linux/tools/memory-model/litmus-tests/LB+unlocklockonceonce+poacquireonce.litmus

C LB+unlocklockonceonce+poacquireonce

(*
 * Result: Never
 *
 * If two locked critical sections execute on the same CPU, all accesses
 * in the first must execute before any accesses in the second, even if the
 * critical sections are protected by different locks.  Note: Even when a
 * write executes before a read, their memory effects can be reordered from
 * the viewpoint of another CPU (the kind of reordering allowed by TSO).
 *)

{}

P0(spinlock_t *s, spinlock_t *t, int *x, int *y)
{
	int r1;

	spin_lock(s);
	r1 = READ_ONCE(*x);
	spin_unlock(s);
	spin_lock(t);
	WRITE_ONCE(*y, 1);
	spin_unlock(t);
}

P1(int *x, int *y)
{
	int r2;

	r2 = smp_load_acquire(y);
	WRITE_ONCE(*x, 1);
}

exists (0:r1=1 /\ 1:r2=1)