162306a36Sopenharmony_ciC Z6.0+pooncerelease+poacquirerelease+fencembonceonce 262306a36Sopenharmony_ci 362306a36Sopenharmony_ci(* 462306a36Sopenharmony_ci * Result: Sometimes 562306a36Sopenharmony_ci * 662306a36Sopenharmony_ci * This litmus test shows that a release-acquire chain, while sufficient 762306a36Sopenharmony_ci * when there is but one non-reads-from (AKA non-rf) link, does not suffice 862306a36Sopenharmony_ci * if there is more than one. Of the three processes, only P1() reads from 962306a36Sopenharmony_ci * P0's write, which means that there are two non-rf links: P1() to P2() 1062306a36Sopenharmony_ci * is a write-to-write link (AKA a "coherence" or just "co" link) and P2() 1162306a36Sopenharmony_ci * to P0() is a read-to-write link (AKA a "from-reads" or just "fr" link). 1262306a36Sopenharmony_ci * When there are two or more non-rf links, you typically will need one 1362306a36Sopenharmony_ci * full barrier for each non-rf link. (Exceptions include some cases 1462306a36Sopenharmony_ci * involving locking.) 1562306a36Sopenharmony_ci *) 1662306a36Sopenharmony_ci 1762306a36Sopenharmony_ci{} 1862306a36Sopenharmony_ci 1962306a36Sopenharmony_ciP0(int *x, int *y) 2062306a36Sopenharmony_ci{ 2162306a36Sopenharmony_ci WRITE_ONCE(*x, 1); 2262306a36Sopenharmony_ci smp_store_release(y, 1); 2362306a36Sopenharmony_ci} 2462306a36Sopenharmony_ci 2562306a36Sopenharmony_ciP1(int *y, int *z) 2662306a36Sopenharmony_ci{ 2762306a36Sopenharmony_ci int r0; 2862306a36Sopenharmony_ci 2962306a36Sopenharmony_ci r0 = smp_load_acquire(y); 3062306a36Sopenharmony_ci smp_store_release(z, 1); 3162306a36Sopenharmony_ci} 3262306a36Sopenharmony_ci 3362306a36Sopenharmony_ciP2(int *x, int *z) 3462306a36Sopenharmony_ci{ 3562306a36Sopenharmony_ci int r1; 3662306a36Sopenharmony_ci 3762306a36Sopenharmony_ci WRITE_ONCE(*z, 2); 3862306a36Sopenharmony_ci smp_mb(); 3962306a36Sopenharmony_ci r1 = READ_ONCE(*x); 4062306a36Sopenharmony_ci} 4162306a36Sopenharmony_ci 4262306a36Sopenharmony_ciexists (1:r0=1 /\ z=2 /\ 2:r1=0) 43