162306a36Sopenharmony_ciC MP+polockmbonce+poacquiresilsil 262306a36Sopenharmony_ci 362306a36Sopenharmony_ci(* 462306a36Sopenharmony_ci * Result: Never 562306a36Sopenharmony_ci * 662306a36Sopenharmony_ci * Do spinlocks combined with smp_mb__after_spinlock() provide order 762306a36Sopenharmony_ci * to outside observers using spin_is_locked() to sense the lock-held 862306a36Sopenharmony_ci * state, ordered by acquire? Note that when the first spin_is_locked() 962306a36Sopenharmony_ci * returns false and the second true, we know that the smp_load_acquire() 1062306a36Sopenharmony_ci * executed before the lock was acquired (loosely speaking). 1162306a36Sopenharmony_ci *) 1262306a36Sopenharmony_ci 1362306a36Sopenharmony_ci{} 1462306a36Sopenharmony_ci 1562306a36Sopenharmony_ciP0(spinlock_t *lo, int *x) // Producer 1662306a36Sopenharmony_ci{ 1762306a36Sopenharmony_ci spin_lock(lo); 1862306a36Sopenharmony_ci smp_mb__after_spinlock(); 1962306a36Sopenharmony_ci WRITE_ONCE(*x, 1); 2062306a36Sopenharmony_ci spin_unlock(lo); 2162306a36Sopenharmony_ci} 2262306a36Sopenharmony_ci 2362306a36Sopenharmony_ciP1(spinlock_t *lo, int *x) // Consumer 2462306a36Sopenharmony_ci{ 2562306a36Sopenharmony_ci int r1; 2662306a36Sopenharmony_ci int r2; 2762306a36Sopenharmony_ci int r3; 2862306a36Sopenharmony_ci 2962306a36Sopenharmony_ci r1 = smp_load_acquire(x); 3062306a36Sopenharmony_ci r2 = spin_is_locked(lo); 3162306a36Sopenharmony_ci r3 = spin_is_locked(lo); 3262306a36Sopenharmony_ci} 3362306a36Sopenharmony_ci 3462306a36Sopenharmony_ciexists (1:r1=1 /\ 1:r2=0 /\ 1:r3=1) (* Bad outcome. *) 35