linux-kernel - Re: [PATCH] futex: Set USER_DS for the futex_detect

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Message-ID: <alpine.DEB.2.21.1809281041420.2004@nanos.tec.linutronix.de>
Date:   Fri, 28 Sep 2018 10:42:36 +0200 (CEST)
From:   Thomas Gleixner <tglx@...utronix.de>
To:     Martin Schwidefsky <schwidefsky@...ibm.com>
cc:     Geert Uytterhoeven <geert@...ux-m68k.org>,
        Andy Lutomirski <luto@...nel.org>,
        the arch/x86 maintainers <x86@...nel.org>,
        Peter Zijlstra <peterz@...radead.org>,
        Ingo Molnar <mingo@...hat.com>,
        Darren Hart <dvhart@...radead.org>,
        Linux Kernel Mailing List <linux-kernel@...r.kernel.org>,
        linux-s390 <linux-s390@...r.kernel.org>,
        Heiko Carstens <heiko.carstens@...ibm.com>,
        Finn Thain <fthain@...egraphics.com.au>
Subject: Re: [PATCH] futex: Set USER_DS for the futex_detect_cmpxchg() test

On Fri, 28 Sep 2018, Martin Schwidefsky wrote:
> On Fri, 28 Sep 2018 09:12:10 +0200
> Geert Uytterhoeven <geert@...ux-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@...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@...ibm.com>
>     Cc: Finn Thain <fthain@...egraphics.com.au>
>     Cc: Geert Uytterhoeven <geert@...ux-m68k.org>
>     Link: http://lkml.kernel.org/r/20140302120947.GA3641@osiris
>     Signed-off-by: Thomas Gleixner <tglx@...utronix.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