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 CA7B0C47425 for ; Mon, 5 Oct 2020 15:16:45 +0000 (UTC) Received: from vger.kernel.org (vger.kernel.org [23.128.96.18]) by mail.kernel.org (Postfix) with ESMTP id A667F208C7 for ; Mon, 5 Oct 2020 15:16:45 +0000 (UTC) Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1727045AbgJEPQk (ORCPT ); Mon, 5 Oct 2020 11:16:40 -0400 Received: from netrider.rowland.org ([192.131.102.5]:55631 "HELO netrider.rowland.org" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with SMTP id S1726617AbgJEPQk (ORCPT ); Mon, 5 Oct 2020 11:16:40 -0400 Received: (qmail 379940 invoked by uid 1000); 5 Oct 2020 11:16:39 -0400 Date: Mon, 5 Oct 2020 11:16:39 -0400 From: Alan Stern To: Will Deacon Cc: "Paul E. McKenney" , parri.andrea@gmail.com, 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, joel@joelfernandes.org, 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: <20201005151639.GE376584@rowland.harvard.edu> 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> <20201005082002.GA23216@willie-the-truck> <20201005091247.GA23575@willie-the-truck> <20201005142351.GB376584@rowland.harvard.edu> <20201005151313.GA23892@willie-the-truck> MIME-Version: 1.0 Content-Type: text/plain; charset=us-ascii Content-Disposition: inline In-Reply-To: <20201005151313.GA23892@willie-the-truck> 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 04:13:13PM +0100, Will Deacon wrote: > > The failure to recognize the dependency in P0 should be considered a > > combined limitation of the memory model and herd7. It's not a simple > > mistake that can be fixed by a small rewrite of herd7; rather it's a > > deliberate choice we made based on herd7's inherent design. We > > explicitly said that control dependencies extend only to the code in the > > branches of an "if" statement; anything beyond the end of the statement > > is not considered to be dependent. > > Interesting. How does this interact with loops that are conditionally broken > out of, e.g. a relaxed cmpxchg() loop or an smp_cond_load_relaxed() call > prior to a WRITE_ONCE()? Heh -- We finesse this issue by not supporting loops at all! :-) Alan