linux-kernel - Re: [PATCH] asm-generic: fix compilation failure in cmpxchg

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Date:   Thu, 23 Mar 2017 09:49:12 +0100
From:   Dmitry Vyukov <dvyukov@...gle.com>
To:     Arnd Bergmann <arnd@...db.de>
Cc:     Andrew Morton <akpm@...ux-foundation.org>,
        Mark Rutland <mark.rutland@....com>,
        Andrey Ryabinin <aryabinin@...tuozzo.com>,
        Peter Zijlstra <peterz@...radead.org>,
        Will Deacon <will.deacon@....com>,
        Linux-MM <linux-mm@...ck.org>,
        Linux Kernel Mailing List <linux-kernel@...r.kernel.org>
Subject: Re: [PATCH] asm-generic: fix compilation failure in cmpxchg_double()

On Wed, Mar 22, 2017 at 10:27 PM, Arnd Bergmann <arnd@...db.de> wrote:
> On Wed, Mar 22, 2017 at 12:27 PM, Arnd Bergmann <arnd@...db.de> wrote:
>> On Wed, Mar 22, 2017 at 12:10 PM, Dmitry Vyukov <dvyukov@...gle.com> wrote:
>>> Arnd reported that the new code leads to compilation failures
>>> with some versions of gcc. I've filed gcc issue 72873,
>>> but we need a kernel fix as well.
>>>
>>> Remove instrumentation from cmpxchg_double() for now.
>>
>> Thanks, I also checked that fixes the build error for me.
>
> I got a new variant of the bug in
> arch/x86/include/asm/cmpxchg_32.h:set_64bit() now.
>
> In file included from /git/arm-soc/arch/x86/include/asm/cmpxchg.h:142:0,
>                  from /git/arm-soc/arch/x86/include/asm/atomic.h:7,
>                  from /git/arm-soc/arch/x86/include/asm/msr.h:66,
>                  from /git/arm-soc/arch/x86/include/asm/processor.h:20,
>                  from /git/arm-soc/arch/x86/include/asm/cpufeature.h:4,
>                  from /git/arm-soc/arch/x86/include/asm/thread_info.h:52,
>                  from /git/arm-soc/include/linux/thread_info.h:25,
>                  from /git/arm-soc/arch/x86/include/asm/preempt.h:6,
>                  from /git/arm-soc/include/linux/preempt.h:80,
>                  from /git/arm-soc/include/linux/spinlock.h:50,
>                  from /git/arm-soc/include/linux/mmzone.h:7,
>                  from /git/arm-soc/include/linux/gfp.h:5,
>                  from /git/arm-soc/include/linux/mm.h:9,
>                  from /git/arm-soc/mm/khugepaged.c:3:
> /git/arm-soc/mm/khugepaged.c: In function 'khugepaged':
> /git/arm-soc/arch/x86/include/asm/cmpxchg_32.h:29:2: error: 'asm'
> operand has impossible constraints
>   asm volatile("\n1:\t"
>
> Defconfig is at http://pastebin.com/raw/Pthhv5iU


I can't reproduce it with gcc 4.8.4, 7.0.0, 7.0.1.

Are you sure it's related to my recent change? I did not touch set_64bit.