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    Subject[229/264] blk-flush: fix invalid BUG_ON in blk_insert_flush
    3.1-stable review patch.  If anyone has any objections, please let me know.

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

    From: Jeff Moyer <jmoyer@redhat.com>

    commit 834f9f61a525d2f6d3d0c93894e26326c8d3ceed upstream.

    A user reported a regression due to commit
    4853abaae7e4a2af938115ce9071ef8684fb7af4 (block: fix flush
    machinery for stacking drivers with differring flush flags).
    Part of the problem is that blk_insert_flush required a
    single bio be attached to the request. In reality, having
    no attached bio is also a valid case, as can be observed with
    an empty flush.

    [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-flush.c | 2 +-
    1 file changed, 1 insertion(+), 1 deletion(-)

    --- a/block/blk-flush.c
    +++ b/block/blk-flush.c
    @@ -320,7 +320,7 @@ void blk_insert_flush(struct request *rq
    return;
    }

    - BUG_ON(!rq->bio || rq->bio != rq->biotail);
    + BUG_ON(rq->bio != rq->biotail); /*assumes zero or single bio rq */

    /*
    * If there's data but flush is not necessary, the request can be



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