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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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