If the root directory exists but has a bad block number Pass1 will
accept it and setup an inoinfo structure for it. When Pass2 runs
and cannot read the root inode's content because of a bad (or
duplicate) block number, it removes the bad root inode and replaces
it. As part of creating the replacement root inode, it creates an
inoinfo entry for it. But Pass2 did delete the inoinfo entry that
Pass1 had set up for the root inode so ended up with two inoinfo
structures for it. The final step of Pass2 checks that all the ".."
entries are correct adding them if they are missing which resulted
in a second ".." entry being added to the root directory which
definitely did not go over well in the kernel name cache!
Reported by: Peter Holm
Sponsored by: The FreeBSD Foundation
f4fc389524