Merge "Implement compare-and-swap for instance update"

nova/db/api.py

@@ -730,17 +730,18 @@ def instance_get_all_hung_in_rebooting(context, reboot_window):
     return IMPL.instance_get_all_hung_in_rebooting(context, reboot_window)
 
 
-def instance_update(context, instance_uuid, values):
+def instance_update(context, instance_uuid, values, expected=None):
     """Set the given properties on an instance and update it.
 
     Raises NotFound if instance does not exist.
 
     """
-    return IMPL.instance_update(context, instance_uuid, values)
+    return IMPL.instance_update(context, instance_uuid, values,
+                                expected=expected)
 
 
 def instance_update_and_get_original(context, instance_uuid, values,
-                                     columns_to_join=None):
+                                     columns_to_join=None, expected=None):
     """Set the given properties on an instance and update it. Return
     a shallow copy of the original instance reference, as well as the
     updated one.
@@ -754,7 +755,8 @@ def instance_update_and_get_original(context, instance_uuid, values,
     Raises NotFound if instance does not exist.
     """
     rv = IMPL.instance_update_and_get_original(context, instance_uuid, values,
-                                               columns_to_join=columns_to_join)
+                                               columns_to_join=columns_to_join,
+                                               expected=expected)
     return rv
 
 

nova/db/sqlalchemy/api.py

@@ -30,6 +30,7 @@ from oslo_db import api as oslo_db_api
 from oslo_db import exception as db_exc
 from oslo_db import options as oslo_db_options
 from oslo_db.sqlalchemy import session as db_session
+from oslo_db.sqlalchemy import update_match
 from oslo_db.sqlalchemy import utils as sqlalchemyutils
 from oslo_log import log as logging
 from oslo_utils import excutils
@@ -2426,15 +2427,29 @@ def instance_get_all_hung_in_rebooting(context, reboot_window):
         manual_joins=[])
 
 
-@require_context
-def instance_update(context, instance_uuid, values):
-    instance_ref = _instance_update(context, instance_uuid, values)[1]
-    return instance_ref
+def _retry_instance_update():
+    """Wrap with oslo_db_api.wrap_db_retry, and also retry on
+    UnknownInstanceUpdateConflict.
+    """
+    exception_checker = \
+        lambda exc: isinstance(exc, (exception.UnknownInstanceUpdateConflict,))
+    return oslo_db_api.wrap_db_retry(max_retries=5, retry_on_deadlock=True,
+                                     exception_checker=exception_checker)
 
 
 @require_context
+@_retry_instance_update()
+def instance_update(context, instance_uuid, values, expected=None):
+    session = get_session()
+    with session.begin():
+        return _instance_update(context, session, instance_uuid,
+                                values, expected)
+
+
+@require_context
+@_retry_instance_update()
 def instance_update_and_get_original(context, instance_uuid, values,
-                                     columns_to_join=None):
+                                     columns_to_join=None, expected=None):
     """Set the given properties on an instance and update it. Return
     a shallow copy of the original instance reference, as well as the
     updated one.
@@ -2451,9 +2466,14 @@ def instance_update_and_get_original(context, instance_uuid, values,
 
     Raises NotFound if instance does not exist.
     """
-    return _instance_update(context, instance_uuid, values,
-                            copy_old_instance=True,
-                            columns_to_join=columns_to_join)
+    session = get_session()
+    with session.begin():
+        instance_ref = _instance_get_by_uuid(context, instance_uuid,
+                                             columns_to_join=columns_to_join,
+                                             session=session)
+        return (copy.copy(instance_ref),
+                _instance_update(context, session, instance_uuid, values,
+                                 expected, original=instance_ref))
 
 
 # NOTE(danms): This updates the instance's metadata list in-place and in
@@ -2490,73 +2510,122 @@ def _instance_metadata_update_in_place(context, instance, metadata_type, model,
         instance[metadata_type].append(newitem)
 
 
-@oslo_db_api.wrap_db_retry(max_retries=5, retry_on_deadlock=True)
-def _instance_update(context, instance_uuid, values, copy_old_instance=False,
-                     columns_to_join=None):
-    session = get_session()
-
+def _instance_update(context, session, instance_uuid, values, expected,
+                     original=None):
     if not uuidutils.is_uuid_like(instance_uuid):
         raise exception.InvalidUUID(instance_uuid)
 
