"cinder backup-create" fails if I mount the volume on instance

Issue

• cinder backup-create fails if I mount the volume on instance:

• Steps to Reproduce:

  • create volume.
  • attach it the instance.
  • mount it on the instance.
  • unmount it
  • detach it from the instance.
  • try to create backup.

• From backup.log:

2016-04-15 16:57:11.645 6880 DEBUG oslo_concurrency.processutils [req-cf67a0a9-38df-450b-b5dd-aecee90930b4 0bd72a79b869497f88619377c1300478 af930979147d4729975c2e58bb891936 - - -] CMD "dd if=/var/lib/cinder/mnt/2bb9c378dd673a3dbaeaa00e037e1c7a/volume-1dc0f384-5f81-4995-8ccd-71b2bc566997 of=/dev/null count=1" returned: 1 in 0.009s execute /usr/lib/python2.7/site-packages/oslo_concurrency/processutils.py:260
2016-04-15 16:57:11.647 6880 DEBUG oslo_concurrency.processutils [req-cf67a0a9-38df-450b-b5dd-aecee90930b4 0bd72a79b869497f88619377c1300478 af930979147d4729975c2e58bb891936 - - -] u'dd if=/var/lib/cinder/mnt/2bb9c378dd673a3dbaeaa00e037e1c7a/volume-1dc0f384-5f81-4995-8ccd-71b2bc566997 of=/dev/null count=1' failed. Not Retrying. execute /usr/lib/python2.7/site-packages/oslo_concurrency/processutils.py:308
2016-04-15 16:57:11.650 6880 DEBUG cinder.volume.driver [req-cf67a0a9-38df-450b-b5dd-aecee90930b4 0bd72a79b869497f88619377c1300478 af930979147d4729975c2e58bb891936 - - -] Device for volume 1dc0f384-5f81-4995-8ccd-71b2bc566997 is unavailable but did attach, detaching it. _attach_volume /usr/lib/python2.7/site-packages/cinder/volume/driver.py:976
2016-04-15 16:57:11.651 6880 DEBUG cinder.volume.driver [req-cf67a0a9-38df-450b-b5dd-aecee90930b4 0bd72a79b869497f88619377c1300478 af930979147d4729975c2e58bb891936 - - -] volume 1dc0f384-5f81-4995-8ccd-71b2bc566997: removing export _detach_volume /usr/lib/python2.7/site-packages/cinder/volume/driver.py:404
2016-04-15 16:57:11.804 6880 ERROR oslo_messaging.rpc.dispatcher [req-cf67a0a9-38df-450b-b5dd-aecee90930b4 0bd72a79b869497f88619377c1300478 af930979147d4729975c2e58bb891936 - - -] Exception during message handling: The device in the path /var/lib/cinder/mnt/2bb9c378dd673a3dbaeaa00e037e1c7a/volume-1dc0f384-5f81-4995-8ccd-71b2bc566997 is unavailable: Unable to access the backend storage via the path /var/lib/cinder/mnt/2bb9c378dd673a3dbaeaa00e037e1c7a/volume-1dc0f384-5f81-4995-8ccd-71b2bc566997.
2016-04-15 16:57:11.804 6880 ERROR oslo_messaging.rpc.dispatcher Traceback (most recent call last):
2016-04-15 16:57:11.804 6880 ERROR oslo_messaging.rpc.dispatcher   File "/usr/lib/python2.7/site-packages/oslo_messaging/rpc/dispatcher.py", line 142, in _dispatch_and_reply
2016-04-15 16:57:11.804 6880 ERROR oslo_messaging.rpc.dispatcher     executor_callback))
2016-04-15 16:57:11.804 6880 ERROR oslo_messaging.rpc.dispatcher   File "/usr/lib/python2.7/site-packages/oslo_messaging/rpc/dispatcher.py", line 186, in _dispatch
2016-04-15 16:57:11.804 6880 ERROR oslo_messaging.rpc.dispatcher     executor_callback)
2016-04-15 16:57:11.804 6880 ERROR oslo_messaging.rpc.dispatcher   File "/usr/lib/python2.7/site-packages/oslo_messaging/rpc/dispatcher.py", line 129, in _do_dispatch
