Fix race with DPDK and vhostuserclient mode

When a VM is rebooted and it has a port in a Neutron trunk with DPDK and
vhostuserclient mode, Nova will delete the OVS port and then recreate it
when the VM reboots. This quick transition can create a race condition
whereby Neutron deletes the trunk's bridge between the interface removal
and addition by os-vif, so the latter operation fails because the bridge
doesn't exist anymore. To fix this, ensuring the bridge existance and
the vif addition becomes an atomic operation from the point of view of
the OVSDB transaction.

This change is associated to [1] on the Neutron side.

[1] https://review.opendev.org/c/openstack/neutron/+/829139

Partial-Bug: #1869244
Change-Id: Id7ece4ebc9239d9776c43b8d7f9e82b0319a08c6

vif_plug_ovs/ovs.py

@@ -196,12 +196,11 @@ class OvsPlugin(plugin.PluginBase):
         return profile.datapath_type
 
     def _plug_vhostuser(self, vif, instance_info):
-        self.ovsdb.ensure_ovs_bridge(
-            vif.network.bridge, self._get_vif_datapath_type(
-                vif, datapath=constants.OVS_DATAPATH_NETDEV))
         vif_name = OvsPlugin.gen_port_name(
             constants.OVS_VHOSTUSER_PREFIX, vif.id)
         args = {}
+        args['datapath_type'] = self._get_vif_datapath_type(vif,
+                datapath=constants.OVS_DATAPATH_NETDEV)
         if vif.mode == "client":
             args['interface_type'] = \
                 constants.OVS_VHOSTUSER_INTERFACE_TYPE

vif_plug_ovs/ovsdb/ovsdb_lib.py

@@ -138,7 +138,7 @@ class BaseOVS(object):
     def create_ovs_vif_port(
         self, bridge, dev, iface_id, mac, instance_id,
         mtu=None, interface_type=None, vhost_server_path=None,
-        tag=None, pf_pci=None, vf_num=None, set_ids=True
+        tag=None, pf_pci=None, vf_num=None, set_ids=True, datapath_type=None
     ):
         """Create OVS port
 
@@ -154,6 +154,7 @@ class BaseOVS(object):
         :param pf_pci: PCI address of PF for dpdk representor port.
         :param vf_num: VF number of PF for dpdk representor port.
         :param set_ids: set external ids on port (bool).
+        :param datapath_type: datapath type for port's bridge
 
         .. note:: create DPDK representor port by setting all three values:
             `interface_type`, `pf_pci` and `vf_num`. if interface type is
@@ -177,6 +178,9 @@ class BaseOVS(object):
             col_values.append(('options',
                               {'dpdk-devargs': devargs_string}))
         with self.ovsdb.transaction() as txn:
+            if datapath_type:
+                txn.add(self.ovsdb.add_br(bridge, may_exist=True,
+                                          datapath_type=datapath_type))
             txn.add(self.ovsdb.add_port(bridge, dev))
             if tag:
                 txn.add(self.ovsdb.db_set('Port', dev, ('tag', tag)))

vif_plug_ovs/tests/unit/test_plugin.py

@@ -362,47 +362,37 @@ class PluginTest(testtools.TestCase):
     def test_unplug_ovs_bridge_windows(self):
         self._check_unplug_ovs_windows(self.vif_ovs_hybrid)
 
-    @mock.patch.object(ovsdb_lib.BaseOVS, 'ensure_ovs_bridge')
     @mock.patch.object(ovs.OvsPlugin, '_create_vif_port')
-    def test_plug_ovs_vhostuser(self, _create_vif_port, ensure_ovs_bridge):
+    def test_plug_ovs_vhostuser(self, _create_vif_port):
         dp_type = ovs.OvsPlugin._get_vif_datapath_type(self.vif_vhostuser)
-        calls = {
-
-            '_create_vif_port': [mock.call(
-                                 self.vif_vhostuser, 'vhub679325f-ca',
-                                 self.instance,
-                                 interface_type='dpdkvhostuser')],
-            'ensure_ovs_bridge': [mock.call('br0', dp_type)]
-        }
+        calls = [mock.call(
+                self.vif_vhostuser, 'vhub679325f-ca',
+                self.instance,
+                interface_type='dpdkvhostuser',
+                datapath_type=dp_type)]
 
         plugin = ovs.OvsPlugin.load(constants.PLUGIN_NAME)
         plugin.plug(self.vif_vhostuser, self.instance)
-        _create_vif_port.assert_has_calls(calls['_create_vif_port'])
-        ensure_ovs_bridge.assert_has_calls(calls['ensure_ovs_bridge'])
+        _create_vif_port.assert_has_calls(calls)
 
-    @mock.patch.object(ovsdb_lib.BaseOVS, 'ensure_ovs_bridge')
     @mock.patch.object(ovsdb_lib.BaseOVS, 'create_ovs_vif_port')
-    def test_plug_ovs_vhostuser_client(self, create_ovs_vif_port,
-                                       ensure_ovs_bridge):
+    def test_plug_ovs_vhostuser_client(self, create_ovs_vif_port):
         dp_type = ovs.OvsPlugin._get_vif_datapath_type(
             self.vif_vhostuser_client)
-        calls = {
-            'create_ovs_vif_port': [
+        calls = [
                  mock.call(
                      'br0', 'vhub679325f-ca',
                      'e65867e0-9340-4a7f-a256-09af6eb7a3aa',
                      'ca:fe:de:ad:be:ef',
                      'f0000000-0000-0000-0000-000000000001',
                      mtu=1500, interface_type='dpdkvhostuserclient',
-                     vhost_server_path='/var/run/openvswitch/vhub679325f-ca'
-                 )],
-            'ensure_ovs_bridge': [mock.call('br0', dp_type)]
-        }
+                     vhost_server_path='/var/run/openvswitch/vhub679325f-ca',
+                     datapath_type=dp_type
+                 )]
 
         plugin = ovs.OvsPlugin.load(constants.PLUGIN_NAME)
         plugin.plug(self.vif_vhostuser_client, self.instance)
-        create_ovs_vif_port.assert_has_calls(calls['create_ovs_vif_port'])
-        ensure_ovs_bridge.assert_has_calls(calls['ensure_ovs_bridge'])
+        create_ovs_vif_port.assert_has_calls(calls)
 
     @mock.patch.object(ovsdb_lib.BaseOVS, 'delete_ovs_vif_port')
     def test_unplug_ovs_vhostuser(self, delete_ovs_vif_port):