LXR linux/Documentation/litmus-tests/rcu/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)
  43