1 files changed, 19 insertions, 6 deletions

diff --git a/block/blk-flush.c b/block/blk-flush.c
index bb21e4c36f70..491eb30a242d 100644
--- a/block/blk-flush.c
+++ b/block/blk-flush.c
@@ -95,11 +95,12 @@ static unsigned int blk_flush_policy(unsigned int fflags, struct request *rq)
 {
         unsigned int policy = 0;
 
+        if (blk_rq_sectors(rq))
+                policy |= REQ_FSEQ_DATA;
+
         if (fflags & REQ_FLUSH) {
                 if (rq->cmd_flags & REQ_FLUSH)
                         policy |= REQ_FSEQ_PREFLUSH;
-                if (blk_rq_sectors(rq))
-                        policy |= REQ_FSEQ_DATA;
                 if (!(fflags & REQ_FUA) && (rq->cmd_flags & REQ_FUA))
                         policy |= REQ_FSEQ_POSTFLUSH;
         }
@@ -122,7 +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;
 }
 
 /**
@@ -300,9 +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.
@@ -312,6 +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.
@@ -319,6 +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;
         }
 
@@ -329,6 +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);