In short, be on the lookout for any backport change which is actually the same Git SHA as on the master branch (probably the most obvious sign will be lack of a cherry-pick header in the commit message, since changes to the commit message also change the Git SHA). Currently Gerrit won't protect us from someone proposing a change from one branch to another if the parent commit of that change is already in the former branch, even though it's not (yet) in the latter.
Nice one, thanks for the heads up Jeremy. Any ideas how to check git history for those? But I guess it would have been noticed, master and stable branches are different enough. Just in case, I've added an explicit note[1] about the additional reason cherry-pick -x required, it was implicit by example and stable reviewers have been enforcing it already. Cheers, Alan [1] https://wiki.openstack.org/w/index.php?title=StableBranch&diff=63196&oldid=62527