1 files changed, 76 insertions, 44 deletions

diff --git a/block/blk-barrier.c b/block/blk-barrier.c
index 6e72d661ae42..8eba4e43bb0c 100644
--- a/block/blk-barrier.c
+++ b/block/blk-barrier.c
@@ -24,8 +24,8 @@
 int blk_queue_ordered(struct request_queue *q, unsigned ordered,
                       prepare_flush_fn *prepare_flush_fn)
 {
-        if (ordered & (QUEUE_ORDERED_PREFLUSH | QUEUE_ORDERED_POSTFLUSH) &&
-            prepare_flush_fn == NULL) {
+        if (!prepare_flush_fn && (ordered & (QUEUE_ORDERED_DO_PREFLUSH |
+                                             QUEUE_ORDERED_DO_POSTFLUSH))) {
                 printk(KERN_ERR "%s: prepare_flush_fn required\n", __func__);
                 return -EINVAL;
         }
@@ -88,7 +88,7 @@ unsigned blk_ordered_req_seq(struct request *rq)
                 return QUEUE_ORDSEQ_DONE;
 }
 
-void blk_ordered_complete_seq(struct request_queue *q, unsigned seq, int error)
+bool blk_ordered_complete_seq(struct request_queue *q, unsigned seq, int error)
 {
         struct request *rq;
 
@@ -99,7 +99,7 @@ void blk_ordered_complete_seq(struct request_queue *q, unsigned seq, int error)
         q->ordseq |= seq;
 
         if (blk_ordered_cur_seq(q) != QUEUE_ORDSEQ_DONE)
-                return;
+                return false;
 
         /*
          * Okay, sequence complete.
@@ -109,6 +109,8 @@ void blk_ordered_complete_seq(struct request_queue *q, unsigned seq, int error)
 
         if (__blk_end_request(rq, q->orderr, blk_rq_bytes(rq)))
                 BUG();
+
+        return true;
 }
 
 static void pre_flush_end_io(struct request *rq, int error)
@@ -134,7 +136,7 @@ static void queue_flush(struct request_queue *q, unsigned which)
         struct request *rq;
         rq_end_io_fn *end_io;
 
-        if (which == QUEUE_ORDERED_PREFLUSH) {
+        if (which == QUEUE_ORDERED_DO_PREFLUSH) {
                 rq = &q->pre_flush_rq;
                 end_io = pre_flush_end_io;
         } else {
@@ -151,80 +153,110 @@ static void queue_flush(struct request_queue *q, unsigned which)
         elv_insert(q, rq, ELEVATOR_INSERT_FRONT);
 }
 
-static inline struct request *start_ordered(struct request_queue *q,
-                                            struct request *rq)
+static inline bool start_ordered(struct request_queue *q, struct request **rqp)
 {
+        struct request *rq = *rqp;
+        unsigned skip = 0;
+
         q->orderr = 0;
         q->ordered = q->next_ordered;
         q->ordseq |= QUEUE_ORDSEQ_STARTED;
 
         /*
-         * Prep proxy barrier request.
+         * 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);
+                /*
+                 * Empty barrier on a write-through device w/ ordered
+                 * tag has no command to issue and without any command
+                 * to issue, ordering by tag can't be used.  Drain
+                 * instead.
+                 */
+                if ((q->ordered & QUEUE_ORDERED_BY_TAG) &&
+                    !(q->ordered & QUEUE_ORDERED_DO_PREFLUSH)) {
+                        q->ordered &= ~QUEUE_ORDERED_BY_TAG;
+                        q->ordered |= QUEUE_ORDERED_BY_DRAIN;
+                }
+        }
+
+        /* stash away the original request */
         elv_dequeue_request(q, rq);
         q->orig_bar_rq = rq;
-        rq = &q->bar_rq;
-        blk_rq_init(q, rq);
-        if (bio_data_dir(q->orig_bar_rq->bio) == WRITE)
-                rq->cmd_flags |= REQ_RW;
-        if (q->ordered & QUEUE_ORDERED_FUA)
-                rq->cmd_flags |= REQ_FUA;
-        init_request_from_bio(rq, q->orig_bar_rq->bio);
-        rq->end_io = bar_end_io;
+        rq = NULL;
 
