On Tue, Feb 04, 2014 at 12:29:12PM +0000, Will Deacon wrote:
> @@ -112,17 +114,20 @@ static inline int atomic_cmpxchg(atomic_t *ptr, int old, int new)
> unsigned long tmp;
> int oldval;
>
> + smp_mb();
> +
> asm volatile("// atomic_cmpxchg\n"
> -"1: ldaxr %w1, %2\n"
> +"1: ldxr %w1, %2\n"
> " cmp %w1, %w3\n"
> " b.ne 2f\n"
> -" stlxr %w0, %w4, %2\n"
> +" stxr %w0, %w4, %2\n"
> " cbnz %w0, 1b\n"
> "2:"
> : "=&r" (tmp), "=&r" (oldval), "+Q" (ptr->counter)
> : "Ir" (old), "r" (new)
> : "cc", "memory");
>
> + smp_mb();
> return oldval;
> }
>
Any particular reason atomic_cmpxchg() doesn't use the proposed rel + mb
scheme? It would be a waste to have atomic_cmpxchg() be more expensive
than it needs to be.
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