blk-flush: move the queue kick into

A dm-multipath user reported[1] a problem when trying to boot
a kernel with commit 4853abaae7e4a2af938115ce9071ef8684fb7af4
(block: fix flush machinery for stacking drivers with differring
flush flags) applied.  It turns out that an empty flush request
can be sent into blk_insert_flush.  When the BUG_ON was fixed
to allow for this, I/O on the underlying device would stall.  The
reason is that blk_insert_cloned_request does not kick the queue.
In the aforementioned commit, I had added a special case to
kick the queue if data was sent down but the queue flags did
not require a flush.  A better solution is to push the queue
kick up into blk_insert_cloned_request.

This patch, along with a follow-on which fixes the BUG_ON, fixes
the issue reported.

[1] http://www.redhat.com/archives/dm-devel/2011-September/msg00154.html

Reported-by: Christophe Saout <christophe@saout.de>
Signed-off-by: Jeff Moyer <jmoyer@redhat.com>
Acked-by: Tejun Heo <tj@kernel.org>

Stable note: 3.1
Cc: stable@vger.kernel.org
Signed-off-by: Jens Axboe <axboe@kernel.dk>

2 files changed, 2 insertions, 1 deletions

diff --git a/block/blk-core.c b/block/blk-core.c
index d34433ae7917..795154e54a75 100644
--- a/block/blk-core.c
+++ b/block/blk-core.c
@@ -1725,6 +1725,8 @@ int blk_insert_cloned_request(struct request_queue *q, struct request *rq)
                 where = ELEVATOR_INSERT_FLUSH;
 
         add_acct_request(q, rq, where);
+        if (where == ELEVATOR_INSERT_FLUSH)
+                __blk_run_queue(q);
         spin_unlock_irqrestore(q->queue_lock, flags);
 
         return 0;
diff --git a/block/blk-flush.c b/block/blk-flush.c
index 89ae3b9bf7ca..720ad607ff91 100644
--- a/block/blk-flush.c
+++ b/block/blk-flush.c
@@ -330,7 +330,6 @@ 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;
         }