Created attachment 640583 [details]
test script triggering the problem

When shutting down a libvirt-lxc container with an NBD mounts, we sometimes get
a crash.

Steps to reproduce:
  * Get libvirt, and virt-sandbox from the Virtualization project
  * Install guestfs-tools
  * systemctl start libvirtd
  * Run the attached test script. The QEMU tests can be commented in it as
those aren't the ones triggering the bug. Note that the crash may not happen at
each run of the script, don't hesitate to run it several times if needed.

What happens:
  * the 'sandbox' container isn't correctly terminated due to the qemu-nbd
segfaulting.