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    Subject[patch 02/48] nbd: fix I/O hang on disconnected nbds
    2.6.28-stable review patch.  If anyone has any objections, please let us know.


    From: Paul Clements <>

    commit 4d48a542b42747c36a5937447d9c3de7c897ea50 upstream.

    Fix a problem that causes I/O to a disconnected (or partially initialized)
    nbd device to hang indefinitely. To reproduce:

    # ioctl NBD_SET_SIZE_BLOCKS /dev/nbd23 514048
    # dd if=/dev/nbd23 of=/dev/null bs=4096 count=1


    This can also occur when an nbd device loses its nbd-client/server
    connection. Although we clear the queue of any outstanding I/Os after the
    client/server connection fails, any additional I/Os that get queued later
    will hang.

    This bug may also be the problem reported in this bug report:

    Testing would need to be performed to determine if the two issues are the

    This problem was introduced by the new request handling thread code ("NBD:
    allow nbd to be used locally", 3/2008), which entered into mainline around

    The fix, which is fairly simple, is to restore the check for lo->sock
    being NULL in do_nbd_request. This causes I/O to an uninitialized nbd to
    immediately fail with an I/O error, as it did prior to the introduction of
    this bug.

    Signed-off-by: Paul Clements <>
    Reported-by: Jon Nelson <>
    Acked-by: Pavel Machek <>
    Signed-off-by: Andrew Morton <>
    Signed-off-by: Linus Torvalds <>
    Signed-off-by: Greg Kroah-Hartman <>

    drivers/block/nbd.c | 9 +++++++++
    1 file changed, 9 insertions(+)

    --- a/drivers/block/nbd.c
    +++ b/drivers/block/nbd.c
    @@ -549,6 +549,15 @@ static void do_nbd_request(struct reques

    BUG_ON(lo->magic != LO_MAGIC);

    + if (unlikely(!lo->sock)) {
    + printk(KERN_ERR "%s: Attempted send on closed socket\n",
    + lo->disk->disk_name);
    + req->errors++;
    + nbd_end_request(req);
    + spin_lock_irq(q->queue_lock);
    + continue;
    + }
    list_add_tail(&req->queuelist, &lo->waiting_queue);

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      Last update: 2009-02-14 02:31    [W:0.036 / U:83.584 seconds]
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