New locking test for the paulmckrcu/litmus github archive

[Alan Stern]

Paul:

Below is a new litmus test for the manual/locked directory in your 
github archive.  It is based on a suggestion from Andrea Parri, and it 
demonstrates a bug in the current LKMM lock.cat file.  Patches to fix 
that file will be sent shortly.

Alan

---

C islocked+lock+islocked+unlock+islocked.litmus

(*
 * Result: Always
 *
 * This tests the memory model's implementation of spin_is_locked().
 *)

{}

P0(spinlock_t *x)
{
        int r0;
	int r1;
	int r2;

	r0 = spin_is_locked(x);
	spin_lock(x);
	r1 = spin_is_locked(x);
	spin_unlock(x);
	r2 = spin_is_locked(x);
}

exists (0:r0=0 /\ 0:r1=1 /\ 0:r2=0)