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    Subject[230/264] blk-flush: move the queue kick into
    3.1-stable review patch.  If anyone has any objections, please let me know.

    ------------------

    From: Jeff Moyer <jmoyer@redhat.com>

    commit e67b77c791ca2778198c9e7088f3266ed2da7a55 upstream.

    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>
    Signed-off-by: Jens Axboe <axboe@kernel.dk>
    Signed-off-by: Greg Kroah-Hartman <gregkh@suse.de>

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

    --- a/block/blk-core.c
    +++ b/block/blk-core.c
    @@ -1725,6 +1725,8 @@ int blk_insert_cloned_request(struct req
    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;
    --- 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;
    }




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