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 5991DC3404B for ; Tue, 18 Feb 2020 20:27:06 +0000 (UTC) Received: from vger.kernel.org (vger.kernel.org [209.132.180.67]) by mail.kernel.org (Postfix) with ESMTP id 339FF2173E for ; Tue, 18 Feb 2020 20:27:06 +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="Oen+0qmN" Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1726609AbgBRU1G (ORCPT ); Tue, 18 Feb 2020 15:27:06 -0500 Received: from bombadil.infradead.org ([198.137.202.133]:40076 "EHLO bombadil.infradead.org" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1726539AbgBRU1F (ORCPT ); Tue, 18 Feb 2020 15:27:05 -0500 DKIM-Signature: v=1; a=rsa-sha256; q=dns/txt; c=relaxed/relaxed; d=infradead.org; s=bombadil.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=MsmkZg6wZrEhezy9R5YbQTUgrdTDhzPB+OkYnO5Pl0U=; b=Oen+0qmNRjfXIHYz20JeeFGcoE QEkZxoj1f8cyZZrwUcdG+/PN62xbB41Ig8cC4hmVseF2UTRP6/MwtB5RjknENoDaVceDgK5dGOhUX 704AD+q+nLumZg0j5/aE3dqIYNE/It3a4G/NhNwCDBj5EqCxTnyS+imld0ZwuUSmV9LrNvbxfnv52 DI4nKSzCxOVDC9+1xH3kWbx2ZvvUM9jP8rm2qDL4yr/S08OSAbypMRojEuzG57MXl/upMFsyiiP/0 PA/WFbjCMGcTdBSgWV0saNu+kZMEr/qIUdvpZGB0q/jvEjQmxmbyHIut7K0tj/g8GYGVEjeoiEyy2 m2EXOsNw==; Received: from j217100.upc-j.chello.nl ([24.132.217.100] helo=worktop.programming.kicks-ass.net) by bombadil.infradead.org with esmtpsa (Exim 4.92.3 #3 (Red Hat Linux)) id 1j49SB-0004D6-3O; Tue, 18 Feb 2020 20:26:47 +0000 Received: by worktop.programming.kicks-ass.net (Postfix, from userid 1000) id 0F2E4980E56; Tue, 18 Feb 2020 21:26:45 +0100 (CET) Date: Tue, 18 Feb 2020 21:26:44 +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 4/4] srcu: Add READ_ONCE() to srcu_struct ->srcu_gp_seq load Message-ID: <20200218202644.GG11457@worktop.programming.kicks-ass.net> References: <20200215002907.GA15895@paulmck-ThinkPad-P72> <20200215002932.15976-4-paulmck@kernel.org> <20200217124507.GT14914@hirez.programming.kicks-ass.net> <20200217183220.GS2935@paulmck-ThinkPad-P72> <20200218114334.GX14914@hirez.programming.kicks-ass.net> <20200218163405.GF2935@paulmck-ThinkPad-P72> MIME-Version: 1.0 Content-Type: text/plain; charset=us-ascii Content-Disposition: inline In-Reply-To: <20200218163405.GF2935@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 08:34:05AM -0800, Paul E. McKenney wrote: > On Tue, Feb 18, 2020 at 12:43:34PM +0100, Peter Zijlstra wrote: > > Well, I didn't get further than the Changelog fails to describe an > > actual problem and it looks like compare-against-a-constant. > > > > (worse, it masks off everything but the 2 lowest bits, so even if there > > was a problem with load-tearing, it still wouldn't matter) > > There is still the possibility of load fusing. Agreed; that can be an issue. But if so, that then needs to be stated. > And the possibility > of defending against possible future changes as well as the current > snapshot of the code base. Sure; and like I said, if you want to use READ_ONCE() I'm not going to argue. > > I'm not going to argue with you if you want to use READ_ONCE() vs > > data_race() and a comment to denote false-positive KCSAN warnings, but I > > do feel somewhat strongly that the Changelog should describe the actual > > problem -- if there is one -- or just flat out state that this is to > > make KCSAN shut up but the code is fine. > > The problem is that "the code is fine" is highly subjective and varies > over time. :-/ > > But in this case there was a real problem, just that I got confused > when analyzing. Shit happens :-) > > That is; every KCSAN report should be analysed, right? All I'm asking is > > for that analysis to end up in the Changelog. > > Before responding further, I have to ask... > > Are you intending your "every KCSAN report should be analyzed" to apply > globally or just when someone creates a patch based on such a report? Ideally every KCSAN report, but that is a longer term effort. But specifically, when someone has written a patch, I expect that same someone to have analysed the code. Then it also makes sense to put that in the Changelog. > In any case, you have acked this patch's successor (thank you very > much!), so on this specific patch (or more accurately, its successor) > I presume that we are all good. We are. That new patch describes a clear problem and fixes it. Anyway, the reaoson I'm being difficuly is partly because on the one hand I'm just an annoying pendant at times, but also because I've seen a bunch of, let's say, hasty, KCSAN patches.