-    with session.begin():
-        instance_ref = _instance_get_by_uuid(context, instance_uuid,
-                                             session=session,
-                                             columns_to_join=columns_to_join)
-        if "expected_task_state" in values:
-            # it is not a db column so always pop out
-            expected = values.pop("expected_task_state")
-            if not isinstance(expected, (tuple, list, set)):
-                expected = (expected,)
-            actual_state = instance_ref["task_state"]
-            if actual_state not in expected:
-                if actual_state == task_states.DELETING:
-                    raise exception.UnexpectedDeletingTaskStateError(
-                            actual=actual_state, expected=expected)
-                else:
-                    raise exception.UnexpectedTaskStateError(
-                            actual=actual_state, expected=expected)
-        if "expected_vm_state" in values:
-            expected = values.pop("expected_vm_state")
-            if not isinstance(expected, (tuple, list, set)):
-                expected = (expected,)
-            actual_state = instance_ref["vm_state"]
-            if actual_state not in expected:
-                raise exception.UnexpectedVMStateError(actual=actual_state,
-                                                       expected=expected)
+    if expected is None:
+        expected = {}
+    else:
+        # Coerce all single values to singleton lists
+        expected = {k: [None] if v is None else sqlalchemyutils.to_list(v)
+                       for (k, v) in six.iteritems(expected)}
 
-        instance_hostname = instance_ref['hostname'] or ''
-        if ("hostname" in values and
-                values["hostname"].lower() != instance_hostname.lower()):
-                _validate_unique_server_name(context,
-                                             session,
-                                             values['hostname'])
+    # Extract 'expected_' values from values dict, as these aren't actually
+    # updates
+    for field in ('task_state', 'vm_state'):
+        expected_field = 'expected_%s' % field
+        if expected_field in values:
+            value = values.pop(expected_field, None)
+            # Coerce all single values to singleton lists
+            if value is None:
+                expected[field] = [None]
+            else:
+                expected[field] = sqlalchemyutils.to_list(value)
 
-        if copy_old_instance:
-            old_instance_ref = copy.copy(instance_ref)
+    # Values which need to be updated separately
+    metadata = values.pop('metadata', None)
+    system_metadata = values.pop('system_metadata', None)
+
+    _handle_objects_related_type_conversions(values)
+
+    # Hostname is potentially unique, but this is enforced in code rather
+    # than the DB. The query below races, but the number of users of
+    # osapi_compute_unique_server_name_scope is small, and a robust fix
+    # will be complex. This is intentionally left as is for the moment.
+    if 'hostname' in values:
+        _validate_unique_server_name(context, session, values['hostname'])
+
+    compare = models.Instance(uuid=instance_uuid, **expected)
+    try:
+        instance_ref = model_query(context, models.Instance,
+                                   project_only=True, session=session).\
+                       update_on_match(compare, 'uuid', values)
+    except update_match.NoRowsMatched:
+        # Update failed. Try to find why and raise a specific error.
+
+        # We should get here only because our expected values were not current
+        # when update_on_match executed. Having failed, we now have a hint that
+        # the values are out of date and should check them.
+
+        # This code is made more complex because we are using repeatable reads.
+        # If we have previously read the original instance in the current
+        # transaction, reading it again will return the same data, even though
+        # the above update failed because it has changed: it is not possible to
+        # determine what has changed in this transaction. In this case we raise
+        # UnknownInstanceUpdateConflict, which will cause the operation to be
+        # retried in a new transaction.
+
+        # Because of the above, if we have previously read the instance in the
+        # current transaction it will have been passed as 'original', and there
+        # is no point refreshing it. If we have not previously read the
+        # instance, we can fetch it here and we will get fresh data.
+        if original is None:
+            original = _instance_get_by_uuid(context, instance_uuid,
+                                             session=session)
+
+        conflicts_expected = {}
+        conflicts_actual = {}
+        for (field, expected_values) in six.iteritems(expected):
+            actual = original[field]
+            if actual not in expected_values:
+                conflicts_expected[field] = expected_values
+                conflicts_actual[field] = actual
+
+        # Exception properties
+        exc_props = {
+            'instance_uuid': instance_uuid,
+            'expected': conflicts_expected,
+            'actual': conflicts_actual
+        }
+
+        # There was a conflict, but something (probably the MySQL read view,
+        # but possibly an exceptionally unlikely second race) is preventing us
+        # from seeing what it is. When we go round again we'll get a fresh
+        # transaction and a fresh read view.
+        if len(conflicts_actual) == 0:
+            raise exception.UnknownInstanceUpdateConflict(**exc_props)
+
+        # Task state gets special handling for convenience. We raise the
+        # specific error UnexpectedDeletingTaskStateError or
+        # UnexpectedTaskStateError as appropriate
+        if 'task_state' in conflicts_actual:
+            conflict_task_state = conflicts_actual['task_state']
+            if conflict_task_state == task_states.DELETING:
+                exc = exception.UnexpectedDeletingTaskStateError
+            else:
+                exc = exception.UnexpectedTaskStateError
+
+        # Everything else is an InstanceUpdateConflict
         else:
-            old_instance_ref = None
+            exc = exception.InstanceUpdateConflict
 
