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    Subject[PATCH 4.19 109/191] nbd: make the config put is called before the notifying the waiter
    Date
    From: Xiubo Li <xiubli@redhat.com>

    [ Upstream commit 87aac3a80af5cbad93e63250e8a1e19095ba0d30 ]

    There has one race case for ceph's rbd-nbd tool. When do mapping
    it may fail with EBUSY from ioctl(nbd, NBD_DO_IT), but actually
    the nbd device has already unmaped.

    It dues to if just after the wake_up(), the recv_work() is scheduled
    out and defers calling the nbd_config_put(), though the map process
    has exited the "nbd->recv_task" is not cleared.

    Signed-off-by: Xiubo Li <xiubli@redhat.com>
    Reviewed-by: Josef Bacik <josef@toxicpanda.com>
    Signed-off-by: Jens Axboe <axboe@kernel.dk>
    Signed-off-by: Sasha Levin <sashal@kernel.org>
    ---
    drivers/block/nbd.c | 2 +-
    1 file changed, 1 insertion(+), 1 deletion(-)

    diff --git a/drivers/block/nbd.c b/drivers/block/nbd.c
    index d7c7232e438c9..52e1e71e81241 100644
    --- a/drivers/block/nbd.c
    +++ b/drivers/block/nbd.c
    @@ -740,9 +740,9 @@ static void recv_work(struct work_struct *work)

    blk_mq_complete_request(blk_mq_rq_from_pdu(cmd));
    }
    + nbd_config_put(nbd);
    atomic_dec(&config->recv_threads);
    wake_up(&config->recv_wq);
    - nbd_config_put(nbd);
    kfree(args);
    }

    --
    2.27.0


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