Always read-deleted=yes on lazy-load

For some reason we were only reading deleted instances when loading generic
fields and not things like flavor. That weird behavior isn't very helpful,
so this makes us always read deleted for that case. Some of the fields, like
tags, will short-circuit that and just immediately lazy-load an empty set.
But for anything else, we should allow reading that data if it's still there.

With this change, we are able to remove a specific read_deleted='yes' usage
from ComputeManager._destroy_evacuated_instances() which is handled with
the generic solution. TestEvacuateDeleteServerRestartOriginalCompute asserts
that the evacuate scenario is still fixed.

Related-Bug: #1794996
Related-Bug: #1745977

Change-Id: I8ec3a3a697e55941ee447d0b52d29785717e4bf0

1 files changed, 21 insertions, 4 deletions

diff --git a/nova/objects/instance.py b/nova/objects/instance.py
index 010efc10a1..15c07663cc 100644
--- a/nova/objects/instance.py
+++ b/nova/objects/instance.py
@@ -899,10 +899,9 @@ class Instance(base.NovaPersistentObject, base.NovaObject,
         self.obj_reset_changes()
 
     def _load_generic(self, attrname):
-        with utils.temporary_mutation(self._context, read_deleted='yes'):
-            instance = self.__class__.get_by_uuid(self._context,
-                                                  uuid=self.uuid,
-                                                  expected_attrs=[attrname])
+        instance = self.__class__.get_by_uuid(self._context,
+                                              uuid=self.uuid,
+                                              expected_attrs=[attrname])
 
         if attrname not in instance:
             # NOTE(danms): Never allow us to recursively-load
@@ -1111,6 +1110,24 @@ class Instance(base.NovaPersistentObject, base.NovaObject,
                    'uuid': self.uuid,
                    })
 
+        with utils.temporary_mutation(self._context, read_deleted='yes'):
+            self._obj_load_attr(attrname)
+
+    def _obj_load_attr(self, attrname):
+        """Internal method for loading attributes from instances.
+
+        NOTE: Do not use this directly.
+
+        This method contains the implementation of lazy-loading attributes
+        from Instance object, minus some massaging of the context and
+        error-checking. This should always be called with the object-local
+        context set for reading deleted instances and with uuid set. All
+        of the code below depends on those two things. Thus, this should
+        only be called from obj_load_attr() itself.
+
+        :param attrname: The name of the attribute to be loaded
+        """
+
         # NOTE(danms): We handle some fields differently here so that we
         # can be more efficient
         if attrname == 'fault':