From: Alan Stern <stern@rowland.harvard.edu>
To: "Paul E. McKenney" <paulmck@kernel.org>
Cc: Luc Maranget <luc.maranget@inria.fr>,
Akira Yokosawa <akiyks@gmail.com>,
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, 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 15:48:34 -0400 [thread overview]
Message-ID: <20201005194834.GB389867@rowland.harvard.edu> (raw)
In-Reply-To: <20201005191801.GF29330@paulmck-ThinkPad-P72>
On Mon, Oct 05, 2020 at 12:18:01PM -0700, Paul E. McKenney wrote:
> Aside from naming and comment, how about my adding the following?
>
> Thanx, Paul
>
> ------------------------------------------------------------------------
>
> C crypto-control-data-1
Let's call it something more along the lines of
dependencies-in-nested-expressions. Maybe you can think of something a
little more succinct, but that's the general idea of the test.
> (*
> * LB plus crypto-mb-data plus data.
The actual pattern is LB+mb+data.
> *
> * Result: Never
> *
> * This is an example of OOTA and we would like it to be forbidden.
> * If you want herd7 to get the right answer, you must use herdtools
> * 0f3f8188a326 (" [herd] Fix dependency definition") or later.
Versions of herd7 prior to commit 0f3f8188a326 ("[herd] Fix dependency
definition") recognize data dependencies only when they flow through an
intermediate local variable. Since the dependency in P1 doesn't, those
versions get the wrong answer for this test.
> *)
>
> {}
>
> P0(int *x, int *y)
> {
> int r1;
>
> r1 = READ_ONCE(*x);
> smp_mb();
> WRITE_ONCE(*y, r1);
> }
>
> P1(int *x, int *y)
> {
> int r2;
No need for r2.
>
> WRITE_ONCE(*x, READ_ONCE(*y));
> }
>
> exists (0:r1=1)
Alan
next prev parent reply other threads:[~2020-10-05 19:48 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 ` Bug in herd7 [Was: Re: Litmus test for question from Al Viro] Luc Maranget
2020-10-05 15:53 ` 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 [this message]
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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