blk-mq: Fix blk_mq_tagset_busy_iter() for shared tags

Since it is now possible for a tagset to share a single set of tags, the
iter function should not re-iter the tags for the count of #hw queues in
that case. Rather it should just iter once.

Fixes: e155b0c238 ("blk-mq: Use shared tags for shared sbitmap support")
Reported-by: Kashyap Desai <kashyap.desai@broadcom.com>
Signed-off-by: John Garry <john.garry@huawei.com>
Reviewed-by: Ming Lei <ming.lei@redhat.com>
Tested-by: Kashyap Desai <kashyap.desai@broadcom.com>
Link: https://lore.kernel.org/r/1634550083-202815-1-git-send-email-john.garry@huawei.com
Signed-off-by: Jens Axboe <axboe@kernel.dk>

block/blk-mq-tag.c

@@ -399,9 +399,12 @@ void blk_mq_all_tag_iter(struct blk_mq_tags *tags, busy_tag_iter_fn *fn,
 void blk_mq_tagset_busy_iter(struct blk_mq_tag_set *tagset,
 		busy_tag_iter_fn *fn, void *priv)
 {
-	int i;
+	unsigned int flags = tagset->flags;
+	int i, nr_tags;
 
-	for (i = 0; i < tagset->nr_hw_queues; i++) {
+	nr_tags = blk_mq_is_shared_tags(flags) ? 1 : tagset->nr_hw_queues;
+
+	for (i = 0; i < nr_tags; i++) {
 		if (tagset->tags && tagset->tags[i])
 			__blk_mq_all_tag_iter(tagset->tags[i], fn, priv,
 					      BT_TAG_ITER_STARTED);