Reset device namespace when adding to the namespace fails

In case when during adding device to the namespace, device will be "shy"
and will disappear for a moment and NetworkInterfaceNotFound exception
will be raised, we need to reset device.namespace to be None.
Otherwise, in the next attempt of adding interface to namespace, when it
will be added back to ovs (and will be in global scope), Neutron will
already look for it in the "namespace" and that will always be failing.

Closes-bug: #1961740
Change-Id: Ie9331c72c44084b0a382598c3359214cce2f2ebd
(cherry picked from commit 7657839)

Author: slawqo

neutron/agent/linux/interface.py

@@ -365,6 +365,11 @@ def _add_device_to_namespace(self, ip_wrapper, device, namespace):
                 LOG.warning("Failed to set interface %s into namespace %s. "
                             "Interface not found, attempt: %s, retrying.",
                             device, namespace, i + 1)
+                # NOTE(slaweq) In such case it's required to reset device's
+                # namespace as it was already set to the "namespace"
+                # and after retry neutron will look for it in that namespace
+                # which is wrong
+                device.namespace = None
                 time.sleep(1)
             except utils.WaitTimeout:
                 # NOTE(slaweq): if the exception was WaitTimeout then it means

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

@@ -518,6 +518,20 @@ def test_unplug(self):
             ovs_br.assert_has_calls([mock.call('br-int'),
                                      mock.call().delete_port('tap0')])
 
+    def test__add_device_to_namespace_retries(self):
+        ovs = interface.OVSInterfaceDriver(self.conf)
+        namespace_obj = self.ip.return_value.ensure_namespace.return_value
+        self.ip.ensure_namespace.return_value = namespace_obj
+        namespace_obj.add_device_to_namespace.side_effect = (
+            ip_lib.NetworkInterfaceNotFound)
+        device = mock.MagicMock()
+        self.assertRaises(
+            ip_lib.NetworkInterfaceNotFound,
+            ovs._add_device_to_namespace,
+            self.ip, device, "test-ns")
+        self.assertEqual(10, namespace_obj.add_device_to_namespace.call_count)
+        self.assertIsNone(device.namespace)
+
 
 class TestOVSInterfaceDriverWithVeth(TestOVSInterfaceDriver):