C SB+mbonceonces

(*
 * Result: Never
 *
 * This litmus test demonstrates that full memory barriers suffice to
 * order the store-buffering pattern, where each process writes to the
 * variable that the preceding process reads.  (Locking and RCU can also
 * suffice, but not much else.)
 *)

{}

P0(int *x, int *y)
{
	int r0;

	WRITE_ONCE(*x, 1);
	smp_mb();
	r0 = READ_ONCE(*y);
}

P1(int *x, int *y)
{
	int r0;

	WRITE_ONCE(*y, 1);
	smp_mb();
	r0 = READ_ONCE(*x);
}

exists (0:r0=0 /\ 1:r0=0)