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C RCU+sync+free
(*
* Result: Never
*
* This litmus test demonstrates that an RCU reader can never see a write that
* follows a grace period, if it did not see writes that precede that grace
* period.
*
* This is a typical pattern of RCU usage, where the write before the grace
* period assigns a pointer, and the writes following the grace period destroy
* the object that the pointer used to point to.
*
* This is one implication of the RCU grace-period guarantee, which says (among
* other things) that an RCU read-side critical section cannot span a grace period.
*)
{
int x = 1;
int *y = &x;
int z = 1;
}
P0(int *x, int *z, int **y)
{
int *r0;
int r1;
rcu_read_lock();
r0 = rcu_dereference(*y);
r1 = READ_ONCE(*r0);
rcu_read_unlock();
}
P1(int *x, int *z, int **y)
{
rcu_assign_pointer(*y, z);
synchronize_rcu();
WRITE_ONCE(*x, 0);
}
exists (0:r0=x /\ 0:r1=0)
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