Re: [PATCH 00/13] [RFC] Rust support

[Peter Zijlstra]

On Mon, Apr 19, 2021 at 11:02:12AM +0200, Paolo Bonzini wrote:
> > void writer(void)
> > {
> >      atomic_store_explicit(&seq, seq+1, memory_order_relaxed);
> >      atomic_thread_fence(memory_order_acquire);
> 
> This needs to be memory_order_release.  The only change in the resulting
> assembly is that "dmb ishld" becomes "dmb ish", which is not as good as the
> "dmb ishst" you get from smp_wmb() but not buggy either.

Yuck! And that is what requires the insides to be
atomic_store_explicit(), otherwise this fence doesn't have to affect
them.

I also don't see how this is better than seq_cst.

But yes, not broken, but also very much not optimal.