[Bug 1623664] Re: [SRU] Race between L3 agent and neutron-ns-cleanup

Chuck Short chuck.short at canonical.com
Mon Mar 27 18:52:50 UTC 2017 

[Description]
A race condition on L3 agents can occur when the cron jobs run when the routing tables are empty. This results in the traceback above.

[Test Case]
Run tempest and then check the namespaces after running neutron-ns-cleanup

[Regression Potential]
None

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Title:
  [SRU] Race between L3 agent and neutron-ns-cleanup

Status in Ubuntu Cloud Archive:
  New
Status in neutron:
  Invalid
Status in neutron package in Ubuntu:
  New
Status in neutron-lbaas package in Ubuntu:
  New
Status in neutron source package in Xenial:
  New
Status in neutron-lbaas source package in Xenial:
  New
Status in neutron source package in Yakkety:
  New
Status in neutron-lbaas source package in Yakkety:
  New

Bug description:
  I suspect a race between the neutron L3 agent and the neutron-netns-
  cleanup script, which runs as a CRON job in Ubuntu. Here's a stack
  trace in the router delete code path:

  2016-08-03 03:30:03.392 2595 ERROR neutron.callbacks.manager [-] Error during notification for neutron.agent.metadata.driver.before_router_removed router, before_delete
  2016-08-03 03:30:03.392 2595 ERROR neutron.callbacks.manager Traceback (most recent call last):
  2016-08-03 03:30:03.392 2595 ERROR neutron.callbacks.manager   File "/usr/lib/python2.7/dist-packages/neutron/callbacks/manager.py", line 141, in _notify_loop
  2016-08-03 03:30:03.392 2595 ERROR neutron.callbacks.manager     callback(resource, event, trigger, **kwargs)
  2016-08-03 03:30:03.392 2595 ERROR neutron.callbacks.manager   File "/usr/lib/python2.7/dist-packages/neutron/agent/metadata/driver.py", line 176, in before_router_removed
  2016-08-03 03:30:03.392 2595 ERROR neutron.callbacks.manager     router.iptables_manager.apply()
  2016-08-03 03:30:03.392 2595 ERROR neutron.callbacks.manager   File "/usr/lib/python2.7/dist-packages/neutron/agent/linux/iptables_manager.py", line 423, in apply
  2016-08-03 03:30:03.392 2595 ERROR neutron.callbacks.manager     return self._apply()
  2016-08-03 03:30:03.392 2595 ERROR neutron.callbacks.manager   File "/usr/lib/python2.7/dist-packages/neutron/agent/linux/iptables_manager.py", line 431, in _apply
  2016-08-03 03:30:03.392 2595 ERROR neutron.callbacks.manager     return self._apply_synchronized()
  2016-08-03 03:30:03.392 2595 ERROR neutron.callbacks.manager   File "/usr/lib/python2.7/dist-packages/neutron/agent/linux/iptables_manager.py", line 457, in _apply_synchronized
  2016-08-03 03:30:03.392 2595 ERROR neutron.callbacks.manager     save_output = self.execute(args, run_as_root=True)
  2016-08-03 03:30:03.392 2595 ERROR neutron.callbacks.manager   File "/usr/lib/python2.7/dist-packages/neutron/agent/linux/utils.py", line 159, in execute
  2016-08-03 03:30:03.392 2595 ERROR neutron.callbacks.manager     raise RuntimeError(m)
  2016-08-03 03:30:03.392 2595 ERROR neutron.callbacks.manager RuntimeError:
  2016-08-03 03:30:03.392 2595 ERROR neutron.callbacks.manager Command: ['sudo', '/usr/bin/neutron-rootwrap', '/etc/neutron/rootwrap.conf', 'ip', 'netns', 'exec', 'qrouter-69ef3d5c-1ad1-42fb-8a1e-8d949837bbf8', 'iptables-save']
  2016-08-03 03:30:03.392 2595 ERROR neutron.callbacks.manager Exit code: 1
  2016-08-03 03:30:03.392 2595 ERROR neutron.callbacks.manager Stdin:
  2016-08-03 03:30:03.392 2595 ERROR neutron.callbacks.manager Stdout:
  2016-08-03 03:30:03.392 2595 ERROR neutron.callbacks.manager Stderr: Cannot open network namespace "qrouter-69ef3d5c-1ad1-42fb-8a1e-8d949837bbf8": No such file or directory
  2016-08-03 03:30:03.392 2595 ERROR neutron.callbacks.manager
  2016-08-03 03:30:03.392 2595 ERROR neutron.callbacks.manager
  2016-08-03 03:30:03.393 2595 ERROR neutron.agent.l3.agent [-] Error while deleting router 69ef3d5c-1ad1-42fb-8a1e-8d949837bbf8
  2016-08-03 03:30:03.393 2595 ERROR neutron.agent.l3.agent Traceback (most recent call last):
  2016-08-03 03:30:03.393 2595 ERROR neutron.agent.l3.agent   File "/usr/lib/python2.7/dist-packages/neutron/agent/l3/agent.py", line 344, in _safe_router_removed
  2016-08-03 03:30:03.393 2595 ERROR neutron.agent.l3.agent     self._router_removed(router_id)
  2016-08-03 03:30:03.393 2595 ERROR neutron.agent.l3.agent   File "/usr/lib/python2.7/dist-packages/neutron/agent/l3/agent.py", line 360, in _router_removed
  2016-08-03 03:30:03.393 2595 ERROR neutron.agent.l3.agent     self, router=ri)
  2016-08-03 03:30:03.393 2595 ERROR neutron.agent.l3.agent   File "/usr/lib/python2.7/dist-packages/neutron/callbacks/registry.py", line 44, in notify
  2016-08-03 03:30:03.393 2595 ERROR neutron.agent.l3.agent     _get_callback_manager().notify(resource, event, trigger, **kwargs)
  2016-08-03 03:30:03.393 2595 ERROR neutron.agent.l3.agent   File "/usr/lib/python2.7/dist-packages/neutron/callbacks/manager.py", line 123, in notify
  2016-08-03 03:30:03.393 2595 ERROR neutron.agent.l3.agent     raise exceptions.CallbackFailure(errors=errors)
  2016-08-03 03:30:03.393 2595 ERROR neutron.agent.l3.agent CallbackFailure: Callback neutron.agent.metadata.driver.before_router_removed failed with "
  2016-08-03 03:30:03.393 2595 ERROR neutron.agent.l3.agent Command: ['sudo', '/usr/bin/neutron-rootwrap', '/etc/neutron/rootwrap.conf', 'ip', 'netns', 'exec', 'qrouter-69ef3d5c-1ad1-42fb-8a1e-8d949837bbf8', 'iptables-save']
  2016-08-03 03:30:03.393 2595 ERROR neutron.agent.l3.agent Exit code: 1
  2016-08-03 03:30:03.393 2595 ERROR neutron.agent.l3.agent Stdin:
  2016-08-03 03:30:03.393 2595 ERROR neutron.agent.l3.agent Stdout:
  2016-08-03 03:30:03.393 2595 ERROR neutron.agent.l3.agent Stderr: Cannot open network namespace "qrouter-69ef3d5c-1ad1-42fb-8a1e-8d949837bbf8": No such file or directory
  2016-08-03 03:30:03.393 2595 ERROR neutron.agent.l3.agent "
  2016-08-03 03:30:03.393 2595 ERROR neutron.agent.l3.agent

