On Wed, Oct 07, 2020 at 07:50:25PM -0700, Paul E. McKenney wrote:
> There are some distractions at the moment.
>
> Please see below. If this is not exactly correct, I will use "git rm"
> and let you submit the patch as you wish.
>
> Thanx, Paul
>
> ------------------------------------------------------------------------
>
> commit dc0119c24b64f9d541b94ba5d17eec0cbc265bfa
> Author: Alan Stern <st...@rowland.harvard.edu>
> Date: Tue Oct 6 09:38:37 2020 -0700
>
> manual/kernel: Add LB data dependency test with no intermediate variable
>
> Test whether herd7 can detect a data dependency when there is no
> intermediate local variable, as in WRITE_ONCE(*x, READ_ONCE(*y)).
> Commit 0f3f8188a326 in herdtools fixed an oversight which caused such
> dependencies to be missed.
>
> Signed-off-by: Alan Stern <st...@rowland.harvard.edu>
> Signed-off-by: Paul E. McKenney <paul...@kernel.org>
>
> diff --git a/manual/kernel/C-LB+mb+data.litmus
> b/manual/kernel/C-LB+mb+data.litmus
> new file mode 100644
> index 0000000..e9e24e0
> --- /dev/null
> +++ b/manual/kernel/C-LB+mb+data.litmus
> @@ -0,0 +1,27 @@
> +C LB+mb+data
> +(*
> + * Result: Never
> + *
> + * Versions of herd7 prior to commit 0f3f8188a326 ("[herd] Fix dependency
> + * definition") recognize data dependencies only when they flow through
> + * an intermediate local variable. Since the dependency in P1 doesn't,
> + * those versions get the wrong answer for this test.
> + *)
> +
> +{}
> +
> +P0(int *x, int *y)
> +{
> + int r1;
> +
> + r1 = READ_ONCE(*x);
> + smp_mb();
> + WRITE_ONCE(*y, r1);
> +}
> +
> +P1(int *x, int *y)
> +{
> + WRITE_ONCE(*x, READ_ONCE(*y));
> +}
> +
> +exists (0:r1=1)
Okay, that's exactly what it should be. :-)
Alan
