Re: [PATCH] ARM: select HAVE_FUTEX_CMPXCHG

[Arnd Bergmann]

On Fri, Sep 17, 2021 at 9:11 AM Arnd Bergmann <arnd@xxxxxxxx> wrote:
>
> Nice! I did remember that we had come up with a number of solutions
> for the build error and that at least one of them was an obvious and
> nice fix, but I could never figure out what it was. This is clearly better
> than any of the other ones I had found when I last looked.

Actually it turns out that I had come up with another approach, removing
the need for HAVE_FUTEX_CMPXCHG and the boot time check altogether:

https://git.kernel.org/pub/scm/linux/kernel/git/arnd/playground.git/commit/?h=randconfig-5.13&id=7bbd7403526a2a9f398f360fcb97f256052ca6bf

Guo Ren fixed the missing csky bit in there, but since the sparc32 support
is still missing, I never sent this before forgetting about it.
I think the only users of sparc32 these days are LEON CPUs, which have
usable atomics and could implement this properly but support for that was
not upstreamed.

        Arnd