1C MP+polocks 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 11 * to see all prior accesses by those other CPUs. 12 *) 13 14{} 15 16P0(int *buf, int *flag, spinlock_t *mylock) // Producer 17{ 18 WRITE_ONCE(*buf, 1); 19 spin_lock(mylock); 20 WRITE_ONCE(*flag, 1); 21 spin_unlock(mylock); 22} 23 24P1(int *buf, int *flag, spinlock_t *mylock) // Consumer 25{ 26 int r0; 27 int r1; 28 29 spin_lock(mylock); 30 r0 = READ_ONCE(*flag); 31 spin_unlock(mylock); 32 r1 = READ_ONCE(*buf); 33} 34 35exists (1:r0=1 /\ 1:r1=0) (* Bad outcome. *) 36