         /*
          * 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_POSTFLUSH) && !blk_empty_barrier(rq))
-                queue_flush(q, QUEUE_ORDERED_POSTFLUSH);
-        else
-                q->ordseq |= QUEUE_ORDSEQ_POSTFLUSH;
+        if (q->ordered & QUEUE_ORDERED_DO_POSTFLUSH) {
+                queue_flush(q, QUEUE_ORDERED_DO_POSTFLUSH);
+                rq = &q->post_flush_rq;
+        } else
+                skip |= QUEUE_ORDSEQ_POSTFLUSH;
 
-        elv_insert(q, rq, ELEVATOR_INSERT_FRONT);
+        if (q->ordered & QUEUE_ORDERED_DO_BAR) {
+                rq = &q->bar_rq;
+
+                /* initialize proxy request and queue it */
+                blk_rq_init(q, rq);
+                if (bio_data_dir(q->orig_bar_rq->bio) == WRITE)
+                        rq->cmd_flags |= REQ_RW;
+                if (q->ordered & QUEUE_ORDERED_DO_FUA)
+                        rq->cmd_flags |= REQ_FUA;
+                init_request_from_bio(rq, q->orig_bar_rq->bio);
+                rq->end_io = bar_end_io;
 
-        if (q->ordered & QUEUE_ORDERED_PREFLUSH) {
-                queue_flush(q, QUEUE_ORDERED_PREFLUSH);
+                elv_insert(q, rq, ELEVATOR_INSERT_FRONT);
+        } else
+                skip |= QUEUE_ORDSEQ_BAR;
+
+        if (q->ordered & QUEUE_ORDERED_DO_PREFLUSH) {
+                queue_flush(q, QUEUE_ORDERED_DO_PREFLUSH);
                 rq = &q->pre_flush_rq;
         } else
-                q->ordseq |= QUEUE_ORDSEQ_PREFLUSH;
+                skip |= QUEUE_ORDSEQ_PREFLUSH;
 
-        if ((q->ordered & QUEUE_ORDERED_TAG) || q->in_flight == 0)
-                q->ordseq |= QUEUE_ORDSEQ_DRAIN;
-        else
+        if ((q->ordered & QUEUE_ORDERED_BY_DRAIN) && q->in_flight)
                 rq = NULL;
+        else
+                skip |= QUEUE_ORDSEQ_DRAIN;
+
+        *rqp = rq;
 
-        return rq;
+        /*
+         * Complete skipped sequences.  If whole sequence is complete,
+         * return false to tell elevator that this request is gone.
+         */
+        return !blk_ordered_complete_seq(q, skip, 0);
 }
 
-int blk_do_ordered(struct request_queue *q, struct request **rqp)
+bool blk_do_ordered(struct request_queue *q, struct request **rqp)
 {
         struct request *rq = *rqp;
         const int is_barrier = blk_fs_request(rq) && blk_barrier_rq(rq);
 
         if (!q->ordseq) {
                 if (!is_barrier)
-                        return 1;
+                        return true;
 
-                if (q->next_ordered != QUEUE_ORDERED_NONE) {
-                        *rqp = start_ordered(q, rq);
-                        return 1;
-                } else {
+                if (q->next_ordered != QUEUE_ORDERED_NONE)
+                        return start_ordered(q, rqp);
+                else {
                         /*
-                         * This can happen when the queue switches to
-                         * ORDERED_NONE while this request is on it.
+                         * Queue ordering not supported.  Terminate
+                         * with prejudice.
                          */
                         elv_dequeue_request(q, rq);
                         if (__blk_end_request(rq, -EOPNOTSUPP,
                                               blk_rq_bytes(rq)))
                                 BUG();
                         *rqp = NULL;
-                        return 0;
+                        return false;
                 }
         }
 
@@ -235,9 +267,9 @@ int blk_do_ordered(struct request_queue *q, struct request **rqp)
         /* Special requests are not subject to ordering rules. */
         if (!blk_fs_request(rq) &&
             rq != &q->pre_flush_rq && rq != &q->post_flush_rq)
-                return 1;
+                return true;
 
-        if (q->ordered & QUEUE_ORDERED_TAG) {
+        if (q->ordered & QUEUE_ORDERED_BY_TAG) {
                 /* Ordered by tag.  Blocking the next barrier is enough. */
                 if (is_barrier && rq != &q->bar_rq)
                         *rqp = NULL;
@@ -248,7 +280,7 @@ int blk_do_ordered(struct request_queue *q, struct request **rqp)
                         *rqp = NULL;
         }
 
-        return 1;
+        return true;
 }
 
 static void bio_end_empty_barrier(struct bio *bio, int err)