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=-2.8 required=3.0 tests=DKIM_SIGNED,DKIM_VALID, HEADER_FROM_DIFFERENT_DOMAINS,MAILING_LIST_MULTI,SPF_PASS,T_DKIMWL_WL_MED, URIBL_BLOCKED,USER_AGENT_NEOMUTT 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 1E1B2C5CFEB for ; Mon, 9 Jul 2018 16:49:53 +0000 (UTC) Received: from vger.kernel.org (vger.kernel.org [209.132.180.67]) by mail.kernel.org (Postfix) with ESMTP id B557E20875 for ; Mon, 9 Jul 2018 16:49:52 +0000 (UTC) Authentication-Results: mail.kernel.org; dkim=pass (1024-bit key) header.d=wavesemi.onmicrosoft.com header.i=@wavesemi.onmicrosoft.com header.b="nciLJJLj" DMARC-Filter: OpenDMARC Filter v1.3.2 mail.kernel.org B557E20875 Authentication-Results: mail.kernel.org; dmarc=none (p=none dis=none) header.from=mips.com Authentication-Results: mail.kernel.org; spf=none smtp.mailfrom=linux-kernel-owner@vger.kernel.org Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S933745AbeGIQtt (ORCPT ); Mon, 9 Jul 2018 12:49:49 -0400 Received: from mail-bn3nam01on0106.outbound.protection.outlook.com ([104.47.33.106]:58760 "EHLO NAM01-BN3-obe.outbound.protection.outlook.com" rhost-flags-OK-OK-OK-FAIL) by vger.kernel.org with ESMTP id S933292AbeGIQtq (ORCPT ); Mon, 9 Jul 2018 12:49:46 -0400 DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/relaxed; d=wavesemi.onmicrosoft.com; s=selector1-wavecomp-com; h=From:Date:Subject:Message-ID:Content-Type:MIME-Version:X-MS-Exchange-SenderADCheck; bh=Ikb2SuMWZfll26sn3a8+aP1ZZ0snyLe0+ZxtWU5Cv2g=; b=nciLJJLjgpUpI5dHO15xA93WsBSVeRUOeg+Nr3YJB7JKs12dWUpdIAo9crQnbICuZ9+++ubY8tEAmo4+LT4KtBHXzh0ndIhc9sGRTk+skqhtQ97bZ2/GxOpTWts3wI2nQI6zcGYCn9VRG8S0o4cbCkddDYhK9iBthslrLEhLyH8= Received: from localhost (4.16.204.77) by SN6PR08MB4944.namprd08.prod.outlook.com (2603:10b6:805:6e::16) with Microsoft SMTP Server (version=TLS1_2, cipher=TLS_ECDHE_RSA_WITH_AES_256_GCM_SHA384) id 15.20.930.19; Mon, 9 Jul 2018 16:49:42 +0000 Date: Mon, 9 Jul 2018 09:49:39 -0700 From: Paul Burton To: Huacai Chen Cc: Ralf Baechle , James Hogan , linux-mips@linux-mips.org, Fuxin Zhang , Zhangjin Wu , Huacai Chen , stable@vger.kernel.org, Alan Stern , Andrea Parri , Will Deacon , Peter Zijlstra , Boqun Feng , Nicholas Piggin , David Howells , Jade Alglave , Luc Maranget , "Paul E. McKenney" , Akira