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. *)
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