Re: [PATCH v2 7/7] ARM: atomics: define our SMP atomics in terms of _relaxed operations

Waiman Long
2015-07-16T20:40:07Z

On 07/16/2015 11:32 AM, Will Deacon wrote:
> By defining our SMP atomics in terms of relaxed operations, we gain
> a small reduction in code size and have acquire/release/fence variants
> generated automatically by the core code.
>
> Signed-off-by: Will Deacon<will.deacon@arm.com>
> ---
> arch/arm/include/asm/atomic.h | 37 ++++++++++++++-------------------
> arch/arm/include/asm/cmpxchg.h | 47 +++++++-----------------------------------
> 2 files changed, 24 insertions(+), 60 deletions(-)
>
>
>
> -#define xchg(ptr, x) ({ \
> +#define xchg_relaxed(ptr, x) ({ \
> (__typeof__(*(ptr)))__xchg((unsigned long)(x), (ptr), \
> sizeof(*(ptr))); \
> })
> @@ -117,6 +115,8 @@ static inline unsigned long __xchg(unsigned long x, volatile void *ptr, int size
> #error "SMP is not supported on this platform"
> #endif
>
> +#define xchg xchg_relaxed

Is that a typo? I think xchg() needs to be a full memory barrier.

Cheers,
Longman