Yokosawa , linux-kernel@vger.kernel.org Subject: Re: [PATCH V2] MIPS: implement smp_cond_load_acquire() for Loongson-3 Message-ID: <20180709164939.uhqsvcv4a7jlbhvp@pburton-laptop> MIME-Version: 1.0 Content-Type: text/plain; charset=us-ascii Content-Disposition: inline In-Reply-To: <1531103198-16764-1-git-send-email-chenhc@lemote.com> User-Agent: NeoMutt/20180622 X-Originating-IP: [4.16.204.77] X-ClientProxiedBy: MWHPR1201CA0007.namprd12.prod.outlook.com (2603:10b6:301:4a::17) To SN6PR08MB4944.namprd08.prod.outlook.com (2603:10b6:805:6e::16) X-MS-PublicTrafficType: Email X-MS-Office365-Filtering-Correlation-Id: c4a7abb5-05a2-47d4-d5bd-08d5e5bbf839 X-Microsoft-Antispam: UriScan:;BCL:0;PCL:0;RULEID:(7020095)(4652040)(7021125)(8989117)(5600053)(711020)(4534165)(7022125)(4603075)(4627221)(201702281549075)(8990107)(7048125)(7024125)(7027125)(7028125)(7023125)(2017052603328)(7153060)(7193020);SRVR:SN6PR08MB4944; X-Microsoft-Exchange-Diagnostics: 1;SN6PR08MB4944;3:n+H0Fcl49iqelc4sGYhL8c5DcRW9Ee66WBD8AfsDxLXWeCUK8EpDCGSBWbIYE/D0ZbccpmQpjAKpuV0kHsNfUurJ6G6kl9d6Kp8BKdAZFk+y0T009aUom/zP8arz1Q7W/iNvqM6X9+VOYNkBCxVA7AsIHTFqTjFQCMew5fm00Urcy89UdIfN0r7hhuppVY3hCPx5c/Rs1FUqXHpEhnem9UihDCOjjX+ARsZUmiWvCpoRZhWoKL5UuOMuuDYx3N/6;25:YNDnZlAUhLadC6GVKXMKvrBegfiES3gJWylMK+rBB2n28qOR2QNA50qFW1X8BeiGxcifDtXN5hyqZ2UWuYbsgcqC1Ted0V1F1E7twa1vjaMRG3ZTwlIbIZ5/XiWc3fL3WCNCm+7EoyDdnvWAKeky/7zMtt3PLnAg/2qHXokMtW1HdZEbj0Ce7lD/Opwnnv88gHmETofczq1ozkJyazGqCjsQql86t9zwgS8H9e/Now2uzVpVj3Gb0Aw+iavVI5clCmfHqiqcVfvHpjuhjw3FBbctko4iW/ejldSs7UMIcqBFFZ9c1ocEhV0VemFe8fN0q0skg1uTNaXCBKdgL0WqJQ==;31:+lsg20Dt7Kvx4/qYUEo4dff0kiTE9jyHe5fvm8RLbQZ922o1O6FimURX7ptfjyeOogKe4WqZKNzeZhuxMa08WfU4oLqRzT0EUTdhJ4em+mTEr7XIRLegQdVIMFFmV/+GOHz73cTC6xnkmV6mGcWKhlsCVl8f5JGpFl3b1TxLNIiTFB14l4d2uorupBoL/gUu1pT9C2UynSsmA9y1iECnoskKRkg07f3hiiiWHAeiwrw= X-MS-TrafficTypeDiagnostic: SN6PR08MB4944: Authentication-Results: spf=none (sender IP is ) smtp.mailfrom=pburton@wavecomp.com; X-Microsoft-Exchange-Diagnostics: 1;SN6PR08MB4944;20:sGrzgSdEwWaH0lmOW/EhAyrNzKNrvfETaBXCsVevZzDpvXt/5RX+Wf88zeKZuXRu0a8yOTMjMHFUGEdcMD2BXMwKq0ZOgERP7EYjVaEzgDbPdz0JPFcLKlYL3mTKUsw6kd8k0ycWTo3OTZWQyEfIiZ1mWjR387m7K4LswYbQpzm39KueCXaDg035xmy1rPKMvCnXA3mku52gyjRJ8LTAwCU/jaf1c6H1Or3oE0336JhPLO2GvqUZyT6AZMcA1CP4;4:fkJuVy1J6/z9ChZ8XsSKXMVD6ILv//aKV9IQOrFHm/RrRbM8AEW8TiWSx+fFtR1vAbAfYbdXdusLZUTVLFwIKzSSor14QIXz5rvkEAGwXyNTdTEh/3TMQgvMNd3FsJ15/1taq+M74aTTeqi0mxqxAQj7h0CUuPFI9V5j3HTkX3h5VFK0RCBvRClQS3w4rb1Chl9QkeP7bo25w2yrWTF6ZBLkhoWpIfxvJGN4EJbsHmesQ7LJoIZ3KyaT+TB8U/91niUmeOUNvn3iymQDO3TtYK0X11UBGWImDwG0oI+70ALvG+0/v9fEB5ZPC93KUtIG