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 <stern@xxxxxxxxxxxxxxxxxxx> > 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 <stern@xxxxxxxxxxxxxxxxxxx> > Signed-off-by: Paul E. McKenney <paulmck@xxxxxxxxxx> > > 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