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    Subject[PATCH AUTOSEL 4.19 097/100] nbd: fix possible sysfs duplicate warning
    Date
    From: Xiubo Li <xiubli@redhat.com>

    [ Upstream commit 862488105b84ca744b3d8ff131e0fcfe10644be1 ]

    1. nbd_put takes the mutex and drops nbd->ref to 0. It then does
    idr_remove and drops the mutex.

    2. nbd_genl_connect takes the mutex. idr_find/idr_for_each fails
    to find an existing device, so it does nbd_dev_add.

    3. just before the nbd_put could call nbd_dev_remove or not finished
    totally, but if nbd_dev_add try to add_disk, we can hit:

    debugfs: Directory 'nbd1' with parent 'block' already present!

    This patch will make sure all the disk add/remove stuff are done
    by holding the nbd_index_mutex lock.

    Reported-by: Mike Christie <mchristi@redhat.com>
    Reviewed-by: Josef Bacik <josef@toxicpanda.com>
    Signed-off-by: Xiubo Li <xiubli@redhat.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 bc2fa4e85f0ca..d445195945618 100644
    --- a/drivers/block/nbd.c
    +++ b/drivers/block/nbd.c
    @@ -228,8 +228,8 @@ static void nbd_put(struct nbd_device *nbd)
    if (refcount_dec_and_mutex_lock(&nbd->refs,
    &nbd_index_mutex)) {
    idr_remove(&nbd_index_idr, nbd->index);
    - mutex_unlock(&nbd_index_mutex);
    nbd_dev_remove(nbd);
    + mutex_unlock(&nbd_index_mutex);
    }
    }

    --
    2.20.1
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