X-Microsoft-Antispam-PRVS: X-Exchange-Antispam-Report-Test: UriScan:(9452136761055); X-MS-Exchange-SenderADCheck: 1 X-Exchange-Antispam-Report-CFA-Test: BCL:0;PCL:0;RULEID:(6040522)(2401047)(8121501046)(5005006)(93006095)(10201501046)(3002001)(3231311)(944501410)(52105095)(149027)(150027)(6041310)(20161123560045)(20161123564045)(20161123558120)(20161123562045)(2016111802025)(6043046)(6072148)(201708071742011)(7699016);SRVR:SN6PR08MB4944;BCL:0;PCL:0;RULEID:;SRVR:SN6PR08MB4944; X-Forefront-PRVS: 07283408BE X-Forefront-Antispam-Report: SFV:NSPM;SFS:(10019020)(6069001)(7916004)(39840400004)(396003)(366004)(376002)(346002)(136003)(199004)(189003)(33716001)(386003)(8936002)(316002)(26005)(486006)(16526019)(7736002)(39060400002)(305945005)(186003)(81166006)(52116002)(6246003)(33896004)(76506005)(81156014)(476003)(6496006)(8676002)(2906002)(58126008)(25786009)(54906003)(42882007)(4326008)(16586007)(1076002)(966005)(478600001)(7416002)(53936002)(68736007)(6116002)(6306002)(3846002)(105586002)(66066001)(9686003)(229853002)(6486002)(47776003)(106356001)(23726003)(50466002)(956004)(6666003)(11346002)(44832011)(6916009)(5660300001)(97736004);DIR:OUT;SFP:1102;SCL:1;SRVR:SN6PR08MB4944;H:localhost;FPR:;SPF:None;LANG:en;PTR:InfoNoRecords;A:1;MX:1; Received-SPF: None (protection.outlook.com: wavecomp.com does not designate permitted sender hosts) X-Microsoft-Exchange-Diagnostics: =?us-ascii?Q?1;SN6PR08MB4944;23:lHID95cj1L+scr4a4+GLdmxK7+XDwFNWSf5ZJk26D?= =?us-ascii?Q?XI3Z7AOzriKz90jOKOam98eh7OhdKQUZ9ajVl8bbDAC3liHpO01IKsVOcq8x?= =?us-ascii?Q?h9o6xvC7Xb55hhmYg1T5S1g8U7ZXQRI7uwrtb0bNYs8/CNBV38djkSLqP2NK?= =?us-ascii?Q?FO1t7/VkU/+C/ZkTQrPPKBZkAHLPmAgPUSgL6+3f+4eEog19My+qt8NJyj3g?= =?us-ascii?Q?JgQRFqmwX35nQOP81JovBxtbIjONT6oBt7aGPKeNFXyS+6a5J3sIIL7uIzOo?= =?us-ascii?Q?FASfizpFwUlN0n5ivgbUrDxbdw5cJ8u2FJcHlNxcPO1HU5L77Vd1AV86qjtd?= =?us-ascii?Q?VOGQ166cTFv38o7TyZ51oFYin4dQIVDQImXGiZItH65EfNtIgTVraiaPgN26?= =?us-ascii?Q?Lca/7u+MxWzHtASK9rmz7/qFgovPLAxs+unCjxPjwnPXgkIQ6B54y95fkHlT?