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=-7.2 required=3.0 tests=HEADER_FROM_DIFFERENT_DOMAINS, MAILING_LIST_MULTI,MENTIONS_GIT_HOSTING,SPF_HELO_NONE,SPF_PASS, USER_AGENT_SANE_1 autolearn=ham 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 49EC8C43603 for ; Thu, 12 Dec 2019 18:29:29 +0000 (UTC) Received: from vger.kernel.org (vger.kernel.org [209.132.180.67]) by mail.kernel.org (Postfix) with ESMTP id 236F82253D for ; Thu, 12 Dec 2019 18:29:29 +0000 (UTC) Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1730424AbfLLS32 (ORCPT ); Thu, 12 Dec 2019 13:29:28 -0500 Received: from mx0a-001b2d01.pphosted.com ([148.163.156.1]:64570 "EHLO mx0a-001b2d01.pphosted.com" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1730380AbfLLS31 (ORCPT ); Thu, 12 Dec 2019 13:29:27 -0500 Received: from pps.filterd (m0098399.ppops.net [127.0.0.1]) by mx0a-001b2d01.pphosted.com (8.16.0.42/8.16.0.42) with SMTP id xBCIM4M0070122 for ; Thu, 12 Dec 2019 13:29:27 -0500 Received: from e06smtp04.uk.ibm.com (e06smtp04.uk.ibm.com [195.75.94.100]) by mx0a-001b2d01.pphosted.com with ESMTP id 2wugd2qba0-1 (version=TLSv1.2 cipher=AES256-GCM-SHA384 bits=256 verify=NOT) for ; Thu, 12 Dec 2019 13:29:26 -0500 Received: from localhost by e06smtp04.uk.ibm.com with IBM ESMTP SMTP Gateway: Authorized Use Only! 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Violators will be prosecuted; (version=TLSv1/SSLv3 cipher=AES256-GCM-SHA384 bits=256/256) Thu, 12 Dec 2019 18:29:20 -0000 Received: from d06av23.portsmouth.uk.ibm.com (d06av23.portsmouth.uk.ibm.com [9.149.105.59]) by b06cxnps4075.portsmouth.uk.ibm.com (8.14.9/8.14.9/NCO v10.0) with ESMTP id xBCITJTv33095812 (version=TLSv1/SSLv3 cipher=DHE-RSA-AES256-GCM-SHA384 bits=256 verify=OK); Thu, 12 Dec 2019 18:29:19 GMT Received: from d06av23.portsmouth.uk.ibm.com (unknown [127.0.0.1]) by IMSVA (Postfix) with ESMTP id 5C4C8A4040; Thu, 12 Dec 2019 18:29:19 +0000 (GMT) Received: from d06av23.portsmouth.uk.ibm.com (unknown [127.0.0.1]) by IMSVA (Postfix) with ESMTP id 04338A4051; Thu, 12 Dec 2019 18:29:19 +0000 (GMT) Received: from oc7455500831.ibm.com (unknown [9.152.224.212]) by d06av23.portsmouth.uk.ibm.com (Postfix) with ESMTP; Thu, 12 Dec 2019 18:29:18 +0000 (GMT) Subject: Re: READ_ONCE() + STACKPROTECTOR_STRONG == :/ (was Re: [GIT PULL] Please pull powerpc/linux.git powerpc-5.5-2 tag (topic/kasan-bitops)) To: Will Deacon , Linus Torvalds Cc: Peter Zijlstra , Michael Ellerman , dja@axtens.net, Linux Kernel Mailing List , linuxppc-dev@lists.ozlabs.org, Christophe Leroy , linux-arch , Mark Rutland , Segher Boessenkool , Arnd Bergmann References: <87blslei5o.fsf@mpe.ellerman.id.au> <20191206131650.GM2827@hirez.programming.kicks-ass.net> <875zimp0ay.fsf@mpe.ellerman.id.au> <20191212080105.GV2844@hirez.programming.kicks-ass.net> <20191212100756.GA11317@willie-the-truck> <20191212104610.GW2827@hirez.programming.kicks-ass.net> <20191212180634.GA19020@willie-the-truck> From: Christian Borntraeger Autocrypt: addr=borntraeger@de.ibm.com; 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Linux x86_64; rv:68.0) Gecko/20100101 Thunderbird/68.2.0 MIME-Version: 1.0 In-Reply-To: <20191212180634.GA19020@willie-the-truck> Content-Type: text/plain; charset=utf-8 Content-Language: en-US Content-Transfer-Encoding: 7bit X-TM-AS-GCONF: 00 x-cbid: 19121218-0016-0000-0000-000002D43707 X-IBM-AV-DETECTION: SAVI=unused REMOTE=unused XFE=unused x-cbparentid: 19121218-0017-0000-0000-000033365EAC Message-Id: X-Proofpoint-Virus-Version: vendor=fsecure engine=2.50.10434:6.0.95,18.0.572 definitions=2019-12-12_06:2019-12-12,2019-12-12 signatures=0 X-Proofpoint-Spam-Details: rule=outbound_notspam policy=outbound score=0 mlxscore=0 suspectscore=0 mlxlogscore=999 clxscore=1015 adultscore=0 malwarescore=0 priorityscore=1501 spamscore=0 bulkscore=0 phishscore=0 lowpriorityscore=0 impostorscore=0 classifier=spam adjust=0 reason=mlx scancount=1 engine=8.12.0-1910280000 definitions=main-1912120141 Sender: linux-kernel-owner@vger.kernel.org Precedence: bulk List-ID: X-Mailing-List: linux-kernel@vger.kernel.org On 12.12.19 19:06, Will Deacon wrote: > On Thu, Dec 12, 2019 at 09:41:32AM -0800, Linus Torvalds wrote: >> On Thu, Dec 12, 2019 at 2:46 AM Peter Zijlstra wrote: >>> >>> +#ifdef GCC_VERSION < 40800 >> >> Where does that 4.8 version check come from, and why? >> >> Yeah, I know, but this really wants a comment. Sadly it looks like gcc >> bugzilla is down, so >> >> https://gcc.gnu.org/bugzilla/show_bug.cgi?id=58145 >> >> currently gives an "Internal Server Error" for me. >> >> [ Delete the horrid code we have because of gcc bugs ] >> >>> +#else /* GCC_VERSION < 40800 */ >>> + >>> +#define READ_ONCE_NOCHECK(x) \ >>> +({ \ >>> + typeof(x) __x = *(volatile typeof(x))&(x); \ >> >> I think we can/should just do this unconditionally if it helps th eissue. > > I'm currently trying to solve the issue by removing volatile from the bitop > function signatures, but it's grotty because there are quite a few callers > to fix up. I'm still trying to do it, because removing volatile fields from > structurs is generally a "good thing", but I'd be keen to simplify > READ_ONCE() as you suggest regardless. As I am the one who added the foundation of READ_ONCEs uglyness, I am now in favour of re-simplifying it again. I was first a bit scared about re-introducing bugs, but the gcc testsuite has this particular case covered, so hopefully we should not see the issue with volatile and aggregate types again. Christian