1C MP+polockmbonce+poacquiresilsil 2 3(* 4 * Result: Never 5 * 6 * Do spinlocks combined with smp_mb__after_spinlock() provide order 7 * to outside observers using spin_is_locked() to sense the lock-held 8 * state, ordered by acquire? Note that when the first spin_is_locked() 9 * returns false and the second true, we know that the smp_load_acquire() 10 * executed before the lock was acquired (loosely speaking). 11 *) 12 13{ 14 spinlock_t lo; 15 int x; 16} 17 18P0(spinlock_t *lo, int *x) // Producer 19{ 20 spin_lock(lo); 21 smp_mb__after_spinlock(); 22 WRITE_ONCE(*x, 1); 23 spin_unlock(lo); 24} 25 26P1(spinlock_t *lo, int *x) // Consumer 27{ 28 int r1; 29 int r2; 30 int r3; 31 32 r1 = smp_load_acquire(x); 33 r2 = spin_is_locked(lo); 34 r3 = spin_is_locked(lo); 35} 36 37exists (1:r1=1 /\ 1:r2=0 /\ 1:r3=1) (* Bad outcome. *) 38