tools/memory-model/litmus-tests/MP+polocks.litmus

C MP+polocks

(*
 * Result: Never
 *
 * This litmus test demonstrates how lock acquisitions and releases can
 * stand in for smp_load_acquire() and smp_store_release(), respectively.
 * In other words, when holding a given lock (or indeed after releasing a
 * given lock), a CPU is not only guaranteed to see the accesses that other
 * CPUs made while previously holding that lock, it is also guaranteed
 * to see all prior accesses by those other CPUs.
 *)

{
	spinlock_t mylock;
	int buf;
	int flag;
}

P0(int *buf, int *flag, spinlock_t *mylock) // Producer
{
	WRITE_ONCE(*buf, 1);
	spin_lock(mylock);
	WRITE_ONCE(*flag, 1);
	spin_unlock(mylock);
}

P1(int *buf, int *flag, spinlock_t *mylock) // Consumer
{
	int r0;
	int r1;

	spin_lock(mylock);
	r0 = READ_ONCE(*flag);
	spin_unlock(mylock);
	r1 = READ_ONCE(*buf);
}

exists (1:r0=1 /\ 1:r1=0) (* Bad outcome. *)