1C Z6.0+pooncerelease+poacquirerelease+fencembonceonce
2
3(*
4 * Result: Sometimes
5 *
6 * This litmus test shows that a release-acquire chain, while sufficient
7 * when there is but one non-reads-from (AKA non-rf) link, does not suffice
8 * if there is more than one.  Of the three processes, only P1() reads from
9 * P0's write, which means that there are two non-rf links: P1() to P2()
10 * is a write-to-write link (AKA a "coherence" or just "co" link) and P2()
11 * to P0() is a read-to-write link (AKA a "from-reads" or just "fr" link).
12 * When there are two or more non-rf links, you typically will need one
13 * full barrier for each non-rf link.  (Exceptions include some cases
14 * involving locking.)
15 *)
16
17{
18	int x;
19	int y;
20	int z;
21}
22
23P0(int *x, int *y)
24{
25	WRITE_ONCE(*x, 1);
26	smp_store_release(y, 1);
27}
28
29P1(int *y, int *z)
30{
31	int r0;
32
33	r0 = smp_load_acquire(y);
34	smp_store_release(z, 1);
35}
36
37P2(int *x, int *z)
38{
39	int r1;
40
41	WRITE_ONCE(*z, 2);
42	smp_mb();
43	r1 = READ_ONCE(*x);
44}
45
46exists (1:r0=1 /\ z=2 /\ 2:r1=0)
47