Looks like this bug is still not fixed. We upgraded to latest stein release and we are facing this problem when starting cinder-volume service:

Error starting thread.: sqlalchemy.orm.exc.DetachedInstanceError: Parent instance <VolumeAttachment at 0x7f04ba5ed3c8> is not bound to a Session; lazy load operation of attribute 'volume' cannot proceed (Background on this error at: http://sqlalche.me/e/bhk3)
2019-07-01 10:29:22.947 16745 ERROR oslo_service.service Traceback (most recent call last):
2019-07-01 10:29:22.947 16745 ERROR oslo_service.service   File "/usr/lib/python3/dist-packages/oslo_service/service.py", line 796, in run_service
2019-07-01 10:29:22.947 16745 ERROR oslo_service.service     service.start()
2019-07-01 10:29:22.947 16745 ERROR oslo_service.service   File "/usr/lib/python3/dist-packages/cinder/service.py", line 222, in start
2019-07-01 10:29:22.947 16745 ERROR oslo_service.service     service_id=Service.service_id)
2019-07-01 10:29:22.947 16745 ERROR oslo_service.service   File "/usr/lib/python3/dist-packages/cinder/volume/manager.py", line 445, in init_host
2019-07-01 10:29:22.947 16745 ERROR oslo_service.service     self._init_host(added_to_cluster, **kwargs)
2019-07-01 10:29:22.947 16745 ERROR oslo_service.service   File "/usr/lib/python3/dist-packages/cinder/volume/manager.py", line 523, in _init_host
2019-07-01 10:29:22.947 16745 ERROR oslo_service.service     volumes = self._get_my_volumes(ctxt)
2019-07-01 10:29:22.947 16745 ERROR oslo_service.service   File "/usr/lib/python3/dist-packages/cinder/volume/manager.py", line 3007, in _get_my_volumes
2019-07-01 10:29:22.947 16745 ERROR oslo_service.service     limit, offset)
2019-07-01 10:29:22.947 16745 ERROR oslo_service.service   File "/usr/lib/python3/dist-packages/cinder/volume/manager.py", line 3003, in _get_my_resources
2019-07-01 10:29:22.947 16745 ERROR oslo_service.service     offset=offset)
2019-07-01 10:29:22.947 16745 ERROR oslo_service.service   File "/usr/lib/python3/dist-packages/cinder/objects/volume.py", line 617, in get_all
2019-07-01 10:29:22.947 16745 ERROR oslo_service.service     volumes, expected_attrs=expected_attrs)
2019-07-01 10:29:22.947 16745 ERROR oslo_service.service   File "/usr/lib/python3/dist-packages/oslo_versionedobjects/base.py", line 1133, in obj_make_list
2019-07-01 10:29:22.947 16745 ERROR oslo_service.service     **extra_args)
2019-07-01 10:29:22.947 16745 ERROR oslo_service.service   File "/usr/lib/python3/dist-packages/cinder/objects/volume.py", line 290, in _from_db_object
2019-07-01 10:29:22.947 16745 ERROR oslo_service.service     db_volume.get('volume_attachment'))
2019-07-01 10:29:22.947 16745 ERROR oslo_service.service   File "/usr/lib/python3/dist-packages/oslo_versionedobjects/base.py", line 1133, in obj_make_list
2019-07-01 10:29:22.947 16745 ERROR oslo_service.service     **extra_args)
2019-07-01 10:29:22.947 16745 ERROR oslo_service.service   File "/usr/lib/python3/dist-packages/cinder/objects/volume_attachment.py", line 102, in _from_db_object
2019-07-01 10:29:22.947 16745 ERROR oslo_service.service     if 'volume' in expected_attrs and hasattr(db_attachment, 'volume'):
2019-07-01 10:29:22.947 16745 ERROR oslo_service.service   File "/usr/lib/python3/dist-packages/sqlalchemy/orm/attributes.py", line 242, in __get__
2019-07-01 10:29:22.947 16745 ERROR oslo_service.service     return self.impl.get(instance_state(instance), dict_)
2019-07-01 10:29:22.947 16745 ERROR oslo_service.service   File "/usr/lib/python3/dist-packages/sqlalchemy/orm/attributes.py", line 601, in get
2019-07-01 10:29:22.947 16745 ERROR oslo_service.service     value = self.callable_(state, passive)
2019-07-01 10:29:22.947 16745 ERROR oslo_service.service   File "/usr/lib/python3/dist-packages/sqlalchemy/orm/strategies.py", line 596, in _load_for_state
2019-07-01 10:29:22.947 16745 ERROR oslo_service.service     (orm_util.state_str(state), self.key)
2019-07-01 10:29:22.947 16745 ERROR oslo_service.service sqlalchemy.orm.exc.DetachedInstanceError: Parent instance <VolumeAttachment at 0x7f04ba5ed3c8> is not bound to a Session; lazy load operation of attribute 'volume' cannot proceed (Background on this error at: http://sqlalche.me/e/bhk3)

Should I open a new bug report? I think this is related to this one. I already looked into the code and the patch is applied at my version.

ii  cinder-api                     2:14.0.0-0ubuntu1~cloud0          all          Cinder storage service - API server
ii  cinder-common                  2:14.0.0-0ubuntu1~cloud0          all          Cinder storage service - common files
ii  cinder-scheduler               2:14.0.0-0ubuntu1~cloud0          all          Cinder storage service - Scheduler server
ii  cinder-volume                  2:14.0.0-0ubuntu1~cloud0          all          Cinder storage service - Volume server
ii  python3-cinder                 2:14.0.0-0ubuntu1~cloud0          all          Cinder Python 3 libraries