[Bug 1697729] Re: port allocator allocates the same SPICE port for multiple guests (race condition)

[ChristianEhrhardt]

In Artful-proposed [1] now, and Zesty SRU is prepared in [2] for
regression tests series.

[1]: http://people.canonical.com/~ubuntu-archive/proposed-migration/update_excuses.html
[2]: https://launchpad.net/~ci-train-ppa-service/+archive/ubuntu/2825

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https://bugs.launchpad.net/bugs/1697729

Title:
  port allocator allocates the same SPICE port for multiple guests (race
  condition)

Status in Ubuntu Cloud Archive:
  Triaged
Status in Ubuntu Cloud Archive ocata series:
  Triaged
Status in Ubuntu Cloud Archive pike series:
  Triaged
Status in libvirt package in Ubuntu:
  In Progress
Status in libvirt source package in Zesty:
  Triaged
Status in libvirt source package in Artful:
  In Progress

Bug description:
  [Impact]

   * VMs start to fail depending on a race around spice port allocation

   * Solution is the Backport of an upstream fix that avoids a double 
     release on the ports

  [Test Case]

   * TBD

  [Regression Potential]

   * It is race after all, so we might miss some corner cases in the 
     testing, but reviewing the patch and given the verifications so far it 
     should be safe. From the patch the change is like:
       Old: Spice-Init -> Fail -> Release [...] QemuStop -> Release
                                            ^
                  If new alloc in this time it was released unintentionally
       New: Spice-Init -> Fail            [...] QemuStop -> Release
     This eliminates the race, but still releases the port as intended.

   * This change only affects users of spice ports.

  [Other Info]
   
   * n/a

  ---

  Using the UCA ocata release of libvirt we sporatically recieve this
  error message in nova-compute.log:

  2017-06-12 14:32:54.359 19007 ERROR nova.compute.manager [instance:
  d1af2a13-0a53-4d9c-ada3-683e4973f28a] libvirtError: internal error:
  process exited while connecting to monitor: ((null):63256): Spice-
  Warning **: reds.c:2463:reds_init_socket: reds_init_socket: binding
  socket to 10.141.112.21:5900 failed

  Please backport the fix for the following bug into UCA ocata/pike releases:
  https://bugzilla.redhat.com/show_bug.cgi?id=1397440

  The patch is documented here:
  https://www.spinics.net/linux/fedora/libvir/msg144093.html

  We've tested backporting this same fix using the ocata UCA libvirt
  2.5.0-3ubuntu5~cloud0 source package and it fixes the problem for us.

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