Fix race condition in dhcp agent

This patch fixes a race condition that can happen in the dhcp agent when
a subnet is created and then a host route is then immediately added to that
subnet following a subnet.update.end notification. The race condition occurs
in refresh_dhcp_helper() where self.enable_dhcp_helper() gets called twice
since the first call had not completed self.cache.put(network). This same race
condition can also occur in the other events so lockutils.synchronized() is
added to synchronize those code segments as well.

Fixes bug 1155748

Change-Id: I2ff52adc3dfebddd6d9c15d5dc79aa65be107179

quantum/agent/dhcp_agent.py

@@ -37,6 +37,7 @@
 from quantum.openstack.common import importutils
 from quantum.openstack.common import jsonutils
 from quantum.openstack.common import log as logging
+from quantum.openstack.common import lockutils
 from quantum.openstack.common import loopingcall
 from quantum.openstack.common.rpc import proxy
 from quantum.openstack.common import service
@@ -226,11 +227,13 @@ def refresh_dhcp_helper(self, network_id):
         else:
             self.disable_dhcp_helper(network.id)
 
+    @lockutils.synchronized('agent', 'dhcp-')
     def network_create_end(self, context, payload):
         """Handle the network.create.end notification event."""
         network_id = payload['network']['id']
         self.enable_dhcp_helper(network_id)
 
+    @lockutils.synchronized('agent', 'dhcp-')
     def network_update_end(self, context, payload):
         """Handle the network.update.end notification event."""
         network_id = payload['network']['id']
@@ -239,10 +242,12 @@ def network_update_end(self, context, payload):
         else:
             self.disable_dhcp_helper(network_id)
 
+    @lockutils.synchronized('agent', 'dhcp-')
     def network_delete_end(self, context, payload):
         """Handle the network.delete.end notification event."""
         self.disable_dhcp_helper(payload['network_id'])
 
+    @lockutils.synchronized('agent', 'dhcp-')
     def subnet_update_end(self, context, payload):
         """Handle the subnet.update.end notification event."""
         network_id = payload['subnet']['network_id']
@@ -251,13 +256,15 @@ def subnet_update_end(self, context, payload):
     # Use the update handler for the subnet create event.
     subnet_create_end = subnet_update_end
 
+    @lockutils.synchronized('agent', 'dhcp-')
     def subnet_delete_end(self, context, payload):
         """Handle the subnet.delete.end notification event."""
         subnet_id = payload['subnet_id']
         network = self.cache.get_network_by_subnet_id(subnet_id)
         if network:
             self.refresh_dhcp_helper(network.id)
 
+    @lockutils.synchronized('agent', 'dhcp-')
     def port_update_end(self, context, payload):
         """Handle the port.update.end notification event."""
         port = DictModel(payload['port'])
@@ -269,6 +276,7 @@ def port_update_end(self, context, payload):
     # Use the update handler for the port create event.
     port_create_end = port_update_end
 
+    @lockutils.synchronized('agent', 'dhcp-')
     def port_delete_end(self, context, payload):
         """Handle the port.delete.end notification event."""
         port = self.cache.get_port_by_id(payload['port_id'])