linux-kernel - Re: [PATCH 4/4] cgroup: move the one-off opts sanity check in cgroup_root_from_opts() to parse_cgroupfs

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Date:	Wed, 29 Jan 2014 08:20:06 -0500
From:	Tejun Heo <tj@...nel.org>
To:	Li Zefan <lizefan@...wei.com>
Cc:	containers@...ts.linux-foundation.org, cgroups@...r.kernel.org,
	linux-kernel@...r.kernel.org
Subject: Re: [PATCH 4/4] cgroup: move the one-off opts sanity check in
 cgroup_root_from_opts() to parse_cgroupfs_options()

On Wed, Jan 29, 2014 at 12:02:44PM +0800, Li Zefan wrote:
> On 2014/1/28 23:32, Tejun Heo wrote:
> > cgroup_root_from_opts() checks whether (!opts->subsys_mask &&
> > !opts->none) and returns NULL if so.  After that, if allocation fails,
> > returns ERR_PTR(-ENOMEM).  The caller, cgroup_mount(), doesn't treat
> > NULL as an error but set opts.new_root to NULL; however, later on,
> > cgroup_set_super() fails with -EINVAL if new_root is NULL.
> 
> This patch changes mount semantics.
> 
> If cgroup_root_from_opts() returns NULL, it means we should be looking
> for existing superblock only.
> 
> This will fail:
> 
>   # mount -t cgroup -o name=abc xxx /mnt
> 
> But this is ok:
> 
>   # mount -t cgroup -o none,name=abc xxx /mnt
>   # mkdir /mnt/sub
>   # umount /mnt
>   # mount -t cgroup -o name=abc xxx /mnt   <-- this won't work with your patch

Ewwwwwwwwwwwwwwwwwwwwwwwwwwwwwwwwwwwwwwwwwwwwwwwwwwwwwwwwwww....
urgghhghghghhh.............

Alright, dropping this patch and will update later patches to maintain
the behavior.

Thanks.

-- 
tejun
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