On Mon, Oct 05, 2020 at 02:19:49PM -0400, Alan Stern wrote:
> On Mon, Oct 05, 2020 at 09:52:23AM -0700, Paul E. McKenney wrote:
> > On Mon, Oct 05, 2020 at 11:53:10AM -0400, Alan Stern wrote:
> > > I tested the new commit -- it does indeed fix the problem.
> >
> > Beat me to it, very good! ;-)
> >
> > But were you using the crypto-control-data litmus test?
>
> I was not. The test I used was what you get by starting from the
> version of crypto-control-data that had the one-liner in P1, and then
> replacing P0 with:
>
> P0(int *x, int *y)
> {
> int r1;
>
> r1 = READ_ONCE(*x);
> smp_mb();
> WRITE_ONCE(*y, 1);
> }
>
> Without the new commit this test is allowed; with the new commit it
> isn't (as we would expect). Also, the graphical output from herd7 shows
> the data dependency in P1 with the commit, and doesn't show it without
> the commit.
>
> > That one still
> > gets me Sometimes:
> >
> > $ herd7 -version
> > 7.56+02~dev, Rev: 0f3f8188a326d5816a82fb9970fcd209a2678859
> > $ herd7 -conf linux-kernel.cfg ~/paper/scalability/LWNLinuxMM/litmus/manual/kernel/crypto-control-data.litmus
> > Test crypto-control-data Allowed
> > States 2
> > 0:r1=0;
> > 0:r1=1;
> > Ok
> > Witnesses
> > Positive: 1 Negative: 4
> > Condition exists (0:r1=1)
> > Observation crypto-control-data Sometimes 1 4
> > Time crypto-control-data 0.00
> > Hash=10898119bac87e11f31dc22bbb7efe17
> >
> > Or did I mess something up?
>
> You didn't mess up anything. That's the whole point of this litmus
> test: It should be forbidden because it is an example of OOTA, but LKMM
> allows it. Even with Luc's new commit.
OK, got it.
Aside from naming and comment, how about my adding the following?
Thanx, Paul
------------------------------------------------------------------------
C crypto-control-data-1
(*
* LB plus crypto-mb-data plus data.
*
* Result: Never
*
* This is an example of OOTA and we would like it to be forbidden.
* If you want herd7 to get the right answer, you must use herdtools
* 0f3f8188a326 (" [herd] Fix dependency definition") or later.
*)
{}
P0(int *x, int *y)
{
int r1;
r1 = READ_ONCE(*x);
smp_mb();
WRITE_ONCE(*y, r1);
}
P1(int *x, int *y)
{
int r2;
WRITE_ONCE(*x, READ_ONCE(*y));
}
exists (0:r1=1)
