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 79E2EC46466 for ; Mon, 5 Oct 2020 15:55:24 +0000 (UTC) Received: from vger.kernel.org (vger.kernel.org [23.128.96.18]) by mail.kernel.org (Postfix) with ESMTP id 42B1B20663 for ; Mon, 5 Oct 2020 15:55:24 +0000 (UTC) DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/simple; d=kernel.org; s=default; t=1601913324; bh=mZz6DAQ3cgu9t/sQQtA5zwSd6+RiP24elAE0E1TFrBk=; h=Date:From:To:Cc:Subject:Reply-To:References:In-Reply-To:List-ID: From; b=iTqFyjmOYDK8TDfC3CX1s2Bzb1j14rRUY3s5cSJXYhV026iXTXoR5WgPAFn9dw0bM iziN6vg8AN0YwLzHJkcB/BPseXEPZgwbH4SiaAIAV2HjVCRBkK/D6qO/YbWiefkw48 ucjeZEmu9OKNuGjI84NHl37PoDQMzbh6IsSm08zQ= Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1728821AbgJEPzX (ORCPT ); Mon, 5 Oct 2020 11:55:23 -0400 Received: from mail.kernel.org ([198.145.29.99]:54696 "EHLO mail.kernel.org" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1726248AbgJEPzX (ORCPT ); Mon, 5 Oct 2020 11:55:23 -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 41C9820639; Mon, 5 Oct 2020 15:55:22 +0000 (UTC) DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/simple; d=kernel.org; s=default; t=1601913322; bh=mZz6DAQ3cgu9t/sQQtA5zwSd6+RiP24elAE0E1TFrBk=; h=Date:From:To:Cc:Subject:Reply-To:References:In-Reply-To:From; b=OpjZLwMr072lbwCtvS+BbbOGRxJ5vLovBfmn5K6qnUa1rOUGWgVfp0ZHu36LmwtIM J/5W2nyl0N4Jiy19hrZmVqUWSeydU7MZBOnRqntDxawa0zHqKpQYsM9TJVU4stQoDX c1B8fzcMay9TlPoAYzwkX4w8uHRWnrOENJlZZuEg= Received: by paulmck-ThinkPad-P72.home (Postfix, from userid 1000) id 0B6B0352301E; Mon, 5 Oct 2020 08:55:22 -0700 (PDT) Date: Mon, 5 Oct 2020 08:55:22 -0700 From: "Paul E. McKenney" To: joel@joelfernandes.org Cc: Alan Stern , 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, akiyks@gmail.com, dlustig@nvidia.com, viro@zeniv.linux.org.uk, linux-kernel@vger.kernel.org, linux-arch@vger.kernel.org Subject: Re: Litmus test for question from Al Viro Message-ID: <20201005155521.GA29330@paulmck-ThinkPad-P72> Reply-To: paulmck@kernel.org References: <20201001045116.GA5014@paulmck-ThinkPad-P72> <20201001161529.GA251468@rowland.harvard.edu> <20201001213048.GF29330@paulmck-ThinkPad-P72> <20201003132212.GB318272@rowland.harvard.edu> <20201004233146.GP29330@paulmck-ThinkPad-P72> <20201005023846.GA359428@rowland.harvard.edu> <20201005140353.GW29330@paulmck-ThinkPad-P72> <20201005144422.GB524504@google.com> MIME-Version: 1.0 Content-Type: text/plain; charset=us-ascii Content-Disposition: inline In-Reply-To: <20201005144422.GB524504@google.com> User-Agent: Mutt/1.9.4 (2018-02-28) Precedence: bulk List-ID: X-Mailing-List: linux-kernel@vger.kernel.org On Mon, Oct 05, 2020 at 10:44:22AM -0400, joel@joelfernandes.org wrote: > On Mon, Oct 05, 2020 at 07:03:53AM -0700, Paul E. McKenney wrote: > > On Sun, Oct 04, 2020 at 10:38:46PM -0400, Alan Stern wrote: > > > On Sun, Oct 04, 2020 at 04:31:46PM -0700, Paul E. McKenney wrote: > > > > Nice simple example! How about like this? > > > > > > > > Thanx, Paul > > > > > > > > ------------------------------------------------------------------------ > > > > > > > > commit c964f404eabe4d8ce294e59dda713d8c19d340cf > > > > Author: Alan Stern > > > > Date: Sun Oct 4 16:27:03 2020 -0700 > > > > > > > > manual/kernel: Add a litmus test with a hidden dependency > > > > > > > > This commit adds a litmus test that has a data dependency that can be > > > > hidden by control flow. In this test, both the taken and the not-taken > > > > branches of an "if" statement must be accounted for in order to properly > > > > analyze the litmus test. But herd7 looks only at individual executions > > > > in isolation, so fails to see the dependency. > > > > > > > > Signed-off-by: Alan Stern > > > > Signed-off-by: Paul E. McKenney > > > > > > > > diff --git a/manual/kernel/crypto-control-data.litmus b/manual/kernel/crypto-control-data.litmus > > > > new file mode 100644 > > > > index 0000000..6baecf9 > > > > --- /dev/null > > > > +++ b/manual/kernel/crypto-control-data.litmus > > > > @@ -0,0 +1,31 @@ > > > > +C crypto-control-data > > > > +(* > > > > + * LB plus crypto-control-data plus data > > > > + * > > > > + * Result: Sometimes > > > > + * > > > > + * 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)); > > > > +} > > > > + > > > > +exists (0:r1=1) > > > > > > Considering the bug in herd7 pointed out by Akira, we should rewrite P1 as: > > > > > > P1(int *x, int *y) > > > { > > > int r2; > > > > > > r = READ_ONCE(*y); > > > WRITE_ONCE(*x, r2); > > > } > > > > > > Other than that, this is fine. > > > > Updated as suggested by Will, like this? > > LGTM as well, > > FWIW: > Reviewed-by: Joel Fernandes (Google) Applied, thank you all! This has been pushed to my github litmus archive. Thanx, Paul > thanks, > > - Joel > > > > > Thanx, Paul > > > > ------------------------------------------------------------------------ > > > > commit adf43667b702582331d68acdf3732a6a017a182c > > Author: Alan Stern > > Date: Sun Oct 4 16:27:03 2020 -0700 > > > > manual/kernel: Add a litmus test with a hidden dependency > > > > This commit adds a litmus test that has a data dependency that can be > > hidden by control flow. In this test, both the taken and the not-taken > > branches of an "if" statement must be accounted for in order to properly > > analyze the litmus test. But herd7 looks only at individual executions > > in isolation, so fails to see the dependency. > > > > Signed-off-by: Alan Stern > > Signed-off-by: Paul E. McKenney > > > > diff --git a/manual/kernel/crypto-control-data.litmus b/manual/kernel/crypto-control-data.litmus > > new file mode 100644 > > index 0000000..cdcdec9 > > --- /dev/null > > +++ b/manual/kernel/crypto-control-data.litmus > > @@ -0,0 +1,34 @@ > > +C crypto-control-data > > +(* > > + * LB plus crypto-control-data plus data > > + * > > + * Result: Sometimes > > + * > > + * 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) > > +{ > > + int r2; > > + > > + r2 = READ_ONCE(*y); > > + WRITE_ONCE(*x, r2); > > +} > > + > > +exists (0:r1=1)