Comment 1 for bug 1908037

This seems likely related to https://bugs.launchpad.net/cinder/+bug/1893107 - we will need special handling for this.

Basically if you upgraded from Stein->Train 15.3 or earlier, it setup a failure that only triggers on the Train->Ussuri upgrade. Detailed in the release notes for 15.4.0 and 16.2.0 under "Upgrade Notes" here:
https://docs.openstack.org/releasenotes/cinder/train.html

This release modifies the online database migrations to address an an upgrade issue (Bug #1893107). The issue does not manifest itself in the Train release of cinder, but under specific circumstances it can prevent a cinder database upgrade from Train to Ussuri.

This upgrade notice applies to you only if all of the following conditions are met:

You upgraded to Train from Stein

Before upgrading from Stein, you did not purge the cinder database

Your original upgrade from Stein was to cinder version 15.3.0 or earlier.

 Note

If you are upgrading a Stein installation directly to this release (cinder 15.4.0) or later, this notice does not apply to you.

If all the above three items apply to you, as part of your upgrade to cinder 15.4.0 you should re-run the online database migrations contained in this release. This will prepare your cinder database for an eventual upgrade to the Ussuri release.