LXR linux/Documentation/litmus-tests/rcu/RCU+sync+read.litmus

   1C RCU+sync+read
   2
   3(*
   4 * Result: Never
   5 *
   6 * This litmus test demonstrates that after a grace period, an RCU updater always
   7 * sees all stores done in prior RCU read-side critical sections. Such
   8 * read-side critical sections would have ended before the grace period ended.
   9 *
  10 * This is one implication of the RCU grace-period guarantee, which says (among
  11 * other things) that an RCU read-side critical section cannot span a grace period.
  12 *)
  13
  14{
  15int x = 0;
  16int y = 0;
  17}
  18
  19P0(int *x, int *y)
  20{
  21        rcu_read_lock();
  22        WRITE_ONCE(*x, 1);
  23        WRITE_ONCE(*y, 1);
  24        rcu_read_unlock();
  25}
  26
  27P1(int *x, int *y)
  28{
  29        int r0;
  30        int r1;
  31
  32        r0 = READ_ONCE(*x);
  33        synchronize_rcu();
  34        r1 = READ_ONCE(*y);
  35}
  36
  37exists (1:r0=1 /\ 1:r1=0)
  38