[Bug 2156566] Re: neutron-ovs-agent crashes on restart with tunneling disabled (tun_br is None)

[Seyeong Kim]

** Also affects: neutron (Ubuntu)
   Importance: Undecided
       Status: New

** Changed in: neutron (Ubuntu)
       Status: New => In Progress

** Also affects: neutron (Ubuntu Resolute)
   Importance: Undecided
       Status: New

** Changed in: neutron (Ubuntu Resolute)
       Status: New => In Progress

** Changed in: neutron (Ubuntu)
     Assignee: (unassigned) => Seyeong Kim (seyeongkim)

** Changed in: neutron (Ubuntu Resolute)
     Assignee: (unassigned) => Seyeong Kim (seyeongkim)

** Changed in: cloud-archive/gazpacho
       Status: New => In Progress

** Changed in: cloud-archive/gazpacho
     Assignee: (unassigned) => Seyeong Kim (seyeongkim)

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https://bugs.launchpad.net/bugs/2156566

Title:
  neutron-ovs-agent crashes on restart with tunneling disabled (tun_br
  is None)

Status in Ubuntu Cloud Archive:
  New
Status in Ubuntu Cloud Archive gazpacho series:
  In Progress
Status in neutron:
  Fix Released
Status in neutron package in Ubuntu:
  In Progress
Status in neutron source package in Resolute:
  In Progress

Bug description:
  Environment

    neutron 28.0.0, OpenStack 2026.1 "Gazpacho" on Ubuntu 24.04 LTS
  (Noble, via Ubuntu Cloud Archive); confirmed still present on master.

  On an ML2/OVS deployment with tunneling disabled
  (enable_tunneling=False, type drivers flat/vlan, no br-tun), neutron-
  openvswitch-agent crashes on restart.

  With tunneling off, self.tun_br is None, but _restore_local_vlan_map()
  calls self.tun_br.get_flood_to_tun_ofports() with no "if self.tun_br
  is not None" guard.

  Call path that crashes

      OVSNeutronAgent.__init__()
          -> _restore_local_vlan_map()
              -> if net_uuid:                 # True only after the agent has run
                     tun_ofports = self.tun_br.get_flood_to_tun_ofports(...)
                                   ^^^^^^^^^^^
                                   self.tun_br is None  ->  AttributeError

  Why it only happens on restart, not first start: the call sits behind
  "if net_uuid:", and an integration-bridge port only carries net_uuid
  in its OVS other_config after the agent has written it during normal
  operation.

      1st start:  ports have NO net_uuid   ->  if net_uuid: False  ->  skipped  -> OK
      restart:    ports HAVE    net_uuid   ->  if net_uuid: True   ->  call     -> crash

  So the first agent start is fine; every restart after that crashes
  deterministically.

  Traceback

      ERROR neutron...ovs_oskenapp Agent main thread died of an exception: AttributeError: 'NoneType' object has no attribute 'get_flood_to_tun_ofports'
        File ".../ovs_neutron_agent.py", line 342, in __init__
          self._restore_local_vlan_map()
        File ".../ovs_neutron_agent.py", line 520, in _restore_local_vlan_map
          tun_ofports = self.tun_br.get_flood_to_tun_ofports(local_vlan)
      AttributeError: 'NoneType' object has no attribute 'get_flood_to_tun_ofports'

  Because the crash is in __init__, the agent never reaches rpc_loop and
  never (re)programs OVS flows; instances on the node lose provider-
  network connectivity until manual recovery, and it recurs on every
  restart.

  Reproduce

  - deploy ML2/OVS with enable_tunneling=False 
  - boot an instance on a flat/VLAN provider network (so the tap ports get other_config:net_uuid)
  - restart neutron-openvswitch-agent.

  Temporary workaround (recurs on next restart)

      ovs-vsctl remove Port <integration-bridge-tap-port> other_config net_uuid
      systemctl restart neutron-openvswitch-agent

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