linux-kernel - Re: [PATCH v2 2/7] x86: use long long for 64-bit atomic ops

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Message-Id: <20170529104916.GB12975@osiris>
Date:   Mon, 29 May 2017 12:49:16 +0200
From:   Heiko Carstens <heiko.carstens@...ibm.com>
To:     Dmitry Vyukov <dvyukov@...gle.com>
Cc:     mark.rutland@....com, peterz@...radead.org, mingo@...hat.com,
        will.deacon@....com, akpm@...ux-foundation.org,
        aryabinin@...tuozzo.com, kasan-dev@...glegroups.com,
        linux-kernel@...r.kernel.org, x86@...nel.org, tglx@...utronix.de,
        hpa@...or.com, willy@...radead.org, linux-mm@...ck.org
Subject: Re: [PATCH v2 2/7] x86: use long long for 64-bit atomic ops

On Fri, May 26, 2017 at 09:09:04PM +0200, Dmitry Vyukov wrote:
> Some 64-bit atomic operations use 'long long' as operand/return type
> (e.g. asm-generic/atomic64.h, arch/x86/include/asm/atomic64_32.h);
> while others use 'long' (e.g. arch/x86/include/asm/atomic64_64.h).
> This makes it impossible to write portable code.
> For example, there is no format specifier that prints result of
> atomic64_read() without warnings. atomic64_try_cmpxchg() is almost
> impossible to use in portable fashion because it requires either
> 'long *' or 'long long *' as argument depending on arch.
> 
> Switch arch/x86/include/asm/atomic64_64.h to 'long long'.
> 
> Signed-off-by: Dmitry Vyukov <dvyukov@...gle.com>
> 
> ---
> Changes since v1:
>  - reverted stray s/long/long long/ replace in comment
>  - added arch/s390 changes to fix build errors/warnings

If you change s390 code, please add the relevant mailing list and/or
maintainers please.

> diff --git a/arch/s390/include/asm/atomic_ops.h b/arch/s390/include/asm/atomic_ops.h
> index ac9e2b939d04..055a9083e52d 100644
> --- a/arch/s390/include/asm/atomic_ops.h
> +++ b/arch/s390/include/asm/atomic_ops.h
> @@ -31,10 +31,10 @@ __ATOMIC_OPS(__atomic_and, int, "lan")
>  __ATOMIC_OPS(__atomic_or,  int, "lao")
>  __ATOMIC_OPS(__atomic_xor, int, "lax")
>  
> -__ATOMIC_OPS(__atomic64_add, long, "laag")
> -__ATOMIC_OPS(__atomic64_and, long, "lang")
> -__ATOMIC_OPS(__atomic64_or,  long, "laog")
> -__ATOMIC_OPS(__atomic64_xor, long, "laxg")
> +__ATOMIC_OPS(__atomic64_add, long long, "laag")
> +__ATOMIC_OPS(__atomic64_and, long long, "lang")
> +__ATOMIC_OPS(__atomic64_or,  long long, "laog")
> +__ATOMIC_OPS(__atomic64_xor, long long, "laxg")
>  
>  #undef __ATOMIC_OPS
>  #undef __ATOMIC_OP
> @@ -46,7 +46,7 @@ static inline void __atomic_add_const(int val, int *ptr)
>  		: [ptr] "+Q" (*ptr) : [val] "i" (val) : "cc");
>  }
>  
> -static inline void __atomic64_add_const(long val, long *ptr)
> +static inline void __atomic64_add_const(long val, long long *ptr)

If you change this then val should be long long (or s64) too.

> -static inline long op_name(long val, long *ptr)				\
> +static inline long op_name(long val, long long *ptr)			\
>  {									\
>  	long old, new;							\

Same here. You only changed the type of *ptr, but left the rest
alone. Everything should have the same type.