Re: [PATCH] block: revert pushing the final release of request_queue to a workqueue.

[Bart Van Assche]

On 2020-02-09 18:13, yukuai (C) wrote:
> I tested following patch fixes the problem, however I'm not sure if
> move blk_trace_shutdown() and blk_mu_exit_queue() is ok or we should
> just move debgfs-related part.

>From blk-mq.c:

/* tags can _not_ be used after returning from blk_mq_exit_queue */
void blk_mq_exit_queue(struct request_queue *q)
{
	struct blk_mq_tag_set	*set = q->tag_set;

	blk_mq_del_queue_tag_set(q);
	blk_mq_exit_hw_queues(q, set, set->nr_hw_queues);
}

I think that calling blk_mq_exit_queue() from blk_unregister_queue()
would break at least the sd driver. The sd driver can issue I/O after
having called del_gendisk(). See also the sd_sync_cache() call in
sd_shutdown().

Bart.