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    Subject[PATCH 4.14 067/237] nbd: add a flush_workqueue in nbd_start_device
    Date
    From: Sun Ke <sunke32@huawei.com>

    [ Upstream commit 5c0dd228b5fc30a3b732c7ae2657e0161ec7ed80 ]

    When kzalloc fail, may cause trying to destroy the
    workqueue from inside the workqueue.

    If num_connections is m (2 < m), and NO.1 ~ NO.n
    (1 < n < m) kzalloc are successful. The NO.(n + 1)
    failed. Then, nbd_start_device will return ENOMEM
    to nbd_start_device_ioctl, and nbd_start_device_ioctl
    will return immediately without running flush_workqueue.
    However, we still have n recv threads. If nbd_release
    run first, recv threads may have to drop the last
    config_refs and try to destroy the workqueue from
    inside the workqueue.

    To fix it, add a flush_workqueue in nbd_start_device.

    Fixes: e9e006f5fcf2 ("nbd: fix max number of supported devs")
    Signed-off-by: Sun Ke <sunke32@huawei.com>
    Signed-off-by: Jens Axboe <axboe@kernel.dk>
    Signed-off-by: Sasha Levin <sashal@kernel.org>
    ---
    drivers/block/nbd.c | 10 ++++++++++
    1 file changed, 10 insertions(+)

    diff --git a/drivers/block/nbd.c b/drivers/block/nbd.c
    index 4c661ad91e7d3..8f56e6b2f114f 100644
    --- a/drivers/block/nbd.c
    +++ b/drivers/block/nbd.c
    @@ -1203,6 +1203,16 @@ static int nbd_start_device(struct nbd_device *nbd)
    args = kzalloc(sizeof(*args), GFP_KERNEL);
    if (!args) {
    sock_shutdown(nbd);
    + /*
    + * If num_connections is m (2 < m),
    + * and NO.1 ~ NO.n(1 < n < m) kzallocs are successful.
    + * But NO.(n + 1) failed. We still have n recv threads.
    + * So, add flush_workqueue here to prevent recv threads
    + * dropping the last config_refs and trying to destroy
    + * the workqueue from inside the workqueue.
    + */
    + if (i)
    + flush_workqueue(nbd->recv_workq);
    return -ENOMEM;
    }
    sk_set_memalloc(config->socks[i]->sock->sk);
    --
    2.20.1


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