1*4882a593SmuzhiyunC R+fencembonceonces 2*4882a593Smuzhiyun 3*4882a593Smuzhiyun(* 4*4882a593Smuzhiyun * Result: Never 5*4882a593Smuzhiyun * 6*4882a593Smuzhiyun * This is the fully ordered (via smp_mb()) version of one of the classic 7*4882a593Smuzhiyun * counterintuitive litmus tests that illustrates the effects of store 8*4882a593Smuzhiyun * propagation delays. Note that weakening either of the barriers would 9*4882a593Smuzhiyun * cause the resulting test to be allowed. 10*4882a593Smuzhiyun *) 11*4882a593Smuzhiyun 12*4882a593Smuzhiyun{} 13*4882a593Smuzhiyun 14*4882a593SmuzhiyunP0(int *x, int *y) 15*4882a593Smuzhiyun{ 16*4882a593Smuzhiyun WRITE_ONCE(*x, 1); 17*4882a593Smuzhiyun smp_mb(); 18*4882a593Smuzhiyun WRITE_ONCE(*y, 1); 19*4882a593Smuzhiyun} 20*4882a593Smuzhiyun 21*4882a593SmuzhiyunP1(int *x, int *y) 22*4882a593Smuzhiyun{ 23*4882a593Smuzhiyun int r0; 24*4882a593Smuzhiyun 25*4882a593Smuzhiyun WRITE_ONCE(*y, 2); 26*4882a593Smuzhiyun smp_mb(); 27*4882a593Smuzhiyun r0 = READ_ONCE(*x); 28*4882a593Smuzhiyun} 29*4882a593Smuzhiyun 30*4882a593Smuzhiyunexists (y=2 /\ 1:r0=0) 31