Cinder leaves quota usage when deleting incremental backup with parent from another project

[Rodrigo Barbieri]

The root cause for this bug is https://bugs.launchpad.net/cinder/+bug/1869746

However, the code could be improved to prevent this specific problem from happening regardless of that bug.

Environment: Same as bug 1869746

This bug was also reproduced on Queens.

Steps to reproduce:

1) Run same steps as bug 1869746
2) Try to delete the backup created.
3) Result: Backup is deleted successfully, but an error is thrown in the logs and quota used by backup is not restored on [0].

Expectation: Delete the backup without errors and successfully restore the quota. Quota should be restored as soon as backup is deleted.

Trace:

2020-03-30 14:56:38.431 25018 ERROR oslo_messaging.rpc.server [req-5e034fe6-0844-4b61-a03c-b6d0bc605b00 3bee8c02ecce4744af287b3b8dd40ca5 9370e1e898214d88bd9eda4f88eccba9 - f883c6315a004471b2ab1b04d8a111d9 f883c6315a004471b2ab1b04d8a111d9] Exception during message handling: cinder.exception.BackupNotFound: Backup 7a15b9ec-7648-483f-ad32-6074567eca2a could not be found.
2020-03-30 14:56:38.431 25018 ERROR oslo_messaging.rpc.server Traceback (most recent call last):
2020-03-30 14:56:38.431 25018 ERROR oslo_messaging.rpc.server File "/usr/lib/python3/dist-packages/oslo_messaging/rpc/server.py", line 165, in _process_incoming
2020-03-30 14:56:38.431 25018 ERROR oslo_messaging.rpc.server res = self.dispatcher.dispatch(message)
2020-03-30 14:56:38.431 25018 ERROR oslo_messaging.rpc.server File "/usr/lib/python3/dist-packages/oslo_messaging/rpc/dispatcher.py", line 274, in dispatch
2020-03-30 14:56:38.431 25018 ERROR oslo_messaging.rpc.server return self._do_dispatch(endpoint, method, ctxt, args)
2020-03-30 14:56:38.431 25018 ERROR oslo_messaging.rpc.server File "/usr/lib/python3/dist-packages/oslo_messaging/rpc/dispatcher.py", line 194, in _do_dispatch
2020-03-30 14:56:38.431 25018 ERROR oslo_messaging.rpc.server result = func(ctxt, **new_args)
2020-03-30 14:56:38.431 25018 ERROR oslo_messaging.rpc.server File "/usr/lib/python3/dist-packages/cinder/backup/manager.py", line 780, in delete_backup
2020-03-30 14:56:38.431 25018 ERROR oslo_messaging.rpc.server backup.parent_id)
2020-03-30 14:56:38.431 25018 ERROR oslo_messaging.rpc.server File "/usr/lib/python3/dist-packages/cinder/objects/base.py", line 352, in get_by_id
2020-03-30 14:56:38.431 25018 ERROR oslo_messaging.rpc.server orm_obj = db.get_by_id(context, cls.model, id, *args, **kwargs)
2020-03-30 14:56:38.431 25018 ERROR oslo_messaging.rpc.server File "/usr/lib/python3/dist-packages/cinder/db/api.py", line 1801, in get_by_id
2020-03-30 14:56:38.431 25018 ERROR oslo_messaging.rpc.server return IMPL.get_by_id(context, model, id, *args, **kwargs)
2020-03-30 14:56:38.431 25018 ERROR oslo_messaging.rpc.server File "/usr/lib/python3/dist-packages/cinder/db/sqlalchemy/api.py", line 189, in wrapper
2020-03-30 14:56:38.431 25018 ERROR oslo_messaging.rpc.server return f(*args, **kwargs)
2020-03-30 14:56:38.431 25018 ERROR oslo_messaging.rpc.server File "/usr/lib/python3/dist-packages/cinder/db/sqlalchemy/api.py", line 7125, in get_by_id
2020-03-30 14:56:38.431 25018 ERROR oslo_messaging.rpc.server return _GET_METHODS[model](context, id, *args, **kwargs)
2020-03-30 14:56:38.431 25018 ERROR oslo_messaging.rpc.server File "/usr/lib/python3/dist-packages/cinder/db/sqlalchemy/api.py", line 189, in wrapper
2020-03-30 14:56:38.431 25018 ERROR oslo_messaging.rpc.server return f(*args, **kwargs)
2020-03-30 14:56:38.431 25018 ERROR oslo_messaging.rpc.server File "/usr/lib/python3/dist-packages/cinder/db/sqlalchemy/api.py", line 5154, in backup_get
2020-03-30 14:56:38.431 25018 ERROR oslo_messaging.rpc.server project_only=project_only)
2020-03-30 14:56:38.431 25018 ERROR oslo_messaging.rpc.server File "/usr/lib/python3/dist-packages/cinder/db/sqlalchemy/api.py", line 5165, in _backup_get
2020-03-30 14:56:38.431 25018 ERROR oslo_messaging.rpc.server raise exception.BackupNotFound(backup_id=backup_id)
2020-03-30 14:56:38.431 25018 ERROR oslo_messaging.rpc.server cinder.exception.BackupNotFound: Backup 7a15b9ec-7648-483f-ad32-6074567eca2a could not be found.
2020-03-30 14:56:38.431 25018 ERROR oslo_messaging.rpc.server

[0] https://github.com/openstack/cinder/blob/e79b98367bd72f0323258dc0506de28b31c4aa48/cinder/backup/manager.py#L786

[Rodrigo Barbieri (rodrigo-barbieri2010)]

This is a consequence of bug https://bugs.launchpad.net/cinder/+bug/1869749 but could be improved to handle quotas in a better way when deleting backups