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SubjectRe: [PATCH 2/2 v2 RFC] tools/memory-model: redefine rb in terms of rcu-fence
On Fri, Mar 02, 2018 at 12:31:41PM +0800, Boqun Feng wrote:
> On Thu, Mar 01, 2018 at 10:37:58AM -0800, Paul E. McKenney wrote:
> > On Thu, Mar 01, 2018 at 09:49:06AM -0800, Paul E. McKenney wrote:

[ . . . ]

> > And as Andrea pointed out off-list, I did indeed mess up Boqun's change.
> > I forgot to change the "irreflexive" into "acyclic". Applying that change
> > makes everything work.
> >
> > Please accept my apologies for my confusion!
> >
>
> np, also I should have provided a proper patch for your testing.
>
> For this Alan's patch, feel free to add:
>
> Reviewed-by: Boqun Feng <boqun.feng@gmail.com>

Alan's last submission was still RFC, so I have not yet queued it.
So this ball is still in Alan's court.

Thanx, Paul

> Regards,
> Boqun
>
> > Thanx, Paul
> >
> > > > > I prefer this because we already treat "gp" as "strong-fence", which
> > > > > already is a "rcu-link".
> > > >
> > > > That's a good point; it had not occurred to me.
> > >
> > > And if I remove the "gp" but leave the last line, it does properly
> > > classify the two new litmus tests.
> > >
> > > Thanx, Paul
> > >
> > > > > Also, recurisively extending rcu-fence with
> > > > > itself is exactly calculating the transitive closure, which we can avoid
> > > > > by using a "acycle" rule. Besides, it looks more consistent with hb and
> > > > > pb.
> > > >
> > > > That _had_ occurred to me. But I couldn't see any way to do it while
> > > > still defining rcu-fence correctly.
> > >
> > > ------------------------------------------------------------------------
> > >
> > > diff --git a/tools/memory-model/linux-kernel.cat b/tools/memory-model/linux-kernel.cat
> > > index 1e5c4653dd12..75d3c225146c 100644
> > > --- a/tools/memory-model/linux-kernel.cat
> > > +++ b/tools/memory-model/linux-kernel.cat
> > > @@ -106,12 +106,11 @@ let rcu-link = hb* ; pb* ; prop
> > > * Any sequence containing at least as many grace periods as RCU read-side
> > > * critical sections (joined by rcu-link) acts as a generalized strong fence.
> > > *)
> > > -let rec rcu-fence = gp |
> > > +let rec rcu-fence =
> > > (gp ; rcu-link ; rscs) |
> > > (rscs ; rcu-link ; gp) |
> > > (gp ; rcu-link ; rcu-fence ; rcu-link ; rscs) |
> > > - (rscs ; rcu-link ; rcu-fence ; rcu-link ; gp) |
> > > - (rcu-fence ; rcu-link ; rcu-fence)
> > > + (rscs ; rcu-link ; rcu-fence ; rcu-link ; gp)
> > >
> > > (* rb orders instructions just as pb does *)
> > > let rb = prop ; rcu-fence ; hb* ; pb*
> >


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