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>

diff --git a/block/elevator.c b/block/elevator.c
index d037623..25f6ef2 100644 (file)
--- 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) {