-        metadata = values.get('metadata')
-        if metadata is not None:
-            _instance_metadata_update_in_place(context, instance_ref,
-                                               'metadata',
-                                               models.InstanceMetadata,
-                                               values.pop('metadata'),
-                                               session)
+        raise exc(**exc_props)
 
-        system_metadata = values.get('system_metadata')
-        if system_metadata is not None:
-            _instance_metadata_update_in_place(context, instance_ref,
-                                               'system_metadata',
-                                               models.InstanceSystemMetadata,
-                                               values.pop('system_metadata'),
-                                               session)
+    if metadata is not None:
+        _instance_metadata_update_in_place(context, instance_ref,
+                                           'metadata',
+                                           models.InstanceMetadata,
+                                           metadata, session)
 
-        _handle_objects_related_type_conversions(values)
-        instance_ref.update(values)
-        session.add(instance_ref)
+    if system_metadata is not None:
+        _instance_metadata_update_in_place(context, instance_ref,
+                                           'system_metadata',
+                                           models.InstanceSystemMetadata,
+                                           system_metadata, session)
 
-    return (old_instance_ref, instance_ref)
+    return instance_ref
 
 
 def instance_add_security_group(context, instance_uuid, security_group_id):

nova/exception.py

@@ -1433,9 +1433,18 @@ class InstanceUserDataMalformed(NovaException):
     msg_fmt = _("User data needs to be valid base 64.")
 
 
-class UnexpectedTaskStateError(NovaException):
-    msg_fmt = _("Unexpected task state: expecting %(expected)s but "
-                "the actual state is %(actual)s")
+class InstanceUpdateConflict(NovaException):
+    msg_fmt = _("Conflict updating instance %(instance_uuid)s. "
+                "Expected: %(expected)s. Actual: %(actual)s")
+
+
+class UnknownInstanceUpdateConflict(InstanceUpdateConflict):
+    msg_fmt = _("Conflict updating instance %(instance_uuid)s, but we were "
+                "unable to determine the cause")
+
+
+class UnexpectedTaskStateError(InstanceUpdateConflict):
+    pass
 
 
 class UnexpectedDeletingTaskStateError(UnexpectedTaskStateError):
@@ -1451,11 +1460,6 @@ class InstanceActionEventNotFound(NovaException):
     msg_fmt = _("Event %(event)s not found for action id %(action_id)s")
 
 
-class UnexpectedVMStateError(NovaException):
-    msg_fmt = _("Unexpected VM state: expecting %(expected)s but "
-                "the actual state is %(actual)s")
-
-
 class CryptoCAFileNotFound(FileNotFound):
     msg_fmt = _("The CA file for %(project)s could not be found")
 

nova/tests/unit/compute/test_compute.py

@@ -1786,7 +1786,9 @@ class ComputeTestCase(BaseTestCase):
 
         with mock.patch.object(instance, 'save') as mock_save:
             mock_save.side_effect = exception.UnexpectedDeletingTaskStateError(
-                actual='foo', expected='bar')
+                instance_uuid=instance['uuid'],
+                expected={'task_state': 'bar'},
+                actual={'task_state': 'foo'})
             self.compute.build_and_run_instance(self.context, instance, {}, {},
                                                 {}, block_device_mapping=[])
             self.assertTrue(mock_save.called)
@@ -3159,7 +3161,9 @@ class ComputeTestCase(BaseTestCase):
 
     def test_snapshot_fails_with_task_state_error(self):
         deleting_state_error = exception.UnexpectedDeletingTaskStateError(
-            expected=task_states.IMAGE_SNAPSHOT, actual=task_states.DELETING)
+            instance_uuid='fake_uuid',
+            expected={'task_state': task_states.IMAGE_SNAPSHOT},
+            actual={'task_state': task_states.DELETING})
         self._test_snapshot_deletes_image_on_failure(
             'error', deleting_state_error)
         self.assertTrue(self.fake_image_delete_called)

