Re: [PATCH] futex: Set USER_DS for the futex_detect_cmpxchg() test

Thomas Gleixner
2018-09-28T08:42:36Z

On Fri, 28 Sep 2018, Martin Schwidefsky wrote:
> On Fri, 28 Sep 2018 09:12:10 +0200
> Geert Uytterhoeven <geert@linux-m68k.org> wrote:
> > I don't know if that has happened, and whether it would work on s390 now.
>
> commit 03b8c7b623c80af264c4c8d6111e5c6289933666
> Author: Heiko Carstens <heiko.carstens@de.ibm.com>
> Date: Sun Mar 2 13:09:47 2014 +0100
>
> futex: Allow architectures to skip futex_atomic_cmpxchg_inatomic() test
>
> If an architecture has futex_atomic_cmpxchg_inatomic() implemented and there
> is no runtime check necessary, allow to skip the test within futex_init().
>
> This allows to get rid of some code which would always give the same result,
> and also allows the compiler to optimize a couple of if statements away.
>
> Signed-off-by: Heiko Carstens <heiko.carstens@de.ibm.com>
> Cc: Finn Thain <fthain@telegraphics.com.au>
> Cc: Geert Uytterhoeven <geert@linux-m68k.org>
> Link: http://lkml.kernel.org/r/20140302120947.GA3641@osiris
> Signed-off-by: Thomas Gleixner <tglx@linutronix.de>
>
>
> Heiko created the CONFIG_HAVE_FUTEX_CMPXCHG to get around this issue.
> We just skip the runtime check as well as arc, m68k and sh. Not sure
> about xtensa, the set it config option only for !MMU.

Duh. grep would have told me. -ENOTENOUGHCOFFEE

Thanks,

tglx