From mboxrd@z Thu Jan  1 00:00:00 1970
From: Tejun Heo <tj-DgEjT+Ai2ygdnm+yROfE0A@public.gmane.org>
Subject: Re: [PATCH] Revert "cgroup: remove redundant variable in
 cgroup_mount()"
Date: Fri, 26 Sep 2014 00:26:17 -0400
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To: Zefan Li <lizefan-hv44wF8Li93QT0dZR+AlfA@public.gmane.org>
Cc: cgroups-u79uwXL29TY76Z2rM5mHXA@public.gmane.org, linux-kernel-u79uwXL29TY76Z2rM5mHXA@public.gmane.org, Al Viro <viro-3bDd1+5oDREiFSDQTTA3OLVCufUGDwFn@public.gmane.org>

On Fri, Sep 26, 2014 at 12:03:25PM +0800, Zefan Li wrote:
> This reverts commit 0c7bf3e8cab7900e17ce7f97104c39927d835469.
> 
> If there are child cgroups in the cgroupfs and then we umount it,
> the superblock will be destroyed but the cgroup_root will be kept
> around. When we mount it again, cgroup_mount() will find this
> cgroup_root and allocate a new sb for it.
> 
> So with this commit we will be trapped in a dead loop in the case
> described above, because kernfs_pin_sb() keeps returning NULL.
> 
> Currently I don't see how we can avoid using both pinned_sb and
> new_sb, so just revert it.
> 
> Cc: Al Viro <viro-3bDd1+5oDREiFSDQTTA3OLVCufUGDwFn@public.gmane.org>
> Reported-by: Andrey Wagin <avagin-Re5JQEeQqe8AvxtiuMwx3w@public.gmane.org>
> Signed-off-by: Zefan Li <lizefan-hv44wF8Li93QT0dZR+AlfA@public.gmane.org>

Applied to cgroup/for-3.18.

Thanks.

-- 
tejun