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=-2.0 required=3.0 tests=DKIM_INVALID,DKIM_SIGNED, 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 B367DC34047 for ; Tue, 18 Feb 2020 20:12:32 +0000 (UTC) Received: from vger.kernel.org (vger.kernel.org [209.132.180.67]) by mail.kernel.org (Postfix) with ESMTP id 807E22176D for ; Tue, 18 Feb 2020 20:12:32 +0000 (UTC) Authentication-Results: mail.kernel.org; dkim=fail reason="signature verification failed" (2048-bit key) header.d=infradead.org header.i=@infradead.org header.b="J+op2zkh" Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1726415AbgBRUMc (ORCPT ); Tue, 18 Feb 2020 15:12:32 -0500 Received: from merlin.infradead.org ([205.233.59.134]:35028 "EHLO merlin.infradead.org" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1726403AbgBRUMc (ORCPT ); Tue, 18 Feb 2020 15:12:32 -0500 DKIM-Signature: v=1; a=rsa-sha256; q=dns/txt; c=relaxed/relaxed; d=infradead.org; s=merlin.20170209; h=In-Reply-To:Content-Type:MIME-Version: References:Message-ID:Subject:Cc:To:From:Date:Sender:Reply-To: Content-Transfer-Encoding:Content-ID:Content-Description; bh=JUY9aCZNkGp5r3GhAmz34nl2t/YX1uUl7G5Ml5dOHcY=; b=J+op2zkhQrmmZG0CHmPk1/T3Kh O/GGJe4A5octVekXAoFs3Qp/NxM8W/vsthAB3yFUP8TqgbFjuQh/gPj5wNWLWS8zoOXQNqqReRtE7 9oiA/69drvLkRivZl/J81Y3OCoZ1OaYf6H+VOEmSIfuSUjWDS/GqFn0nab6ZSStW9p/ORciSXLVL6 1hS//7tFMZ3ecIXAR5sNlEeqSN7BRUlugD48vXsm6GVlIxluASNfl0swbmoFGYDn+oTtFOhn/KF/P 10oTe+MeeaR904MMBDg5Y1zpvF7OLCOLufdUQGMX8VSdMjbcVfnetbi8sMdEb0UgdxCrux76b9dgg HeR1Fq3A==; Received: from j217100.upc-j.chello.nl ([24.132.217.100] helo=worktop.programming.kicks-ass.net) by merlin.infradead.org with esmtpsa (Exim 4.92.3 #3 (Red Hat Linux)) id 1j49DZ-0005mU-Ks; Tue, 18 Feb 2020 20:11:41 +0000 Received: by worktop.programming.kicks-ass.net (Postfix, from userid 1000) id 58E7D980E53; Tue, 18 Feb 2020 21:11:42 +0100 (CET) Date: Tue, 18 Feb 2020 21:11:42 +0100 From: Peter Zijlstra To: "Paul E. McKenney" Cc: 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, rostedt@goodmis.org, 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: <20200218201142.GF11457@worktop.programming.kicks-ass.net> 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> MIME-Version: 1.0 Content-Type: text/plain; charset=us-ascii Content-Disposition: inline In-Reply-To: <20200218162719.GE2935@paulmck-ThinkPad-P72> User-Agent: Mutt/1.10.1 (2018-07-13) Sender: rcu-owner@vger.kernel.org Precedence: bulk List-ID: X-Mailing-List: rcu@vger.kernel.org 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.