On Fri, Jan 15, 2016 at 11:28:45AM -0800, Paul E. McKenney wrote:
> On Fri, Jan 15, 2016 at 09:54:01AM -0800, Paul E. McKenney wrote:
> > On Fri, Jan 15, 2016 at 10:24:32AM +0000, Will Deacon wrote:
> > > See my earlier reply [1] (but also, your WRC Linux example looks more
> > > like a variant on WWC and I couldn't really follow it).
> >
> > I will revisit my WRC Linux example. And yes, creating litmus tests
> > that use non-fake dependencies is still a bit of an undertaking. :-/
> > I am sure that it will seem more natural with time and experience...
>
> Hmmm... You are quite right, I did do WWC. I need to change cpu2()'s
> last access from a store to a load to get WRC. Plus the levels of
> indirection definitely didn't match up, did they?
Nope, it was pretty baffling!
> struct foo {
> struct foo *next;
> };
> struct foo a;
> struct foo b;
> struct foo c = { &a };
> struct foo d = { &b };
> struct foo x = { &c };
> struct foo y = { &d };
> struct foo *r1, *r2, *r3;
>
> void cpu0(void)
> {
> WRITE_ONCE(x.next, &y);
> }
>
> void cpu1(void)
> {
> r1 = lockless_dereference(x.next);
> WRITE_ONCE(r1->next, &x);
> }
>
> void cpu2(void)
> {
> r2 = lockless_dereference(y.next);
> r3 = READ_ONCE(r2->next);
> }
>
> In this case, it is legal to end the run with:
>
> r1 == &y && r2 == &x && r3 == &c
>
> Please see below for a ppcmem litmus test.
>
> So, did I get it right this time? ;-)
The code above looks correct to me (in that it matches WRC+addrs),
but your litmus test:
> PPC WRCnf+addrs
> ""
> {
> 0:r2=x; 0:r3=y;
> 1:r2=x; 1:r3=y;
> 2:r2=x; 2:r3=y;
> c=a; d=b; x=c; y=d;
> }
> P0 | P1 | P2 ;
> stw r3,0(r2) | lwz r8,0(r2) | lwz r8,0(r3) ;
> | stw r2,0(r3) | lwz r9,0(r8) ;
> exists
> (1:r8=y /\ 2:r8=x /\ 2:r9=c)
Seems to be missing the address dependency on P1.
Will
