On Sat, Dec 04, 2021 at 04:03:53PM +0800, "yukuai (C)" <yukuai3@xxxxxxxxxx> wrote: > I was thinking that if there are active blkgs, holding queue_lock will > ensure blkcg won't be freed. My take is that the function traverses the whole blkcg tree (from global root) and nothing prevents concurrent blkcg_css_free() in a possibly unrelated branch (or queue). > By the way, does spin_lock can guarantee this since it disables preempt > like what rcu_read_lock() does? Yes (but don't quoRTe me on that :-). (It even isn't issue with a non-preemptible kernel neither but the code IMO should be generic to allow for different configs -- or as I mentioned initially, make a comment why the tree traversal is not affected by concurrent frees.) Thanks, Michal
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