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=-0.6 required=3.0 tests=DKIM_INVALID,DKIM_SIGNED, HEADER_FROM_DIFFERENT_DOMAINS,MAILING_LIST_MULTI,SPF_HELO_NONE,SPF_PASS 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 1597CC433E1 for ; Thu, 14 May 2020 13:56:47 +0000 (UTC) Received: from vger.kernel.org (vger.kernel.org [23.128.96.18]) by mail.kernel.org (Postfix) with ESMTP id D97DA205CB for ; Thu, 14 May 2020 13:56:46 +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="ukgueQqJ" Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1727107AbgENN4q (ORCPT ); Thu, 14 May 2020 09:56:46 -0400 Received: from lindbergh.monkeyblade.net ([23.128.96.19]:58486 "EHLO lindbergh.monkeyblade.net" rhost-flags-OK-FAIL-OK-FAIL) by vger.kernel.org with ESMTP id S1726050AbgENN4p (ORCPT ); Thu, 14 May 2020 09:56:45 -0400 Received: from bombadil.infradead.org (bombadil.infradead.org [IPv6:2607:7c80:54:e::133]) by lindbergh.monkeyblade.net (Postfix) with ESMTPS id 9A809C061A0C for ; Thu, 14 May 2020 06:56:45 -0700 (PDT) DKIM-Signature: v=1; a=rsa-sha256; q=dns/txt; c=relaxed/relaxed; d=infradead.org; s=bombadil.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; bh=yuNZv20GvjcB3xZG0jnCz4zo0tfhmHdfTS3Cc7Ab6N8=; b=ukgueQqJZ77CbN4yIO3mK6vCnP 9TzP7TKK5ROW/AwOsp+pUneoZpOHrIKvKb00mB8IhFn4bYTr5MP4gLLkiPyfZ/Bzx9FtOjLcfBvOH lOgdxXjMff+zMe+IWDlGW1Pnwsf2aVrAIucTVnHJLLL00JOY/2M5Vg8SQd8ttlQB5zLnQfVEzt/+c QsJy7cG2CfzY6kTHb6XSnlUkKRKPzIDdHDKILWsVhbmOXJokovvT8Y8bR2GLHcTBd2vjxodUp/kze epH/ujHLaMp1YccjnSht2i/68FrmkhUUDjKneI861j1Q8u2cd2CSYj3gJuu/mLRCTlunXxHDHTGQg 0FM4I34Q==; Received: from j217100.upc-j.chello.nl ([24.132.217.100] helo=noisy.programming.kicks-ass.net) by bombadil.infradead.org with esmtpsa (Exim 4.92.3 #3 (Red Hat Linux)) id 1jZELp-0004gL-EQ; Thu, 14 May 2020 13:56:41 +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 BC2F3302753; Thu, 14 May 2020 15:56:39 +0200 (CEST) Received: by hirez.programming.kicks-ass.net (Postfix, from userid 1000) id A79DF2B852D67; Thu, 14 May 2020 15:56:39 +0200 (CEST) Date: Thu, 14 May 2020 15:56:39 +0200 From: Peter Zijlstra To: Marco Elver Cc: Will Deacon , kasan-dev , LKML , Thomas Gleixner , "Paul E. McKenney" , Ingo Molnar , Dmitry Vyukov Subject: Re: [PATCH v5 00/18] Rework READ_ONCE() to improve codegen Message-ID: <20200514135639.GA2978@hirez.programming.kicks-ass.net> References: <20200513124021.GB20278@willie-the-truck> <20200513165008.GA24836@willie-the-truck> <20200513174747.GB24836@willie-the-truck> <20200513212520.GC28594@willie-the-truck> <20200514110537.GC4280@willie-the-truck> MIME-Version: 1.0 Content-Type: text/plain; charset=us-ascii Content-Disposition: inline In-Reply-To: Sender: linux-kernel-owner@vger.kernel.org Precedence: bulk List-ID: X-Mailing-List: linux-kernel@vger.kernel.org On Thu, May 14, 2020 at 03:35:58PM +0200, Marco Elver wrote: > 5. we should not break atomic_{read,set} for KCSAN. [Because of #1, > we'd need to add data_race() around the arch-calls in > atomic_{read,set}; or rely on Clang 11's -tsan-distinguish-volatile > support (GCC 11 might get this as well).] Putting the data_race() in atomic_{read,set} would 'break' any sanitized user of arch_atomic_{read,set}(). Now it so happens there aren't any such just now, but we need to be aware of that. I'm thinking the volatile thing is the nicest solution, but yes, that'll make us depend on 11 everything.