Incorrect port unbind request on instance delete

Tried following fix seemed to work
diff --git a/nova/network/neutronv2/api.py b/nova/network/neutronv2/api.py
index 7192031..c526393 100644
--- a/nova/network/neutronv2/api.py
+++ b/nova/network/neutronv2/api.py
@@ -1170,7 +1170,11 @@ class API(base_api.NetworkAPI):
         ports = set(ports) - ports_to_skip

         # Reset device_id and device_owner for the ports that are skipped
- self._unbind_ports(context, ports_to_skip, neutron)
+ # Only unbind port if neutron sees this port as bound
+ if data.get('ports', []):
+ self._unbind_ports(context, ports_to_skip, neutron)
+ else:
+ LOG.debug("Skipping port unbind as neutron does not see any ports attached")
         # Delete the rest of the ports
         self._delete_ports(neutron, instance, ports, raise_if_fail=True)

Marking as Low priority as I don't see this as anything more than a corner case.

This is a means to re-use the port (and its allocated address and MAC) without deleting the port and creating a new one with the same address and MAC. Obviously, you can't create a port before deletion with the same address and MAC, but you also can't create the port reliably after deletion because you can lose either address to another port - it's a race condition.

In the original test case, the issue was a host going down cauing a VM failure. The VM doesn't delete promptly on a freshly downed host (and deleting a VM takes an uncertain amount of time in any case), so it's impossible to free the port by conventional means, and replacing the VM requires recycling its address.

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Found open reviews for this bug in gerrit, setting to In Progress.

review: https://review.openstack.org/387687 in branch: master