nova/tests/unit/compute/test_compute_api.py

@@ -1268,7 +1268,9 @@ class _ComputeAPIUnitTestMixIn(object):
             self.context, delta, fake_inst).AndReturn(fake_quotas)
 
         exc = exception.UnexpectedTaskStateError(
-            actual=task_states.RESIZE_REVERTING, expected=None)
+            instance_uuid=fake_inst['uuid'],
+            actual={'task_state': task_states.RESIZE_REVERTING},
+            expected={'task_state': [None]})
         fake_inst.save(expected_task_state=[None]).AndRaise(exc)
 
         fake_quotas.rollback()

nova/tests/unit/compute/test_compute_mgr.py

@@ -3032,8 +3032,8 @@ class ComputeManagerBuildInstanceTestCase(test.NoDBTestCase):
 
     def test_build_and_run_unexpecteddeleting_exception(self):
         self._test_build_and_run_exceptions(
-                exception.UnexpectedDeletingTaskStateError(expected='',
-                    actual=''))
+                exception.UnexpectedDeletingTaskStateError(
+                    instance_uuid='fake_uuid', expected={}, actual={}))
 
     def test_build_and_run_buildabort_exception(self):
         self._test_build_and_run_exceptions(exception.BuildAbortException(
@@ -3281,7 +3281,9 @@ class ComputeManagerBuildInstanceTestCase(test.NoDBTestCase):
                     return_value=self.network_info),
                 mock.patch.object(self.instance, 'save',
                     side_effect=exception.UnexpectedDeletingTaskStateError(
-                        actual=task_states.DELETING, expected='None')),
+                        instance_uuid='fake_uuid',
+                        actual={'task_state': task_states.DELETING},
+                        expected={'task_state': None})),
         ) as (_build_networks_for_instance, save):
 
             try:
@@ -3319,8 +3321,10 @@ class ComputeManagerBuildInstanceTestCase(test.NoDBTestCase):
                 '_build_networks_for_instance') as _build_networks:
 
             exc = exception.UnexpectedDeletingTaskStateError
-            _build_networks.side_effect = exc(actual=task_states.DELETING,
-                    expected='None')
+            _build_networks.side_effect = exc(
+                instance_uuid='fake_uuid',
+                actual={'task_state': task_states.DELETING},
+                expected={'task_state': None})
 
             try:
                 with self.compute._build_resources(self.context, self.instance,
@@ -3413,7 +3417,7 @@ class ComputeManagerBuildInstanceTestCase(test.NoDBTestCase):
             self, mock_save, mock_build_network, mock_info_wait):
         mock_build_network.return_value = self.network_info
         mock_save.side_effect = exception.UnexpectedTaskStateError(
-            expected='', actual='')
+            instance_uuid='fake_uuid', expected={}, actual={})
         try:
             with self.compute._build_resources(self.context, self.instance,
                     self.requested_networks, self.security_groups,

nova/tests/unit/conductor/test_conductor.py

@@ -460,8 +460,9 @@ class ConductorTestCase(_BaseTestCase, test.TestCase):
     def test_instance_update_expected_exceptions(self):
         errors = (exc.InvalidUUID(uuid='foo'),
                   exc.InstanceNotFound(instance_id=1),
-                  exc.UnexpectedTaskStateError(expected='foo',
-                                               actual='bar'))
+                  exc.UnexpectedTaskStateError(instance_uuid='fake_uuid',
+                                               expected={'task_state': 'foo'},
+                                               actual={'task_state': 'bar'}))
         self._test_expected_exceptions(
             'instance_update', self.conductor.instance_update,
             errors, None, {'foo': 'bar'}, None)

nova/tests/unit/db/test_db_api.py

@@ -29,6 +29,7 @@ from oslo_config import cfg
 from oslo_db import api as oslo_db_api
 from oslo_db import exception as db_exc
 from oslo_db.sqlalchemy import test_base
+from oslo_db.sqlalchemy import update_match
 from oslo_db.sqlalchemy import utils as sqlalchemyutils
 from oslo_serialization import jsonutils
 from oslo_utils import timeutils
@@ -48,6 +49,7 @@ from sqlalchemy import Table
 
 from nova import block_device
 from nova.compute import arch
+from nova.compute import task_states
 from nova.compute import vm_states
 from nova import context
 from nova import db
@@ -2465,7 +2467,7 @@ class InstanceTestCase(test.TestCase, ModelsObjectComparatorMixin):
 
     def test_instance_update_with_unexpected_vm_state(self):
         instance = self.create_instance_with_args(vm_state='foo')
-        self.assertRaises(exception.UnexpectedVMStateError,
+        self.assertRaises(exception.InstanceUpdateConflict,
                     db.instance_update, self.ctxt, instance['uuid'],
                     {'host': 'h1', 'expected_vm_state': ('spam', 'bar')})
 
