Re: [RFC v2 3/3] tools/memory-model: litmus: Add two tests for unlock(A)+lock(B) ordering

[Peter Zijlstra]

On Mon, Oct 25, 2021 at 10:54:16PM +0800, Boqun Feng wrote:
> diff --git a/tools/memory-model/litmus-tests/LB+unlocklockonceonce+poacquireonce.litmus b/tools/memory-model/litmus-tests/LB+unlocklockonceonce+poacquireonce.litmus
> new file mode 100644
> index 000000000000..955b9c7cdc7f
> --- /dev/null
> +++ b/tools/memory-model/litmus-tests/LB+unlocklockonceonce+poacquireonce.litmus
> @@ -0,0 +1,33 @@
> +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.

One small nit; the above "all accesses" reads as if:

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

would also work, except of course that's the one reorder 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)