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    Subject[ 24/54] dm: fix deadlock with request based dm and queue request_fn recursion
    Date
    3.6-stable review patch.  If anyone has any objections, please let me know.

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

    From: Jens Axboe <axboe@kernel.dk>

    commit a8c32a5c98943d370ea606a2e7dc04717eb92206 upstream.

    Request based dm attempts to re-run the request queue off the
    request completion path. If used with a driver that potentially does
    end_io from its request_fn, we could deadlock trying to recurse
    back into request dispatch. Fix this by punting the request queue
    run to kblockd.

    Tested to fix a quickly reproducible deadlock in such a scenario.

    Acked-by: Alasdair G Kergon <agk@redhat.com>
    Signed-off-by: Jens Axboe <axboe@kernel.dk>
    Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>

    ---
    drivers/md/dm.c | 8 +++++++-
    1 file changed, 7 insertions(+), 1 deletion(-)

    --- a/drivers/md/dm.c
    +++ b/drivers/md/dm.c
    @@ -754,8 +754,14 @@ static void rq_completed(struct mapped_d
    if (!md_in_flight(md))
    wake_up(&md->wait);

    + /*
    + * Run this off this callpath, as drivers could invoke end_io while
    + * inside their request_fn (and holding the queue lock). Calling
    + * back into ->request_fn() could deadlock attempting to grab the
    + * queue lock again.
    + */
    if (run_queue)
    - blk_run_queue(md->queue);
    + blk_run_queue_async(md->queue);

    /*
    * dm_put() must be at the end of this function. See the comment above



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