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

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Date:   Thu, 13 Jul 2023 07:00:37 -0700 (PDT)
From:   Palmer Dabbelt <palmer@...osinc.com>
To:     Mark Rutland <mark.rutland@....com>
CC:     arnd@...nel.org, davem@...emloft.net, keescook@...omium.org,
        peterz@...radead.org, Arnd Bergmann <arnd@...db.de>,
        linux@...ck-us.net, geert@...ux-m68k.org, mingo@...nel.org,
        andi.shyti@...ux.intel.com, andrzej.hajda@...el.com,
        sparclinux@...r.kernel.org, linux-kernel@...r.kernel.org
Subject:     Re: [PATCH] sparc: mark __arch_xchg() as __always_inline

On Wed, 28 Jun 2023 04:45:43 PDT (-0700), Mark Rutland wrote:
> 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>

Acked-by: Palmer Dabbelt <palmer@...osinc.com>

Though I'm not sure that means a whole lot over here ;)

> 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
>>