Re: [PATCH v4 2/2] block: cancel all throttled bios in del_gendisk()
From: Michal Koutný
Date: Mon Dec 06 2021 - 11:00:30 EST
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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