C auto/C-WW-G+WW-G+WW-R+WW-R (* * Result: Never * * Process 0 starts (t=100000). * * P0 advances one grace period (t=200000). * * P1 advances one grace period (t=300001). * * P2 goes back a bit less than one grace period (t=201002). * * P3 goes back a bit less than one grace period (t=102003). * * Process 0 start at t=100000, process 4 end at t=102003: Cycle forbidden. *) { } P0(int *x0, int *x1) { WRITE_ONCE(*x0, 2); synchronize_rcu(); WRITE_ONCE(*x1, 1); } P1(int *x1, int *x2) { WRITE_ONCE(*x1, 2); synchronize_rcu(); 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=1; x2=2; x1=2; x0=2;