Comment 5 for bug 1536509

debugging informations about the root cause:

2016-01-25 13:56:59.277 DEBUG nova.compute.utils [req-c3dcb81e-18d7-45f2-a5cc-7254f037b088 tempest-ServersWithSpecificFlavorTestJSON-1773823374 tempest-ServersWithSpecificFlavorTestJSON-573174746] ***********fault_payload is None 'NoneType' object has no attribute 'to_dict' notify_about_instance_usage /opt/stack/nova/nova/compute/utils.py:285
Traceback (most recent call last):
  File "/opt/stack/nova/nova/compute/manager.py", line 2007, in _build_and_run_instance
    with rt.instance_claim(context, instance, limits):
  File "/usr/local/lib/python2.7/dist-packages/oslo_concurrency/lockutils.py", line 271, in inner
    return f(*args, **kwargs)
  File "/opt/stack/nova/nova/compute/resource_tracker.py", line 181, in instance_claim
    overhead=overhead, limits=limits)
  File "/opt/stack/nova/nova/compute/claims.py", line 94, in __init__
    self._claim_test(resources, limits)
  File "/opt/stack/nova/nova/compute/claims.py", line 152, in _claim_test
    self._test_pci()]
  File "/opt/stack/nova/nova/compute/claims.py", line 194, in _test_pci
    self.instance)
  File "/opt/stack/nova/nova/pci/manager.py", line 211, in claim_instance
    devs = self._claim_instance(context, instance)
  File "/opt/stack/nova/nova/pci/manager.py", line 184, in _claim_instance
    instance_cells)
  File "/opt/stack/nova/nova/pci/stats.py", line 175, in consume_requests
    self._handle_device_dependents(pci_dev)
  File "/opt/stack/nova/nova/pci/stats.py", line 202, in _handle_device_dependents
    pci_dev.parent_addr)
  File "/usr/local/lib/python2.7/dist-packages/oslo_versionedobjects/base.py", line 172, in wrapper
    args, kwargs)
  File "/opt/stack/nova/nova/conductor/rpcapi.py", line 241, in object_class_action_versions
    args=args, kwargs=kwargs)
  File "/usr/local/lib/python2.7/dist-packages/oslo_messaging/rpc/client.py", line 146, in call
    msg_ctxt = self.serializer.serialize_context(ctxt)
  File "/opt/stack/nova/nova/rpc.py", line 139, in serialize_context
    return context.to_dict()
AttributeError: 'NoneType' object has no attribute 'to_dict'