blk-mq: Warn when attempting to run a hardware queue that is not mapped

A queue must be frozen while the mapped state of a hardware queue
is changed. Additionally, any change of the mapped state is
followed by a call to blk_mq_map_swqueue() (see also
blk_mq_init_allocated_queue() and blk_mq_update_nr_hw_queues()).
Since blk_mq_map_swqueue() does not map any unmapped hardware
queue onto any software queue, no attempt will be made to run
an unmapped hardware queue. Hence issue a warning upon attempts
to run an unmapped hardware queue.

Signed-off-by: Bart Van Assche <bart.vanassche@sandisk.com>
Reviewed-by: Christoph Hellwig <hch@lst.de>
Cc: Hannes Reinecke <hare@suse.com>
Cc: Omar Sandoval <osandov@fb.com>
Cc: Ming Lei <ming.lei@redhat.com>
Signed-off-by: Jens Axboe <axboe@kernel.dk>

block/blk-mq.c

@@ -1129,8 +1129,10 @@ static int blk_mq_hctx_next_cpu(struct blk_mq_hw_ctx *hctx)
 static void __blk_mq_delay_run_hw_queue(struct blk_mq_hw_ctx *hctx, bool async,
 					unsigned long msecs)
 {
-	if (unlikely(blk_mq_hctx_stopped(hctx) ||
-		     !blk_mq_hw_queue_mapped(hctx)))
+	if (WARN_ON_ONCE(!blk_mq_hw_queue_mapped(hctx)))
+		return;
+
+	if (unlikely(blk_mq_hctx_stopped(hctx)))
 		return;
 
 	if (!async && !(hctx->flags & BLK_MQ_F_BLOCKING)) {
@@ -1295,7 +1297,7 @@ static void blk_mq_run_work_fn(struct work_struct *work)
 
 void blk_mq_delay_queue(struct blk_mq_hw_ctx *hctx, unsigned long msecs)
 {
-	if (unlikely(!blk_mq_hw_queue_mapped(hctx)))
+	if (WARN_ON_ONCE(!blk_mq_hw_queue_mapped(hctx)))
 		return;
 
 	/*