1*4882a593SmuzhiyunC Z6.0+pooncelock+pooncelock+pombonce
2*4882a593Smuzhiyun
3*4882a593Smuzhiyun(*
4*4882a593Smuzhiyun * Result: Sometimes
5*4882a593Smuzhiyun *
6*4882a593Smuzhiyun * This example demonstrates that a pair of accesses made by different
7*4882a593Smuzhiyun * processes each while holding a given lock will not necessarily be
8*4882a593Smuzhiyun * seen as ordered by a third process not holding that lock.
9*4882a593Smuzhiyun *)
10*4882a593Smuzhiyun
11*4882a593Smuzhiyun{}
12*4882a593Smuzhiyun
13*4882a593SmuzhiyunP0(int *x, int *y, spinlock_t *mylock)
14*4882a593Smuzhiyun{
15*4882a593Smuzhiyun	spin_lock(mylock);
16*4882a593Smuzhiyun	WRITE_ONCE(*x, 1);
17*4882a593Smuzhiyun	WRITE_ONCE(*y, 1);
18*4882a593Smuzhiyun	spin_unlock(mylock);
19*4882a593Smuzhiyun}
20*4882a593Smuzhiyun
21*4882a593SmuzhiyunP1(int *y, int *z, spinlock_t *mylock)
22*4882a593Smuzhiyun{
23*4882a593Smuzhiyun	int r0;
24*4882a593Smuzhiyun
25*4882a593Smuzhiyun	spin_lock(mylock);
26*4882a593Smuzhiyun	r0 = READ_ONCE(*y);
27*4882a593Smuzhiyun	WRITE_ONCE(*z, 1);
28*4882a593Smuzhiyun	spin_unlock(mylock);
29*4882a593Smuzhiyun}
30*4882a593Smuzhiyun
31*4882a593SmuzhiyunP2(int *x, int *z)
32*4882a593Smuzhiyun{
33*4882a593Smuzhiyun	int r1;
34*4882a593Smuzhiyun
35*4882a593Smuzhiyun	WRITE_ONCE(*z, 2);
36*4882a593Smuzhiyun	smp_mb();
37*4882a593Smuzhiyun	r1 = READ_ONCE(*x);
38*4882a593Smuzhiyun}
39*4882a593Smuzhiyun
40*4882a593Smuzhiyunexists (1:r0=1 /\ z=2 /\ 2:r1=0)
41