Error while upgrading to 1.91

When upgrading from 1.90 to 1.91, I get the following error:

[root@bgp2]/usr/local/etc# fetch 'https://bodems.net/BSDRP-1.91-upgrade-amd64-vga.img.xz' -o - | xzcat | upgrade
-                                             100% of   93 MB   28 kBps 56m33s
931707+0 records in
7278+1 records out
477033984 bytes transferred in 3393.987416 secs (140553 bytes/sec)
** /dev/vtbd0s2a (NO WRITE)
** Last Mounted on /usr/obj/BSDRP.amd64/_.mnt
** Phase 1 - Check Blocks and Sizes
** Phase 2 - Check Pathnames
** Phase 3 - Check Connectivity
** Phase 4 - Check Reference Counts
** Phase 5 - Check Cyl groups
15539 files, 818985 used, 97120 free (1048 frags, 12009 blocks, 0.1% fragmentation)
umount: unmount of /cfg failed: Device busy
EXIT: ERROR: Can't umount /cfg

Any idea about this?

Oh no 'umount: unmount of /cfg failed: Device busy' I've believe to have fixed this problem: Do you have autosave enabled ?

Yes, autosave is enabled. Is there anything I can test or should I just disable autosave?

What I mean is I've improved the upgrade script of 1.91 release (check this commit and this one), but when you're upgrading a 1.90, it still use upgrade script 1.90 (the older one) :-(

For fixing your error, try to issue a second time the upgrade process after the first one failed: It (theorically) should works the second time. Once upgraded to 1.91 (and rebooted), you can verify if the new upgrade script is better by upgrading it to same 1.91 version( it will be a useless upgrade): it should works fine.