Skip DBDuplicateEntry exception in security group creation

An DBDuplicateEntry expection appeared if it is attempted to
create secutity groups in more then one thread. In this situation
at one moment it is trying to be created 2 default security groups
which is not allowed. In this case exception should skipped with
a message about failed attempt.

Closes-bug: #1419723

Change-Id: Id6fe997ad3b72f875160e1e31a3dc17c3cc53b75

neutron/db/securitygroups_db.py

@@ -13,6 +13,7 @@
 #    under the License.
 
 import netaddr
+from oslo_db import exception
 import sqlalchemy as sa
 from sqlalchemy import orm
 from sqlalchemy.orm import exc
@@ -24,8 +25,10 @@ from neutron.db import db_base_plugin_v2
 from neutron.db import model_base
 from neutron.db import models_v2
 from neutron.extensions import securitygroup as ext_sg
+from neutron.openstack.common import log as logging
 from neutron.openstack.common import uuidutils
 
+LOG = logging.getLogger(__name__)
 
 IP_PROTOCOL_MAP = {constants.PROTO_NAME_TCP: constants.PROTO_NUM_TCP,
                    constants.PROTO_NAME_UDP: constants.PROTO_NUM_UDP,
@@ -124,7 +127,11 @@ class SecurityGroupDbMixin(ext_sg.SecurityGroupPluginBase):
         tenant_id = self._get_tenant_id_for_create(context, s)
 
         if not default_sg:
-            self._ensure_default_security_group(context, tenant_id)
+            try:
+                self._ensure_default_security_group(context, tenant_id)
+            except exception.DBDuplicateEntry as ex:
+                LOG.debug("Duplicate default security group %s was not"
+                          " created", ex.value)
 
         with context.session.begin(subtransactions=True):
             security_group_db = SecurityGroup(id=s.get('id') or (

neutron/tests/unit/test_extension_security_group.py

@@ -16,6 +16,7 @@
 import contextlib
 
 import mock
+import oslo_db.exception as exc
 import webob.exc
 
 from neutron.api.v2 import attributes as attr
@@ -270,6 +271,12 @@ class TestSecurityGroups(SecurityGroupDBTestCase):
                     'port_range_min': None}
         self._assert_sg_rule_has_kvs(v6_rule, expected)
 
+    def test_skip_duplicate_default_sg_error(self):
+        with mock.patch.object(SecurityGroupTestPlugin,
+                               '_ensure_default_security_group',
+                               side_effect=exc.DBDuplicateEntry()):
+            self._make_security_group(self.fmt, 'test_sg', 'test_desc')
+
     def test_update_security_group(self):
         with self.security_group() as sg:
             data = {'security_group': {'name': 'new_name',