There’s a bunch of clean up to do.
New kernel isn’t working properly – boot from old one.
Try yum update again, get an error message about an existing transaction.
Have yum-utils already installed, so yum-complete-transactions is a command away.
Even after repeating it multiple times, yum still complains about broken packages.
Turns out yum died in the middle of cleanup, so old packages were still in the rpmDB.
Discovery of the day: package-cleanup –cleandupes will fix that error, even though the list of packages to remove looks very scary.