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SubjectRe: Trial of conflict resolution of Alan's patch
On Thu, Feb 15, 2018 at 11:29:14AM -0800, Paul E. McKenney wrote:
> 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 <paulmck@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 <paulmck@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

nit: s/Somtimes/Sometimes

Andrea


> *
> * This example demonstrates that a pair of accesses made by different
> * processes each while holding a given lock will not necessarily be
>

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