4 files changed, 25 insertions, 6 deletions

diff --git a/block/blk-core.c b/block/blk-core.c
index b850bedad229..7c59b0f5eae8 100644
--- a/block/blk-core.c
+++ b/block/blk-core.c
@@ -1700,6 +1700,7 @@ EXPORT_SYMBOL_GPL(blk_rq_check_limits);
 int blk_insert_cloned_request(struct request_queue *q, struct request *rq)
 {
         unsigned long flags;
+        int where = ELEVATOR_INSERT_BACK;
 
         if (blk_rq_check_limits(q, rq))
                 return -EIO;
@@ -1716,7 +1717,10 @@ int blk_insert_cloned_request(struct request_queue *q, struct request *rq)
          */
         BUG_ON(blk_queued_rq(rq));
 
-        add_acct_request(q, rq, ELEVATOR_INSERT_BACK);
+        if (rq->cmd_flags & (REQ_FLUSH|REQ_FUA))
+                where = ELEVATOR_INSERT_FLUSH;
+
+        add_acct_request(q, rq, where);
         spin_unlock_irqrestore(q->queue_lock, flags);
 
         return 0;
@@ -2273,7 +2277,7 @@ static bool blk_end_bidi_request(struct request *rq, int error,
  *     %false - we are done with this request
  *     %true  - still buffers pending for this request
  **/
-static bool __blk_end_bidi_request(struct request *rq, int error,
+bool __blk_end_bidi_request(struct request *rq, int error,
                                    unsigned int nr_bytes, unsigned int bidi_bytes)
 {
         if (blk_update_bidi_request(rq, error, nr_bytes, bidi_bytes))
diff --git a/block/blk-flush.c b/block/blk-flush.c
index 2d162bd840d3..491eb30a242d 100644
--- a/block/blk-flush.c
+++ b/block/blk-flush.c
@@ -123,7 +123,7 @@ static void blk_flush_restore_request(struct request *rq)
 
         /* make @rq a normal request */
         rq->cmd_flags &= ~REQ_FLUSH_SEQ;
-        rq->end_io = NULL;
+        rq->end_io = rq->flush.saved_end_io;
 }
 
 /**
@@ -301,9 +301,6 @@ void blk_insert_flush(struct request *rq)
         unsigned int fflags = q->flush_flags;   /* may change, cache */
         unsigned int policy = blk_flush_policy(fflags, rq);
 
-        BUG_ON(rq->end_io);
-        BUG_ON(!rq->bio || rq->bio != rq->biotail);
-
         /*
          * @policy now records what operations need to be done.  Adjust
          * REQ_FLUSH and FUA for the driver.
@@ -313,6 +310,19 @@ void blk_insert_flush(struct request *rq)
                 rq->cmd_flags &= ~REQ_FUA;
 
         /*
+         * An empty flush handed down from a stacking driver may
+         * translate into nothing if the underlying device does not
+         * advertise a write-back cache.  In this case, simply
+         * complete the request.
+         */
+        if (!policy) {
+                __blk_end_bidi_request(rq, 0, 0, 0);
+                return;
+        }
+
+        BUG_ON(!rq->bio || rq->bio != rq->biotail);
+
+        /*
          * If there's data but flush is not necessary, the request can be
          * processed directly without going through flush machinery.  Queue
          * for normal execution.
@@ -320,6 +330,7 @@ void blk_insert_flush(struct request *rq)
         if ((policy & REQ_FSEQ_DATA) &&
             !(policy & (REQ_FSEQ_PREFLUSH | REQ_FSEQ_POSTFLUSH))) {
                 list_add_tail(&rq->queuelist, &q->queue_head);
+                blk_run_queue_async(q);
                 return;
         }
 
@@ -330,6 +341,7 @@ void blk_insert_flush(struct request *rq)
         memset(&rq->flush, 0, sizeof(rq->flush));
         INIT_LIST_HEAD(&rq->flush.list);
         rq->cmd_flags |= REQ_FLUSH_SEQ;
+        rq->flush.saved_end_io = rq->end_io; /* Usually NULL */
         rq->end_io = flush_data_end_io;
 
         blk_flush_complete_seq(rq, REQ_FSEQ_ACTIONS & ~policy, 0);
diff --git a/block/blk.h b/block/blk.h
index d6586287adc9..20b900a377c9 100644
--- a/block/blk.h
+++ b/block/blk.h
@@ -17,6 +17,8 @@ int blk_rq_append_bio(struct request_queue *q, struct request *rq,
                       struct bio *bio);
 void blk_dequeue_request(struct request *rq);
 void __blk_queue_free_tags(struct request_queue *q);
+bool __blk_end_bidi_request(struct request *rq, int error,
+                            unsigned int nr_bytes, unsigned int bidi_bytes);
 
 void blk_rq_timed_out_timer(unsigned long data);
 void blk_delete_timer(struct request *);
diff --git a/include/linux/blkdev.h b/include/linux/blkdev.h
index 847928546076..84b15d54f8c2 100644
--- a/include/linux/blkdev.h
+++ b/include/linux/blkdev.h
@@ -118,6 +118,7 @@ struct request {
                 struct {
                         unsigned int            seq;
                         struct list_head        list;
+                        rq_end_io_fn            *saved_end_io;
                 } flush;
         };