  In this case, the cleanup first deleted the qrouter namespace it found
  to be empty (not containing any netdevs other than lo). The router
  delete flow attempts to delete iptables rules within the namespace
  before deleting the namespace itself. However, if the namespace is
  deleted first, the iptables-save command on a non-existent namespace
  fails. The resulting exception prevents the router delete flow from
  succeeding and the L3 agent gets stuck in a failure loop.

  Can somebody confirm if this is a known issue or if I've misunderstood
  the problem. Assuming my analysis is correct, would the following fix
  work?

  diff --git a/neutron/agent/l3/agent.py b/neutron/agent/l3/agent.py
  index b096091..8d3e8ae 100644
  --- a/neutron/agent/l3/agent.py
  +++ b/neutron/agent/l3/agent.py
  @@ -358,8 +358,16 @@ class L3NATAgent(firewall_l3_agent.FWaaSL3AgentRpcCallback,
               self.namespaces_manager.ensure_router_cleanup(router_id)
               return
   
  -        registry.notify(resources.ROUTER, events.BEFORE_DELETE,
  -                        self, router=ri)
  +        try:
  +            registry.notify(resources.ROUTER, events.BEFORE_DELETE,
  +                            self, router=ri)
  +        except Exception as e:
  +            ns_err = "Cannot open network namespace qrouter-" + router_id
  +            if ns_err not in e:
  +                raise
  +            else:
  +                LOG.warn(_LW("Namespace for router %s already deleted"),
  +                             router_id)

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