Unable to detach volume from the instance(HP 3PAR)

Issue

• Unable to detach volume from the instance(HP 3PAR)
• When we try to detach the volume from the Horizon dashboard. The volume is detached from the instance, but the state on the horizon dashboard keeps as detaching even after very long time.
• compute logs:

2016-02-16 16:09:16.818 3273 ERROR oslo.messaging.rpc.dispatcher [req-4dbcf4d1-1665-4ac6-a24c-80fa2587bbab ] Exception during message handling: Unable to terminate volume connection from backend. (HTTP 500) (Req
uest-ID: req-14261273-8618-49de-aa64-f27314ab0249)
2016-02-16 16:09:16.818 3273 TRACE oslo.messaging.rpc.dispatcher Traceback (most recent call last):
2016-02-16 16:09:16.818 3273 TRACE oslo.messaging.rpc.dispatcher   File "/usr/lib/python2.7/site-packages/oslo/messaging/rpc/dispatcher.py", line 134, in _dispatch_and_reply
2016-02-16 16:09:16.818 3273 TRACE oslo.messaging.rpc.dispatcher     incoming.message))
2016-02-16 16:09:16.818 3273 TRACE oslo.messaging.rpc.dispatcher   File "/usr/lib/python2.7/site-packages/oslo/messaging/rpc/dispatcher.py", line 177, in _dispatch
2016-02-16 16:09:16.818 3273 TRACE oslo.messaging.rpc.dispatcher     return self._do_dispatch(endpoint, method, ctxt, args)
2016-02-16 16:09:16.818 3273 TRACE oslo.messaging.rpc.dispatcher   File "/usr/lib/python2.7/site-packages/oslo/messaging/rpc/dispatcher.py", line 123, in _do_dispatch
2016-02-16 16:09:16.818 3273 TRACE oslo.messaging.rpc.dispatcher     result = getattr(endpoint, method)(ctxt, **new_args)
2016-02-16 16:09:16.818 3273 TRACE oslo.messaging.rpc.dispatcher   File "/usr/lib/python2.7/site-packages/nova/compute/manager.py", line 435, in decorated_function
2016-02-16 16:09:16.818 3273 TRACE oslo.messaging.rpc.dispatcher     return function(self, context, *args, **kwargs)
2016-02-16 16:09:16.818 3273 TRACE oslo.messaging.rpc.dispatcher   File "/usr/lib/python2.7/site-packages/nova/exception.py", line 88, in wrapped
2016-02-16 16:09:16.818 3273 TRACE oslo.messaging.rpc.dispatcher   File "/usr/lib/python2.7/site-packages/nova/openstack/common/excutils.py", line 82, in __exit__
2016-02-16 16:09:16.818 3273 TRACE oslo.messaging.rpc.dispatcher     six.reraise(self.type_, self.value, self.tb)
2016-02-16 16:09:16.818 3273 TRACE oslo.messaging.rpc.dispatcher   File "/usr/lib/python2.7/site-packages/nova/exception.py", line 71, in wrapped
2016-02-16 16:09:16.818 3273 TRACE oslo.messaging.rpc.dispatcher     return f(self, context, *args, **kw)
2016-02-16 16:09:16.818 3273 TRACE oslo.messaging.rpc.dispatcher   File "/usr/lib/python2.7/site-packages/nova/compute/manager.py", line 315, in decorated_function
2016-02-16 16:09:16.818 3273 TRACE oslo.messaging.rpc.dispatcher     LOG.warning(msg, e, instance_uuid=instance_uuid)
2016-02-16 16:09:16.818 3273 TRACE oslo.messaging.rpc.dispatcher   File "/usr/lib/python2.7/site-packages/nova/openstack/common/excutils.py", line 82, in __exit__
2016-02-16 16:09:16.818 3273 TRACE oslo.messaging.rpc.dispatcher     six.reraise(self.type_, self.value, self.tb)
2016-02-16 16:09:16.818 3273 TRACE oslo.messaging.rpc.dispatcher   File "/usr/lib/python2.7/site-packages/nova/compute/manager.py", line 292, in decorated_function
2016-02-16 16:09:16.818 3273 TRACE oslo.messaging.rpc.dispatcher     return function(self, context, *args, **kwargs)
2016-02-16 16:09:16.818 3273 TRACE oslo.messaging.rpc.dispatcher   File "/usr/lib/python2.7/site-packages/nova/compute/manager.py", line 343, in decorated_function
