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=-0.8 required=3.0 tests=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 25896C433E0 for ; Fri, 15 May 2020 13:55:50 +0000 (UTC) Received: from vger.kernel.org (vger.kernel.org [23.128.96.18]) by mail.kernel.org (Postfix) with ESMTP id F292120759 for ; Fri, 15 May 2020 13:55:49 +0000 (UTC) Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1726204AbgEONzt convert rfc822-to-8bit (ORCPT ); Fri, 15 May 2020 09:55:49 -0400 Received: from eu-smtp-delivery-151.mimecast.com ([207.82.80.151]:36592 "EHLO eu-smtp-delivery-151.mimecast.com" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1726144AbgEONzs (ORCPT ); Fri, 15 May 2020 09:55:48 -0400 Received: from AcuMS.aculab.com (156.67.243.126 [156.67.243.126]) (Using TLS) by relay.mimecast.com with ESMTP id uk-mta-152-DguEuvUTNmShAeVBwZOssg-1; Fri, 15 May 2020 14:55:43 +0100 X-MC-Unique: DguEuvUTNmShAeVBwZOssg-1 Received: from AcuMS.Aculab.com (fd9f:af1c:a25b:0:43c:695e:880f:8750) by AcuMS.aculab.com (fd9f:af1c:a25b:0:43c:695e:880f:8750) with Microsoft SMTP Server (TLS) id 15.0.1347.2; Fri, 15 May 2020 14:55:43 +0100 Received: from AcuMS.Aculab.com ([fe80::43c:695e:880f:8750]) by AcuMS.aculab.com ([fe80::43c:695e:880f:8750%12]) with mapi id 15.00.1347.000; Fri, 15 May 2020 14:55:43 +0100 From: David Laight To: 'Peter Zijlstra' , 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 Thread-Topic: [PATCH v5 00/18] Rework READ_ONCE() to improve codegen Thread-Index: AQHWKfttZor7e2JWdEKPvqldyEhGwKipLI7w Date: Fri, 15 May 2020 13:55:43 +0000 Message-ID: <26283b5bccc8402cb8c243c569676dbd@AcuMS.aculab.com> 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> <20200514142450.GC2978@hirez.programming.kicks-ass.net> In-Reply-To: <20200514142450.GC2978@hirez.programming.kicks-ass.net> Accept-Language: en-GB, en-US Content-Language: en-US X-MS-Has-Attach: X-MS-TNEF-Correlator: x-ms-exchange-transport-fromentityheader: Hosted x-originating-ip: [10.202.205.107] MIME-Version: 1.0 X-Mimecast-Spam-Score: 0 X-Mimecast-Originator: aculab.com Content-Type: text/plain; charset=UTF-8 Content-Transfer-Encoding: 8BIT Sender: linux-kernel-owner@vger.kernel.org Precedence: bulk List-ID: X-Mailing-List: linux-kernel@vger.kernel.org From: Peter Zijlstra > Sent: 14 May 2020 15:25 .. > Exact same requirements, KASAN even has the data_race() problem through > READ_ONCE_NOCHECK(), UBSAN doesn't and might be simpler because of it. What happens if you implement READ_ONCE_NOCHECK() with an asm() statement containing a memory load? Is that enough to kill all the instrumentation? David - Registered Address Lakeside, Bramley Road, Mount Farm, Milton Keynes, MK1 1PT, UK Registration No: 1397386 (Wales)