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[dm-devel] [PATCH 1/2] blk-flush: move the queue kick into blk_insert_cloned_request

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>
 block/blk-core.c  |    2 ++
 block/blk-flush.c |    1 -
 2 files changed, 2 insertions(+), 1 deletions(-)

diff --git a/block/blk-core.c b/block/blk-core.c
index d34433a..795154e 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)
 	add_acct_request(q, rq, where);
+		__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 491eb30..0ff29c6 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) &&
 		list_add_tail(&rq->queuelist, &q->queue_head);
-		blk_run_queue_async(q);

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