From: Luc Maranget <luc.maranget@inria.fr>
To: Alan Stern <stern@rowland.harvard.edu>
Cc: Akira Yokosawa <akiyks@gmail.com>,
"Paul E. McKenney" <paulmck@kernel.org>,
parri.andrea@gmail.com, will@kernel.org, peterz@infradead.org,
boqun.feng@gmail.com, npiggin@gmail.com, dhowells@redhat.com,
j.alglave@ucl.ac.uk, luc.maranget@inria.fr, dlustig@nvidia.com,
joel@joelfernandes.org, viro@zeniv.linux.org.uk,
linux-kernel@vger.kernel.org, linux-arch@vger.kernel.org
Subject: Re: Bug in herd7 [Was: Re: Litmus test for question from Al Viro]
Date: Mon, 5 Oct 2020 17:15:57 +0200 [thread overview]
Message-ID: <20201005151557.4bcxumreoekgwmsa@yquem.inria.fr> (raw)
In-Reply-To: <20201003171338.GA323226@rowland.harvard.edu>
> On Sun, Oct 04, 2020 at 12:16:31AM +0900, Akira Yokosawa wrote:
> > Hi Alan,
> >
> > Just a minor nit in the litmus test.
> >
> > On Sat, 3 Oct 2020 09:22:12 -0400, Alan Stern wrote:
> > > To expand on my statement about the LKMM's weakness regarding control
> > > constructs, here is a litmus test to illustrate the issue. You might
> > > want to add this to one of the archives.
> > >
> > > Alan
> > >
> > > C crypto-control-data
> > > (*
> > > * LB plus crypto-control-data plus data
> > > *
> > > * Expected result: allowed
> > > *
> > > * This is an example of OOTA and we would like it to be forbidden.
> > > * The WRITE_ONCE in P0 is both data-dependent and (at the hardware level)
> > > * control-dependent on the preceding READ_ONCE. But the dependencies are
> > > * hidden by the form of the conditional control construct, hence the
> > > * name "crypto-control-data". The memory model doesn't recognize them.
> > > *)
> > >
> > > {}
> > >
> > > P0(int *x, int *y)
> > > {
> > > int r1;
> > >
> > > r1 = 1;
> > > if (READ_ONCE(*x) == 0)
> > > r1 = 0;
> > > WRITE_ONCE(*y, r1);
> > > }
> > >
> > > P1(int *x, int *y)
> > > {
> > > WRITE_ONCE(*x, READ_ONCE(*y));
> >
> > Looks like this one-liner doesn't provide data-dependency of y -> x on herd7.
>
> You're right. This is definitely a bug in herd7.
>
> Luc, were you aware of this?
Hi Alan,
No I was not aware of it. Now I am, the bug is normally fixed in the master branch of herd git deposit.
<https://github.com/herd/herdtools7/commit/0f3f8188a326d5816a82fb9970fcd209a2678859>
Thanks for the report.
--Luc
next prev parent reply other threads:[~2020-10-05 15:16 UTC|newest]
Thread overview: 52+ messages / expand[flat|nested] mbox.gz Atom feed top
2020-10-01 4:51 Litmus test for question from Al Viro Paul E. McKenney
2020-10-01 16:15 ` Alan Stern
2020-10-01 16:36 ` Al Viro
2020-10-01 18:39 ` Alan Stern
2020-10-01 19:29 ` Al Viro
2020-10-01 21:30 ` Paul E. McKenney
2020-10-03 2:01 ` Alan Stern
2020-10-03 13:22 ` Alan Stern
2020-10-03 15:16 ` Akira Yokosawa
2020-10-03 17:13 ` Bug in herd7 [Was: Re: Litmus test for question from Al Viro] Alan Stern
2020-10-03 22:50 ` Akira Yokosawa
2020-10-04 1:40 ` [PATCH] tools: memory-model: Document that the LKMM can easily miss control dependencies Alan Stern
2020-10-04 21:07 ` joel
2020-10-04 23:12 ` Paul E. McKenney
2020-10-05 15:15 ` Luc Maranget [this message]
2020-10-05 15:53 ` Bug in herd7 [Was: Re: Litmus test for question from Al Viro] Alan Stern
2020-10-05 16:52 ` Paul E. McKenney
2020-10-05 18:19 ` Alan Stern
2020-10-05 19:18 ` Paul E. McKenney
2020-10-05 19:48 ` Alan Stern
2020-10-06 16:39 ` Paul E. McKenney
2020-10-06 17:05 ` Alan Stern
2020-10-07 17:50 ` Paul E. McKenney
2020-10-07 19:40 ` Alan Stern
2020-10-07 22:38 ` Paul E. McKenney
2020-10-08 2:25 ` Alan Stern
2020-10-08 2:50 ` Paul E. McKenney
2020-10-08 14:01 ` Alan Stern
2020-10-08 18:32 ` Paul E. McKenney
2020-10-05 15:54 ` Paul E. McKenney
2020-10-04 23:31 ` Litmus test for question from Al Viro Paul E. McKenney
2020-10-05 2:38 ` Alan Stern
2020-10-05 8:20 ` Will Deacon
2020-10-05 9:12 ` Will Deacon
2020-10-05 14:01 ` Paul E. McKenney
2020-10-05 14:23 ` Alan Stern
2020-10-05 15:13 ` Will Deacon
2020-10-05 15:16 ` Alan Stern
2020-10-05 15:35 ` Peter Zijlstra
2020-10-05 15:49 ` Paul E. McKenney
2020-10-05 14:16 ` Alan Stern
2020-10-05 14:03 ` Paul E. McKenney
2020-10-05 14:24 ` Alan Stern
2020-10-05 14:44 ` joel
2020-10-05 15:55 ` Paul E. McKenney
2020-10-05 8:36 ` David Laight
2020-10-05 13:59 ` Paul E. McKenney
2020-10-03 16:08 ` joel
2020-10-03 16:11 ` joel
2020-10-04 23:13 ` Paul E. McKenney
2020-10-03 2:35 ` Jon Masters
2020-10-04 23:32 ` Paul E. McKenney
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