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Date: Wed, 4 Jul 2012 14:19:15 +0800
From: Li Zefan <lizefan@huawei.com>
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To: Tejun Heo <tj@kernel.org>
CC: shyju pv <shyju.pv@huawei.com>, Sanil kumar <sanil.kumar@huawei.com>,
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Subject: Re: [PATCH] cgroup: fix dentry still in use bug when dropping css
 refs after umount
References: <4FEEA5CB.8070809@huawei.com> <20120703170317.GB555@google.com> <20120703225218.GF555@google.com>
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On 2012/7/4 6:52, Tejun Heo wrote:

> Hello,
> 
> Shyju, can you please test the following patch?
> 
> Sasha, can you please re-test your test case with this patch?  I don't
> think fa980ca87d "cgroup: superblock can't be released with active
> dentries" did anything useful.  cgroup always calls d_iput() and
> d_release() in succession from the same context.  It may just have
> stretched the timing a bit to hide the race.
> 
> Li, this patch reverts fa980ca87d and wraps dput() in css_dput_fn()
> with s_active refs.  Positive dentry ref means that we have active ref
> on sb, so wrapping the final dput() with extra s_active ref should
> avoid premature super destruction. 


> I think we're horridly broken for

> root cgroup tho - and it has been broken for very long time.  I think
> it's mostly hidden because most (all?) controllers short-circuit root
> cgroup.  Eh, well....
> 

Could you elaborate a bit on what's broken for root cgroup?