Make _ensure_default_security_group method atomic

Method _ensure_default_security_group wasn't atomic as it first tries to get
default SG and if that not exists in DB, it tries to create it.

It may happend, like e.g. in Calico plugin that between
get_default_sg_id method and create_security_group method, this default
SG will be created by other neutron worker. And in such case there will
be Duplicate entry exception raised.

So this patch is adding handling of such exception.

Change-Id: I515c310f221e7d9ae3be59a26260538d1bc591c2
Closes-Bug: #1883730

neutron/db/securitygroups_db.py

@@ -26,6 +26,7 @@ from neutron_lib.db import model_query
 from neutron_lib.db import resource_extend
 from neutron_lib.db import utils as db_utils
 from neutron_lib import exceptions as n_exc
+from neutron_lib.objects import exceptions as obj_exc
 from neutron_lib.utils import helpers
 from neutron_lib.utils import net
 from oslo_log import log as logging
@@ -45,6 +46,8 @@ from neutron import quota
 
 LOG = logging.getLogger(__name__)
 
+DEFAULT_SG_DESCRIPTION = _('Default security group')
+
 
 @resource_extend.has_resource_extenders
 @registry.has_registry_receivers
@@ -865,10 +868,13 @@ class SecurityGroupDbMixin(ext_sg.SecurityGroupPluginBase,
             'security_group':
                 {'name': 'default',
                  'tenant_id': tenant_id,
-                 'description': _('Default security group')}
+                 'description': DEFAULT_SG_DESCRIPTION}
         }
-        return self.create_security_group(context, security_group,
-                                          default_sg=True)['id']
+        try:
+            return self.create_security_group(context, security_group,
+                                              default_sg=True)['id']
+        except obj_exc.NeutronDbObjectDuplicateEntry:
+            return self._get_default_sg_id(context, tenant_id)
 
     def _get_security_groups_on_port(self, context, port):
         """Check that all security groups on port belong to tenant.

neutron/tests/unit/db/test_securitygroups_db.py

@@ -20,6 +20,7 @@ from neutron_lib.callbacks import registry
 from neutron_lib.callbacks import resources
 from neutron_lib import constants
 from neutron_lib import context
+from neutron_lib.objects import exceptions as obj_exc
 import sqlalchemy
 import testtools
 
@@ -554,3 +555,49 @@ class SecurityGroupDbMixinTestCase(testlib_api.SqlTestCase):
         for rule in (rule for rule in rules_after if rule not in rules_before):
             self.assertEqual('tenant_1', rule['tenant_id'])
             self.assertEqual(self.sg_user['id'], rule['security_group_id'])
+
+    def test__ensure_default_security_group(self):
+        with mock.patch.object(
+                self.mixin, '_get_default_sg_id') as get_default_sg_id,\
+                mock.patch.object(
+                        self.mixin, 'create_security_group') as create_sg:
+            get_default_sg_id.return_value = None
+            self.mixin._ensure_default_security_group(self.ctx, 'tenant_1')
+            create_sg.assert_called_once_with(
+                self.ctx,
+                {'security_group': {
+                    'name': 'default',
+                    'tenant_id': 'tenant_1',
+                    'description': securitygroups_db.DEFAULT_SG_DESCRIPTION}},
+                default_sg=True)
+            get_default_sg_id.assert_called_once_with(self.ctx, 'tenant_1')
+
+    def test__ensure_default_security_group_already_exists(self):
+        with mock.patch.object(
+                self.mixin, '_get_default_sg_id') as get_default_sg_id,\
+                mock.patch.object(
+                        self.mixin, 'create_security_group') as create_sg:
+            get_default_sg_id.return_value = 'default_sg_id'
+            self.mixin._ensure_default_security_group(self.ctx, 'tenant_1')
+            create_sg.assert_not_called()
+            get_default_sg_id.assert_called_once_with(self.ctx, 'tenant_1')
+
+    def test__ensure_default_security_group_created_in_parallel(self):
+        with mock.patch.object(
+                self.mixin, '_get_default_sg_id') as get_default_sg_id,\
+                mock.patch.object(
+                        self.mixin, 'create_security_group') as create_sg:
+            get_default_sg_id.side_effect = [None, 'default_sg_id']
+            create_sg.side_effect = obj_exc.NeutronDbObjectDuplicateEntry(
+                mock.Mock(), mock.Mock())
+            self.mixin._ensure_default_security_group(self.ctx, 'tenant_1')
+            create_sg.assert_called_once_with(
+                self.ctx,
+                {'security_group': {
+                    'name': 'default',
+                    'tenant_id': 'tenant_1',
+                    'description': securitygroups_db.DEFAULT_SG_DESCRIPTION}},
+                default_sg=True)
+            get_default_sg_id.assert_has_calls([
+                mock.call(self.ctx, 'tenant_1'),
+                mock.call(self.ctx, 'tenant_1')])