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=-3.8 required=3.0 tests=BAYES_00, 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 66CF3C433ED for ; Tue, 13 Apr 2021 10:54:45 +0000 (UTC) Received: from vger.kernel.org (vger.kernel.org [23.128.96.18]) by mail.kernel.org (Postfix) with ESMTP id 4FE9161278 for ; Tue, 13 Apr 2021 10:54:45 +0000 (UTC) Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1344187AbhDMKzD convert rfc822-to-8bit (ORCPT ); Tue, 13 Apr 2021 06:55:03 -0400 Received: from eu-smtp-delivery-151.mimecast.com ([185.58.85.151]:40439 "EHLO eu-smtp-delivery-151.mimecast.com" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1344172AbhDMKzB (ORCPT ); Tue, 13 Apr 2021 06:55:01 -0400 Received: from AcuMS.aculab.com (156.67.243.121 [156.67.243.121]) (Using TLS) by relay.mimecast.com with ESMTP id uk-mta-196-tpOvhhP9PI6OZgNvLUAArQ-1; Tue, 13 Apr 2021 11:54:37 +0100 X-MC-Unique: tpOvhhP9PI6OZgNvLUAArQ-1 Received: from AcuMS.Aculab.com (fd9f:af1c:a25b:0:994c:f5c2:35d6:9b65) by AcuMS.aculab.com (fd9f:af1c:a25b:0:994c:f5c2:35d6:9b65) with Microsoft SMTP Server (TLS) id 15.0.1497.2; Tue, 13 Apr 2021 11:54:36 +0100 Received: from AcuMS.Aculab.com ([fe80::994c:f5c2:35d6:9b65]) by AcuMS.aculab.com ([fe80::994c:f5c2:35d6:9b65%12]) with mapi id 15.00.1497.012; Tue, 13 Apr 2021 11:54:36 +0100 From: David Laight To: 'Catalin Marinas' , =?iso-8859-1?Q?Christoph_M=FCllner?= CC: Peter Zijlstra , Palmer Dabbelt , Anup Patel , Guo Ren , linux-riscv , "Linux Kernel Mailing List" , Guo Ren , "will.deacon@arm.com" , "Arnd Bergmann" Subject: RE: [PATCH] riscv: locks: introduce ticket-based spinlock implementation Thread-Topic: [PATCH] riscv: locks: introduce ticket-based spinlock implementation Thread-Index: AQHXMFIUXH3Voi0JlEKNZc90N7zZnaqyRXDQ Date: Tue, 13 Apr 2021 10:54:36 +0000 Message-ID: <73cab48b63ea4ba3b1ef532f47d146f4@AcuMS.aculab.com> References: <20210413104503.GD15806@arm.com> In-Reply-To: <20210413104503.GD15806@arm.com> Accept-Language: en-GB, 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 Authentication-Results: relay.mimecast.com; auth=pass smtp.auth=C51A453 smtp.mailfrom=david.laight@aculab.com X-Mimecast-Spam-Score: 0 X-Mimecast-Originator: aculab.com Content-Language: en-US Content-Type: text/plain; charset=UTF-8 Content-Transfer-Encoding: 8BIT Precedence: bulk List-ID: X-Mailing-List: linux-kernel@vger.kernel.org From: Catalin Marinas > Sent: 13 April 2021 11:45 ... > This indeed needs some care. IIUC RISC-V has similar restrictions as arm > here, no load/store instructions are allowed between LR and SC. You > can't guarantee that the compiler won't spill some variable onto the > stack. You can probably never guarantee the compiler won't spill to stack. Especially if someone compiles with -O0. Which probably means that anything using LR/SC must be written in asm and the C wrappers disabled. David - Registered Address Lakeside, Bramley Road, Mount Farm, Milton Keynes, MK1 1PT, UK Registration No: 1397386 (Wales)