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[OpenStack Infra <1775308@xxxxxxxxxxxxxxxxxx>]

Reviewed:  https://review.openstack.org/572652
Committed: https://git.openstack.org/cgit/openstack/nova/commit/?id=724d440122232a5bfdfec51eb0d37ca4f1d748d8
Submitter: Zuul
Branch:    master

commit 724d440122232a5bfdfec51eb0d37ca4f1d748d8
Author: Chris Dent <cdent@xxxxxxxxxxxxx>
Date:   Tue Jun 5 18:07:05 2018 -0700

    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


** Changed in: nova
       Status: In Progress => Fix Released

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https://bugs.launchpad.net/bugs/1775308

Title:
  Listing placement usages (total or per resource provider) in a new
  process can result in a 500

Status in OpenStack Compute (nova):
  Fix Released

Bug description:
  When requesting /usages or /resource_providers/{uuid}/usages it is
  possible to cause a 500 error if placement is running in a multi-
  process scenario and the usages query is the first request a process
  has received. This is because the methods which provide UsageLists do
  not _ensure_rc_cache, resulting in:

    File "/usr/lib/python3.6/site-packages/nova/api/openstack/placement/objects/resource_provider.py", line 2374, in _from_db_object
         rc_str = _RC_CACHE.string_from_id(source['resource_class_id'])
     AttributeError: 'NoneType' object has no attribute 'string_from_id'

  We presumably don't see this in our usual testing because any process
  has already had other requests happen, setting the cache.

  For now, the fix is to add the _ensure_rc_cache call in the right
  places, but long term if/when we switch to the os-resource-class model
  we can do the caching or syncing a bit differently (see
  https://review.openstack.org/#/c/553857/ for an example).

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