1 files changed, 17 insertions, 10 deletions

diff --git a/block/blk-merge.c b/block/blk-merge.c
index 5efc9e7a68b7..6cf8f0c70a51 100644
--- a/block/blk-merge.c
+++ b/block/blk-merge.c
@@ -11,7 +11,7 @@
 
 void blk_recalc_rq_sectors(struct request *rq, int nsect)
 {
-        if (blk_fs_request(rq)) {
+        if (blk_fs_request(rq) || blk_discard_rq(rq)) {
                 rq->hard_sector += nsect;
                 rq->hard_nr_sectors -= nsect;
 
@@ -131,13 +131,17 @@ static int blk_phys_contig_segment(struct request_queue *q, struct bio *bio,
         if (!test_bit(QUEUE_FLAG_CLUSTER, &q->queue_flags))
                 return 0;
 
-        if (!BIOVEC_PHYS_MERGEABLE(__BVEC_END(bio), __BVEC_START(nxt)))
-                return 0;
         if (bio->bi_size + nxt->bi_size > q->max_segment_size)
                 return 0;
 
+        if (!bio_has_data(bio))
+                return 1;
+
+        if (!BIOVEC_PHYS_MERGEABLE(__BVEC_END(bio), __BVEC_START(nxt)))
+                return 0;
+
         /*
-         * bio and nxt are contigous in memory, check if the queue allows
+         * bio and nxt are contiguous in memory; check if the queue allows
          * these two to be merged into one
          */
         if (BIO_SEG_BOUNDARY(q, bio, nxt))
@@ -153,8 +157,9 @@ static int blk_hw_contig_segment(struct request_queue *q, struct bio *bio,
                 blk_recount_segments(q, bio);
         if (!bio_flagged(nxt, BIO_SEG_VALID))
                 blk_recount_segments(q, nxt);
-        if (!BIOVEC_VIRT_MERGEABLE(__BVEC_END(bio), __BVEC_START(nxt)) ||
-            BIOVEC_VIRT_OVERSIZE(bio->bi_hw_back_size + nxt->bi_hw_front_size))
+        if (bio_has_data(bio) &&
+            (!BIOVEC_VIRT_MERGEABLE(__BVEC_END(bio), __BVEC_START(nxt)) ||
+             BIOVEC_VIRT_OVERSIZE(bio->bi_hw_back_size + nxt->bi_hw_front_size)))
                 return 0;
         if (bio->bi_hw_back_size + nxt->bi_hw_front_size > q->max_segment_size)
                 return 0;
@@ -317,8 +322,9 @@ int ll_back_merge_fn(struct request_queue *q, struct request *req,
         if (!bio_flagged(bio, BIO_SEG_VALID))
                 blk_recount_segments(q, bio);
         len = req->biotail->bi_hw_back_size + bio->bi_hw_front_size;
-        if (BIOVEC_VIRT_MERGEABLE(__BVEC_END(req->biotail), __BVEC_START(bio))
-            && !BIOVEC_VIRT_OVERSIZE(len)) {
+        if (!bio_has_data(bio) || 
+            (BIOVEC_VIRT_MERGEABLE(__BVEC_END(req->biotail), __BVEC_START(bio))
+             && !BIOVEC_VIRT_OVERSIZE(len))) {
                 int mergeable =  ll_new_mergeable(q, req, bio);
 
                 if (mergeable) {
@@ -356,8 +362,9 @@ int ll_front_merge_fn(struct request_queue *q, struct request *req,
                 blk_recount_segments(q, bio);
         if (!bio_flagged(req->bio, BIO_SEG_VALID))
                 blk_recount_segments(q, req->bio);
-        if (BIOVEC_VIRT_MERGEABLE(__BVEC_END(bio), __BVEC_START(req->bio)) &&
-            !BIOVEC_VIRT_OVERSIZE(len)) {
+        if (!bio_has_data(bio) || 
+            (BIOVEC_VIRT_MERGEABLE(__BVEC_END(bio), __BVEC_START(req->bio)) &&
+             !BIOVEC_VIRT_OVERSIZE(len))) {
                 int mergeable =  ll_new_mergeable(q, req, bio);
 
                 if (mergeable) {