Hello,

On Thu, Feb 22, 2018 at 02:14:34PM +0800, Joseph Qi wrote:
> I still don't get how css_tryget can work here.
> 
> The race happens when:
> 1) writeback kworker has found the blkg with rcu;
> 2) blkcg is during offlining and blkg_destroy() has already been called.
> Then, writeback kworker will take queue lock and access the blkg with
> refcount 0.

Yeah, then tryget would fail and it should go through the root.

Thanks.

-- 
tejun

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