Re: [PATCH 2/5] blk-mq: Keep set->nr_hw_queues and set->map[].nr_queues in sync

[Ming Lei <ming.lei@xxxxxxxxxx>]

On Mon, Feb 17, 2020 at 01:08:36PM -0800, Bart Van Assche wrote:
> This patch fixes the following kernel warning:
> 
> WARNING: CPU: 0 PID: 2501 at include/linux/cpumask.h:137
> Call Trace:
>  blk_mq_run_hw_queue+0x19d/0x350 block/blk-mq.c:1508
>  blk_mq_run_hw_queues+0x112/0x1a0 block/blk-mq.c:1525
>  blk_mq_requeue_work+0x502/0x780 block/blk-mq.c:775
>  process_one_work+0x9af/0x1740 kernel/workqueue.c:2269
>  worker_thread+0x98/0xe40 kernel/workqueue.c:2415
>  kthread+0x361/0x430 kernel/kthread.c:255
> 
> Cc: Christoph Hellwig <hch@xxxxxxxxxxxxx>
> Cc: Ming Lei <ming.lei@xxxxxxxxxx>
> Cc: Hannes Reinecke <hare@xxxxxxxx>
> Cc: Johannes Thumshirn <jth@xxxxxxxxxx>
> Reported-by: syzbot+d44e1b26ce5c3e77458d@xxxxxxxxxxxxxxxxxxxxxxxxx
> Fixes: ed76e329d74a ("blk-mq: abstract out queue map") # v5.0
> Signed-off-by: Bart Van Assche <bvanassche@xxxxxxx>
> ---
>  block/blk-mq.c | 16 +++++++++++++---
>  1 file changed, 13 insertions(+), 3 deletions(-)
> 
> diff --git a/block/blk-mq.c b/block/blk-mq.c
> index f298500e6dda..2b9f490f5a64 100644
> --- a/block/blk-mq.c
> +++ b/block/blk-mq.c
> @@ -3050,6 +3050,16 @@ static int blk_mq_update_queue_map(struct blk_mq_tag_set *set)
>  	}
>  }
>  
> +static void blk_mq_set_nr_hw_queues(struct blk_mq_tag_set *set,
> +				    int new_nr_hw_queues)
> +{
> +	int i;
> +
> +	set->nr_hw_queues = new_nr_hw_queues;
> +	for (i = 0; i < set->nr_maps; i++)
> +		set->map[i].nr_queues = new_nr_hw_queues;
> +}
> +
>  static int blk_mq_realloc_tag_set_tags(struct blk_mq_tag_set *set,
>  				  int cur_nr_hw_queues, int new_nr_hw_queues)
>  {
> @@ -3068,7 +3078,7 @@ static int blk_mq_realloc_tag_set_tags(struct blk_mq_tag_set *set,
>  		       sizeof(*set->tags));
>  	kfree(set->tags);
>  	set->tags = new_tags;
> -	set->nr_hw_queues = new_nr_hw_queues;
> +	blk_mq_set_nr_hw_queues(set, new_nr_hw_queues);
>  
>  	return 0;
>  }
> @@ -3330,7 +3340,7 @@ static void __blk_mq_update_nr_hw_queues(struct blk_mq_tag_set *set,
>  		goto reregister;
>  
>  	prev_nr_hw_queues = set->nr_hw_queues;
> -	set->nr_hw_queues = nr_hw_queues;
> +	blk_mq_set_nr_hw_queues(set, nr_hw_queues);
>  	blk_mq_update_queue_map(set);
>  fallback:
>  	list_for_each_entry(q, &set->tag_list, tag_set_list) {
> @@ -3338,7 +3348,7 @@ static void __blk_mq_update_nr_hw_queues(struct blk_mq_tag_set *set,
>  		if (q->nr_hw_queues != set->nr_hw_queues) {
>  			pr_warn("Increasing nr_hw_queues to %d fails, fallback to %d\n",
>  					nr_hw_queues, prev_nr_hw_queues);
> -			set->nr_hw_queues = prev_nr_hw_queues;
> +			blk_mq_set_nr_hw_queues(set, prev_nr_hw_queues);
>  			blk_mq_map_queues(&set->map[HCTX_TYPE_DEFAULT]);
>  			goto fallback;
>  		}
> 

I guess the issue can be fixed by the following change, and we do not
need to touch each queue map:

diff --git a/block/blk-mq.c b/block/blk-mq.c
index 5f5c43ae3792..f7340afb89ec 100644
--- a/block/blk-mq.c
+++ b/block/blk-mq.c
@@ -3046,6 +3046,7 @@ static int blk_mq_update_queue_map(struct blk_mq_tag_set *set)
                return set->ops->map_queues(set);
        } else {
                BUG_ON(set->nr_maps > 1);
+               set->map[HCTX_TYPE_DEFAULT].nr_queues = set->nr_hw_queues;
                return blk_mq_map_queues(&set->map[HCTX_TYPE_DEFAULT]);
        }
 }


Thanks,
Ming