162306a36Sopenharmony_ciC MP+polockonce+poacquiresilsil 262306a36Sopenharmony_ci 362306a36Sopenharmony_ci(* 462306a36Sopenharmony_ci * Result: Sometimes 562306a36Sopenharmony_ci * 662306a36Sopenharmony_ci * Do spinlocks provide order to outside observers using spin_is_locked() 762306a36Sopenharmony_ci * to sense the lock-held state, ordered by acquire? Note that when the 862306a36Sopenharmony_ci * first spin_is_locked() returns false and the second true, we know that 962306a36Sopenharmony_ci * the smp_load_acquire() executed before the lock was acquired (loosely 1062306a36Sopenharmony_ci * 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 WRITE_ONCE(*x, 1); 1962306a36Sopenharmony_ci spin_unlock(lo); 2062306a36Sopenharmony_ci} 2162306a36Sopenharmony_ci 2262306a36Sopenharmony_ciP1(spinlock_t *lo, int *x) // Consumer 2362306a36Sopenharmony_ci{ 2462306a36Sopenharmony_ci int r1; 2562306a36Sopenharmony_ci int r2; 2662306a36Sopenharmony_ci int r3; 2762306a36Sopenharmony_ci 2862306a36Sopenharmony_ci r1 = smp_load_acquire(x); 2962306a36Sopenharmony_ci r2 = spin_is_locked(lo); 3062306a36Sopenharmony_ci r3 = spin_is_locked(lo); 3162306a36Sopenharmony_ci} 3262306a36Sopenharmony_ci 3362306a36Sopenharmony_ciexists (1:r1=1 /\ 1:r2=0 /\ 1:r3=1) (* Bad outcome. *) 34