Test auto/C-WW-G+WW-B+WW-R+WW-R

C auto/C-WW-G+WW-B+WW-R+WW-R
(*
 * Result: Sometimes
 * 
 * Process 0 starts (t=197996).
 * 
 * P0 advances one grace period (t=297996).
 * 
 * P1 advances slightly (t=297998).
 * 
 * P2 goes back a bit less than one grace period (t=198999).
 * 
 * P3 goes back a bit less than one grace period (t=100000).
 * 
 * Process 0 start at t=197996, process 4 end at t=100000: Cycle allowed.
 *)
{
}

P0(int *x0, int *x1)
{
 WRITE_ONCE(*x0, 2);
 synchronize_rcu();
 WRITE_ONCE(*x1, 1);
}


P1(int *x1, int *x2)
{
 WRITE_ONCE(*x1, 2);
 smp_mb();
 WRITE_ONCE(*x2, 1);
}


P2(int *x2, int *x3)
{
 rcu_read_lock();
 WRITE_ONCE(*x2, 2);
 WRITE_ONCE(*x3, 1);
 rcu_read_unlock();
}


P3(int *x0, int *x3)
{
 rcu_read_lock();
 WRITE_ONCE(*x3, 2);
 WRITE_ONCE(*x0, 1);
 rcu_read_unlock();
}

Observed
    x3=2; x2=2; x1=2; x0=2;