linux-kernel - Re: [PATCH v1] locking/atomic: xtensa: define arch_cmpxchg_local as __cmpxchg

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Message-ID: <8e83e099-c689-410a-b889-7d8a299bf4e5@bytedance.com>
Date:   Sat, 4 Nov 2023 18:34:20 +0800
From:   "wuqiang.matt" <wuqiang.matt@...edance.com>
To:     Max Filippov <jcmvbkbc@...il.com>
Cc:     chris@...kel.net, andi.shyti@...ux.intel.com,
        andrzej.hajda@...el.com, palmer@...osinc.com, geert@...ux-m68k.org,
        linux-kernel@...r.kernel.org, mattwu@....com
Subject: Re: [PATCH v1] locking/atomic: xtensa: define arch_cmpxchg_local as
 __cmpxchg_local

On 2023/11/4 17:31, Max Filippov wrote:
> On Sat, Nov 4, 2023 at 2:06 AM wuqiang.matt <wuqiang.matt@...edance.com> wrote:
>>
>> The xtensa architecture already has __cmpxchg_local defined upon the
>> native __cmpxchg_u32 and __generic_cmpxchg_local
> 
> This description does not make clear why this change is needed. Could you
> please expand it to cover the 'why' part?

The purpose of __cmpxchg_local() should be for arch_cmpxchg_local(), similarly
for other architectures like x86/arm/powerpc.

I noticed that arc/hexagon/openrisc/sh don't have arch_cmpxchg_local defined
because my patch triggered an error in kernel building. Then found xtensa's
definition of arch_cmpxchg_local() is not reasonable, so proposed this patch
to improve.

This change is not a must, but an improvement to simply make the codes of
arch_cmpxchg_local() more reasonable.

The patch link that introduced try_cmpxchg_local and triggered building error:
https://lore.kernel.org/all/20231023112452.6290-1-wuqiang.matt@bytedance.com/

>> Signed-off-by: wuqiang.matt <wuqiang.matt@...edance.com>
>> ---
>>   arch/xtensa/include/asm/cmpxchg.h | 2 +-
>>   1 file changed, 1 insertion(+), 1 deletion(-)
>>
>> diff --git a/arch/xtensa/include/asm/cmpxchg.h b/arch/xtensa/include/asm/cmpxchg.h
>> index 675a11ea8de7..956c9925df1c 100644
>> --- a/arch/xtensa/include/asm/cmpxchg.h
>> +++ b/arch/xtensa/include/asm/cmpxchg.h
>> @@ -108,7 +108,7 @@ static inline unsigned long __cmpxchg_local(volatile void *ptr,
>>    * them available.
>>    */
>>   #define arch_cmpxchg_local(ptr, o, n)                                         \
>> -       ((__typeof__(*(ptr)))__generic_cmpxchg_local((ptr), (unsigned long)(o),\
>> +       ((__typeof__(*(ptr)))__cmpxchg_local((ptr), (unsigned long)(o),        \
>>                          (unsigned long)(n), sizeof(*(ptr))))
>>   #define arch_cmpxchg64_local(ptr, o, n) __generic_cmpxchg64_local((ptr), (o), (n))
>>   #define arch_cmpxchg64(ptr, o, n)    arch_cmpxchg64_local((ptr), (o), (n))
>> --
>> 2.40.1
>>
> 
>