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 spinlock_t mylock; 16 int buf; 17 int flag; 18} 19 20P0(int *buf, int *flag, spinlock_t *mylock) // Consumer 21{ 22 int r0; 23 int r1; 24 25 r0 = READ_ONCE(*flag); 26 spin_lock(mylock); 27 r1 = READ_ONCE(*buf); 28 spin_unlock(mylock); 29} 30 31P1(int *buf, int *flag, spinlock_t *mylock) // Producer 32{ 33 spin_lock(mylock); 34 WRITE_ONCE(*buf, 1); 35 spin_unlock(mylock); 36 WRITE_ONCE(*flag, 1); 37} 38 39exists (0:r0=1 /\ 0:r1=0) (* Bad outcome. *) 40