On Thu, Dec 17, 2015 at 12:29:03PM +0200, Michael S. Tsirkin wrote:
> +static inline __virtio16 virtio_load_acquire(bool weak_barriers, __virtio16 *p)
> +{
> + if (!weak_barriers) {
> + rmb();
> + return READ_ONCE(*p);
> + }
> +#ifdef CONFIG_SMP
> + return smp_load_acquire(p);
> +#else
> + dma_rmb();
> + return READ_ONCE(*p);
> +#endif
> +}
This too is wrong. Look for example at arm.
dma_rmb() is dmb(osh), while the smp_mb() used by smp_load_acquire() is
dmb(ish). They order completely different types of memory accesses.
Also, load_acquire() is first load, then barrier, and an ACQUIRE barrier
at that, not a READ barrier.
So your #else branch should look something like:
var = READ_ONCE(*p);
dma_mb();
return var;
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