43 lines · plain
1C Z6.0+pooncerelease+poacquirerelease+fencembonceonce2 3(*4 * Result: Sometimes5 *6 * This litmus test shows that a release-acquire chain, while sufficient7 * when there is but one non-reads-from (AKA non-rf) link, does not suffice8 * if there is more than one. Of the three processes, only P1() reads from9 * 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 one13 * full barrier for each non-rf link. (Exceptions include some cases14 * involving locking.)15 *)16 17{}18 19P0(int *x, int *y)20{21 WRITE_ONCE(*x, 1);22 smp_store_release(y, 1);23}24 25P1(int *y, int *z)26{27 int r0;28 29 r0 = smp_load_acquire(y);30 smp_store_release(z, 1);31}32 33P2(int *x, int *z)34{35 int r1;36 37 WRITE_ONCE(*z, 2);38 smp_mb();39 r1 = READ_ONCE(*x);40}41 42exists (1:r0=1 /\ z=2 /\ 2:r1=0)43