linux-kernel - Re: [PATCH] riscv/atomic: Do proper sign extension also for unsigned in arch

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Message-ID: <6c129a4e822e8504a48daa0db7b385a813f96c69.camel@xry111.site>
Date: Sat, 01 Feb 2025 20:17:45 +0800
From: Xi Ruoyao <xry111@...111.site>
To: Andreas Schwab <schwab@...e.de>, linux-riscv@...ts.infradead.org
Cc: linux-kernel@...r.kernel.org
Subject: Re: [PATCH] riscv/atomic: Do proper sign extension also for
 unsigned in arch_cmpxchg

On Thu, 2025-01-30 at 10:25 +0100, Andreas Schwab wrote:
> Sign extend also an unsigned compare value to match what lr.w is doing.
> Otherwise try_cmpxchg may spuriously return true when used on a u32 value
> that has the sign bit set, as it happens often in inode_set_ctime_current.
> 
> Do this in three conversion steps.  The first conversion to long is needed
> to avoid a -Wpointer-to-int-cast warning when arch_cmpxchg is used with a
> pointer type.  Then convert to int and back to long to always sign extend
> the 32-bit value to 64-bit.
> 
> Fixes: 6c58f25e6938 ("riscv/atomic: Fix sign extension for RV64I")
> Signed-off-by: Andreas Schwab <schwab@...e.de>

It fixes the gnulib test-stat-time failure for me.

Tested-by: Xi Ruoyao <xry111@...111.site>

> ---
>  arch/riscv/include/asm/cmpxchg.h | 2 +-
>  1 file changed, 1 insertion(+), 1 deletion(-)
> 
> diff --git a/arch/riscv/include/asm/cmpxchg.h b/arch/riscv/include/asm/cmpxchg.h
> index 4cadc56220fe..427c41dde643 100644
> --- a/arch/riscv/include/asm/cmpxchg.h
> +++ b/arch/riscv/include/asm/cmpxchg.h
> @@ -231,7 +231,7 @@
>  		__arch_cmpxchg(".w", ".w" sc_sfx, ".w" cas_sfx,		\
>  			       sc_prepend, sc_append,			\
>  			       cas_prepend, cas_append,			\
> -			       __ret, __ptr, (long), __old, __new);	\
> +			       __ret, __ptr, (long)(int)(long), __old, __new);	\
>  		break;							\
>  	case 8:								\
>  		__arch_cmpxchg(".d", ".d" sc_sfx, ".d" cas_sfx,		\
> -- 
> 2.48.1

-- 
Xi Ruoyao <xry111@...111.site>
School of Aerospace Science and Technology, Xidian University