After multiple panics/locks, hitting KKASSERT in hammer_init_cursor
After quite a few locks (machine stopped responding, nothing on serial console, unable to panic the machine), the hammer FS (v6) got a corrupted(?) UNDO.
Booting the latest snapshot and mounting with ro,noatime it looked as if it was able to rerun the UNDO/FIFO. But trying to mount the "clean" FS result in triping over a KKASSERT (error == 0 at hammer_cursor.c:202)