Test LISA2R2G

LISA LISA2R2G
(*
 * Result: Never
 *
 * Two RCU grace periods and two RCU read-side critical sections.
 * Cycle prohibited.
 *)
{
x0 = 0;
x1 = 0;
x2 = 0;
x3 = 0;
}
 P0                 | P1            | P2            | P3                 ;
 f[rcu_read_lock]   | r[once] r1 x1 | r[once] r2 x2 | f[rcu_read_lock]   ;
 r[once] r2 x0      | f[sync]       | f[sync]       | r[once] r3 x3      ;
 w[once] x1 1       | w[once] x2 1  | w[once] x3 1  | w[once] x0 1       ;
 f[rcu_read_unlock] |               |               | f[rcu_read_unlock] ;
Observed
    3:r3=1; 2:r2=0; 1:r1=1; 0:r2=1;
and 3:r3=1; 2:r2=1; 1:r1=0; 0:r2=1;