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=-2.2 required=3.0 tests=HEADER_FROM_DIFFERENT_DOMAINS, MAILING_LIST_MULTI,SPF_HELO_NONE,SPF_PASS,USER_AGENT_SANE_2 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 1990EC3404C for ; Tue, 18 Feb 2020 22:45:09 +0000 (UTC) Received: from vger.kernel.org (vger.kernel.org [209.132.180.67]) by mail.kernel.org (Postfix) with ESMTP id EE1F724125 for ; Tue, 18 Feb 2020 22:45:08 +0000 (UTC) Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1726716AbgBRWpH (ORCPT ); Tue, 18 Feb 2020 17:45:07 -0500 Received: from mail.kernel.org ([198.145.29.99]:60396 "EHLO mail.kernel.org" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1726438AbgBRWpH (ORCPT ); Tue, 18 Feb 2020 17:45:07 -0500 Received: from gandalf.local.home (cpe-66-24-58-225.stny.res.rr.com [66.24.58.225]) (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 2BB682173E; Tue, 18 Feb 2020 22:45:05 +0000 (UTC) Date: Tue, 18 Feb 2020 17:45:03 -0500 From: Steven Rostedt To: "Paul E. McKenney" Cc: Peter Zijlstra , rcu@vger.kernel.org, linux-kernel@vger.kernel.org, kernel-team@fb.com, mingo@kernel.org, jiangshanlai@gmail.com, dipankar@in.ibm.com, akpm@linux-foundation.org, mathieu.desnoyers@efficios.com, josh@joshtriplett.org, tglx@linutronix.de, dhowells@redhat.com, edumazet@google.com, fweisbec@gmail.com, oleg@redhat.com, joel@joelfernandes.org Subject: Re: [PATCH tip/core/rcu 1/3] rcu-tasks: *_ONCE() for rcu_tasks_cbs_head Message-ID: <20200218174503.3d4e4750@gandalf.local.home> In-Reply-To: <20200218202226.GJ2935@paulmck-ThinkPad-P72> References: <20200215002446.GA15663@paulmck-ThinkPad-P72> <20200215002520.15746-1-paulmck@kernel.org> <20200217123851.GR14914@hirez.programming.kicks-ass.net> <20200217181615.GP2935@paulmck-ThinkPad-P72> <20200218075648.GW14914@hirez.programming.kicks-ass.net> <20200218162719.GE2935@paulmck-ThinkPad-P72> <20200218201142.GF11457@worktop.programming.kicks-ass.net> <20200218202226.GJ2935@paulmck-ThinkPad-P72> X-Mailer: Claws Mail 3.17.3 (GTK+ 2.24.32; x86_64-pc-linux-gnu) MIME-Version: 1.0 Content-Type: text/plain; charset=US-ASCII Content-Transfer-Encoding: 7bit Sender: linux-kernel-owner@vger.kernel.org Precedence: bulk List-ID: X-Mailing-List: linux-kernel@vger.kernel.org On Tue, 18 Feb 2020 12:22:26 -0800 "Paul E. McKenney" wrote: > On Tue, Feb 18, 2020 at 09:11:42PM +0100, Peter Zijlstra wrote: > > On Tue, Feb 18, 2020 at 08:27:19AM -0800, Paul E. McKenney wrote: > > > On Tue, Feb 18, 2020 at 08:56:48AM +0100, Peter Zijlstra wrote: > > > > > > I just took offence at the Changelog wording. It seems to suggest there > > > > actually is a problem, there is not. > > > > > > Quoting the changelog: "Not appropriate for backporting due to failure > > > being unlikely." > > > > That implies there is failure, however unlikely. > > > > In this particular case there is absolutely no failure, except perhaps > > in KCSAN. This patch is a pure annotation such that KCSAN can understand > > the code. > > > > Like said, I don't object to the actual patch, but I do think it is > > important to call out false negatives or to describe the actual problem > > found. > > I don't feel at all comfortable declaring that there is absolutely > no possibility of failure. Perhaps wording it like so: "There's know known issue with the current code, but the *_ONCE() annotations here makes KCSAN happy, allowing us to focus on KCSAN warnings that can help bring about known issues in other code that we can fix, without being distracted by KCSAN warnings that we do not see a problem with." ? -- Steve