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=-2.4 required=3.0 tests=DKIM_SIGNED,DKIM_VALID, DKIM_VALID_AU,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 DA0E6C2D0CE for ; Tue, 21 Jan 2020 09:16:41 +0000 (UTC) Received: from vger.kernel.org (vger.kernel.org [209.132.180.67]) by mail.kernel.org (Postfix) with ESMTP id ADC6D20882 for ; Tue, 21 Jan 2020 09:16:41 +0000 (UTC) Authentication-Results: mail.kernel.org; dkim=pass (1024-bit key) header.d=alien8.de header.i=@alien8.de header.b="J64FB2M6" Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1729043AbgAUJQk (ORCPT ); Tue, 21 Jan 2020 04:16:40 -0500 Received: from mail.skyhub.de ([5.9.137.197]:36260 "EHLO mail.skyhub.de" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1725789AbgAUJQk (ORCPT ); Tue, 21 Jan 2020 04:16:40 -0500 Received: from zn.tnic (p200300EC2F0B0400A009400066D53C66.dip0.t-ipconnect.de [IPv6:2003:ec:2f0b:400:a009:4000:66d5:3c66]) (using TLSv1.2 with cipher ECDHE-RSA-AES256-GCM-SHA384 (256/256 bits)) (No client certificate requested) by mail.skyhub.de (SuperMail on ZX Spectrum 128k) with ESMTPSA id 35D291EC0B7A; Tue, 21 Jan 2020 10:16:39 +0100 (CET) DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/relaxed; d=alien8.de; s=dkim; t=1579598199; 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: content-transfer-encoding:in-reply-to:in-reply-to: references:references; bh=ANXkNq5QvqcOwrIgPpsFYa4JWlL8ZcM65Bre6rHpQbs=; b=J64FB2M6EXfWriRaoAsTY1CSeMYYgdPGWM+OZUYjcNmFBa81Rcrx0MyBQafpYQzunZV8Kl 5pXsYdJcL2VCJjYhHsEQRTW/IQkOFnMYdo+Nh/qSHUL0EQkmueKW0TCxX78uw82UE+GS0y A5PzeCM2IDJ3O9spe8T/6TvqEUUNBK4= Date: Tue, 21 Jan 2020 10:16:33 +0100 From: Borislav Petkov To: Marco Elver Cc: Qian Cai , Thomas Gleixner , Ingo Molnar , Dave Hansen , Andy Lutomirski , Peter Zijlstra , the arch/x86 maintainers , LKML Subject: Re: [PATCH -next] x86/mm/pat: fix a data race in cpa_inc_4k_install Message-ID: <20200121091633.GF7808@zn.tnic> References: <20200121041200.2260-1-cai@lca.pw> <20200121072744.GA7808@zn.tnic> MIME-Version: 1.0 Content-Type: text/plain; charset=utf-8 Content-Disposition: inline In-Reply-To: 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 09:19:18AM +0100, Marco Elver wrote: > As I said in my email that you also copied to the message, this is > just a stats counter. For the general case, I think we reached > consensus that such accesses should intentionally remain data races: > https://lore.kernel.org/linux-fsdevel/CAHk-=wg5CkOEF8DTez1Qu0XTEFw_oHhxN98bDnFqbY7HL5AB2g@mail.gmail.com/T/#u Yap, I agree with Linus on the legibility aspect. > Either you can use the data_race() macro, making this > 'data_race(cpa_4k_install++)' -- this effectively documents the > intentional data race -- > > or just blacklist the entire file by putting > KCSAN_SANITIZE_set_memory.o := n > into the Makefile. > > [ Note that there are 2 more ways to blacklist: > - __no_kcsan function attribute, for blacklisting entire functions. > - KCSAN_SANITIZE :=n in the Makefile, blacklisting all compilation > units in the Makefile. ] Do we have all those official methods how to make KCSAN happy, documented somewhere? > I leave it to you what makes more sense. I don't know if there are > other data races lurking here, since cpa_4k_install is not the only > stats counter. In this particular case and if it were me, I'd prefer the __no_kcsan function attribute because it is kept outside of the function body. But I can't find __no_kcsan in current tip: $ git grep __no_kcsan .h:204:static __no_kcsan_or_inline bool constant_test_bit(long nr, const volatile unsigned long *addr) include/linux/compiler.h:215:# define __no_kcsan_or_inline __no_sanitize_thread notrace __maybe_unused include/linux/compiler.h:216:# define __no_sanitize_or_inline __no_kcsan_or_inline include/linux/compiler.h:218:# define __no_kcsan_or_inline __always_inline include/linux/compiler.h:225:static __no_kcsan_or_inline include/linux/compiler.h:238:static __no_kcsan_or_inline just this "glued together" thing __no_kcsan_or_inline. -- Regards/Gruss, Boris. https://people.kernel.org/tglx/notes-about-netiquette