linux-kernel - Re: [PATCH v2 00/33] locking/atomic: convert all architectures to ARCH

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Message-ID: <e500f4e2-d9bf-9374-c2fc-8fcf1ad43d57@synopsys.com>
Date:   Mon, 28 Jun 2021 22:21:01 +0000
From:   Vineet Gupta <Vineet.Gupta1@...opsys.com>
To:     Peter Zijlstra <peterz@...radead.org>,
        Randy Dunlap <rdunlap@...radead.org>
CC:     Mark Rutland <mark.rutland@....com>,
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        arcml <linux-snps-arc@...ts.infradead.org>
Subject: Re: [PATCH v2 00/33] locking/atomic: convert all architectures to
 ARCH_ATOMIC

On 6/28/21 3:13 PM, Peter Zijlstra wrote:
> On Mon, Jun 28, 2021 at 02:22:15PM -0700, Randy Dunlap wrote:
>> However, something in arch/arc/ did look suspicious so I decided to
>> try an ARC allmodconfig build, where I did see a few errors FYI:
>>
>>
>>    CC      drivers/iommu/io-pgtable-arm.o
>> In file included from ../include/linux/atomic.h:80,
>>                   from ../drivers/iommu/io-pgtable-arm.c:12:
>> ../drivers/iommu/io-pgtable-arm.c: In function 'arm_lpae_install_table':
>> ../include/linux/atomic-arch-fallback.h:60:32: error: implicit declaration of function 'arch_cmpxchg64'; did you mean 'arch_cmpxchg'? [-Werror=implicit-function-declaration]
>>     60 | #define arch_cmpxchg64_relaxed arch_cmpxchg64
>>        |                                ^~~~~~~~~~~~~~
>> ../include/asm-generic/atomic-instrumented.h:1261:2: note: in expansion of macro 'arch_cmpxchg64_relaxed'
>>   1261 |  arch_cmpxchg64_relaxed(__ai_ptr, __VA_ARGS__); \
>>        |  ^~~~~~~~~~~~~~~~~~~~~~
>> ../drivers/iommu/io-pgtable-arm.c:320:8: note: in expansion of macro 'cmpxchg64_relaxed'
>>    320 |  old = cmpxchg64_relaxed(ptep, curr, new);
>>        |        ^~~~~~~~~~~~~~~~~
> 0day also reported something like that. We found that this was a
> pre-existing error, and Mark's patches only changed the error, it never
> successfully build.
>
> cmpxchg64 is an optional feature for 32bit architectures, one that ARMv7
> does provide, and uses, for it's iommu bits. Building the ARM iommu
> drivers on ARC seem somewhat daft but is a result of that COMPILE_TEST
> config.

Out of my ARC64 work, I have a boat-load of changes piled up in this 
area. Once Mark's changes hit mainline I can send those out for review 
and we can also consider adding cmpxchg64 for 32-bit ARC.

-Vineet