Re: [PATCH] block: don't call blk_mq_run_hw_queues() for dead or dying queues

[Keith Busch <kbusch@kernel.org>]

On Tue, Mar 26, 2019 at 01:07:12PM +0100, Hannes Reinecke wrote:
> When a queue is dying or dead there is no point in calling
> blk_mq_run_hw_queues() in blk_mq_unquiesce_queue(); in fact, doing
> so might crash the machine as the queue structures are in the
> process of being deleted.
> 
> Signed-off-by: Hannes Reinecke <hare@suse.com>
> ---
>  block/blk-mq.c | 3 ++-
>  1 file changed, 2 insertions(+), 1 deletion(-)
> 
> diff --git a/block/blk-mq.c b/block/blk-mq.c
> index a9c181603cbd..b1eeba38bc79 100644
> --- a/block/blk-mq.c
> +++ b/block/blk-mq.c
> @@ -258,7 +258,8 @@ void blk_mq_unquiesce_queue(struct request_queue *q)
>  	blk_queue_flag_clear(QUEUE_FLAG_QUIESCED, q);
>  
>  	/* dispatch requests which are inserted during quiescing */
> -	blk_mq_run_hw_queues(q, true);
> +	if (!blk_queue_dying(q) && !blk_queue_dead(q))
> +		blk_mq_run_hw_queues(q, true);
>  }
>  EXPORT_SYMBOL_GPL(blk_mq_unquiesce_queue);

We actually still have to unquieces the queue to flush entered requests to
a failed completion after killing that queue, like in nvme_set_queue_dying().