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    Subject[PATCH 138/241] dm: fix deadlock with request based dm and queue request_fn recursion
    Date
    3.5.7.2 -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: Herton Ronaldo Krzesinski <herton.krzesinski@canonical.com>
    ---
    drivers/md/dm.c | 8 +++++++-
    1 file changed, 7 insertions(+), 1 deletion(-)

    diff --git a/drivers/md/dm.c b/drivers/md/dm.c
    index 9ff3019..32370ea 100644
    --- a/drivers/md/dm.c
    +++ b/drivers/md/dm.c
    @@ -754,8 +754,14 @@ static void rq_completed(struct mapped_device *md, int rw, int run_queue)
    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
    --
    1.7.9.5


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