1 files changed, 25 insertions, 1 deletions

diff --git a/block/elevator.c b/block/elevator.c
index f9736fbdab03..8cd5775acd7a 100644
--- a/block/elevator.c
+++ b/block/elevator.c
@@ -741,7 +741,21 @@ struct request *elv_next_request(struct request_queue *q)
                         q->boundary_rq = NULL;
                 }
 
-                if ((rq->cmd_flags & REQ_DONTPREP) || !q->prep_rq_fn)
+                if (rq->cmd_flags & REQ_DONTPREP)
+                        break;
+
+                if (q->dma_drain_size && rq->data_len) {
+                        /*
+                         * make sure space for the drain appears we
+                         * know we can do this because max_hw_segments
+                         * has been adjusted to be one fewer than the
+                         * device can handle
+                         */
+                        rq->nr_phys_segments++;
+                        rq->nr_hw_segments++;
+                }
+
+                if (!q->prep_rq_fn)
                         break;
 
                 ret = q->prep_rq_fn(q, rq);
@@ -754,6 +768,16 @@ struct request *elv_next_request(struct request_queue *q)
                          * avoid resource deadlock.  REQ_STARTED will
                          * prevent other fs requests from passing this one.
                          */
+                        if (q->dma_drain_size && rq->data_len &&
+                            !(rq->cmd_flags & REQ_DONTPREP)) {
+                                /*
+                                 * remove the space for the drain we added
+                                 * so that we don't add it again
+                                 */
+                                --rq->nr_phys_segments;
+                                --rq->nr_hw_segments;
+                        }
+
                         rq = NULL;
                         break;
                 } else if (ret == BLKPREP_KILL) {