block: simplify blk_mq_plug

Drop the unused q argument, and invert the check to move the exception
into a branch and the regular path as the normal return.

Signed-off-by: Christoph Hellwig <hch@lst.de>
Reviewed-by: Chaitanya Kulkarni <kch@nvidia.com>
Reviewed-by: Damien Le Moal <damien.lemoal@opensource.wdc.com>
Reviewed-by: Johannes Thumshirn <johannes.thumshirn@wdc.com>
Link: https://lore.kernel.org/r/20220706070350.1703384-5-hch@lst.de
Signed-off-by: Jens Axboe <axboe@kernel.dk>

block/blk-core.c

@@ -719,7 +719,7 @@ void submit_bio_noacct(struct bio *bio)
 
 	might_sleep();
 
-	plug = blk_mq_plug(q, bio);
+	plug = blk_mq_plug(bio);
 	if (plug && plug->nowait)
 		bio->bi_opf |= REQ_NOWAIT;
 

block/blk-merge.c

@@ -1051,7 +1051,7 @@ bool blk_attempt_plug_merge(struct request_queue *q, struct bio *bio,
 	struct blk_plug *plug;
 	struct request *rq;
 
-	plug = blk_mq_plug(q, bio);
+	plug = blk_mq_plug(bio);
 	if (!plug || rq_list_empty(plug->mq_list))
 		return false;
 

block/blk-mq.c

@@ -2808,7 +2808,7 @@ static void bio_set_ioprio(struct bio *bio)
 void blk_mq_submit_bio(struct bio *bio)
 {
 	struct request_queue *q = bdev_get_queue(bio->bi_bdev);
-	struct blk_plug *plug = blk_mq_plug(q, bio);
+	struct blk_plug *plug = blk_mq_plug(bio);
 	const int is_sync = op_is_sync(bio->bi_opf);
 	struct request *rq;
 	unsigned int nr_segs = 1;

block/blk-mq.h

@@ -294,7 +294,6 @@ static inline void blk_mq_clear_mq_map(struct blk_mq_queue_map *qmap)
 
 /*
  * blk_mq_plug() - Get caller context plug
- * @q: request queue
  * @bio : the bio being submitted by the caller context
  *
  * Plugging, by design, may delay the insertion of BIOs into the elevator in
@@ -305,23 +304,22 @@ static inline void blk_mq_clear_mq_map(struct blk_mq_queue_map *qmap)
  * order. While this is not a problem with regular block devices, this ordering
  * change can cause write BIO failures with zoned block devices as these
  * require sequential write patterns to zones. Prevent this from happening by
- * ignoring the plug state of a BIO issuing context if the target request queue
- * is for a zoned block device and the BIO to plug is a write operation.
+ * ignoring the plug state of a BIO issuing context if it is for a zoned block
+ * device and the BIO to plug is a write operation.
  *
  * Return current->plug if the bio can be plugged and NULL otherwise
  */
-static inline struct blk_plug *blk_mq_plug(struct request_queue *q,
-					   struct bio *bio)
+static inline struct blk_plug *blk_mq_plug( struct bio *bio)
 {
+	/* Zoned block device write operation case: do not plug the BIO */
+	if (bdev_is_zoned(bio->bi_bdev) && op_is_write(bio_op(bio)))
+		return NULL;
+
 	/*
 	 * For regular block devices or read operations, use the context plug
 	 * which may be NULL if blk_start_plug() was not executed.
 	 */
-	if (!bdev_is_zoned(bio->bi_bdev) || !op_is_write(bio_op(bio)))
-		return current->plug;
-
-	/* Zoned block device write operation case: do not plug the BIO */
-	return NULL;
+	return current->plug;
 }
 
 /* Free all requests on the list */