[PATCH 1/2] block: modify blk_mq_plug() to allow only reads for zoned block devices

[Pankaj Raghav <p.raghav@samsung.com>]

Modify blk_mq_plug() to allow plugging only for read operations in zoned
block devices as there are alternative IO paths in the linux block
layer which can end up doing a write via driver private requests in
sequential write zones.

Signed-off-by: Pankaj Raghav <p.raghav@samsung.com>
---
 block/blk-mq.h | 7 ++++---
 1 file changed, 4 insertions(+), 3 deletions(-)

diff --git a/block/blk-mq.h b/block/blk-mq.h
index 8ca453ac243d..005343df64ca 100644
--- a/block/blk-mq.h
+++ b/block/blk-mq.h
@@ -305,14 +305,15 @@ static inline void blk_mq_clear_mq_map(struct blk_mq_queue_map *qmap)
  * 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 it is for a zoned block
- * device and the BIO to plug is a write operation.
+ * device and the BIO to plug is not a read operation.
+ *
  *
  * Return current->plug if the bio can be plugged and NULL otherwise
  */
 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)))
+	/* Allow plugging only for read operations in zoned block devices */
+	if (bdev_is_zoned(bio->bi_bdev) && bio_op(bio) != REQ_OP_READ)
 		return NULL;
 
 	/*
-- 
2.25.1