[Nbd] "nbd-client -d" hangs indefinitely

[Peter Simons <simons@...813...>]

Hi,

I'm using Linux kernel 2.6.37 with nbd 2.9.20. Recently, my nbd-client
has taken up the habit of hanging indefinitely during an attempt to
detach the device:

  # nbd-client -d /dev/nbd0
  Disconnecting: que,

Nothing happens after that point, neither the CPU nor the network is
active.

Does anyone have an idea how to explain, fix, or even debug that
phenomenon?

Take care,
Peter