@@ -2532,7 +2534,7 @@ class InstanceTestCase(test.TestCase, ModelsObjectComparatorMixin):
         # Make sure instance faults is deleted as well
         self.assertEqual(0, len(faults[uuid]))
 
-    def test_instance_update_with_and_get_original(self):
+    def test_instance_update_and_get_original(self):
         instance = self.create_instance_with_args(vm_state='building')
         (old_ref, new_ref) = db.instance_update_and_get_original(self.ctxt,
                             instance['uuid'], {'vm_state': 'needscoffee'})
@@ -2588,6 +2590,174 @@ class InstanceTestCase(test.TestCase, ModelsObjectComparatorMixin):
         # 4. the "old" object is detached from this Session.
         self.assertTrue(old_insp.detached)
 
+    def test_instance_update_and_get_original_conflict_race(self):
+        # Ensure that we retry if update_on_match fails for no discernable
+        # reason
+        instance = self.create_instance_with_args()
+
+        orig_update_on_match = update_match.update_on_match
+
+        # Reproduce the conditions of a race between fetching and updating the
+        # instance by making update_on_match fail for no discernable reason the
+        # first time it is called, but work normally the second time.
+        with mock.patch.object(update_match, 'update_on_match',
+                        side_effect=[update_match.NoRowsMatched,
+                                     orig_update_on_match]):
+            db.instance_update_and_get_original(
+                self.ctxt, instance['uuid'], {'metadata': {'mk1': 'mv3'}})
+            self.assertEqual(update_match.update_on_match.call_count, 2)
+
+    def test_instance_update_and_get_original_conflict_race_fallthrough(self):
+        # Ensure that is update_match continuously fails for no discernable
+        # reason, we evantually raise UnknownInstanceUpdateConflict
+        instance = self.create_instance_with_args()
+
+        # Reproduce the conditions of a race between fetching and updating the
+        # instance by making update_on_match fail for no discernable reason.
+        with mock.patch.object(update_match, 'update_on_match',
+                        side_effect=update_match.NoRowsMatched):
+            self.assertRaises(exception.UnknownInstanceUpdateConflict,
+                              db.instance_update_and_get_original,
+                              self.ctxt,
+                              instance['uuid'],
+                              {'metadata': {'mk1': 'mv3'}})
+
+    def test_instance_update_and_get_original_expected_host(self):
+        # Ensure that we allow update when expecting a host field
+        instance = self.create_instance_with_args()
+
+        (orig, new) = db.instance_update_and_get_original(
+            self.ctxt, instance['uuid'], {'host': None},
+            expected={'host': 'h1'})
+
+        self.assertIsNone(new['host'])
+
+    def test_instance_update_and_get_original_expected_host_fail(self):
+        # Ensure that we detect a changed expected host and raise
+        # InstanceUpdateConflict
+        instance = self.create_instance_with_args()
+
+        try:
+            db.instance_update_and_get_original(
+                self.ctxt, instance['uuid'], {'host': None},
+                expected={'host': 'h2'})
+        except exception.InstanceUpdateConflict as ex:
+            self.assertEqual(ex.kwargs['instance_uuid'], instance['uuid'])
+            self.assertEqual(ex.kwargs['actual'], {'host': 'h1'})
+            self.assertEqual(ex.kwargs['expected'], {'host': ['h2']})
+        else:
+            self.fail('InstanceUpdateConflict was not raised')
+
+    def test_instance_update_and_get_original_expected_host_none(self):
+        # Ensure that we allow update when expecting a host field of None
+        instance = self.create_instance_with_args(host=None)
+
+        (old, new) = db.instance_update_and_get_original(
+            self.ctxt, instance['uuid'], {'host': 'h1'},
+            expected={'host': None})
+        self.assertEqual('h1', new['host'])
+
+    def test_instance_update_and_get_original_expected_host_none_fail(self):
+        # Ensure that we detect a changed expected host of None and raise
+        # InstanceUpdateConflict
+        instance = self.create_instance_with_args()
+
+        try:
+            db.instance_update_and_get_original(
+                self.ctxt, instance['uuid'], {'host': None},
+                expected={'host': None})
+        except exception.InstanceUpdateConflict as ex:
