block: simplify empty barrier implementation

[deliverable/linux.git] / block / blk-barrier.c

diff --git a/block/blk-barrier.c b/block/blk-barrier.c
index b03d88013e1ef6a2cacf0b9e8317813fcfcbbb27..c63044e9c4c0276165ada0dfacdc2c54196dd040 100644 (file)
--- a/block/blk-barrier.c
+++ b/block/blk-barrier.c
@@ -162,6 +162,14 @@ static inline bool start_ordered(struct request_queue *q, struct request **rqp)
        q->ordered = q->next_ordered;
        q->ordseq |= QUEUE_ORDSEQ_STARTED;
 
+       /*
+        * For an empty barrier, there's no actual BAR request, which
+        * in turn makes POSTFLUSH unnecessary.  Mask them off.
+        */
+       if (!rq->hard_nr_sectors)
+               q->ordered &= ~(QUEUE_ORDERED_DO_BAR |
+                               QUEUE_ORDERED_DO_POSTFLUSH);
+
        /* stash away the original request */
        elv_dequeue_request(q, rq);
        q->orig_bar_rq = rq;
@@ -171,13 +179,9 @@ static inline bool start_ordered(struct request_queue *q, struct request **rqp)
         * Queue ordered sequence.  As we stack them at the head, we
         * need to queue in reverse order.  Note that we rely on that
         * no fs request uses ELEVATOR_INSERT_FRONT and thus no fs
-        * request gets inbetween ordered sequence. If this request is
-        * an empty barrier, we don't need to do a postflush ever since
-        * there will be no data written between the pre and post flush.
-        * Hence a single flush will suffice.
+        * request gets inbetween ordered sequence.
         */
-       if ((q->ordered & QUEUE_ORDERED_DO_POSTFLUSH) &&
-           !blk_empty_barrier(q->orig_bar_rq)) {
+       if (q->ordered & QUEUE_ORDERED_DO_POSTFLUSH) {
                queue_flush(q, QUEUE_ORDERED_DO_POSTFLUSH);
                rq = &q->post_flush_rq;
        } else