Optimize the code that fixes the race condition of DHCP agent.

https://review.opendev.org/#/c/236983/
https://review.opendev.org/#/c/606383/
The above patchs that resolve the race condition of DHCP agent will
result in neutron-server raise DhcpPortInUse ERROR log. And, the
second patch may result in old dhcp agent create a redundant port.

Conflicts:
	neutron/api/rpc/handlers/dhcp_rpc.py

Closes-Bug: #1829332
Change-Id: If7a7ac2f88ce5b0e799c1104c936735a6cc860aa
(cherry picked from commit 494b65d951)

neutron/agent/dhcp/agent.py

@@ -162,7 +162,8 @@ class DhcpAgent(manager.Manager):
             if (isinstance(e, oslo_messaging.RemoteError) and
                     e.exc_type == 'NetworkNotFound' or
                     isinstance(e, exceptions.NetworkNotFound)):
-                LOG.debug("Network %s has been deleted.", network.id)
+                LOG.debug("Network %s has been removed from the agent "
+                          "or deleted from DB.", network.id)
             else:
                 LOG.exception('Unable to %(action)s dhcp for %(net_id)s.',
                               {'net_id': network.id, 'action': action})

neutron/agent/linux/dhcp.py

@@ -26,7 +26,6 @@ from neutron_lib import constants
 from neutron_lib import exceptions
 from neutron_lib.utils import file as file_utils
 from oslo_log import log as logging
-import oslo_messaging
 from oslo_utils import excutils
 from oslo_utils import fileutils
 from oslo_utils import uuidutils
@@ -1368,16 +1367,9 @@ class DeviceManager(object):
         for port in network.ports:
             port_device_id = getattr(port, 'device_id', None)
             if port_device_id == constants.DEVICE_ID_RESERVED_DHCP_PORT:
-                try:
                 port = self.plugin.update_dhcp_port(
                     port.id, {'port': {'network_id': network.id,
                                        'device_id': device_id}})
-                except oslo_messaging.RemoteError as e:
-                    if e.exc_type == 'DhcpPortInUse':
-                        LOG.info("Skipping DHCP port %s as it is "
-                                 "already in use", port.id)
-                        continue
-                    raise
                 if port:
                     return port
 

neutron/api/rpc/handlers/dhcp_rpc.py

@@ -33,7 +33,6 @@ from oslo_utils import excutils
 
 from neutron._i18n import _
 from neutron.common import constants as n_const
-from neutron.common import exceptions as n_exc
 from neutron.common import utils
 from neutron.db import provisioning_blocks
 from neutron.extensions import segment as segment_ext
@@ -280,6 +279,7 @@ class DhcpRpcCallback(object):
                                                          hosts=[host])
         return len(agents) != 0
 
+    @oslo_messaging.expected_exceptions(exceptions.NetworkNotFound)
     @oslo_messaging.expected_exceptions(exceptions.IpAddressGenerationFailure)
     @db_api.retry_db_errors
     def update_dhcp_port(self, context, **kwargs):
@@ -295,10 +295,14 @@ class DhcpRpcCallback(object):
             if (old_port['device_id'] !=
                     constants.DEVICE_ID_RESERVED_DHCP_PORT and
                 old_port['device_id'] !=
-                    utils.get_dhcp_agent_device_id(network_id, host) or
+                    utils.get_dhcp_agent_device_id(network_id, host)):
-                not self._is_dhcp_agent_hosting_network(plugin, context, host,
+                return
-                    network_id)):
+            if not self._is_dhcp_agent_hosting_network(plugin, context, host,
-                raise n_exc.DhcpPortInUse(port_id=port['id'])
+                                                       network_id):
+                LOG.warning("The DHCP agent on %(host)s does not host the "
+                            "network %(net_id)s.", {"host": host,
+                                                    "net_id": network_id})
+                raise exceptions.NetworkNotFound(net_id=network_id)
             LOG.debug('Update dhcp port %(port)s '
                       'from %(host)s.',
                       {'port': port,
@@ -308,7 +312,6 @@ class DhcpRpcCallback(object):
             LOG.debug('Host %(host)s tried to update port '
                       '%(port_id)s which no longer exists.',
                       {'host': host, 'port_id': port['id']})
-            return None
 
