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=-2.6 required=3.0 tests=DKIMWL_WL_HIGH,DKIM_SIGNED, DKIM_VALID,DKIM_VALID_AU,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 A21F5C3404B for ; Tue, 18 Feb 2020 20:22:28 +0000 (UTC) Received: from vger.kernel.org (vger.kernel.org [209.132.180.67]) by mail.kernel.org (Postfix) with ESMTP id 7C46724655 for ; Tue, 18 Feb 2020 20:22:28 +0000 (UTC) DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/simple; d=kernel.org; s=default; t=1582057348; bh=JMQSKrxWNzcCHhq6OGdWBkakZuwE3K//goQJu/DR/YY=; h=Date:From:To:Cc:Subject:Reply-To:References:In-Reply-To:List-ID: From; b=weeYBHr+5YZInOyAXGMxj8bNTMmaXHVdTsPtV8c9zWdEODOj3CewEFbexBDyg0GqT 6SndJyohrodu9mjscjbnma3DjHtNFjl0gI/rVmRN0K7rp4ltBZpNCr+rXGzskMxYdi 2j1rj4UX+DbV8Sohc8pBrBlGWBT5XndMs4bQnH4w= Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1726829AbgBRUW1 (ORCPT ); Tue, 18 Feb 2020 15:22:27 -0500 Received: from mail.kernel.org ([198.145.29.99]:54798 "EHLO mail.kernel.org" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1726403AbgBRUW1 (ORCPT ); Tue, 18 Feb 2020 15:22:27 -0500 Received: from paulmck-ThinkPad-P72.home (50-39-105-78.bvtn.or.frontiernet.net [50.39.105.78]) (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 726E92173E; Tue, 18 Feb 2020 20:22:26 +0000 (UTC) DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/simple; d=kernel.org; s=default; t=1582057346; bh=JMQSKrxWNzcCHhq6OGdWBkakZuwE3K//goQJu/DR/YY=; h=Date:From:To:Cc:Subject:Reply-To:References:In-Reply-To:From; b=zYDITELqb4XVqamQklQJ+27ONZKS9+wl9YQiwqVKfrJFH4oEHURio1O9wtkfpyC/T 0KwW9CcwbHr+zfgsfya9x1hIKybJ/mVpf2XAqYCMnsMXfN/1RYCyEj846pWkfsbG7b ylUUthKEieEi8TY31Xzx6uwDmPOLojXmH+1SSm80= Received: by paulmck-ThinkPad-P72.home (Postfix, from userid 1000) id 4A8403520856; Tue, 18 Feb 2020 12:22:26 -0800 (PST) Date: Tue, 18 Feb 2020 12:22:26 -0800 From: "Paul E. McKenney" To: Peter Zijlstra 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: <20200218202226.GJ2935@paulmck-ThinkPad-P72> Reply-To: paulmck@kernel.org 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> MIME-Version: 1.0 Content-Type: text/plain; charset=us-ascii Content-Disposition: inline In-Reply-To: <20200218201142.GF11457@worktop.programming.kicks-ass.net> User-Agent: Mutt/1.9.4 (2018-02-28) Sender: linux-kernel-owner@vger.kernel.org Precedence: bulk List-ID: X-Mailing-List: linux-kernel@vger.kernel.org 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. Thanx, Paul