On Wed, Feb 21, 2018 at 11:50:31AM -0500, Alan Stern wrote:
> On Wed, 21 Feb 2018, Paul E. McKenney wrote:
>
> > On Wed, Feb 21, 2018 at 10:09:00AM -0500, Alan Stern wrote:
> > > On Tue, 20 Feb 2018, Paul E. McKenney wrote:
> > >
> > > > From: Alan Stern <stern@xxxxxxxxxxxxxxxxxxx>
> > > >
> > > > This commit adds a litmus test in which P0() and P1() form a lock-based S
> > > > litmus test, with the addition of P2(), which observes P0()'s and P1()'s
> > >
> > > Why do you call this an "S" litmus test? Isn't ISA2 a better
> > > description?
> >
> > Indeed, the name of the test is in fact ISA2.
>
> Sure; and the Changelog entry should reflect this.
No argument.
> > > > accesses with a full memory barrier but without the lock. This litmus
> > > > test asks whether writes carried out by two different processes under the
> > > > same lock will be seen in order by a third process not holding that lock.
> > > > The answer to this question is "yes" for all architectures supporting
> > > > the Linux kernel, but is "no" according to the current version of LKMM.
> > > >
> > > > A patch to LKMM is under development.
> > > >
> > > > Signed-off-by: Alan Stern <stern@xxxxxxxxxxxxxxxxxxx>
> > > > Signed-off-by: Paul E. McKenney <paulmck@xxxxxxxxxxxxxxxxxx>
> > > > ---
> > > > .../ISA2+pooncelock+pooncelock+pombonce.litmus | 41 ++++++++++++++++++++++
> > > > 1 file changed, 41 insertions(+)
> > > > create mode 100644 tools/memory-model/litmus-tests/ISA2+pooncelock+pooncelock+pombonce.litmus
> > >
> > > Aren't these tests supposed to be described in litmus-tests/README?
>
> You apparently missed this recommendation.
I did, please accept my apologies and please see below.
> > > > diff --git a/tools/memory-model/litmus-tests/ISA2+pooncelock+pooncelock+pombonce.litmus b/tools/memory-model/litmus-tests/ISA2+pooncelock+pooncelock+pombonce.litmus
> > > > new file mode 100644
> > > > index 000000000000..7a39a0aaa976
> > > > --- /dev/null
> > > > +++ b/tools/memory-model/litmus-tests/ISA2+pooncelock+pooncelock+pombonce.litmus
> > > > @@ -0,0 +1,41 @@
> > > > +C ISA2+pooncelock+pooncelock+pombonce.litmus
> > > > +
> > > > +(*
> > > > + * Result: Sometimes
> > > > + *
> > > > + * This test shows that the ordering provided by a lock-protected S
> > > > + * litmus test (P0() and P1()) are not visible to external process P2().
> > > > + * This is likely to change soon.
> > >
> > > That last line may be premature. We haven't reached any consensus on
> > > how RISC-V will handle this. If RISC-V allows the test then the memory
> > > model can't forbid it.
> >
> > Agreed. How about this? If the RISC-V question is answered by the
> > end of next week, I update accordingly. If not, I update the comment
> > to give the details.
>
> The README also should be updated.
Agreed.
> > Hey, at least having the memory model go in at about the same time as
> > a new architecture is giving us good practice! ;-)
>
> Hopefully things will settle down in a week or two.
Here is hoping!
Thanx, Paul
------------------------------------------------------------------------
commit e6658d1d7fcc6391f3d00beaadc484243123a893
Author: Paul E. McKenney <paulmck@xxxxxxxxxxxxxxxxxx>
Date: Wed Feb 21 09:49:01 2018 -0800
tools/memory-order: Add documentation of new litmus test
The litmus-tests/README file lacked any mention of then litmus test
named ISA2+pooncelock+pooncelock+pombonce.litmus. This commit therefore
adds this test.
Reported-by: Alan Stern <stern@xxxxxxxxxxxxxxxxxxx>
Signed-off-by: Paul E. McKenney <paulmck@xxxxxxxxxxxxxxxxxx>
diff --git a/tools/memory-model/litmus-tests/README b/tools/memory-model/litmus-tests/README
index dca7d823ad57..aff3eb90e067 100644
--- a/tools/memory-model/litmus-tests/README
+++ b/tools/memory-model/litmus-tests/README
@@ -32,6 +32,11 @@ IRIW+poonceonces+OnceOnce.litmus
order of a pair of writes, where each write is to a different
variable by a different process?
+ISA2+pooncelock+pooncelock+pombonce.litmus
+ Tests whether the ordering provided by a lock-protected S litmus
+ test is visible to an external process whose accesses are
+ separated by smp_mb().
+
ISA2+poonceonces.litmus
As below, but with store-release replaced with WRITE_ONCE()
and load-acquire replaced with READ_ONCE().
