linux-kernel - Re: [PATCH] cmpxchg: Discard unnecessary cast to volatile

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Date:	Mon, 20 Oct 2014 16:22:27 -0400
From:	Pranith Kumar <bobby.prani@...il.com>
To:	Thomas Gleixner <tglx@...utronix.de>,
	Ingo Molnar <mingo@...hat.com>,
	"H. Peter Anvin" <hpa@...or.com>,
	"maintainer:X86 ARCHITECTURE..." <x86@...nel.org>,
	Borislav Petkov <bp@...e.de>,
	"open list:X86 ARCHITECTURE..." <linux-kernel@...r.kernel.org>,
	Peter Zijlstra <peterz@...radead.org>
Subject: Re: [PATCH] cmpxchg: Discard unnecessary cast to volatile

ping.

On Wed, Oct 1, 2014 at 1:57 PM, Pranith Kumar <bobby.prani@...il.com> wrote:
> Generating a volatile pointer is really not necessary here. This is the only
> location where a volatile pointer is being generated for use in asm.
>
> This commit removes the unnecessary volatile pointer being created.
>
> Signed-off-by: Pranith Kumar <bobby.prani@...il.com>
> ---
>  arch/x86/include/asm/cmpxchg.h | 12 ++++--------
>  1 file changed, 4 insertions(+), 8 deletions(-)
>
> diff --git a/arch/x86/include/asm/cmpxchg.h b/arch/x86/include/asm/cmpxchg.h
> index 99c105d7..f0baea8 100644
> --- a/arch/x86/include/asm/cmpxchg.h
> +++ b/arch/x86/include/asm/cmpxchg.h
> @@ -90,36 +90,32 @@ extern void __add_wrong_size(void)
>         switch (size) {                                                 \
>         case __X86_CASE_B:                                              \
>         {                                                               \
> -               volatile u8 *__ptr = (volatile u8 *)(ptr);              \
>                 asm volatile(lock "cmpxchgb %2,%1"                      \
> -                            : "=a" (__ret), "+m" (*__ptr)              \
> +                            : "=a" (__ret), "+m" (*ptr)                \
>                              : "q" (__new), "0" (__old)                 \
>                              : "memory");                               \
>                 break;                                                  \
>         }                                                               \
>         case __X86_CASE_W:                                              \
>         {                                                               \
> -               volatile u16 *__ptr = (volatile u16 *)(ptr);            \
>                 asm volatile(lock "cmpxchgw %2,%1"                      \
> -                            : "=a" (__ret), "+m" (*__ptr)              \
> +                            : "=a" (__ret), "+m" (*ptr)                \
>                              : "r" (__new), "0" (__old)                 \
>                              : "memory");                               \
>                 break;                                                  \
>         }                                                               \
>         case __X86_CASE_L:                                              \
>         {                                                               \
> -               volatile u32 *__ptr = (volatile u32 *)(ptr);            \
>                 asm volatile(lock "cmpxchgl %2,%1"                      \
> -                            : "=a" (__ret), "+m" (*__ptr)              \
> +                            : "=a" (__ret), "+m" (*ptr)                \
>                              : "r" (__new), "0" (__old)                 \
>                              : "memory");                               \
>                 break;                                                  \
>         }                                                               \
>         case __X86_CASE_Q:                                              \
>         {                                                               \
> -               volatile u64 *__ptr = (volatile u64 *)(ptr);            \
>                 asm volatile(lock "cmpxchgq %2,%1"                      \
> -                            : "=a" (__ret), "+m" (*__ptr)              \
> +                            : "=a" (__ret), "+m" (*ptr)                \
>                              : "r" (__new), "0" (__old)                 \
>                              : "memory");                               \
>                 break;                                                  \
> --
> 1.9.1
>



-- 
Pranith
--
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