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=-12.3 required=3.0 tests=BAYES_00,DKIMWL_WL_HIGH, DKIM_SIGNED,DKIM_VALID,DKIM_VALID_AU,INCLUDES_PATCH,MAILING_LIST_MULTI, SIGNED_OFF_BY,SPF_HELO_NONE,SPF_PASS,URIBL_BLOCKED,USER_AGENT_SANE_1 autolearn=unavailable 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 E60A4C47095 for ; Wed, 7 Oct 2020 17:50:43 +0000 (UTC) Received: from vger.kernel.org (vger.kernel.org [23.128.96.18]) by mail.kernel.org (Postfix) with ESMTP id 8E73921707 for ; Wed, 7 Oct 2020 17:50:43 +0000 (UTC) DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/simple; d=kernel.org; s=default; t=1602093043; bh=2r8QhxaGVcFKHatlMGugEjl6fF8fB3vwQqJtndwDl5E=; h=Date:From:To:Cc:Subject:Reply-To:References:In-Reply-To:List-ID: From; b=t148BT16SKu9EdT2rY4fKBLIjRt8FHX7rwwZjHFWrhDkj/vwehOV5DWxU799K+ny9 6P1MRZJPCvKIVhbZnQ+PXctV6D3sBzodmgwy0RZFE95/COzgOWlOvxr+wk5jA1zeM/ nFfGyL7lnSSt6Nt+aoSniUiDeC9Ko8Nngt7v8btM= Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1728623AbgJGRum (ORCPT ); Wed, 7 Oct 2020 13:50:42 -0400 Received: from mail.kernel.org ([198.145.29.99]:47032 "EHLO mail.kernel.org" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1728564AbgJGRum (ORCPT ); Wed, 7 Oct 2020 13:50:42 -0400 Received: from paulmck-ThinkPad-P72.home (50-39-104-11.bvtn.or.frontiernet.net [50.39.104.11]) (using TLSv1.2 with cipher ECDHE-RSA-AES256-GCM-SHA384 (256/256 bits)) (No client certificate requested) by mail.kernel.org (Postfix) with ESMTPSA id 09AE02168B; Wed, 7 Oct 2020 17:50:41 +0000 (UTC) DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/simple; d=kernel.org; s=default; t=1602093041; bh=2r8QhxaGVcFKHatlMGugEjl6fF8fB3vwQqJtndwDl5E=; h=Date:From:To:Cc:Subject:Reply-To:References:In-Reply-To:From; b=yM/7cuc1H3gsoNSL+teHEhXh+jzDACIWVs9igk4et0EMgOoIn0u2wt6pU1xrcNB8L NuzC3H/Jm9QEB/C7icQV6pPSbz3dIf7m658lTBVh3IEU6x8zyhofbEoruZReuFq2Y7 vx6WwgatunUxzNeh3Ibl6irgzU2QtIpC4XwZu41s= Received: by paulmck-ThinkPad-P72.home (Postfix, from userid 1000) id 9FCD33522FA4; Wed, 7 Oct 2020 10:50:40 -0700 (PDT) Date: Wed, 7 Oct 2020 10:50:40 -0700 From: "Paul E. McKenney" To: Alan Stern 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: <20201007175040.GQ29330@paulmck-ThinkPad-P72> Reply-To: paulmck@kernel.org References: <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> <20201005194834.GB389867@rowland.harvard.edu> <20201006163954.GM29330@paulmck-ThinkPad-P72> <20201006170525.GA423499@rowland.harvard.edu> MIME-Version: 1.0 Content-Type: text/plain; charset=us-ascii Content-Disposition: inline In-Reply-To: <20201006170525.GA423499@rowland.harvard.edu> User-Agent: Mutt/1.9.4 (2018-02-28) Precedence: bulk List-ID: X-Mailing-List: linux-kernel@vger.kernel.org On Tue, Oct 06, 2020 at 01:05:25PM -0400, Alan Stern wrote: > On Tue, Oct 06, 2020 at 09:39:54AM -0700, Paul E. McKenney wrote: > > On Mon, Oct 05, 2020 at 03:48:34PM -0400, Alan Stern wrote: > > > 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. > > > > Thank you for looking this over! > > > > Like this, then? > > > > Thanx, Paul > > > > ------------------------------------------------------------------------ > > > > commit 51898676302d8ebc93856209f7c587f1ac0fdd11 > > Author: Alan Stern > > Date: Tue Oct 6 09:38:37 2020 -0700 > > > > manual/kernel: Add LB+mb+data litmus test > > > > 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. > > Shouldn't the commit message be different from the actual contents of > the update? It's supposed to explain why the update was made, not just > say what it does. How about this: > > Test whether herd7 can detect a data dependency when there is no > intermediate local variable, as in WRITE_ONCE(*x, READ_ONCE(*y)). > Commit 0f3f8188a326 fixed an oversight which caused such dependencies > to be missed. Much better, thank you! I added "in herdtools" just in case someone was confused enough to look for this commit in the Linux kernel or some such. Which I should have done more explicitly in the original, to be sure. > > Signed-off-by: Alan Stern > > Signed-off-by: Paul E. McKenney > > > > diff --git a/manual/kernel/C-LB+mb+data.litmus b/manual/kernel/C-LB+mb+data.litmus > > new file mode 100644 > > index 0000000..673eec9 > > --- /dev/null > > +++ b/manual/kernel/C-LB+mb+data.litmus > > @@ -0,0 +1,29 @@ > > +C LB+mb+data.litmus > > Do you normally put ".litmus" at the end of test names? I leave it out, > including it only in the filename. No, I don't, and thank you for catching this. > > +(* > > + * LB plus crypto-mb-data plus data. > > As I said earlier, the actual pattern is LB+mb+data. There's nothing > "crypto" about this litmus test (for example, no control dependencies). > > Besides, it hardly seems worthwhile making the first comment line a > repeat of the test name immediately above it. Just leave it out. Done! ;-) > > + * > > + * Result: Never > > + * > > + * 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) > > +{ > > + WRITE_ONCE(*x, READ_ONCE(*y)); > > +} > > + > > +exists (0:r1=1) > > Otherwise okay. And here is the updated version. Thanx, Paul ------------------------------------------------------------------------ commit b7cd60d4b41ad56b32b36b978488f509c4f7e228 Author: Alan Stern Date: Tue Oct 6 09:38:37 2020 -0700 manual/kernel: Add LB+mb+data litmus test Test whether herd7 can detect a data dependency when there is no intermediate local variable, as in WRITE_ONCE(*x, READ_ONCE(*y)). Commit 0f3f8188a326 in herdtools fixed an oversight which caused such dependencies to be missed. Signed-off-by: Alan Stern Signed-off-by: Paul E. McKenney diff --git a/manual/kernel/C-LB+mb+data.litmus b/manual/kernel/C-LB+mb+data.litmus new file mode 100644 index 0000000..0cf9a7a --- /dev/null +++ b/manual/kernel/C-LB+mb+data.litmus @@ -0,0 +1,27 @@ +C LB+mb+data +(* + * Result: Never + * + * Test whether herd7 can detect a data dependency when there is no + * intermediate local variable, as in WRITE_ONCE(*x, READ_ONCE(*y)). + * Commit 0f3f8188a326 in herdtools fixed an oversight which caused such + * dependencies to be missed. + *) + +{} + +P0(int *x, int *y) +{ + int r1; + + r1 = READ_ONCE(*x); + smp_mb(); + WRITE_ONCE(*y, r1); +} + +P1(int *x, int *y) +{ + WRITE_ONCE(*x, READ_ONCE(*y)); +} + +exists (0:r1=1)