[RFC][PATCH 0/5] arch: atomic rework

[Peter Zijlstra]

On Mon, Feb 10, 2014 at 01:27:51AM +0100, Torvald Riegel wrote:
> > Initial state: x == y == 0
> > 
> > T1:	r1 = atomic_load_explicit(x, memory_order_relaxed);
> > 	atomic_store_explicit(42, y, memory_order_relaxed);
> > 	if (r1 != 42)
> > 		atomic_store_explicit(r1, y, memory_order_relaxed);
> > 
> > T2:	r2 = atomic_load_explicit(y, memory_order_relaxed);
> > 	atomic_store_explicit(r2, x, memory_order_relaxed);
> 
> Intuitively, this is wrong because this let's the program take a step
> the abstract machine wouldn't do.  This is different to the sequential
> code that Peter posted because it uses atomics, and thus one can't
> easily assume that the difference is not observable.

Yeah, my bad for not being familiar with the atrocious crap C11 made of
atomics :/