1C R+fencembonceonces
2
3(*
4 * Result: Never
5 *
6 * This is the fully ordered (via smp_mb()) version of one of the classic
7 * counterintuitive litmus tests that illustrates the effects of store
8 * propagation delays.  Note that weakening either of the barriers would
9 * cause the resulting test to be allowed.
10 *)
11
12{}
13
14P0(int *x, int *y)
15{
16	WRITE_ONCE(*x, 1);
17	smp_mb();
18	WRITE_ONCE(*y, 1);
19}
20
21P1(int *x, int *y)
22{
23	int r0;
24
25	WRITE_ONCE(*y, 2);
26	smp_mb();
27	r0 = READ_ONCE(*x);
28}
29
30exists (y=2 /\ 1:r0=0)
31