1 files changed, 5 insertions, 1 deletions

diff --git a/block/blk-merge.c b/block/blk-merge.c
index d3b84bbb776a..7506c4fe0264 100644
--- a/block/blk-merge.c
+++ b/block/blk-merge.c
@@ -220,7 +220,10 @@ new_segment:
                 bvprv = bvec;
         } /* segments in rq */
 
-        if (q->dma_drain_size) {
+        if (q->dma_drain_size && q->dma_drain_needed(rq)) {
+                if (rq->cmd_flags & REQ_RW)
+                        memset(q->dma_drain_buffer, 0, q->dma_drain_size);
+
                 sg->page_link &= ~0x02;
                 sg = sg_next(sg);
                 sg_set_page(sg, virt_to_page(q->dma_drain_buffer),
@@ -228,6 +231,7 @@ new_segment:
                             ((unsigned long)q->dma_drain_buffer) &
                             (PAGE_SIZE - 1));
                 nsegs++;
+                rq->data_len += q->dma_drain_size;
         }
 
         if (sg)