Decouple slub_debug and no_hash_pointers

[kees]

When booting with "slub_debug=FZ", hashed pointers are disabled.

The source of the problem is commit
7927029 ("slub: force on no_hash_pointers when slub_debug is enabled")

I objected at the time:
https://lore.kernel.org/all/202109200726.2EFEDC5@keescook/
But it was never reverted.

If someone could send a patch that would decouple these again, I'd appreciate it. I think it would be best to refactor the boot param "no_hash_pointers" into "hash_pointers={auto,always,never}", with the old setting meaning "hash_pointers=never", but the default being "=auto" that falls back to this case where slub debug turns it off. But that would allow for "slub_debug=FZ hash_pointers=always" and we could have the best of both worlds.

See https://bugs.debian.org/cgi-bin/bugreport.cgi?bug=1098362

[sperezglz]

Hi, I saw this issue and started to look into it. I have a patch cf76d5a, but before sending it for wider review I wanted to check-in and see if this is what you had in mind and looks ok.