linux-kernel - Re: [PATCH] ARM: select HAVE_FUTEX

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Message-ID: <CAK8P3a04ZGgxNf6mmufwOmCY37JJkN9CHDJGQe2wY4CabwafuQ@mail.gmail.com>
Date:   Fri, 17 Sep 2021 22:33:51 +0200
From:   Arnd Bergmann <arnd@...db.de>
To:     Arnd Bergmann <arnd@...db.de>
Cc:     Nick Desaulniers <ndesaulniers@...gle.com>,
        Linux ARM <linux-arm-kernel@...ts.infradead.org>,
        llvm@...ts.linux.dev, Nathan Chancellor <nathan@...nel.org>,
        Thomas Gleixner <tglx@...utronix.de>,
        Russell King <linux@...linux.org.uk>,
        Geert Uytterhoeven <geert+renesas@...der.be>,
        Linus Walleij <linus.walleij@...aro.org>,
        Andrew Morton <akpm@...ux-foundation.org>,
        Anshuman Khandual <anshuman.khandual@....com>,
        Ard Biesheuvel <ardb@...nel.org>,
        YiFei Zhu <yifeifz2@...inois.edu>,
        Uwe Kleine-König 
        <u.kleine-koenig@...gutronix.de>, Mike Rapoport <rppt@...nel.org>,
        Linux Kernel Mailing List <linux-kernel@...r.kernel.org>,
        clang-built-linux <clang-built-linux@...glegroups.com>
Subject: Re: [PATCH] ARM: select HAVE_FUTEX_CMPXCHG

On Fri, Sep 17, 2021 at 9:11 AM Arnd Bergmann <arnd@...db.de> 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