Re: [PATCH] sparc: Provide cmpxchg64 for 32-bit builds

[Guenter Roeck <linux@roeck-us.net>]

On 09/27/2017 09:38 PM, David Miller wrote:
> From: Guenter Roeck <linux@roeck-us.net>
> Date: Sun, 24 Sep 2017 10:29:31 -0700
> 
>> Fix the following build error, seen when building sparc32:allmodconfig.
>>
>> drivers/net/ethernet/intel/i40e/i40e_ethtool.c:
>> 	In function 'i40e_set_priv_flags':
>> drivers/net/ethernet/intel/i40e/i40e_ethtool.c:4150:2: error:
>> 	implicit declaration of function 'cmpxchg64'
>>
>> Signed-off-by: Guenter Roeck <linux@roeck-us.net>
> 
> That fixes the build:
> 
>> @@ -72,5 +72,6 @@ __cmpxchg(volatile void *ptr, unsigned long old, unsigned long new_, int size)
>>   	((__typeof__(*(ptr)))__cmpxchg_local_generic((ptr), (unsigned long)(o),\
>>   			(unsigned long)(n), sizeof(*(ptr))))
>>   #define cmpxchg64_local(ptr, o, n) __cmpxchg64_local_generic((ptr), (o), (n))
>> +#define cmpxchg64(ptr, o, n)	cmpxchg64_local((ptr), (o), (n))
>>   
>>   #endif /* __ARCH_SPARC_CMPXCHG__ */
> 
> but it's wrong.  cmpxchg64_local() is only atomic on the current cpu
> so using it for plain cmpxchg64() is not going to work.
> 

Yeah, I was concerned about that. My bad.

Unfortunately I don't know enough about sparc to provide a better solution.
Consider this a problem report, then.

Guenter