On Sun, Oct 04, 2020 at 04:31:46PM -0700, Paul E. McKenney wrote: > Nice simple example! How about like this? > > Thanx, Paul > > ------------------------------------------------------------------------ > > commit c964f404eabe4d8ce294e59dda713d8c19d340cf > Author: Alan Stern <stern@xxxxxxxxxxxxxxxxxxx> > Date: Sun Oct 4 16:27:03 2020 -0700 > > manual/kernel: Add a litmus test with a hidden dependency > > This commit adds a litmus test that has a data dependency that can be > hidden by control flow. In this test, both the taken and the not-taken > branches of an "if" statement must be accounted for in order to properly > analyze the litmus test. But herd7 looks only at individual executions > in isolation, so fails to see the dependency. > > Signed-off-by: Alan Stern <stern@xxxxxxxxxxxxxxxxxxx> > Signed-off-by: Paul E. McKenney <paulmck@xxxxxxxxxx> > > diff --git a/manual/kernel/crypto-control-data.litmus b/manual/kernel/crypto-control-data.litmus > new file mode 100644 > index 0000000..6baecf9 > --- /dev/null > +++ b/manual/kernel/crypto-control-data.litmus > @@ -0,0 +1,31 @@ > +C crypto-control-data > +(* > + * LB plus crypto-control-data plus data > + * > + * Result: Sometimes > + * > + * This is an example of OOTA and we would like it to be forbidden. > + * The WRITE_ONCE in P0 is both data-dependent and (at the hardware level) > + * control-dependent on the preceding READ_ONCE. But the dependencies are > + * hidden by the form of the conditional control construct, hence the > + * name "crypto-control-data". The memory model doesn't recognize them. > + *) > + > +{} > + > +P0(int *x, int *y) > +{ > + int r1; > + > + r1 = 1; > + if (READ_ONCE(*x) == 0) > + r1 = 0; > + WRITE_ONCE(*y, r1); > +} > + > +P1(int *x, int *y) > +{ > + WRITE_ONCE(*x, READ_ONCE(*y)); > +} > + > +exists (0:r1=1) Considering the bug in herd7 pointed out by Akira, we should rewrite P1 as: P1(int *x, int *y) { int r2; r = READ_ONCE(*y); WRITE_ONCE(*x, r2); } Other than that, this is fine. Alan