On Thu, Feb 15, 2018 at 12:51:56PM -0500, Alan Stern wrote:
> On Fri, 16 Feb 2018, Akira Yokosawa wrote:
>
> > So, I attempted to rebase the patch to current (somewhat old) master of
> > https://github.com/aparri/memory-model. Why? Because the lkmm branch
> > in Paul's -rcu tree doesn't have linux-kernel-hardware.cat.
> >
> > However, after this change, Z6.0+pooncelock+pooncelock+pombonce still
> > has the result "Sometimes". I must have done something wrong in the
> > conflict resolution.
> >
> > Note: I have almost no idea what this patch is doing. I'm just hoping
> > to give a starting point of a discussion.
>
> Yes, that litmus test gives "Sometimes" both with and without the
> patch. But consider instead this slightly changed version of that
> test, in which P2 reads Z instead of writing it:
>
> C Z6.0-variant
>
> {}
>
> P0(int *x, int *y, spinlock_t *mylock)
> {
> spin_lock(mylock);
> WRITE_ONCE(*x, 1);
> WRITE_ONCE(*y, 1);
> spin_unlock(mylock);
> }
>
> P1(int *y, int *z, spinlock_t *mylock)
> {
> int r0;
>
> spin_lock(mylock);
> r0 = READ_ONCE(*y);
> WRITE_ONCE(*z, 1);
> spin_unlock(mylock);
> }
>
> P2(int *x, int *z)
> {
> int r1;
> int r2;
>
> r2 = READ_ONCE(*z);
> smp_mb();
> r1 = READ_ONCE(*x);
> }
>
> exists (1:r0=1 /\ 2:r2=1 /\ 2:r1=0)
>
> Without the patch, this test gives "Sometimes"; with the patch it gives
> "Never". That is what I thought Paul was talking about originally.
>
> Sorry if my misunderstanding caused too much confusion for other
> people.
Ah, I did indeed get confused. I have changed the "Result:" for
Z6.0+pooncelock+pooncelock+pombonce.litmus back to "Never", as in
the patch below (which I merged into the patch adding all the
comments).
I have added the above test as ISA2+pooncelock+pooncelock+pombonce.litmus,
with the Result: of Sometimes with you (Alan) as author and with your
Signed-off-by -- please let me know if you would prefer some other
approach.
Please change the Result: when sending the proposed patch. Or please let
me know if you would like me to apply the forward-port that Akira sent,
in which case I will add the Result: change to that patch. Or for that
matter, Akira might repost his forward-port of your patch with this change.
Thanx, Paul
------------------------------------------------------------------------
commit b2950420e1154131c0667f1ac58666bad3a06a69
Author: Paul E. McKenney <paul...@linux.vnet.ibm.com>
Date: Thu Feb 15 10:35:25 2018 -0800
fixup! EXP litmus_tests: Add comments explaining tests' purposes
Signed-off-by: Paul E. McKenney <paul...@linux.vnet.ibm.com>
diff --git
a/tools/memory-model/litmus-tests/Z6.0+pooncelock+pooncelock+pombonce.litmus
b/tools/memory-model/litmus-tests/Z6.0+pooncelock+pooncelock+pombonce.litmus
index fad47258a3e3..95890669859b 100644
--- a/tools/memory-model/litmus-tests/Z6.0+pooncelock+pooncelock+pombonce.litmus
+++ b/tools/memory-model/litmus-tests/Z6.0+pooncelock+pooncelock+pombonce.litmus
@@ -1,7 +1,7 @@
C Z6.0+pooncelock+pooncelock+pombonce
(*
- * Result: Never
+ * Result: Somtimes
*
* This example demonstrates that a pair of accesses made by different
* processes each while holding a given lock will not necessarily be