+            self.assertEqual(ex.kwargs['instance_uuid'], instance['uuid'])
+            self.assertEqual(ex.kwargs['actual'], {'host': 'h1'})
+            self.assertEqual(ex.kwargs['expected'], {'host': [None]})
+        else:
+            self.fail('InstanceUpdateConflict was not raised')
+
+    def test_instance_update_and_get_original_expected_task_state_single_fail(self):  # noqa
+        # Ensure that we detect a changed expected task and raise
+        # UnexpectedTaskStateError
+        instance = self.create_instance_with_args()
+
+        try:
+            db.instance_update_and_get_original(
+                self.ctxt, instance['uuid'], {
+                    'host': None,
+                    'expected_task_state': task_states.SCHEDULING
+                })
+        except exception.UnexpectedTaskStateError as ex:
+            self.assertEqual(ex.kwargs['instance_uuid'], instance['uuid'])
+            self.assertEqual(ex.kwargs['actual'], {'task_state': None})
+            self.assertEqual(ex.kwargs['expected'],
+                             {'task_state': [task_states.SCHEDULING]})
+        else:
+            self.fail('UnexpectedTaskStateError was not raised')
+
+    def test_instance_update_and_get_original_expected_task_state_single_pass(self):  # noqa
+        # Ensure that we allow an update when expected task is correct
+        instance = self.create_instance_with_args()
+
+        (orig, new) = db.instance_update_and_get_original(
+            self.ctxt, instance['uuid'], {
+                'host': None,
+                'expected_task_state': None
+            })
+        self.assertIsNone(new['host'])
+
+    def test_instance_update_and_get_original_expected_task_state_multi_fail(self):  # noqa
+        # Ensure that we detect a changed expected task and raise
+        # UnexpectedTaskStateError when there are multiple potential expected
+        # tasks
+        instance = self.create_instance_with_args()
+
+        try:
+            db.instance_update_and_get_original(
+                self.ctxt, instance['uuid'], {
+                    'host': None,
+                    'expected_task_state': [task_states.SCHEDULING,
+                                            task_states.REBUILDING]
+                })
+        except exception.UnexpectedTaskStateError as ex:
+            self.assertEqual(ex.kwargs['instance_uuid'], instance['uuid'])
+            self.assertEqual(ex.kwargs['actual'], {'task_state': None})
+            self.assertEqual(ex.kwargs['expected'],
+                             {'task_state': [task_states.SCHEDULING,
+                                              task_states.REBUILDING]})
+        else:
+            self.fail('UnexpectedTaskStateError was not raised')
+
+    def test_instance_update_and_get_original_expected_task_state_multi_pass(self):  # noqa
+        # Ensure that we allow an update when expected task is in a list of
+        # expected tasks
+        instance = self.create_instance_with_args()
+
+        (orig, new) = db.instance_update_and_get_original(
+            self.ctxt, instance['uuid'], {
+                'host': None,
+                'expected_task_state': [task_states.SCHEDULING, None]
+            })
+        self.assertIsNone(new['host'])
+
+    def test_instance_update_and_get_original_expected_task_state_deleting(self):  # noqa
+        # Ensure that we raise UnepectedDeletingTaskStateError when task state
+        # is not as expected, and it is DELETING
+        instance = self.create_instance_with_args(
+            task_state=task_states.DELETING)
+
+        try:
+            db.instance_update_and_get_original(
+                self.ctxt, instance['uuid'], {
+                    'host': None,
+                    'expected_task_state': task_states.SCHEDULING
+                })
+        except exception.UnexpectedDeletingTaskStateError as ex:
+            self.assertEqual(ex.kwargs['instance_uuid'], instance['uuid'])
+            self.assertEqual(ex.kwargs['actual'],
+                             {'task_state': task_states.DELETING})
+            self.assertEqual(ex.kwargs['expected'],
+                             {'task_state': [task_states.SCHEDULING]})
+        else:
+            self.fail('UnexpectedDeletingTaskStateError was not raised')
+
     def test_instance_update_unique_name(self):
         context1 = context.RequestContext('user1', 'p1')
         context2 = context.RequestContext('user2', 'p2')