1C MP+porevlocks 2 3(* 4 * Result: Never 5 * 6 * This litmus test demonstrates how lock acquisitions and releases can 7 * stand in for smp_load_acquire() and smp_store_release(), respectively. 8 * In other words, when holding a given lock (or indeed after releasing a 9 * given lock), a CPU is not only guaranteed to see the accesses that other 10 * CPUs made while previously holding that lock, it is also guaranteed to 11 * see all prior accesses by those other CPUs. 12 *) 13 14{} 15 16P0(int *buf, int *flag, spinlock_t *mylock) // Consumer 17{ 18 int r0; 19 int r1; 20 21 r0 = READ_ONCE(*flag); 22 spin_lock(mylock); 23 r1 = READ_ONCE(*buf); 24 spin_unlock(mylock); 25} 26 27P1(int *buf, int *flag, spinlock_t *mylock) // Producer 28{ 29 spin_lock(mylock); 30 WRITE_ONCE(*buf, 1); 31 spin_unlock(mylock); 32 WRITE_ONCE(*flag, 1); 33} 34 35exists (0:r0=1 /\ 0:r1=0) (* Bad outcome. *) 36