     @db_api.retry_db_errors
     def dhcp_ready_on_ports(self, context, port_ids):

neutron/tests/unit/agent/linux/test_dhcp.py

@@ -2949,8 +2949,7 @@ class TestDeviceManager(TestConfBase):
 
     def test__setup_reserved_dhcp_port_with_fake_remote_error(self):
         """Test scenario where a fake_network has two reserved ports, and
-        update_dhcp_port fails for the first of those with a RemoteError
+        update_dhcp_port fails for the first of those with a RemoteError.
-        different than DhcpPortInUse.
         """
         # Setup with a reserved DHCP port.
         fake_network = FakeDualNetworkReserved2()
@@ -2967,31 +2966,6 @@ class TestDeviceManager(TestConfBase):
         with testtools.ExpectedException(oslo_messaging.RemoteError):
             dh.setup_dhcp_port(fake_network)
 
-    def test__setup_reserved_dhcp_port_with_known_remote_error(self):
-        """Test scenario where a fake_network has two reserved ports, and
-        update_dhcp_port fails for the first of those with a DhcpPortInUse
-        RemoteError.
-        """
-        # Setup with a reserved DHCP port.
-        fake_network = FakeDualNetworkReserved2()
-        fake_network.tenant_id = 'Tenant A'
-        reserved_port_1 = fake_network.ports[-2]
-        reserved_port_2 = fake_network.ports[-1]
-
-        mock_plugin = mock.Mock()
-        dh = dhcp.DeviceManager(cfg.CONF, mock_plugin)
-        messaging_error = oslo_messaging.RemoteError(exc_type='DhcpPortInUse')
-        mock_plugin.update_dhcp_port.side_effect = [messaging_error,
-                                                    reserved_port_2]
-
-        with mock.patch.object(dhcp.LOG, 'info') as log:
-            dh.setup_dhcp_port(fake_network)
-            self.assertEqual(1, log.call_count)
-        expected_calls = [mock.call(reserved_port_1.id, mock.ANY),
-                          mock.call(reserved_port_2.id, mock.ANY)]
-        self.assertEqual(expected_calls,
-                         mock_plugin.update_dhcp_port.call_args_list)
-
 
 class TestDictModel(base.BaseTestCase):
 

neutron/tests/unit/api/rpc/handlers/test_dhcp_rpc.py

@@ -21,9 +21,9 @@ from neutron_lib import exceptions as n_exc
 from neutron_lib.plugins import constants as plugin_constants
 from neutron_lib.plugins import directory
 from oslo_db import exception as db_exc
+from oslo_messaging.rpc import dispatcher as rpc_dispatcher
 
 from neutron.api.rpc.handlers import dhcp_rpc
-from neutron.common import exceptions
 from neutron.common import utils
 from neutron.db import provisioning_blocks
 from neutron.tests import base
@@ -304,12 +304,9 @@ class TestDhcpRpcCallback(base.BaseTestCase):
 
         self.plugin.get_port.return_value = {
             'device_id': 'other_id'}
-        self.assertRaises(exceptions.DhcpPortInUse,
+        res = self.callbacks.update_dhcp_port(mock.Mock(), host='foo_host',
-                          self.callbacks.update_dhcp_port,
+                                        port_id='foo_port_id', port=port)
-                          mock.Mock(),
+        self.assertIsNone(res)
-                          host='foo_host',
-                          port_id='foo_port_id',
-                          port=port)
 
     def test_update_dhcp_port(self):
         port = {'port': {'network_id': 'foo_network_id',
@@ -340,7 +337,7 @@ class TestDhcpRpcCallback(base.BaseTestCase):
         self.plugin.get_port.return_value = {
             'device_id': constants.DEVICE_ID_RESERVED_DHCP_PORT}
         self.mock_agent_hosting_network.return_value = False
-        self.assertRaises(exceptions.DhcpPortInUse,
+        self.assertRaises(rpc_dispatcher.ExpectedException,
                           self.callbacks.update_dhcp_port,
                           mock.Mock(),
                           host='foo_host',