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. > > > 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. > > > 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. > 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. Alan
