linux-kernel - Re: [PATCH] locking/atomic: sh: Use generic_cmpxchg_local for arch_cmpxchg

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Message-ID: <ZTfd3A3Unz6SWFD3@FVFF77S0Q05N.cambridge.arm.com>
Date:   Tue, 24 Oct 2023 16:08:12 +0100
From:   Mark Rutland <mark.rutland@....com>
To:     "Masami Hiramatsu (Google)" <mhiramat@...nel.org>
Cc:     Yoshinori Sato <ysato@...rs.sourceforge.jp>,
        Rich Felker <dalias@...c.org>,
        John Paul Adrian Glaubitz <glaubitz@...sik.fu-berlin.de>,
        "wuqiang . matt" <wuqiang.matt@...edance.com>,
        Peter Zijlstra <peterz@...radead.org>,
        linux-sh@...r.kernel.org, linux-kernel@...r.kernel.org,
        linux-trace-kernel@...r.kernel.org
Subject: Re: [PATCH] locking/atomic: sh: Use generic_cmpxchg_local for
 arch_cmpxchg_local()

On Tue, Oct 24, 2023 at 11:52:54PM +0900, Masami Hiramatsu (Google) wrote:
> From: Masami Hiramatsu (Google) <mhiramat@...nel.org>
> 
> Use generic_cmpxchg_local() for arch_cmpxchg_local() implementation
> in SH architecture because it does not implement arch_cmpxchg_local().

I do not think this is correct.

The implementation in <asm-generic/cmpxchg-local.h> is UP-only (and it only
disables interrupts), whereas arch/sh can be built SMP. We should probably add
some guards into <asm-generic/cmpxchg-local.h> for that as we have in
<asm-generic/cmpxchg.h>.

I think the right thing to do here is to define arch_cmpxchg_local() in terms
of arch_cmpxchg(), i.e. at the bottom of arch/sh's <asm/cmpxchg.h> add:

#define arch_cmpxchg_local              arch_cmpxchg

Mark.

> 
> Reported-by: kernel test robot <lkp@...el.com>
> Closes: https://lore.kernel.org/oe-kbuild-all/202310241310.Ir5uukOG-lkp@intel.com/
> Signed-off-by: Masami Hiramatsu (Google) <mhiramat@...nel.org>
> ---
>  arch/sh/include/asm/cmpxchg.h |    2 ++
>  1 file changed, 2 insertions(+)
> 
> diff --git a/arch/sh/include/asm/cmpxchg.h b/arch/sh/include/asm/cmpxchg.h
> index 288f6f38d98f..e920e61fb817 100644
> --- a/arch/sh/include/asm/cmpxchg.h
> +++ b/arch/sh/include/asm/cmpxchg.h
> @@ -71,4 +71,6 @@ static inline unsigned long __cmpxchg(volatile void * ptr, unsigned long old,
>  				    (unsigned long)_n_, sizeof(*(ptr))); \
>    })
>  
> +#include <asm-generic/cmpxchg-local.h>
> +
>  #endif /* __ASM_SH_CMPXCHG_H */
>