Comment 4 for bug 1703581

Well, the stacktrace is pretty useless, because it's wrapped into timeout exception:

2017-09-21 15:12:46.684 30033 ERROR oslo_messaging.rpc.server [req-f9d5ed41-1dd5-4757-9341-d4243d05385c 73979cf70cac4f8995e65bdd833765ac d1c044d0731d42af942c165fc4c801a8 - - -] Exception during message handling: ShareExtendingError: Share 51aeabaa-6471-465e-8e51-0d7f108beaae could not be extended due to error in the driver: Volume has not been extended in 180s. Giving up
2017-09-21 15:12:46.684 30033 ERROR oslo_messaging.rpc.server Traceback (most recent call last):
2017-09-21 15:12:46.684 30033 ERROR oslo_messaging.rpc.server File "/usr/local/lib/python2.7/dist-packages/oslo_messaging/rpc/server.py", line 160, in _process_incoming
2017-09-21 15:12:46.684 30033 ERROR oslo_messaging.rpc.server res = self.dispatcher.dispatch(message)
2017-09-21 15:12:46.684 30033 ERROR oslo_messaging.rpc.server File "/usr/local/lib/python2.7/dist-packages/oslo_messaging/rpc/dispatcher.py", line 213, in dispatch
2017-09-21 15:12:46.684 30033 ERROR oslo_messaging.rpc.server return self._do_dispatch(endpoint, method, ctxt, args)
2017-09-21 15:12:46.684 30033 ERROR oslo_messaging.rpc.server File "/usr/local/lib/python2.7/dist-packages/oslo_messaging/rpc/dispatcher.py", line 183, in _do_dispatch
2017-09-21 15:12:46.684 30033 ERROR oslo_messaging.rpc.server result = func(ctxt, **new_args)
2017-09-21 15:12:46.684 30033 ERROR oslo_messaging.rpc.server File "/opt/stack/manila/manila/share/manager.py", line 186, in wrapped
2017-09-21 15:12:46.684 30033 ERROR oslo_messaging.rpc.server return f(self, *args, **kwargs)
2017-09-21 15:12:46.684 30033 ERROR oslo_messaging.rpc.server File "/opt/stack/manila/manila/utils.py", line 560, in wrapper
2017-09-21 15:12:46.684 30033 ERROR oslo_messaging.rpc.server return func(self, *args, **kwargs)
2017-09-21 15:12:46.684 30033 ERROR oslo_messaging.rpc.server File "/opt/stack/manila/manila/share/manager.py", line 3544, in extend_share
2017-09-21 15:12:46.684 30033 ERROR oslo_messaging.rpc.server reason=six.text_type(e), share_id=share_id)
2017-09-21 15:12:46.684 30033 ERROR oslo_messaging.rpc.server ShareExtendingError: Share 51aeabaa-6471-465e-8e51-0d7f108beaae could not be extended due to error in the driver: Volume has not been extended in 180s. Giving up
2017-09-21 15:12:46.684 30033 ERROR oslo_messaging.rpc.server

Further investigation reveals the reason - the samba processes holding volume making it unavailable to unmount.