Ensure resource class cache when listing usages

In rare circumstances it is possible to list usages in a new placement
process that has not yet instantiated the _RC_CACHE but for which
there are inventories and allocations in the database (added by
other processes running against the same db). Before this change
that would cause a 500 error (AttributeError) when the Usage objects
in the UsageList were instantiated.

The fix is to added _ensure_rc_cache to the two list methods. The
addition is done there rather than in the _from_db_object as the
latter would cause a lot of redundant checks.

While we could probably devise a test for this, it's perhaps good
enough to evaluate the change by inspection. If not, suggestions
welcome.

Change-Id: I00f7dee26f031366dbc0d3d6a03abe89afeb85fd
Closes-Bug: #1775308
(cherry picked from commit 724d440122232a5bfdfec51eb0d37ca4f1d748d8)

1 files changed, 2 insertions, 0 deletions

diff --git a/nova/objects/resource_provider.py b/nova/objects/resource_provider.py
index b57d0ed780..b81aa1805f 100644
--- a/nova/objects/resource_provider.py
+++ b/nova/objects/resource_provider.py
@@ -2224,11 +2224,13 @@ class UsageList(base.ObjectListBase, base.NovaObject):
 
     @classmethod
     def get_all_by_resource_provider_uuid(cls, context, rp_uuid):
+        _ensure_rc_cache(context)
         usage_list = cls._get_all_by_resource_provider_uuid(context, rp_uuid)
         return base.obj_make_list(context, cls(context), Usage, usage_list)
 
     @classmethod
     def get_all_by_project_user(cls, context, project_id, user_id=None):
+        _ensure_rc_cache(context)
         usage_list = cls._get_all_by_project_user(context, project_id,
                                                   user_id=user_id)
         return base.obj_make_list(context, cls(context), Usage, usage_list)