Re: [RFC PATCH] text_poke/ftrace/x86: Allow text_poke() to be called in early boot

[Linus Torvalds]

On Mon, Oct 24, 2022 at 4:03 PM Steven Rostedt <rostedt@xxxxxxxxxxx> wrote:
>
> This required some updates to fork and the maple_tree code to allow it to
> be called with enabling interrupts in the time when interrupts must remain
> disabled.

Yeah, moving special cases from one place to another doesn't really
help. Particularly to something as core as dup_mm().

All of this comes from "poking_init()" being a steaming pile of bovine
excrement, doing random odd things, and having that special
"copy_init_mm()" helper that just makes things even worse. Nothing
else uses that, and it shouldn't have called "dup_mm()" in the first
place.

At this point, there is no actual user VM to even copy, so 99% of
everything that duip_mm() does is not just pointless, but actively
wrong, like the mmap_write_lock_nested() when we're in early boot.

I'm not even sure why "poking_mm" exists at all, and why it has
created a whole new copy of "init_mm", and why this code isn't just
using '&init_mm' like everything else that wants to just walk the
kernel page tables.

Yes, I see that commit 4fc19708b165 ("x86/alternatives: Initialize
temporary mm for patching"), and no, none of that makes any sense to
me. It seems just (mis-)designed to fail.

                 Linus