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Merge "Reset the cell cache for database access in Service" into stable/rocky

changes/27/729527/1
Zuul 1 month ago
committed by Gerrit Code Review
parent
commit
3cb5c1512e
3 changed files with 137 additions and 4 deletions
  1. +0
    -3
      nova/context.py
  2. +36
    -1
      nova/service.py
  3. +101
    -0
      nova/tests/functional/test_service.py

+ 0
- 3
nova/context.py View File

@@ -38,9 +38,6 @@ from nova import policy
from nova import utils

LOG = logging.getLogger(__name__)
# TODO(melwitt): This cache should be cleared whenever WSGIService receives a
# SIGHUP and periodically based on an expiration time. Currently, none of the
# cell caches are purged, so neither is this one, for now.
CELL_CACHE = {}
# NOTE(melwitt): Used for the scatter-gather utility to indicate we timed out
# waiting for a result from a cell.


+ 36
- 1
nova/service.py View File

@@ -153,6 +153,20 @@ class Service(service.Service):
This includes starting an RPC service, initializing
periodic tasks, etc.
"""
# NOTE(melwitt): Clear the cell cache holding database transaction
# context manager objects. We do this to ensure we create new internal
# oslo.db locks to avoid a situation where a child process receives an
# already locked oslo.db lock when it is forked. When a child process
# inherits a locked oslo.db lock, database accesses through that
# transaction context manager will never be able to acquire the lock
# and requests will fail with CellTimeout errors.
# See https://bugs.python.org/issue6721 for more information.
# With python 3.7, it would be possible for oslo.db to make use of the
# os.register_at_fork() method to reinitialize its lock. Until we
# require python 3.7 as a mininum version, we must handle the situation
# outside of oslo.db.
context.CELL_CACHE = {}

assert_eventlet_uses_monotonic_clock()

verstr = version.version_string_with_package()
@@ -308,6 +322,8 @@ class Service(service.Service):
def reset(self):
"""reset the service."""
self.manager.reset()
# Reset the cell cache that holds database transaction context managers
context.CELL_CACHE = {}


class WSGIService(service.Service):
@@ -362,13 +378,18 @@ class WSGIService(service.Service):
setup_profiler(name, self.host)

def reset(self):
"""Reset server greenpool size to default and service version cache.
"""Reset the following:

* server greenpool size to default
* service version cache
* cell cache holding database transaction context managers

:returns: None

"""
self.server.reset()
service_obj.Service.clear_min_version_cache()
context.CELL_CACHE = {}

def _get_manager(self):
"""Initialize a Manager object appropriate for this service.
@@ -396,6 +417,20 @@ class WSGIService(service.Service):
:returns: None

"""
# NOTE(melwitt): Clear the cell cache holding database transaction
# context manager objects. We do this to ensure we create new internal
# oslo.db locks to avoid a situation where a child process receives an
# already locked oslo.db lock when it is forked. When a child process
# inherits a locked oslo.db lock, database accesses through that
# transaction context manager will never be able to acquire the lock
# and requests will fail with CellTimeout errors.
# See https://bugs.python.org/issue6721 for more information.
# With python 3.7, it would be possible for oslo.db to make use of the
# os.register_at_fork() method to reinitialize its lock. Until we
# require python 3.7 as a mininum version, we must handle the situation
# outside of oslo.db.
context.CELL_CACHE = {}

ctxt = context.get_admin_context()
service_ref = objects.Service.get_by_host_and_binary(ctxt, self.host,
self.binary)


+ 101
- 0
nova/tests/functional/test_service.py View File

@@ -0,0 +1,101 @@
# Licensed under the Apache License, Version 2.0 (the "License"); you may
# not use this file except in compliance with the License. You may obtain
# a copy of the License at
#
# http://www.apache.org/licenses/LICENSE-2.0
#
# Unless required by applicable law or agreed to in writing, software
# distributed under the License is distributed on an "AS IS" BASIS, WITHOUT
# WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied. See the
# License for the specific language governing permissions and limitations
# under the License.

from nova import context as nova_context
from nova import test
from nova.tests import fixtures as nova_fixtures
from nova.tests.functional import integrated_helpers
from nova.tests.unit.image import fake as fake_image
from nova.tests.unit import policy_fixture


class ServiceTestCase(test.TestCase,
integrated_helpers.InstanceHelperMixin):
"""Contains scenarios for testing services.
"""

def setUp(self):
super(ServiceTestCase, self).setUp()
# Use the standard fixtures.
self.useFixture(policy_fixture.RealPolicyFixture())
self.useFixture(nova_fixtures.NeutronFixture(self))
self.useFixture(nova_fixtures.PlacementFixture())
fake_image.stub_out_image_service(self)
self.addCleanup(fake_image.FakeImageService_reset)
# Start nova controller services.
self.api = self.useFixture(nova_fixtures.OSAPIFixture(
api_version='v2.1')).api
self.start_service('conductor')
self.scheduler = self.start_service('scheduler')
# Our OSAPIFixture does not use a WSGIService, so just use the metadata
# server fixture (which uses WSGIService) for testing.
self.metadata = self.useFixture(
nova_fixtures.OSMetadataServer()).metadata
# Start one compute service.
self.start_service('compute')

def test_service_reset_resets_cell_cache(self):
"""Tests that the cell cache for database transaction context managers
is cleared after a service reset (example scenario: SIGHUP).
"""
server_req = self._build_minimal_create_server_request(
self.api, 'test-service-reset')
server = self.api.post_server({'server': server_req})
self._wait_for_state_change(self.api, server, 'ACTIVE')
# Cell cache should be populated after creating a server.
self.assertTrue(nova_context.CELL_CACHE)
self.scheduler.reset()
# Cell cache should be empty after the service reset.
self.assertEqual({}, nova_context.CELL_CACHE)

# Now test the WSGI service.
server = self.api.post_server({'server': server_req})
self._wait_for_state_change(self.api, server, 'ACTIVE')
# Cell cache should be populated after creating a server.
self.assertTrue(nova_context.CELL_CACHE)
self.metadata.reset()
# Cell cache should be empty after the service reset.
self.assertEqual({}, nova_context.CELL_CACHE)

def test_service_start_resets_cell_cache(self):
"""Tests that the cell cache for database transaction context managers
is cleared upon a service start (example scenario: service start after
a SIGTERM and the parent process forks child process workers).
"""
server_req = self._build_minimal_create_server_request(
self.api, 'test-service-start')
server = self.api.post_server({'server': server_req})
self._wait_for_state_change(self.api, server, 'ACTIVE')
# Cell cache should be populated after creating a server.
self.assertTrue(nova_context.CELL_CACHE)
self.scheduler.stop()
# NOTE(melwitt): Simulate a service starting after being stopped. The
# scenario we want to handle is one where during start, the parent
# process forks child process workers while one or more of its cached
# database transaction context managers is inside a locked code
# section. If the child processes are forked while the lock is locked,
# the child processes begin with an already locked lock that can never
# be acquired again. The result is that requests gets stuck and fail
# with a CellTimeout error.
self.scheduler.start()
# Cell cache should be empty after the service start.
self.assertEqual({}, nova_context.CELL_CACHE)

# Now test the WSGI service.
server = self.api.post_server({'server': server_req})
self._wait_for_state_change(self.api, server, 'ACTIVE')
# Cell cache should be populated after creating a server.
self.assertTrue(nova_context.CELL_CACHE)
self.metadata.stop()
self.metadata.start()
# Cell cache should be empty after the service reset.
self.assertEqual({}, nova_context.CELL_CACHE)

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