Unity: failed to delete snapshots when backups are canceled

[Ryan Liang]

Version of OpenStack: 9.1.4, Newton

How to reproduce:
1. Create a snapshot of a volume.
2. Create a backup from the snapshot.
3. Although the backup is created from the snapshot, a temp volume is still created from the snapshot before doing the backup due to not setting `backup_use_same_host`.
4. Cancel the backup before it finishes.
5. The snapshot cannot be deleted using OpenStack command.

An exception is logged in the cinder volume log.

2018-10-18 06:14:56.589 WARNING cinder.volume.drivers.dell_emc.unity.client [req-235f994d-67c6-4faa-864b-8d522d20b5d5 admin] Failed to delete snapshot snapshot-e7f4568b-c97b-43fd-926e-bc39dacc4a97 which is in use. Message: The snapshot cannot be destroyed because it is attached. (Error Code:0x716d8003)
2018-10-18 06:14:56.631 ERROR oslo_messaging.rpc.server [req-235f994d-67c6-4faa-864b-8d522d20b5d5 admin] Exception during message handling
2018-10-18 06:14:56.631 28094 ERROR oslo_messaging.rpc.server Traceback (most recent call last):
2018-10-18 06:14:56.631 28094 ERROR oslo_messaging.rpc.server File "/usr/local/lib/python2.7/dist-packages/oslo_messaging/rpc/server.py", line 133, in _process_incoming
2018-10-18 06:14:56.631 28094 ERROR oslo_messaging.rpc.server res = self.dispatcher.dispatch(message)
2018-10-18 06:14:56.631 28094 ERROR oslo_messaging.rpc.server File "/usr/local/lib/python2.7/dist-packages/oslo_messaging/rpc/dispatcher.py", line 150, in dispatch
2018-10-18 06:14:56.631 28094 ERROR oslo_messaging.rpc.server return self._do_dispatch(endpoint, method, ctxt, args)
2018-10-18 06:14:56.631 28094 ERROR oslo_messaging.rpc.server File "/usr/local/lib/python2.7/dist-packages/oslo_messaging/rpc/dispatcher.py", line 121, in _do_dispatch
2018-10-18 06:14:56.631 28094 ERROR oslo_messaging.rpc.server result = func(ctxt, **new_args)
2018-10-18 06:14:56.631 28094 ERROR oslo_messaging.rpc.server File "/opt/stack/cinder/cinder/volume/manager.py", line 4381, in delete_snapshot
2018-10-18 06:14:56.631 28094 ERROR oslo_messaging.rpc.server context, snapshot, unmanage_only=unmanage_only)
2018-10-18 06:14:56.631 28094 ERROR oslo_messaging.rpc.server File "/opt/stack/cinder/cinder/coordination.py", line 285, in wrapped
2018-10-18 06:14:56.631 28094 ERROR oslo_messaging.rpc.server return f(*a, **k)
2018-10-18 06:14:56.631 28094 ERROR oslo_messaging.rpc.server File "/opt/stack/cinder/cinder/volume/manager.py", line 916, in delete_snapshot
2018-10-18 06:14:56.631 28094 ERROR oslo_messaging.rpc.server snapshot.save()
2018-10-18 06:14:56.631 28094 ERROR oslo_messaging.rpc.server File "/usr/local/lib/python2.7/dist-packages/oslo_utils/excutils.py", line 220, in __exit__
2018-10-18 06:14:56.631 28094 ERROR oslo_messaging.rpc.server self.force_reraise()
2018-10-18 06:14:56.631 28094 ERROR oslo_messaging.rpc.server File "/usr/local/lib/python2.7/dist-packages/oslo_utils/excutils.py", line 196, in force_reraise
2018-10-18 06:14:56.631 28094 ERROR oslo_messaging.rpc.server six.reraise(self.type_, self.value, self.tb)
2018-10-18 06:14:56.631 28094 ERROR oslo_messaging.rpc.server File "/opt/stack/cinder/cinder/volume/manager.py", line 906, in delete_snapshot
2018-10-18 06:14:56.631 28094 ERROR oslo_messaging.rpc.server self.driver.delete_snapshot(snapshot)
2018-10-18 06:14:56.631 28094 ERROR oslo_messaging.rpc.server File "/opt/stack/cinder/cinder/volume/drivers/dell_emc/unity/driver.py", line 113, in delete_snapshot
2018-10-18 06:14:56.631 28094 ERROR oslo_messaging.rpc.server self.adapter.delete_snapshot(snapshot)
2018-10-18 06:14:56.631 28094 ERROR oslo_messaging.rpc.server File "/opt/stack/cinder/cinder/volume/drivers/dell_emc/unity/adapter.py", line 416, in delete_snapshot
2018-10-18 06:14:56.631 28094 ERROR oslo_messaging.rpc.server snap, even_attached=self.force_delete_attached_snapshots)
2018-10-18 06:14:56.631 28094 ERROR oslo_messaging.rpc.server File "/opt/stack/cinder/cinder/volume/drivers/dell_emc/unity/client.py", line 179, in delete_snap
2018-10-18 06:14:56.631 28094 ERROR oslo_messaging.rpc.server {'snap_name': snap.name, 'err': err})
2018-10-18 06:14:56.631 28094 ERROR oslo_messaging.rpc.server File "/usr/local/lib/python2.7/dist-packages/oslo_utils/excutils.py", line 220, in __exit__
2018-10-18 06:14:56.631 28094 ERROR oslo_messaging.rpc.server self.force_reraise()
2018-10-18 06:14:56.631 28094 ERROR oslo_messaging.rpc.server File "/usr/local/lib/python2.7/dist-packages/oslo_utils/excutils.py", line 196, in force_reraise
2018-10-18 06:14:56.631 28094 ERROR oslo_messaging.rpc.server six.reraise(self.type_, self.value, self.tb)
2018-10-18 06:14:56.631 28094 ERROR oslo_messaging.rpc.server File "/opt/stack/cinder/cinder/volume/drivers/dell_emc/unity/client.py", line 169, in delete_snap
2018-10-18 06:14:56.631 28094 ERROR oslo_messaging.rpc.server snap.delete(even_attached=even_attached)
2018-10-18 06:14:56.631 28094 ERROR oslo_messaging.rpc.server File "/home/stack/storops/storops/unity/resource/snap.py", line 209, in delete
2018-10-18 06:14:56.631 28094 ERROR oslo_messaging.rpc.server return super(UnitySnap, self).delete(async=async)
2018-10-18 06:14:56.631 28094 ERROR oslo_messaging.rpc.server File "/home/stack/storops/storops/unity/resource/__init__.py", line 68, in delete
2018-10-18 06:14:56.631 28094 ERROR oslo_messaging.rpc.server resp.raise_if_err()
2018-10-18 06:14:56.631 28094 ERROR oslo_messaging.rpc.server File "/home/stack/storops/storops/unity/resp.py", line 131, in raise_if_err
2018-10-18 06:14:56.631 28094 ERROR oslo_messaging.rpc.server raise ex_clz(self.error)
2018-10-18 06:14:56.631 28094 ERROR oslo_messaging.rpc.server UnityDeleteAttachedSnapError: The snapshot cannot be destroyed because it is attached. (Error Code:0x716d8003)
2018-10-18 06:14:56.631 28094 ERROR oslo_messaging.rpc.server

[OpenStack Infra (hudson-openstack)]

Fix proposed to branch: master
Review: https://review.openstack.org/611515