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 2E9ABC2D0CE for ; Tue, 21 Jan 2020 14:48:16 +0000 (UTC) Received: from vger.kernel.org (vger.kernel.org [209.132.180.67]) by mail.kernel.org (Postfix) with ESMTP id 0601B21569 for ; Tue, 21 Jan 2020 14:48:16 +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="bwKVHF7s" Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1729191AbgAUOsP (ORCPT ); Tue, 21 Jan 2020 09:48:15 -0500 Received: from merlin.infradead.org ([205.233.59.134]:44236 "EHLO merlin.infradead.org" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1726968AbgAUOsP (ORCPT ); Tue, 21 Jan 2020 09:48:15 -0500 DKIM-Signature: v=1; a=rsa-sha256; q=dns/txt; c=relaxed/relaxed; d=infradead.org; s=merlin.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:Resent-Date: Resent-From:Resent-Sender:Resent-To:Resent-Cc:Resent-Message-ID:List-Id: List-Help:List-Unsubscribe:List-Subscribe:List-Post:List-Owner:List-Archive; bh=uyryvzrOJVnY2Rp4qJ6rxjhfB8x1mJVRx6ecxsTZGfA=; b=bwKVHF7soQKI2IrooaVefjguG fiAGC74P3bvssr0+css1C8EDCghS7r8UidTgSfsCcsr7l9MJtQOBGEztGXa+draot+IJe1QsvNUWm ooyuPGZu7ltO1acjhyi9PTgOZgKMhjfDCTAsoatpnl18p88qhPu6Jw06F9KBUyv45wlBW4yWwNqwf qQUW6g192epkfBVw2EcZj1iaUt2shzGMxi7C4M24doGP/9t+u8zmdVnImpXEgvqjV/4AzBqRIpC5v /cN7vv8avgOlqsmMtRk9CNvAThOodw2QTHJ0HW3GkIngZk5JmjpHEyfUwikqFK1R7crtZdrOPJlKM 5nYFbT79Q==; Received: from j217100.upc-j.chello.nl ([24.132.217.100] helo=noisy.programming.kicks-ass.net) by merlin.infradead.org with esmtpsa (Exim 4.92.3 #3 (Red Hat Linux)) id 1ituoJ-0007N0-GP; Tue, 21 Jan 2020 14:47:19 +0000 Received: from hirez.programming.kicks-ass.net (hirez.programming.kicks-ass.net [192.168.1.225]) (using TLSv1.2 with cipher ECDHE-RSA-AES256-GCM-SHA384 (256/256 bits)) (Client did not present a certificate) by noisy.programming.kicks-ass.net (Postfix) with ESMTPS id 1CE8E30067C; Tue, 21 Jan 2020 15:45:37 +0100 (CET) Received: by hirez.programming.kicks-ass.net (Postfix, from userid 1000) id 35E7C20983E32; Tue, 21 Jan 2020 15:47:16 +0100 (CET) Date: Tue, 21 Jan 2020 15:47:16 +0100 From: Peter Zijlstra To: "Paul E. McKenney" 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: <20200121144716.GQ14879@hirez.programming.kicks-ass.net> 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> MIME-Version: 1.0 Content-Type: text/plain; charset=us-ascii Content-Disposition: inline In-Reply-To: <20200121142109.GQ2935@paulmck-ThinkPad-P72> User-Agent: Mutt/1.10.1 (2018-07-13) 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 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.