11c27b644SPaul E. McKenneyC MP+polocks 21c27b644SPaul E. McKenney 38f32543bSPaul E. McKenney(* 48f32543bSPaul E. McKenney * Result: Never 58f32543bSPaul E. McKenney * 68f32543bSPaul E. McKenney * This litmus test demonstrates how lock acquisitions and releases can 78f32543bSPaul E. McKenney * stand in for smp_load_acquire() and smp_store_release(), respectively. 88f32543bSPaul E. McKenney * In other words, when holding a given lock (or indeed after releasing a 98f32543bSPaul E. McKenney * given lock), a CPU is not only guaranteed to see the accesses that other 108f32543bSPaul E. McKenney * CPUs made while previously holding that lock, it is also guaranteed 118f32543bSPaul E. McKenney * to see all prior accesses by those other CPUs. 128f32543bSPaul E. McKenney *) 138f32543bSPaul E. McKenney 141947bfcfSPaul E. McKenney{ 151947bfcfSPaul E. McKenney spinlock_t mylock; 16acc4bdc5SPaul E. McKenney int buf; 17acc4bdc5SPaul E. McKenney int flag; 181947bfcfSPaul E. McKenney} 191c27b644SPaul E. McKenney 20*b6ff3084SPaul E. McKenneyP0(int *buf, int *flag, spinlock_t *mylock) // Producer 211c27b644SPaul E. McKenney{ 22acc4bdc5SPaul E. McKenney WRITE_ONCE(*buf, 1); 231c27b644SPaul E. McKenney spin_lock(mylock); 24acc4bdc5SPaul E. McKenney WRITE_ONCE(*flag, 1); 251c27b644SPaul E. McKenney spin_unlock(mylock); 261c27b644SPaul E. McKenney} 271c27b644SPaul E. McKenney 28*b6ff3084SPaul E. McKenneyP1(int *buf, int *flag, spinlock_t *mylock) // Consumer 291c27b644SPaul E. McKenney{ 301c27b644SPaul E. McKenney int r0; 311c27b644SPaul E. McKenney int r1; 321c27b644SPaul E. McKenney 331c27b644SPaul E. McKenney spin_lock(mylock); 34acc4bdc5SPaul E. McKenney r0 = READ_ONCE(*flag); 351c27b644SPaul E. McKenney spin_unlock(mylock); 36acc4bdc5SPaul E. McKenney r1 = READ_ONCE(*buf); 371c27b644SPaul E. McKenney} 381c27b644SPaul E. McKenney 39*b6ff3084SPaul E. McKenneyexists (1:r0=1 /\ 1:r1=0) (* Bad outcome. *) 40