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[Thierry Carrez <thierry.carrez+lp@xxxxxxxxx>]

** Changed in: neutron
       Status: Fix Committed => Fix Released

** Changed in: neutron
    Milestone: None => juno-1

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https://bugs.launchpad.net/bugs/1290068

Title:
  Some dhcp tap devices remain after tempest run

Status in OpenStack Neutron (virtual network service):
  Fix Released

Bug description:
  After running tempest.api.network, 'ip link' shows many tap devices
  that were not cleaned up. These are tap devices for dhcp ports that no
  longer exist in neutron.

  The sequence why these taps remain is:

  - in dhcp_agent.py call_driver() is called with 'enable' for the
  network.

  - in dhcp.py DeviceManager, setup() RPCs to creates the logical dhcp
  port and the tap device successfully. Setup() finally calls
  _set_default_route(), and this attempts to do a RPC to the plugin to
  get the port. But tempest has finished the test and deleted the
  network in the time since the port was created, so a NetworkNotFound
  is raised.
  https://github.com/openstack/neutron/blob/5f8617bacf05d02db995289e734345bebab8124e/neutron/agent/linux/dhcp.py#L652

  - the NetworkNotFound is caught by call_driver() and the network is
  not put into the cache.
  https://github.com/openstack/neutron/blob/5f8617bacf05d02db995289e734345bebab8124e/neutron/agent/dhcp_agent.py#L214

  - then network_delete_end is processed, but this does nothing as there is no network in the cache.
  https://github.com/openstack/neutron/blob/5f8617bacf05d02db995289e734345bebab8124e/neutron/agent/dhcp_agent.py#L224 So unplug() is never called for the dhcp tap device.
   

  It's not clear to me why _set_default_route() ever needs to do the plugin.get_dhcp_port() RPC. When the dhcp agent calls the 'enable' method on the helper, DeviceManager.setup() has the port and could pass it in the chained call to _set_default_route(). 
  And when the dhcp agent calls the 'restart' method, that calls enable(), but it then also calls DeviceManager.update() which just calls _set_default_route() for a second time. Also _set_default_route() gets called on every reload_allocation, so this is frequent enough.

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