linux-kernel - Re: [PATCH RFC tools/memory-model 2/5] tools/memory-model: Add litmus test for multicopy atomicity

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Message-Id: <20180419000630.GX26088@linux.vnet.ibm.com>
Date:   Wed, 18 Apr 2018 17:06:30 -0700
From:   "Paul E. McKenney" <paulmck@...ux.vnet.ibm.com>
To:     Andrea Parri <andrea.parri@...rulasolutions.com>
Cc:     linux-kernel@...r.kernel.org, linux-arch@...r.kernel.org,
        mingo@...nel.org, stern@...land.harvard.edu,
        parri.andrea@...il.com, will.deacon@....com, peterz@...radead.org,
        boqun.feng@...il.com, npiggin@...il.com, dhowells@...hat.com,
        j.alglave@....ac.uk, luc.maranget@...ia.fr, akiyks@...il.com
Subject: Re: [PATCH RFC tools/memory-model 2/5] tools/memory-model: Add
 litmus test for multicopy atomicity

On Wed, Apr 18, 2018 at 11:40:33AM +0200, Andrea Parri wrote:
> On Mon, Apr 16, 2018 at 09:22:48AM -0700, Paul E. McKenney wrote:
> > This commit adds a litmus test suggested by Alan Stern that is forbidden
> > on multicopy atomic systems, but allowed on non-multicopy atomic systems.
> > Note that other-multicopy atomic systems are examples of non-multicopy
> > atomic systems.
> > 
> > Suggested-by: Alan Stern <stern@...land.harvard.edu>
> > Signed-off-by: Paul E. McKenney <paulmck@...ux.vnet.ibm.com>
> > ---
> >  .../litmus-tests/SB+poonceoncescoh.litmus          | 31 ++++++++++++++++++++++
> >  1 file changed, 31 insertions(+)
> >  create mode 100644 tools/memory-model/litmus-tests/SB+poonceoncescoh.litmus
> 
> We seem to be missing an entry in litmus-tests/README...

We are, and I will add one once ...

> > diff --git a/tools/memory-model/litmus-tests/SB+poonceoncescoh.litmus b/tools/memory-model/litmus-tests/SB+poonceoncescoh.litmus
> > new file mode 100644
> > index 000000000000..991a2d6dec63
> > --- /dev/null
> > +++ b/tools/memory-model/litmus-tests/SB+poonceoncescoh.litmus
> > @@ -0,0 +1,31 @@
> > +C SB+poonceoncescoh
> > +
> > +(*
> > + * Result: Sometimes
> > + *
> > + * This litmus test demonstrates that LKMM is not multicopy atomic.
> > + *)
> > +
> > +{}
> > +
> > +P0(int *x, int *y)
> > +{
> > +	int r1;
> > +	int r2;
> > +
> > +	WRITE_ONCE(*x, 1);
> > +	r1 = READ_ONCE(*x);
> > +	r2 = READ_ONCE(*y);
> > +}
> > +
> > +P1(int *x, int *y)
> > +{
> > +	int r3;
> > +	int r4;
> > +
> > +	WRITE_ONCE(*y, 1);
> > +	r3 = READ_ONCE(*y);
> > +	r4 = READ_ONCE(*x);
> > +}
> > +
> > +exists (0:r2=0 /\ 1:r4=0 /\ 0:r1=1 /\ 1:r3=1)
> 
> This test has a normalised name:  why don't use that?

... we come to agreement on the documentation on how to produce a
normalized name given a standard litmus test.

Ditto for the tests whose names include the string "silsil", but
those involve locking so might be considered lower priority.

							Thanx, Paul