Re: [PATCH] blk-mq: quiesce queue while reallocating hctxs

[Keith Busch]

On Tue, Feb 21, 2023 at 05:24:36PM +0800, Yu Kuai wrote:
> From: Yu Kuai <yukuai3@xxxxxxxxxx>
> 
> commit 8237c01f1696 ("blk-mq: use quiesced elevator switch when
> reinitializing queues") add quiesce queue while switching elevator,
> however, if old elevator is none, queue is still not quiesced. Hence
> reallocating hctxs can concurrent with run queue. Fix it by also
> quiesce queue in the beginning of __blk_mq_update_nr_hw_queues().

Is this actually fixing anything? The quiesced elevator switch was to prevent
use-after-free from an elevator being torn down, but if you are not switching
elevators, then what resource does quiescing protect?