elevator: don't sort reads between writes

Don't allow elv_dispatch_sort() to mix reads and writes together,
it's rarely a good idea.

Signed-off-by: Jens Axboe <jens.axboe@oracle.com>

1 files changed, 2 insertions, 0 deletions

diff --git a/block/elevator.c b/block/elevator.c
index d03762399147..25f6ef28e3bb 100644
--- a/block/elevator.c
+++ b/block/elevator.c
@@ -413,6 +413,8 @@ void elv_dispatch_sort(request_queue_t *q, struct request *rq)
         list_for_each_prev(entry, &q->queue_head) {
                 struct request *pos = list_entry_rq(entry);
 
+                if (rq_data_dir(rq) != rq_data_dir(pos))
+                        break;
                 if (pos->cmd_flags & (REQ_SOFTBARRIER|REQ_HARDBARRIER|REQ_STARTED))
                         break;
                 if (rq->sector >= boundary) {