2016-04-15 16:57:11.804 6880 ERROR oslo_messaging.rpc.dispatcher     result = func(ctxt, **new_args)
2016-04-15 16:57:11.804 6880 ERROR oslo_messaging.rpc.dispatcher   File "/usr/lib/python2.7/site-packages/osprofiler/profiler.py", line 105, in wrapper
2016-04-15 16:57:11.804 6880 ERROR oslo_messaging.rpc.dispatcher     return f(*args, **kwargs)
2016-04-15 16:57:11.804 6880 ERROR oslo_messaging.rpc.dispatcher   File "/usr/lib/python2.7/site-packages/cinder/backup/manager.py", line 399, in create_backup
2016-04-15 16:57:11.804 6880 ERROR oslo_messaging.rpc.dispatcher     self._update_backup_error(backup, context, six.text_type(err))
2016-04-15 16:57:11.804 6880 ERROR oslo_messaging.rpc.dispatcher   File "/usr/lib/python2.7/site-packages/oslo_utils/excutils.py", line 204, in __exit__
2016-04-15 16:57:11.804 6880 ERROR oslo_messaging.rpc.dispatcher     six.reraise(self.type_, self.value, self.tb)
2016-04-15 16:57:11.804 6880 ERROR oslo_messaging.rpc.dispatcher   File "/usr/lib/python2.7/site-packages/cinder/backup/manager.py", line 393, in create_backup
2016-04-15 16:57:11.804 6880 ERROR oslo_messaging.rpc.dispatcher     backup_service)
2016-04-15 16:57:11.804 6880 ERROR oslo_messaging.rpc.dispatcher   File "/usr/lib/python2.7/site-packages/osprofiler/profiler.py", line 105, in wrapper
2016-04-15 16:57:11.804 6880 ERROR oslo_messaging.rpc.dispatcher     return f(*args, **kwargs)
2016-04-15 16:57:11.804 6880 ERROR oslo_messaging.rpc.dispatcher   File "/usr/lib/python2.7/site-packages/cinder/volume/driver.py", line 1094, in backup_volume
2016-04-15 16:57:11.804 6880 ERROR oslo_messaging.rpc.dispatcher     backup_service)
2016-04-15 16:57:11.804 6880 ERROR oslo_messaging.rpc.dispatcher   File "/usr/lib/python2.7/site-packages/cinder/volume/driver.py", line 1119, in _backup_volume_temp_volume
2016-04-15 16:57:11.804 6880 ERROR oslo_messaging.rpc.dispatcher     self._backup_device(context, backup, backup_service, device_to_backup)
2016-04-15 16:57:11.804 6880 ERROR oslo_messaging.rpc.dispatcher   File "/usr/lib/python2.7/site-packages/cinder/volume/driver.py", line 1172, in _backup_device
2016-04-15 16:57:11.804 6880 ERROR oslo_messaging.rpc.dispatcher     properties)
2016-04-15 16:57:11.804 6880 ERROR oslo_messaging.rpc.dispatcher   File "/usr/lib/python2.7/site-packages/cinder/volume/driver.py", line 968, in _attach_volume
2016-04-15 16:57:11.804 6880 ERROR oslo_messaging.rpc.dispatcher     attach_info = self._connect_device(conn)
2016-04-15 16:57:11.804 6880 ERROR oslo_messaging.rpc.dispatcher   File "/usr/lib/python2.7/site-packages/cinder/volume/driver.py", line 1076, in _connect_device
2016-04-15 16:57:11.804 6880 ERROR oslo_messaging.rpc.dispatcher     {'path': host_device}))
2016-04-15 16:57:11.804 6880 ERROR oslo_messaging.rpc.dispatcher DeviceUnavailable: The device in the path /var/lib/cinder/mnt/2bb9c378dd673a3dbaeaa00e037e1c7a/volume-1dc0f384-5f81-4995-8ccd-71b2bc566997 is unavailable: Unable to access the backend storage via the path /var/lib/cinder/mnt/2bb9c378dd673a3dbaeaa00e037e1c7a/volume-1dc0f384-5f81-4995-8ccd-71b2bc566997.