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From:   Max Filippov <jcmvbkbc@gmail.com>
Date:   Fri, 28 Sep 2018 14:36:33 -0700
Message-ID: <CAMo8Bf+mfK72DPehvphfJnvLc=ne-0bn52drOnMawp1oKjYsig@mail.gmail.com>
Subject: Re: [PATCH] futex: Set USER_DS for the futex_detect_cmpxchg() test
To:     Andy Lutomirski <luto@amacapital.net>
Cc:     Thomas Gleixner <tglx@linutronix.de>,
        Martin Schwidefsky <schwidefsky@de.ibm.com>,
        Geert Uytterhoeven <geert@linux-m68k.org>,
        Andrew Lutomirski <luto@kernel.org>, X86 ML <x86@kernel.org>,
        Peter Zijlstra <peterz@infradead.org>,
        Ingo Molnar <mingo@redhat.com>,
        Darren Hart <dvhart@infradead.org>,
        LKML <linux-kernel@vger.kernel.org>,
        linux-s390 <linux-s390@vger.kernel.org>,
        Heiko Carstens <heiko.carstens@de.ibm.com>,
        fthain@telegraphics.com.au
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On Fri, Sep 28, 2018 at 2:08 PM, Andy Lutomirski <luto@amacapital.net> wrot=
e:
>
>
>> On Sep 28, 2018, at 1:26 PM, Thomas Gleixner <tglx@linutronix.de> wrote:
>>
>>> On Fri, 28 Sep 2018, Max Filippov wrote:
>>>
>>>> On Fri, Sep 28, 2018 at 11:02 AM, Andy Lutomirski <luto@amacapital.net=
> wrote:
>>>> There may be a much nicer solution.  Unless I missed something, only
>>>> mips and xtensa even have the possibility of cmpxchg being missing.
>>>> We could just make those arches supply a futex-detecting helper.
>>>
>>> In case of xtensa availability of cmpxchg is known at build time.
>>
>> That makes it even simpler. Could you provide a patch which selects
>> CONFIG_HAVE_FUTEX_CMPXCHG for the right set of CPUs please?
>>
>>
>
> I think that=E2=80=99s the wrong approach, since it won=E2=80=99t cover m=
ips. How about adding this to mips and xtensa only:
>
> static inline void arch_have_futex_cmpxchg(void) {...};
> #define arch_have_futex_cmpxchg arch_have_futex_cmpxchg
>
> And getting rid of the config option.

I'd rather do that, given that defining Kconfig entries that describe
parts of xtensa configuration is somewhat awkward and redundant.

--=20
Thanks.
-- Max