Re: [PATCH 1/2] percpu-rw-semaphores: use light/heavy barriers

[Peter Zijlstra]

On Mon, 2012-10-22 at 19:37 -0400, Mikulas Patocka wrote:
> -       /*
> -        * On X86, write operation in this_cpu_dec serves as a memory unlock
> -        * barrier (i.e. memory accesses may be moved before the write, but
> -        * no memory accesses are moved past the write).
> -        * On other architectures this may not be the case, so we need smp_mb()
> -        * there.
> -        */
> -#if defined(CONFIG_X86) && (!defined(CONFIG_X86_PPRO_FENCE) && !defined(CONFIG_X86_OOSTORE))
> -       barrier();
> -#else
> -       smp_mb();
> -#endif
> +       light_mb(); /* B, between read of the data and write to p->counter, paired with C */ 

If we're going to invent new primitives for this, shouldn't we call
this: smp_unlock_barrier() or something? That at least has well defined
semantics.


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