Lazy-load instance attributes with read_deleted=yes

If we're doing a lazy-load of a generic attribute on instance, we
should be using read_deleted=yes. Otherwise we just fail in the load
process which is confusing and not helpful to a cleanup routine that
needs to handle the deleted instance. This makes us load those things
with read_deleted=yes.

Change-Id: Ide6cc5bb1fce2c9aea9fa3efdf940e8308cd9ed0
Closes-Bug: #1745977

nova/objects/instance.py

@@ -855,9 +855,10 @@ def refresh(self, use_slave=False):
         self.obj_reset_changes()
 
     def _load_generic(self, attrname):
-        instance = self.__class__.get_by_uuid(self._context,
-                                              uuid=self.uuid,
-                                              expected_attrs=[attrname])
+        with utils.temporary_mutation(self._context, read_deleted='yes'):
+            instance = self.__class__.get_by_uuid(self._context,
+                                                  uuid=self.uuid,
+                                                  expected_attrs=[attrname])
 
         # NOTE(danms): Never allow us to recursively-load
         if instance.obj_attr_is_set(attrname):

nova/tests/unit/objects/test_instance.py

@@ -220,6 +220,22 @@ def test_lazy_load_tags_on_deleted_instance(self):
                                     deleted=True)
         self.assertEqual(0, len(instance.tags))
 
+    def test_lazy_load_generic_on_deleted_instance(self):
+        # For generic fields, we try to load the deleted record from the
+        # database.
+        instance = objects.Instance(self.context, uuid=uuids.instance,
+                                    user_id=self.context.user_id,
+                                    project_id=self.context.project_id)
+        instance.create()
+        instance.destroy()
+        # Re-create our local object to make sure it doesn't have sysmeta
+        # filled in by create()
+        instance = objects.Instance(self.context, uuid=uuids.instance,
+                                    user_id=self.context.user_id,
+                                    project_id=self.context.project_id)
+        self.assertNotIn('system_metadata', instance)
+        self.assertEqual(0, len(instance.system_metadata))
+
     def test_lazy_load_tags(self):
         instance = objects.Instance(self.context, uuid=uuids.instance,
                                     user_id=self.context.user_id,