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