Re: [PATCH] blk-mq: Swap two calls in blk_mq_exit_queue()

[Ming Lei <ming.lei@redhat.com>]

On Thu, May 13, 2021 at 10:15:29AM -0700, Bart Van Assche wrote:
> If a tag set is shared across request queues (e.g. SCSI LUNs) then the
> block layer core keeps track of the number of active request queues in
> tags->active_queues. blk_mq_tag_busy() and blk_mq_tag_idle() update that
> atomic counter if the hctx flag BLK_MQ_F_TAG_QUEUE_SHARED is set. Make
> sure that blk_mq_exit_queue() calls blk_mq_tag_idle() before that flag is
> cleared by blk_mq_del_queue_tag_set().
> 
> Cc: Christoph Hellwig <hch@infradead.org>
> Cc: Ming Lei <ming.lei@redhat.com>
> Cc: Hannes Reinecke <hare@suse.com>
> Fixes: 0d2602ca30e4 ("blk-mq: improve support for shared tags maps")
> Signed-off-by: Bart Van Assche <bvanassche@acm.org>
> ---
>  block/blk-mq.c | 6 ++++--
>  1 file changed, 4 insertions(+), 2 deletions(-)
> 
> diff --git a/block/blk-mq.c b/block/blk-mq.c
> index 1ea012de60eb..96b8e3164835 100644
> --- a/block/blk-mq.c
> +++ b/block/blk-mq.c
> @@ -3289,10 +3289,12 @@ EXPORT_SYMBOL(blk_mq_init_allocated_queue);
>  /* 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;
> +	struct blk_mq_tag_set *set = q->tag_set;
>  
> -	blk_mq_del_queue_tag_set(q);
> +	/* Checks hctx->flags & BLK_MQ_F_TAG_QUEUE_SHARED. */
>  	blk_mq_exit_hw_queues(q, set, set->nr_hw_queues);
> +	/* May clear BLK_MQ_F_TAG_QUEUE_SHARED in hctx->flags. */
> +	blk_mq_del_queue_tag_set(q);
>  }
>  
>  static int __blk_mq_alloc_rq_maps(struct blk_mq_tag_set *set)
> 

Looks fine:

Reviewed-by: Ming Lei <ming.lei@redhat.com>

-- 
Ming