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=-10.3 required=3.0 tests=BAYES_00, HEADER_FROM_DIFFERENT_DOMAINS,MAILING_LIST_MULTI,MENTIONS_GIT_HOSTING, SPF_HELO_NONE,SPF_PASS,USER_AGENT_SANE_1 autolearn=ham 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 A6F1AC4727F for ; Mon, 5 Oct 2020 15:16:44 +0000 (UTC) Received: from vger.kernel.org (vger.kernel.org [23.128.96.18]) by mail.kernel.org (Postfix) with ESMTP id 61039208B6 for ; Mon, 5 Oct 2020 15:16:44 +0000 (UTC) Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1726882AbgJEPQA (ORCPT ); Mon, 5 Oct 2020 11:16:00 -0400 Received: from mail2-relais-roc.national.inria.fr ([192.134.164.83]:59540 "EHLO mail2-relais-roc.national.inria.fr" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1726784AbgJEPQA (ORCPT ); Mon, 5 Oct 2020 11:16:00 -0400 From: Luc Maranget X-IronPort-AV: E=Sophos;i="5.77,338,1596492000"; d="scan'208";a="471039281" Received: from yquem.paris.inria.fr (HELO yquem.inria.fr) ([128.93.101.33]) by mail2-relais-roc.national.inria.fr with ESMTP; 05 Oct 2020 17:15:57 +0200 Received: by yquem.inria.fr (Postfix, from userid 18041) id D9085E1E95; Mon, 5 Oct 2020 17:15:57 +0200 (CEST) Date: Mon, 5 Oct 2020 17:15:57 +0200 To: Alan Stern Cc: Akira Yokosawa , "Paul E. McKenney" , 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] Message-ID: <20201005151557.4bcxumreoekgwmsa@yquem.inria.fr> References: <20201001045116.GA5014@paulmck-ThinkPad-P72> <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> MIME-Version: 1.0 Content-Type: text/plain; charset=utf-8 Content-Disposition: inline In-Reply-To: <20201003171338.GA323226@rowland.harvard.edu> User-Agent: NeoMutt/20170113 (1.7.2) Precedence: bulk List-ID: X-Mailing-List: linux-kernel@vger.kernel.org > 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. Thanks for the report. --Luc