nicira plugin - metadata ops in delete_router might trigger eventlet deadlock

[Salvatore Orlando]

https://github.com/openstack/neutron/blob/master/neutron/plugins/nicira/NeutronPlugin.py#L1540

delete_router calls handle_router_metadata_access.
The latter method creates 1 network, 1 subnet, and attaches that subnet to the router, performing db and nvp operations.
This results in a very long transaction which can trigger eventlet deadlocks which have already been observed.

However, this is unlikely to happen in practice as router deletion is not allowed until the last interface has been removed. This means handle_router_metadata_access is likely to be a no-op.

while a simple fix might be just removing the metadata network mgmt code, it might be worth keeping it there in case the logic for router deletion might change in the future.

[Armando Migliaccio (armando-migliaccio)]

I noticed that too when I did the refactoring...however I can see the plugin to move away from that metadata model once the agentless is introduced and supported by NVP. That does not mean that mitigation should be put in place in the meantime.