2016-02-16 16:09:16.818 3273 TRACE oslo.messaging.rpc.dispatcher     kwargs['instance'], e, sys.exc_info())
2016-02-16 16:09:16.818 3273 TRACE oslo.messaging.rpc.dispatcher   File "/usr/lib/python2.7/site-packages/nova/openstack/common/excutils.py", line 82, in __exit__
2016-02-16 16:09:16.818 3273 TRACE oslo.messaging.rpc.dispatcher     six.reraise(self.type_, self.value, self.tb)
2016-02-16 16:09:16.818 3273 TRACE oslo.messaging.rpc.dispatcher   File "/usr/lib/python2.7/site-packages/nova/compute/manager.py", line 331, in decorated_function
2016-02-16 16:09:16.818 3273 TRACE oslo.messaging.rpc.dispatcher     return function(self, context, *args, **kwargs)
2016-02-16 16:09:16.818 3273 TRACE oslo.messaging.rpc.dispatcher   File "/usr/lib/python2.7/site-packages/nova/compute/manager.py", line 4738, in detach_volume
2016-02-16 16:09:16.818 3273 TRACE oslo.messaging.rpc.dispatcher     self._detach_volume(context, volume_id, instance)
2016-02-16 16:09:16.818 3273 TRACE oslo.messaging.rpc.dispatcher   File "/usr/lib/python2.7/site-packages/nova/compute/manager.py", line 4721, in _detach_volume
2016-02-16 16:09:16.818 3273 TRACE oslo.messaging.rpc.dispatcher     self.volume_api.terminate_connection(context, volume_id, connector)
2016-02-16 16:09:16.818 3273 TRACE oslo.messaging.rpc.dispatcher   File "/usr/lib/python2.7/site-packages/nova/volume/cinder.py", line 185, in wrapper
2016-02-16 16:09:16.818 3273 TRACE oslo.messaging.rpc.dispatcher     res = method(self, ctx, volume_id, *args, **kwargs)
2016-02-16 16:09:16.818 3273 TRACE oslo.messaging.rpc.dispatcher   File "/usr/lib/python2.7/site-packages/nova/volume/cinder.py", line 354, in terminate_connection
2016-02-16 16:09:16.818 3273 TRACE oslo.messaging.rpc.dispatcher     connector)
2016-02-16 16:09:16.818 3273 TRACE oslo.messaging.rpc.dispatcher   File "/usr/lib/python2.7/site-packages/cinderclient/v1/volumes.py", line 331, in terminate_connection
2016-02-16 16:09:16.818 3273 TRACE oslo.messaging.rpc.dispatcher     {'connector': connector})
2016-02-16 16:09:16.818 3273 TRACE oslo.messaging.rpc.dispatcher   File "/usr/lib/python2.7/site-packages/cinderclient/v1/volumes.py", line 250, in _action
2016-02-16 16:09:16.818 3273 TRACE oslo.messaging.rpc.dispatcher     return self.api.client.post(url, body=body)
2016-02-16 16:09:16.818 3273 TRACE oslo.messaging.rpc.dispatcher   File "/usr/lib/python2.7/site-packages/cinderclient/client.py", line 305, in post
2016-02-16 16:09:16.818 3273 TRACE oslo.messaging.rpc.dispatcher     return self._cs_request(url, 'POST', **kwargs)
2016-02-16 16:09:16.818 3273 TRACE oslo.messaging.rpc.dispatcher   File "/usr/lib/python2.7/site-packages/cinderclient/client.py", line 269, in _cs_request
2016-02-16 16:09:16.818 3273 TRACE oslo.messaging.rpc.dispatcher     **kwargs)
2016-02-16 16:09:16.818 3273 TRACE oslo.messaging.rpc.dispatcher   File "/usr/lib/python2.7/site-packages/cinderclient/client.py", line 252, in request
2016-02-16 16:09:16.818 3273 TRACE oslo.messaging.rpc.dispatcher     raise exceptions.from_response(resp, body)
2016-02-16 16:09:16.818 3273 TRACE oslo.messaging.rpc.dispatcher ClientException: Unable to terminate volume connection from backend. (HTTP 500) (Request-ID: req-14261273-8618-49de-aa64-f27314ab0249)
2016-02-16 16:09:16.818 3273 TRACE oslo.messaging.rpc.dispatcher