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 6C9ECC41604 for ; Wed, 7 Oct 2020 22:38:54 +0000 (UTC) Received: from vger.kernel.org (vger.kernel.org [23.128.96.18]) by mail.kernel.org (Postfix) with ESMTP id 1ED7720872 for ; Wed, 7 Oct 2020 22:38:54 +0000 (UTC) DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/simple; d=kernel.org; s=default; t=1602110334; bh=s+E4diQaUoles/wvU02TGDNEIMhFsUXsvArP98/GAJY=; h=Date:From:To:Cc:Subject:Reply-To:References:In-Reply-To:List-ID: From; b=IzmO4Z9YzRJkcU2X/fKdW62D0oJhnGHLl7mjoZbG06PzlmVcn6K3ev9z5PtLeq1pZ og2YDt0Mxr0St1ybHCgYtyzyPTRCSFegHDlT7UjFSnbOf6leudmKlT0acuGNWdGQ0a CanYVtfCdezE2s4BEH+8IPhAwG95vRbXHPHf78Ss= Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1728885AbgJGWix (ORCPT ); Wed, 7 Oct 2020 18:38:53 -0400 Received: from mail.kernel.org ([198.145.29.99]:51028 "EHLO mail.kernel.org" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1728339AbgJGWiw (ORCPT ); Wed, 7 Oct 2020 18:38:52 -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 7C2702083B; Wed, 7 Oct 2020 22:38:51 +0000 (UTC) DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/simple; d=kernel.org; s=default; t=1602110331; bh=s+E4diQaUoles/wvU02TGDNEIMhFsUXsvArP98/GAJY=; h=Date:From:To:Cc:Subject:Reply-To:References:In-Reply-To:From; b=encrKLzgTu9qv8pgWJTw5SYUYRj3dFE75oPzVPpNleQKgHvV3t5a8pfmC+plxH1wK 0lLPDKG9OMcBpHnhYmuOm4WFbAN2xHZMtHDmMCjNwbggFOSmnoiJDMCQH0nof+CRt8 wiuJdYO5vgj7HCwPk6z706LyuxoAlOB9yGs/VYgM= Received: by paulmck-ThinkPad-P72.home (Postfix, from userid 1000) id 3F2123522FA4; Wed, 7 Oct 2020 15:38:51 -0700 (PDT) Date: Wed, 7 Oct 2020 15:38:51 -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: <20201007223851.GV29330@paulmck-ThinkPad-P72> Reply-To: paulmck@kernel.org References: <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> <20201007175040.GQ29330@paulmck-ThinkPad-P72> <20201007194050.GC468921@rowland.harvard.edu> MIME-Version: 1.0 Content-Type: text/plain; charset=us-ascii Content-Disposition: inline In-Reply-To: <20201007194050.GC468921@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 Wed, Oct 07, 2020 at 03:40:50PM -0400, Alan Stern wrote: > On Wed, Oct 07, 2020 at 10:50:40AM -0700, Paul E. McKenney wrote: > > 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 > > Let's change this to: > > manual/kernel: Add LB data dependency test with no intermediate variable > > Without that extra qualification, people reading just the title would > wonder why we need a simple LB litmus test in the archive. > > > > > 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. > > You changed this comment! It should have remained the way it was: I might get this right sooner or later. You never know. Like this? Thanx, Paul ------------------------------------------------------------------------ commit 5b6a4ff2c8ad25fc77f4151e71e6cbd8f3268d7b 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..e9e24e0 --- /dev/null +++ b/manual/kernel/C-LB+mb+data.litmus @@ -0,0 +1,27 @@ +C LB+mb+data +(* + * 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)