On Thu, Dec 17, 2015 at 12:32:53PM +0200, Michael S. Tsirkin wrote:
> +static inline void virtio_store_mb(bool weak_barriers,
> + __virtio16 *p, __virtio16 v)
> +{
> +#ifdef CONFIG_SMP
> + if (weak_barriers)
> + smp_store_mb(*p, v);
> + else
> +#endif
> + {
> + WRITE_ONCE(*p, v);
> + mb();
> + }
> +}
This is a different barrier depending on SMP, that seems wrong.
smp_mb(), as (should be) used by smp_store_mb() does not provide a
barrier against IO. mb() otoh does.
Since this is virtIO I would expect you always want mb().
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