[Bug 1420572] Please test proposed package

[Chris J Arges]

Hello Liang, or anyone else affected,

Accepted nova into utopic-proposed. The package will build now and be
available at
http://launchpad.net/ubuntu/+source/nova/1:2014.2.2-0ubuntu2 in a few
hours, and then in the -proposed repository.

Please help us by testing this new package.  See
https://wiki.ubuntu.com/Testing/EnableProposed for documentation how to
enable and use -proposed.  Your feedback will aid us getting this update
out to other Ubuntu users.

If this package fixes the bug for you, please add a comment to this bug,
mentioning the version of the package you tested, and change the tag
from verification-needed to verification-done. If it does not fix the
bug for you, please add a comment stating that, and change the tag to
verification-failed.  In either case, details of your testing will help
us make a better decision.

Further information regarding the verification process can be found at
https://wiki.ubuntu.com/QATeam/PerformingSRUVerification .  Thank you in
advance!

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https://bugs.launchpad.net/bugs/1420572

Title:
  [SRU] race between neutron-ovs-cleanup and nova-compute

Status in nova package in Ubuntu:
  Fix Released
Status in nova source package in Trusty:
  Fix Committed
Status in nova source package in Utopic:
  Fix Committed
Status in nova source package in Vivid:
  Fix Released

Bug description:
  [Impact]

   * We run neutron-ovs-cleanup in startup if neutron installed. If
     nova-compute does not wait for completion it will try to use
     veth/bridge devices that may be in the process of bring deleted.

  [Test Case]

   * Create neutron (ovs) network and boot an instance with this network
     as --nic

   * Check that creation was successful and network is functional. Also make
     a note corresponding veth and bridge devices (ip a).

   * Reboot system, check that expected veth and bridge devices are still
     there and that nova-compute is happy e.g. try sshing to your instance.
     Also check /var/log/upstart/nova-compute.log to see if service waited
     for ovs-cleanup to finish.

  [Regression Potential]

   * None

  ---- ---- ---- ----

  There is a race when both neutron-ovs-cleanup and nova-compute trying
  to do operations on the qvb*** and qvo*** devices. Below is a scenario
  I recently met,

  1. nova-compute was started and creating the veth_pair for VM
  instances running on the host -
  https://github.com/openstack/nova/blob/stable/icehouse/nova/network/linux_net.py#L1298

  2. neutron-ovs-cleanup was kicked off and deleted all the ports.

  3. when nova-compute tried to set the MTU at
  https://github.com/openstack/nova/blob/stable/icehouse/nova/network/linux_net.py#L1280
  , Stderr: u'Cannot find device "qvo***"\n' was reported. Because the
  device that was just created was deleted again by neutron-ovs-cleanup.

  As they both operate on the same resources, there needs a way to
  synchronize the operations the two processes do on those resources.

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