[kolla-ansible] How to recover from unfinished upgrade

Hi, I am testing the upgrade from xena to yoga and I made a mistake in globals.yml, I forgot to specify the correct name of gnocchi ceph pool, so my deployment went wrong. I interrupted the deployment Ctrl+C I corrected the mistake, then I restarted the upgrade and it got stuck somewhere else, but I couldn't find where, I interrupted then restarted the deployment again and it got stuck at the same place. My questions : - Is there a way to rollback the upgrade in case of a problem, then start over? - What is the best way to restart a broken upgrade process? Regards.