From mboxrd@z Thu Jan 1 00:00:00 1970 Return-Path: X-Spam-Checker-Version: SpamAssassin 3.4.0 (2014-02-07) on aws-us-west-2-korg-lkml-1.web.codeaurora.org X-Spam-Level: X-Spam-Status: No, score=-5.3 required=3.0 tests=BAYES_00, HEADER_FROM_DIFFERENT_DOMAINS,MAILING_LIST_MULTI,SPF_HELO_NONE,SPF_PASS, USER_AGENT_SANE_1 autolearn=no autolearn_force=no version=3.4.0 Received: from mail.kernel.org (mail.kernel.org [198.145.29.99]) by smtp.lore.kernel.org (Postfix) with ESMTP id 5B596C4727D for ; Mon, 5 Oct 2020 19:48:37 +0000 (UTC) Received: from vger.kernel.org (vger.kernel.org [23.128.96.18]) by mail.kernel.org (Postfix) with ESMTP id 018CF208C3 for ; Mon, 5 Oct 2020 19:48:36 +0000 (UTC) Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1729508AbgJETsg (ORCPT ); Mon, 5 Oct 2020 15:48:36 -0400 Received: from netrider.rowland.org ([192.131.102.5]:52837 "HELO netrider.rowland.org" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with SMTP id S1729428AbgJETsf (ORCPT ); Mon, 5 Oct 2020 15:48:35 -0400 Received: (qmail 391029 invoked by uid 1000); 5 Oct 2020 15:48:34 -0400 Date: Mon, 5 Oct 2020 15:48:34 -0400 From: Alan Stern To: "Paul E. McKenney" Cc: Luc Maranget , Akira Yokosawa , 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] Message-ID: <20201005194834.GB389867@rowland.harvard.edu> References: <20201001161529.GA251468@rowland.harvard.edu> <20201001213048.GF29330@paulmck-ThinkPad-P72> <20201003132212.GB318272@rowland.harvard.edu> <045c643f-6a70-dfdf-2b1e-f369a667f709@gmail.com> <20201003171338.GA323226@rowland.harvard.edu> <20201005151557.4bcxumreoekgwmsa@yquem.inria.fr> <20201005155310.GH376584@rowland.harvard.edu> <20201005165223.GB29330@paulmck-ThinkPad-P72> <20201005181949.GA387079@rowland.harvard.edu> <20201005191801.GF29330@paulmck-ThinkPad-P72> MIME-Version: 1.0 Content-Type: text/plain; charset=us-ascii Content-Disposition: inline In-Reply-To: <20201005191801.GF29330@paulmck-ThinkPad-P72> User-Agent: Mutt/1.10.1 (2018-07-13) Precedence: bulk List-ID: X-Mailing-List: linux-kernel@vger.kernel.org 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