Re: [PATCH] cgroup: fix dentry still in use bug when dropping cssrefs after umount

From: Li Zefan
Date: Wed Jul 04 2012 - 02:20:15 EST

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?

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