan <lizefan@...wei.com>
Cc:	shyju pv <shyju.pv@...wei.com>,
	"linux-kernel@...r.kernel.org" <linux-kernel@...r.kernel.org>,
	"cgroups@...r.kernel.org" <cgroups@...r.kernel.org>,
	Sanil kumar <sanil.kumar@...wei.com>,
	Masanari Iida <standby24x7@...il.com>
Subject: Re: 3.5-rc3: BUG: Dentry still in use (1) [unmount of cgroup
 cgroup]

Hello, Li.

On Thu, Jun 28, 2012 at 02:07:51PM +0800, Li Zefan wrote:
> > Hmm... fa980ca87d "cgroup: superblock can't be released with active
> > dentries" is supposed to have fixed that.  Looking into it.
> > 
> 
> 
> I think I know what happened here:
> 
> umount
>   deativate_super(sb)
>                        dput(subdir)
>                          subdir->d_count--
>                          d_release(subdir)
>                            deactivate_super(sb)
>                              shrink_dcache_for_umount(sb)
>                                BUG(root->d_count)!!
>                          root->d_count--

Can you please elaborate a bit?  I'm not really following?  Where does
the last root->d_count-- come from?

> I use this script to reproduce the bug:
> 
> mount -t cgroup -o cpu xxx /mnt
> mkdir /mnt/sub
> sleep 100 < /mnt/sub &
> kill $!
> wait $!
> rmdir /mnt/sub
> umount /mnt

Unfortunately, this doesn't reproduce the bug here either. :(

Thanks.

-- 
tejun
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