Add a semaphore to some ML2 operations

This patch adds a semaphore for serializing the delete port API
calls and update_port_status calls to avoid simultaneous
attempts to acquire SQL update locks on the port table from
the same thread pool.

This semaphore has been introduced to avoid undesired eventlet
yields which trigger 'lock wait timeout' errors in the DB backend;
it should have a negligible impact on the overall performance.

Change-Id: I0ec947086e533945942ae93402943dec69b218ef
Partial-Bug: 1283522

diff --git a/neutron/plugins/ml2/plugin.py b/neutron/plugins/ml2/plugin.py
index 8240e09f6db4b22c8e9d78758e77ff09016ef10c..f548b9d19a82d1b716690f390250f65fb4d5a4c1 100644 (file)
--- a/neutron/plugins/ml2/plugin.py
+++ b/neutron/plugins/ml2/plugin.py
@@ -12,6 +12,7 @@
 #    WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied. See the
 #    License for the specific language governing permissions and limitations
 #    under the License.
+import contextlib
 
 from oslo.config import cfg
 from sqlalchemy import exc as sql_exc
@@ -41,6 +42,7 @@ from neutron.openstack.common import db as os_db
 from neutron.openstack.common import excutils
 from neutron.openstack.common import importutils
 from neutron.openstack.common import jsonutils
+from neutron.openstack.common import lockutils
 from neutron.openstack.common import log
 from neutron.openstack.common import rpc as c_rpc
 from neutron.plugins.common import constants as service_constants
@@ -699,7 +701,10 @@ class Ml2Plugin(db_base_plugin_v2.NeutronDbPluginV2,
             l3plugin.prevent_l3_port_deletion(context, id)
 
         session = context.session
-        with session.begin(subtransactions=True):
+        # REVISIT: Serialize this operation with a semaphore to prevent
+        # undesired eventlet yields leading to 'lock wait timeout' errors
+        with contextlib.nested(lockutils.lock('db-access'),
+                               session.begin(subtransactions=True)):
             try:
                 port_db = (session.query(models_v2.Port).
                            enable_eagerloads(False).
@@ -735,7 +740,10 @@ class Ml2Plugin(db_base_plugin_v2.NeutronDbPluginV2,
     def update_port_status(self, context, port_id, status):
         updated = False
         session = context.session
-        with session.begin(subtransactions=True):
+        # REVISIT: Serialize this operation with a semaphore to prevent
+        # undesired eventlet yields leading to 'lock wait timeout' errors
+        with contextlib.nested(lockutils.lock('db-access'),
+                               session.begin(subtransactions=True)):
             port = db.get_port(session, port_id)
             if not port:
                 LOG.warning(_("Port %(port)s updated up by agent not found"),