linux-kernel - Re: [PATCH] block: revert pushing the final release of request

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Message-ID: <46a5ec83-5a26-fc8a-4cd9-a77d100b7833@acm.org>
Date:   Sun, 9 Feb 2020 19:14:48 -0800
From:   Bart Van Assche <bvanassche@....org>
To:     "yukuai (C)" <yukuai3@...wei.com>, axboe@...nel.dk,
        ming.lei@...hat.com, chaitanya.kulkarni@....com,
        damien.lemoal@....com, dhowells@...hat.com, asml.silence@...il.com,
        ajay.joshi@....com
Cc:     linux-block@...r.kernel.org, linux-kernel@...r.kernel.org,
        yi.zhang@...wei.com, zhangxiaoxu5@...wei.com,
        luoshijie1@...wei.com, jan kara <jack@...e.cz>
Subject: Re: [PATCH] block: revert pushing the final release of request_queue
 to a workqueue.

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.