I am also hitting the same issue in master (cloned today) when using DevStack:

Jul 08 14:58:50  cinder-volume[30192]: DEBUG oslo_db.sqlalchemy.engines [None req-fc47b79c-441d-4051-9cfc-b0df3df5e8d9 None None] MySQL server mode set to STRICT_TRANS_TABLES,STRICT_ALL_TABLES,NO_ZERO_IN_DATE,NO_ZERO_DATE,ERROR_FOR_DIVISION_BY_ZERO,TRADITIONAL,NO_AUTO_CREATE_USER,NO_ENGINE_SUBSTITUTION {{(pid=30242) _check_effective_sql_mode /usr/local/lib/python3.6/dist-packages/oslo_db/sqlalchemy/engines.py:307}}
Jul 08 14:58:50  cinder-volume[30192]: ERROR oslo_service.service [None req-fc47b79c-441d-4051-9cfc-b0df3df5e8d9 None None] Error starting thread.: sqlalchemy.orm.exc.DetachedInstanceError: Parent instance <VolumeAttachment at 0x7f86e98e0898> is not bound to a Session; lazy load operation of attribute 'volume' cannot proceed (Background on this error at: http://sqlalche.me/e/bhk3)
Jul 08 14:58:50  cinder-volume[30192]: ERROR oslo_service.service Traceback (most recent call last):
Jul 08 14:58:50  cinder-volume[30192]: ERROR oslo_service.service   File "/usr/local/lib/python3.6/dist-packages/oslo_service/service.py", line 796, in run_service
Jul 08 14:58:50  cinder-volume[30192]: ERROR oslo_service.service     service.start()
Jul 08 14:58:50  cinder-volume[30192]: ERROR oslo_service.service   File "/opt/stack/cinder/cinder/service.py", line 229, in start
Jul 08 14:58:50  cinder-volume[30192]: ERROR oslo_service.service     service_id=Service.service_id)
Jul 08 14:58:50  cinder-volume[30192]: ERROR oslo_service.service   File "/opt/stack/cinder/cinder/volume/manager.py", line 444, in init_host
Jul 08 14:58:50  cinder-volume[30192]: ERROR oslo_service.service     self._init_host(added_to_cluster, **kwargs)
Jul 08 14:58:50  cinder-volume[30192]: ERROR oslo_service.service   File "/opt/stack/cinder/cinder/volume/manager.py", line 522, in _init_host
Jul 08 14:58:50  cinder-volume[30192]: ERROR oslo_service.service     volumes = self._get_my_volumes(ctxt)
Jul 08 14:58:50  cinder-volume[30192]: ERROR oslo_service.service   File "/opt/stack/cinder/cinder/volume/manager.py", line 3036, in _get_my_volumes
Jul 08 14:58:50  cinder-volume[30192]: ERROR oslo_service.service     limit, offset)
Jul 08 14:58:50  cinder-volume[30192]: ERROR oslo_service.service   File "/opt/stack/cinder/cinder/volume/manager.py", line 3032, in _get_my_resources
Jul 08 14:58:50  cinder-volume[30192]: ERROR oslo_service.service     offset=offset)
Jul 08 14:58:50  cinder-volume[30192]: ERROR oslo_service.service   File "/opt/stack/cinder/cinder/objects/volume.py", line 617, in get_all
Jul 08 14:58:50  cinder-volume[30192]: ERROR oslo_service.service     volumes, expected_attrs=expected_attrs)
Jul 08 14:58:50  cinder-volume[30192]: ERROR oslo_service.service   File "/usr/local/lib/python3.6/dist-packages/oslo_versionedobjects/base.py", line 1133, in obj_make_list
Jul 08 14:58:50  cinder-volume[30192]: ERROR oslo_service.service     **extra_args)
Jul 08 14:58:50  cinder-volume[30192]: ERROR oslo_service.service   File "/opt/stack/cinder/cinder/objects/volume.py", line 290, in _from_db_object
Jul 08 14:58:50  cinder-volume[30192]: ERROR oslo_service.service     db_volume.get('volume_attachment'))
Jul 08 14:58:50  cinder-volume[30192]: ERROR oslo_service.service   File "/usr/local/lib/python3.6/dist-packages/oslo_versionedobjects/base.py", line 1133, in obj_make_list
Jul 08 14:58:50  cinder-volume[30192]: ERROR oslo_service.service     **extra_args)
Jul 08 14:58:50  cinder-volume[30192]: ERROR oslo_service.service   File "/opt/stack/cinder/cinder/objects/volume_attachment.py", line 102, in _from_db_object
Jul 08 14:58:50  cinder-volume[30192]: ERROR oslo_service.service     if 'volume' in expected_attrs and hasattr(db_attachment, 'volume'):
Jul 08 14:58:50  cinder-volume[30192]: ERROR oslo_service.service   File "/usr/local/lib/python3.6/dist-packages/sqlalchemy/orm/attributes.py", line 282, in __get__
Jul 08 14:58:50  cinder-volume[30192]: ERROR oslo_service.service     return self.impl.get(instance_state(instance), dict_)
Jul 08 14:58:50  cinder-volume[30192]: ERROR oslo_service.service   File "/usr/local/lib/python3.6/dist-packages/sqlalchemy/orm/attributes.py", line 699, in get
Jul 08 14:58:50  cinder-volume[30192]: ERROR oslo_service.service     value = self.callable_(state, passive)
Jul 08 14:58:50  cinder-volume[30192]: ERROR oslo_service.service   File "/usr/local/lib/python3.6/dist-packages/sqlalchemy/orm/strategies.py", line 686, in _load_for_state
Jul 08 14:58:50  cinder-volume[30192]: ERROR oslo_service.service     % (orm_util.state_str(state), self.key)
Jul 08 14:58:50  cinder-volume[30192]: ERROR oslo_service.service sqlalchemy.orm.exc.DetachedInstanceError: Parent instance <VolumeAttachment at 0x7f86e98e0898> is not bound to a Session; lazy load operation of attribute 'volume' cannot proceed (Background on this error at: http://sqlalche.me/e/bhk3)
Jul 08 14:58:50  cinder-volume[30192]: ERROR oslo_service.service