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 C17A4C2BA19 for ; Tue, 21 Apr 2020 08:00:54 +0000 (UTC) Received: from vger.kernel.org (vger.kernel.org [23.128.96.18]) by mail.kernel.org (Postfix) with ESMTP id A0C9F20B1F for ; Tue, 21 Apr 2020 08:00:54 +0000 (UTC) Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1727854AbgDUIAx convert rfc822-to-8bit (ORCPT ); Tue, 21 Apr 2020 04:00:53 -0400 Received: from eu-smtp-delivery-151.mimecast.com ([207.82.80.151]:57369 "EHLO eu-smtp-delivery-151.mimecast.com" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1726013AbgDUIAx (ORCPT ); Tue, 21 Apr 2020 04:00:53 -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-250-fgIk9mZoMF6JMJUCrlMd3g-1; Tue, 21 Apr 2020 09:00:48 +0100 X-MC-Unique: fgIk9mZoMF6JMJUCrlMd3g-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; Tue, 21 Apr 2020 09:00:48 +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; Tue, 21 Apr 2020 09:00:48 +0100 From: David Laight To: 'Petko Manolov' , "Paul E. McKenney" CC: LKML Subject: RE: [RFC] WRITE_ONCE_INC() and friends Thread-Topic: [RFC] WRITE_ONCE_INC() and friends Thread-Index: AQHWFi8qKt3GQH4qWkGP1JyWbckPg6iAvLKQ///3OoCAAELwsIABP0tugAECeAA= Date: Tue, 21 Apr 2020 08:00:48 +0000 Message-ID: <3a6f974efad4453e9af7a3152ca0bbce@AcuMS.aculab.com> References: <20200419094439.GA32841@carbon> <491f0b0bc9e4419d93a78974fd7f44c7@AcuMS.aculab.com> <20200419182957.GA36919@carbon> <8e5a0283ed76465aac19a2b97a27ff15@AcuMS.aculab.com> <20200420150545.GB17661@paulmck-ThinkPad-P72> <20200420163215.GA43378@carbon> In-Reply-To: <20200420163215.GA43378@carbon> 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: Petko Manolov > Sent: 20 April 2020 17:32 ... > > But one downside of declaring variables volatile is that it can prevent KCSAN > > from spotting violations of the concurrency design for those variables. > > Which would be unfortunate. > > I just wish there was C type declaration that would force the compiler to do > what READ/WRITE_ONCE() does now, but i also know this is too naive... :) It does, it is called 'volatile'. All READ_ONCE() does is force the access through a volatile pointer. The thing to do is mark the structure elements 'volatile' rather than using a 'pointer to volatile structure'. I'm sure KASAN could be taught about volatile structure members. David. - Registered Address Lakeside, Bramley Road, Mount Farm, Milton Keynes, MK1 1PT, UK Registration No: 1397386 (Wales)