block: Fix front merge check

For a front merge, the maximum number of sectors of the
request must be checked against the front merge BIO sector,
not the current sector of the request.

Signed-off-by: Damien Le Moal <damien.lemoal@hgst.com>
Reviewed-by: Hannes Reinecke <hare@suse.com>
Signed-off-by: Jens Axboe <axboe@fb.com>

2 files changed, 6 insertions, 5 deletions

diff --git a/block/blk-merge.c b/block/blk-merge.c
index e7c2fbc3f656..5e4d93edeaf7 100644
--- a/block/blk-merge.c
+++ b/block/blk-merge.c
@@ -500,7 +500,7 @@ int ll_back_merge_fn(struct request_queue *q, struct request *req,
             integrity_req_gap_back_merge(req, bio))
                 return 0;
         if (blk_rq_sectors(req) + bio_sectors(bio) >
-            blk_rq_get_max_sectors(req)) {
+            blk_rq_get_max_sectors(req, blk_rq_pos(req))) {
                 req->cmd_flags |= REQ_NOMERGE;
                 if (req == q->last_merge)
                         q->last_merge = NULL;
@@ -524,7 +524,7 @@ int ll_front_merge_fn(struct request_queue *q, struct request *req,
             integrity_req_gap_front_merge(req, bio))
                 return 0;
         if (blk_rq_sectors(req) + bio_sectors(bio) >
-            blk_rq_get_max_sectors(req)) {
+            blk_rq_get_max_sectors(req, bio->bi_iter.bi_sector)) {
                 req->cmd_flags |= REQ_NOMERGE;
                 if (req == q->last_merge)
                         q->last_merge = NULL;
@@ -570,7 +570,7 @@ static int ll_merge_requests_fn(struct request_queue *q, struct request *req,
          * Will it become too large?
          */
         if ((blk_rq_sectors(req) + blk_rq_sectors(next)) >
-            blk_rq_get_max_sectors(req))
+            blk_rq_get_max_sectors(req, blk_rq_pos(req)))
                 return 0;
 
         total_phys_segments = req->nr_phys_segments + next->nr_phys_segments;
diff --git a/include/linux/blkdev.h b/include/linux/blkdev.h
index 9d84c98b5c79..48f05d768a53 100644
--- a/include/linux/blkdev.h
+++ b/include/linux/blkdev.h
@@ -922,7 +922,8 @@ static inline unsigned int blk_max_size_offset(struct request_queue *q,
                         (offset & (q->limits.chunk_sectors - 1));
 }
 
-static inline unsigned int blk_rq_get_max_sectors(struct request *rq)
+static inline unsigned int blk_rq_get_max_sectors(struct request *rq,
+                                                  sector_t offset)
 {
         struct request_queue *q = rq->q;
 
@@ -932,7 +933,7 @@ static inline unsigned int blk_rq_get_max_sectors(struct request *rq)
         if (!q->limits.chunk_sectors || (req_op(rq) == REQ_OP_DISCARD))
                 return blk_queue_get_max_sectors(q, req_op(rq));
 
-        return min(blk_max_size_offset(q, blk_rq_pos(rq)),
+        return min(blk_max_size_offset(q, offset),
                         blk_queue_get_max_sectors(q, req_op(rq)));
 }