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=-7.5 required=3.0 tests=BAYES_00,DKIMWL_WL_HIGH, DKIM_SIGNED,DKIM_VALID,DKIM_VALID_AU,MAILING_LIST_MULTI,SPF_HELO_NONE, SPF_PASS,URIBL_BLOCKED,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 5B64EC433FE for ; Mon, 7 Dec 2020 22:56:39 +0000 (UTC) Received: from vger.kernel.org (vger.kernel.org [23.128.96.18]) by mail.kernel.org (Postfix) with ESMTP id 1E1E3239EF for ; Mon, 7 Dec 2020 22:56:39 +0000 (UTC) Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1726320AbgLGW4X (ORCPT ); Mon, 7 Dec 2020 17:56:23 -0500 Received: from mail.kernel.org ([198.145.29.99]:47582 "EHLO mail.kernel.org" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1725814AbgLGW4W (ORCPT ); Mon, 7 Dec 2020 17:56:22 -0500 Date: Mon, 7 Dec 2020 14:55:42 -0800 DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/simple; d=kernel.org; s=k20201202; t=1607381742; bh=MTovbSNum3TKJoGnhB5Nq3ImaKuoaau0JkrY19YWFUc=; h=From:To:Cc:Subject:Reply-To:References:In-Reply-To:From; b=HzKGZEMulkSmll0/GZq/AdfLDIFFXu0jWuGNZFuyPNxYs1R//yvVMnKlO/5mwZKjs /ZAbDlwKvwO/wiiB4Ul4qbKWGpOSm1pXf8YuzkYl33ng+3l34VseCKXHdxV1jMmFsH HLgYil+3DkGusl593ZglXIa53KUF2SSFBBC6pTT0tx0bTjgIGy+PSMnKTCCOqXcExz 7Enr7HlVZDTCrOR46Pzvd7VNv6Y8vupv2Y7AKAbdVoiP1BYwRAKkirVH91HhBR11TV DPjHTdMgAXAHVKWWYJVj3fcC23WefrjIoP1RPCIPi6xFjIThc5AWpF5anO/tL30xwU 4Vki12++ZYnFw== From: "Paul E. McKenney" To: Thomas Gleixner Cc: Marco Elver , Peter Zijlstra , LKML , kasan-dev , Ingo Molnar , Frederic Weisbecker , Will Deacon , Naresh Kamboju , syzbot+23a256029191772c2f02@syzkaller.appspotmail.com, syzbot+56078ac0b9071335a745@syzkaller.appspotmail.com, syzbot+867130cb240c41f15164@syzkaller.appspotmail.com Subject: Re: [patch 3/3] tick: Annotate tick_do_timer_cpu data races Message-ID: <20201207225542.GM2657@paulmck-ThinkPad-P72> Reply-To: paulmck@kernel.org References: <20201206211253.919834182@linutronix.de> <20201206212002.876987748@linutronix.de> <20201207120943.GS3021@hirez.programming.kicks-ass.net> <87y2i94igo.fsf@nanos.tec.linutronix.de> <20201207194406.GK2657@paulmck-ThinkPad-P72> <87blf547d2.fsf@nanos.tec.linutronix.de> <20201207223853.GL2657@paulmck-ThinkPad-P72> <878sa944kn.fsf@nanos.tec.linutronix.de> MIME-Version: 1.0 Content-Type: text/plain; charset=us-ascii Content-Disposition: inline In-Reply-To: <878sa944kn.fsf@nanos.tec.linutronix.de> User-Agent: Mutt/1.9.4 (2018-02-28) Precedence: bulk List-ID: X-Mailing-List: linux-kernel@vger.kernel.org On Mon, Dec 07, 2020 at 11:46:48PM +0100, Thomas Gleixner wrote: > On Mon, Dec 07 2020 at 14:38, Paul E. McKenney wrote: > > > On Mon, Dec 07, 2020 at 10:46:33PM +0100, Thomas Gleixner wrote: > >> On Mon, Dec 07 2020 at 11:44, Paul E. McKenney wrote: > >> > On Mon, Dec 07, 2020 at 07:19:51PM +0100, Marco Elver wrote: > >> >> On Mon, 7 Dec 2020 at 18:46, Thomas Gleixner wrote: > >> >> I currently don't know what the rule for Peter's preferred variant > >> >> would be, without running the risk of some accidentally data_race()'d > >> >> accesses. > >> >> > >> >> Thoughts? > >> > > >> > I am also concerned about inadvertently covering code with data_race(). > >> > > >> > Also, in this particular case, why data_race() rather than READ_ONCE()? > >> > Do we really expect the compiler to be able to optimize this case > >> > significantly without READ_ONCE()? > >> > >> That was your suggestion a week or so ago :) > > > > You expected my suggestion to change? ;-) > > Your suggestion was data_race() IIRC but I might have lost track in that > conversation. OK, I am inconsistent after all. I would have suggested READ_ONCE() given no difference between them, so it is probably best to assume that there is (or at least was) a good reason for data_race() instead of READ_ONCE(). Couldn't tell you what it might be, though. :-/ Thanx, Paul