On Fri, Dec 03, 2021 at 03:50:01PM +0800, "yukuai (C)" <yukuai3@huawei.com> wrote:
> blkg_destroy() is protected by the queue_lock，so I think queue_lock can
> protect such concurrent scenario.

blkg_destroy() is not as destroying :-) as actual free, you should
synchronize against (the queue_lock ensures this for
pd_free_fn=throtl_pd_free but you may still trip on blkcg after
blkcg_css_free()).

[Actually, I think you should see a warning in your situation if you
enable CONFIG_PROVE_RCU.]

HTH,
Michal