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=-5.7 required=3.0 tests=BAYES_00,DKIM_SIGNED, DKIM_VALID,DKIM_VALID_AU,HEADER_FROM_DIFFERENT_DOMAINS,MAILING_LIST_MULTI, SPF_HELO_NONE,SPF_PASS,URIBL_BLOCKED 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 0AF5FC433FE for ; Mon, 7 Dec 2020 21:47:23 +0000 (UTC) Received: from vger.kernel.org (vger.kernel.org [23.128.96.18]) by mail.kernel.org (Postfix) with ESMTP id C601122C7C for ; Mon, 7 Dec 2020 21:47:22 +0000 (UTC) Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1727571AbgLGVrV (ORCPT ); Mon, 7 Dec 2020 16:47:21 -0500 Received: from Galois.linutronix.de ([193.142.43.55]:38994 "EHLO galois.linutronix.de" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1726092AbgLGVrV (ORCPT ); Mon, 7 Dec 2020 16:47:21 -0500 From: Thomas Gleixner DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/relaxed; d=linutronix.de; s=2020; t=1607377599; h=from:from:reply-to:subject:subject:date:date:message-id:message-id: to:to:cc:cc:mime-version:mime-version:content-type:content-type: in-reply-to:in-reply-to:references:references; bh=XezsoOvo1QH3xJ+aBZ86D9VZCPnhkhJ5Z+Xl0ZlweKY=; b=ou/lhMrIJDMZQDwxidg5VuFXnC6SB9N3++ayblAcgNHcU1eZumhu759vJrBAc7pU5IPzO1 vXs1lK/DFueDOXyY+rRnXaKB/vC9f3upDubBPRoaC4EEqN5azaWAr/9lP5rhh7e5JVb6Ok pzs6ARW10Iu+x5GTcDsxZUxN0dp78Cw1Tbo1zfN8aWUYopEjJYAyuDSDBrXOWA4OSb/ixQ UGHqYIQRaWuDxPRKXqB8C1RyWoLBuTpV7egnO+MTuHrviHuy9CGzrYBYwZ4S5z8PM3Ur2+ I0QmBB6HRGXbN+xk4iMiq9bcm0Psm8fr4lhVOnlKdhJo4WY/AQ0o5GvMgW2KJQ== DKIM-Signature: v=1; a=ed25519-sha256; c=relaxed/relaxed; d=linutronix.de; s=2020e; t=1607377599; h=from:from:reply-to:subject:subject:date:date:message-id:message-id: to:to:cc:cc:mime-version:mime-version:content-type:content-type: in-reply-to:in-reply-to:references:references; bh=XezsoOvo1QH3xJ+aBZ86D9VZCPnhkhJ5Z+Xl0ZlweKY=; b=GWn3H1bKeJVhH7CoxtzEyz1N8YeBWYN6HyCfmRvWB91JLgmHXvA7vj/Lc6pfeOHjXHZc48 ZHFsL3NoRj+tPpCg== To: paulmck@kernel.org, Marco Elver Cc: 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 In-Reply-To: <20201207194406.GK2657@paulmck-ThinkPad-P72> 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> Date: Mon, 07 Dec 2020 22:46:33 +0100 Message-ID: <87blf547d2.fsf@nanos.tec.linutronix.de> MIME-Version: 1.0 Content-Type: text/plain Precedence: bulk List-ID: X-Mailing-List: linux-kernel@vger.kernel.org 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 :) Thanks, tglx