RCU+sync+free.litmus

 1C RCU+sync+free
 2
 3(*
 4 * Result: Never
 5 *
 6 * This litmus test demonstrates that an RCU reader can never see a write that
 7 * follows a grace period, if it did not see writes that precede that grace
 8 * period.
 9 *
10 * This is a typical pattern of RCU usage, where the write before the grace
11 * period assigns a pointer, and the writes following the grace period destroy
12 * the object that the pointer used to point to.
13 *
14 * This is one implication of the RCU grace-period guarantee, which says (among
15 * other things) that an RCU read-side critical section cannot span a grace period.
16 *)
17
18{
19int x = 1;
20int *y = &x;
21int z = 1;
22}
23
24P0(int *x, int *z, int **y)
25{
26	int *r0;
27	int r1;
28
29	rcu_read_lock();
30	r0 = rcu_dereference(*y);
31	r1 = READ_ONCE(*r0);
32	rcu_read_unlock();
33}
34
35P1(int *x, int *z, int **y)
36{
37	rcu_assign_pointer(*y, z);
38	synchronize_rcu();
39	WRITE_ONCE(*x, 0);
40}
41
42exists (0:r0=x /\ 0:r1=0)