ext4: deal with legacy signed xattr name hash values

ext4: deal with legacy signed xattr name hash values

We potentially have old hashes of the xattr names generated on systems
with signed 'char' types.  Now that everybody uses '-funsigned-char',
those hashes will no longer match.

This only happens if you use xattrs names that have the high bit set,
which probably doesn't happen in practice, but the xfstest generic/454
shows it.

Instead of adding a new "signed xattr hash filesystem" bit and having to
deal with all the possible combinations, just calculate the hash both
ways if the first one fails, and always generate new hashes with the
proper unsigned char version.

Reported-by: kernel test robot <[email protected]>
Link: https://lore.kernel.org/oe-lkp/[email protected]
Link: https://lore.kernel.org/all/CAHk-=whUNjwqZXa-MH9KMmc_CpQpoFKFjAB9ZKHuu=TbsouT4A@mail.gmail.com/
Exposed-by: 3bc753c06dd0 ("kbuild: treat char as always unsigned")
Cc: Eric Biggers <[email protected]>
Cc: Andreas Dilger <[email protected]>
Cc: Theodore Ts'o <[email protected]>,
Cc: Jason Donenfeld <[email protected]>
Cc: Masahiro Yamada <[email protected]>
Signed-off-by: Linus Torvalds <[email protected]>