linux-kernel - Re: [PATCH] sparc: mark __arch_xchg() as __always

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Date:   Wed, 28 Jun 2023 12:45:43 +0100
From:   Mark Rutland <mark.rutland@....com>
To:     Arnd Bergmann <arnd@...nel.org>
Cc:     "David S. Miller" <davem@...emloft.net>,
        Kees Cook <keescook@...omium.org>,
        "Peter Zijlstra (Intel)" <peterz@...radead.org>,
        Arnd Bergmann <arnd@...db.de>,
        Guenter Roeck <linux@...ck-us.net>,
        Geert Uytterhoeven <geert@...ux-m68k.org>,
        Ingo Molnar <mingo@...nel.org>,
        Andi Shyti <andi.shyti@...ux.intel.com>,
        Andrzej Hajda <andrzej.hajda@...el.com>,
        Palmer Dabbelt <palmer@...osinc.com>,
        sparclinux@...r.kernel.org, linux-kernel@...r.kernel.org
Subject: Re: [PATCH] sparc: mark __arch_xchg() as __always_inline

On Wed, Jun 28, 2023 at 11:49:18AM +0200, Arnd Bergmann wrote:
> From: Arnd Bergmann <arnd@...db.de>
> 
> An otherwise correct change to the atomic operations uncovered an
> existing bug in the sparc __arch_xchg() function, which is calls
> __xchg_called_with_bad_pointer() when its arguments are unknown at
> compile time:
> 
> ERROR: modpost: "__xchg_called_with_bad_pointer" [lib/atomic64_test.ko] undefined!
> 
> This now happens because gcc determines that it's better to not inline the
> function. Avoid this by just marking the function as __always_inline
> to force the compiler to do the right thing here.
> 
> Reported-by: Guenter Roeck <linux@...ck-us.net>
> Link: https://lore.kernel.org/all/c525adc9-6623-4660-8718-e0c9311563b8@roeck-us.net/
> Fixes: d12157efc8e08 ("locking/atomic: make atomic*_{cmp,}xchg optional")
> Signed-off-by: Arnd Bergmann <arnd@...db.de>

Aha; you saved me writing a patch! :)

We should probably do likewise for all the other bits like __cmpxchg(), but
either way:

Acked-by: Mark Rutland <mark.rutland@....com>

Mark.

> ---
>  arch/sparc/include/asm/cmpxchg_32.h | 2 +-
>  arch/sparc/include/asm/cmpxchg_64.h | 2 +-
>  2 files changed, 2 insertions(+), 2 deletions(-)
> 
> diff --git a/arch/sparc/include/asm/cmpxchg_32.h b/arch/sparc/include/asm/cmpxchg_32.h
> index 7a1339533d1d7..d0af82c240b73 100644
> --- a/arch/sparc/include/asm/cmpxchg_32.h
> +++ b/arch/sparc/include/asm/cmpxchg_32.h
> @@ -15,7 +15,7 @@
>  unsigned long __xchg_u32(volatile u32 *m, u32 new);
>  void __xchg_called_with_bad_pointer(void);
>  
> -static inline unsigned long __arch_xchg(unsigned long x, __volatile__ void * ptr, int size)
> +static __always_inline unsigned long __arch_xchg(unsigned long x, __volatile__ void * ptr, int size)
>  {
>  	switch (size) {
>  	case 4:
> diff --git a/arch/sparc/include/asm/cmpxchg_64.h b/arch/sparc/include/asm/cmpxchg_64.h
> index 66cd61dde9ec1..3de25262c4118 100644
> --- a/arch/sparc/include/asm/cmpxchg_64.h
> +++ b/arch/sparc/include/asm/cmpxchg_64.h
> @@ -87,7 +87,7 @@ xchg16(__volatile__ unsigned short *m, unsigned short val)
>  	return (load32 & mask) >> bit_shift;
>  }
>  
> -static inline unsigned long
> +static __always_inline unsigned long
>  __arch_xchg(unsigned long x, __volatile__ void * ptr, int size)
>  {
>  	switch (size) {
> -- 
> 2.39.2
>