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 A8B72C2D0CE for ; Tue, 21 Jan 2020 16:16:34 +0000 (UTC) Received: from vger.kernel.org (vger.kernel.org [209.132.180.67]) by mail.kernel.org (Postfix) with ESMTP id 76C2624656 for ; Tue, 21 Jan 2020 16:16:34 +0000 (UTC) DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/simple; d=kernel.org; s=default; t=1579623394; bh=QeSKKD6PfrbbZOwfYV8hICQ+MCLi4jauPz7wyQelez8=; h=Date:From:To:Cc:Subject:Reply-To:References:In-Reply-To:List-ID: From; b=K1rl6LCohhsDbWAF5SYSVsNJb6vG5za1MuKclrCrAbH2Xexvbqa95Y62Rg99tO5mS 4Ts893u35H85vzRfQdfG1DZWdfrIGO5EN5EHoRbkMFJ0tdVPJYZEh8lchbzG/F3Vog oHXD6yOUtHFQQ2Cz7HolP9Lkm3yP4gXgyg2g1ixE= Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1729277AbgAUQQd (ORCPT ); Tue, 21 Jan 2020 11:16:33 -0500 Received: from mail.kernel.org ([198.145.29.99]:48542 "EHLO mail.kernel.org" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1726555AbgAUQQd (ORCPT ); Tue, 21 Jan 2020 11:16:33 -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 CCD43217F4; Tue, 21 Jan 2020 16:16:32 +0000 (UTC) DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/simple; d=kernel.org; s=default; t=1579623392; bh=QeSKKD6PfrbbZOwfYV8hICQ+MCLi4jauPz7wyQelez8=; h=Date:From:To:Cc:Subject:Reply-To:References:In-Reply-To:From; b=Il7G75GLGL9BYlH35+SMX/L6VBP/oLIMGiRkoA99QP49hy6FgnqV7/3fGSwKEVz4T gn7tnHJmIaly9Ua5+BSqlpRJS3e3S/uyuC7G8BCbJK2VPnaKShgTYsuAONkYPko1Ix 94CNdGU/2JGEwDWIXc+3suGyu7MgSWaUF5YA8XuI= Received: by paulmck-ThinkPad-P72.home (Postfix, from userid 1000) id A677E3520DC0; Tue, 21 Jan 2020 08:16:32 -0800 (PST) Date: Tue, 21 Jan 2020 08:16:32 -0800 From: "Paul E. McKenney" To: Peter Zijlstra Cc: Marco Elver , andreyknvl@google.com, glider@google.com, dvyukov@google.com, kasan-dev@googlegroups.com, linux-kernel@vger.kernel.org, mark.rutland@arm.com, will@kernel.org, boqun.feng@gmail.com, arnd@arndb.de, viro@zeniv.linux.org.uk, christophe.leroy@c-s.fr, dja@axtens.net, mpe@ellerman.id.au, rostedt@goodmis.org, mhiramat@kernel.org, mingo@kernel.org, christian.brauner@ubuntu.com, daniel@iogearbox.net, cyphar@cyphar.com, keescook@chromium.org, linux-arch@vger.kernel.org Subject: Re: [PATCH 3/5] asm-generic, kcsan: Add KCSAN instrumentation for bitops Message-ID: <20200121161632.GV2935@paulmck-ThinkPad-P72> Reply-To: paulmck@kernel.org References: <20200120141927.114373-1-elver@google.com> <20200120141927.114373-3-elver@google.com> <20200120144048.GB14914@hirez.programming.kicks-ass.net> <20200120162725.GE2935@paulmck-ThinkPad-P72> <20200120165223.GC14914@hirez.programming.kicks-ass.net> <20200120202359.GF2935@paulmck-ThinkPad-P72> <20200121091501.GF14914@hirez.programming.kicks-ass.net> <20200121142109.GQ2935@paulmck-ThinkPad-P72> <20200121144716.GQ14879@hirez.programming.kicks-ass.net> MIME-Version: 1.0 Content-Type: text/plain; charset=us-ascii Content-Disposition: inline In-Reply-To: <20200121144716.GQ14879@hirez.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, Jan 21, 2020 at 03:47:16PM +0100, Peter Zijlstra wrote: > On Tue, Jan 21, 2020 at 06:21:09AM -0800, Paul E. McKenney wrote: > > On Tue, Jan 21, 2020 at 10:15:01AM +0100, Peter Zijlstra wrote: > > > On Mon, Jan 20, 2020 at 12:23:59PM -0800, Paul E. McKenney wrote: > > > > We also don't have __atomic_read() and __atomic_set(), yet atomic_read() > > > > and atomic_set() are considered to be non-racy, right? > > > > > > What is racy? :-) You can make data races with atomic_{read,set}() just > > > fine. > > > > Like "fairness", lots of definitions of "racy". ;-) > > > > > Anyway, traditionally we call the read-modify-write stuff atomic, not > > > the trivial load-store stuff. The only reason we care about the > > > load-store stuff in the first place is because C compilers are shit. > > > > > > atomic_read() / test_bit() are just a load, all we need is the C > > > compiler not to be an ass and split it. Yes, we've invented the term > > > single-copy atomicity for that, but that doesn't make it more or less of > > > a load. > > > > > > And exactly because it is just a load, there is no __test_bit(), which > > > would be the exact same load. > > > > Very good! Shouldn't KCSAN then define test_bit() as non-racy just as > > for atomic_read()? > > Sure it does; but my comment was aimed at the gripe that test_bit() > lives in the non-atomic bitops header. That is arguably entirely > correct. Fair enough! Thanx, Paul