= =?us-ascii?Q?HkzzgMMgPYZYdRbRXs3YfL9O/QeDylrkNuARrEs11Y8X2X+NBQ2eiCH/Nua2?= =?us-ascii?Q?uqbNblwKomeEUW0HCbxECfLoXPD/ovu0lJPQ84dY5Rjw2bQ2rITSFf/Bvb8b?= =?us-ascii?Q?Rko/U/fUD0jOyqk6GxIzcxQmZsuNah+GYnoJQksZky00ul5Kl+/jDNXOtXvu?= =?us-ascii?Q?86+4bib43RHKpq9fpyEjy1cWInO1hygWek5uzrjt2Rc6AFmQjTsAYblFH6Mx?= =?us-ascii?Q?puJMOE8KyKnZPqBrzq9wACo3UHgoxdCwOHp9oaCQZaI1t2vOfuARv0nHXqtF?= =?us-ascii?Q?JSPryHJM4SuYujoi6Ix/VonaJz3OnAZP9NUowhjqyLPxsKSTF8FnYPXSLTHP?= =?us-ascii?Q?YTJXzLr2ej3PZlpbvTim+hZNXJ7rp8YQwhMayKzOkrTL3LicqVB1L9U3AGLF?= =?us-ascii?Q?DMzEcwVvamBx09N9Wb31fpu5eekRy6GCZSnX7/ceZ1G5nc0WEnHaQGmhL69+?= =?us-ascii?Q?2/fdKuUJ4glMDkserGj9hGrpBHwD0NwfIfAhT96hsdCZIlSFiWAGBljJLQHi?= =?us-ascii?Q?gdkKOs2FYzZiqjqeJJH8PTfS4+xPqWTvVRtD9Dso5v+WaNJx2vZ9HY5oVMnr?= =?us-ascii?Q?fnF3Zgsp4V1iebSjIC3izLN3/+RkmMErqU8FEbBtQFxAPffoIuK3sfA1WfQw?= =?us-ascii?Q?AgH9jB7ZXj65xyl23oCkKHMBAwGFmfXLi9JgfnCq+wLE0ULp3tQq99UAsUAf?= =?us-ascii?Q?0i/k7l4MkoEmKdxtKdGYEaAF6OqYoz9FMuYnWUc4n+lKyg/YD4GBdxb4qUHO?= =?us-ascii?Q?NnizwFrHxU2HFlF6epbD7W7LexWpWTrCyQV/pgX8AOZu4l2kWsTficaJi3AB?= =?us-ascii?Q?oTp3Xtd1dh8o2zeGEUrbUd5CoKTm9C0K77AcuWqHYA/rDOWr8b9MzdU/BMdf?= =?us-ascii?Q?DwewQ=3D=3D?= X-Microsoft-Antispam-Message-Info: HvJ//td7KAkruDgR5KTqDJks7zZByVpz+SBQRJHXNCHwm8ydNcHkh8yWw+8AmrJvU4VLoAqFoPa3aD9X0Iv0egqssic1vdwobblNmy1fb28bGJfeuC6LDoqXlRBW0YlDAYn4qS03LnDSeaywqLsoAJPUgq8m1/qWgqxBaYbK00igtWd3AEVCgoCGYmEXG4Ls8QhvCsiq7mmjVEno0gU7ZLkN+CKPXFoa0SlAmu7UN0Re+SoM9hby7J0MdiRUWfoM4XK3ydeoEpBTsmL9uECnGdnNozWdrOkevI5qqLchQszGiysULEE1wpz2kDXtTQZOdNBq9ArfhPRLyNgrjpwVMD5K3MIlHVKLR10EFnLTPeg= X-Microsoft-Exchange-Diagnostics: 1;SN6PR08MB4944;6:xyPDN/Vm+ZO1C5R8S0FHXlaWDffXXY70GNPMlfHd6HU/DB8/Mu3CEgEPIpVZx0CNuvI0CL55LgTyfThFIjWR/Kpw7ADYgzPQmLiCFCAGS8qINVdxDAK5hg38a1DnbfdHny085hDQYZ8oWkbGlLcHcgFU6Ypd95RsmtSsShs3PrlLPhXki72JZmwnv7rr4/HWW/VDDYj3OUeId5/nWSjrDWKlaWUrn3SsnuJjkKj8giNiLf38b11UBcjfKNEV2INHxFLoPWRmy3sAn4+mJlJPzbwr61SH5tmnA0HiOsR05pJILZ/V6ZQiFtJcP/NgKuwik/+ldkeR7jdVkRsTYKR/cYeI+a+15uYvFMmyLriSGeaQuQw5dFupKobMozPaG3nncSx1tCnKpZo/n5zco4QPmyUw6gJ6J3SV60kpyaA9JqTticiZsxaGvbODK5dEHb2YttORs0gFPZIBOg/OMnwl/w==;5:9l1mC2AJYwuhS6KMigUDnMHHxa/YDyLu8tyFRie5jZoWcx9paHRG8iC/jun6/744mDYIokAq8q1J+b3J7oz3R6A+LynkRTL9ZzL8j2IBcOwYVCowPaqgZY2DJvfMlIZwquTlEHu/qtJ1Ht48FOsdvN8cBJC1x6z1AObHy2de5Mc=;24:zjpqOQIWLAfb/COcF9YOAZWtfUWZH0Ty27TUVyz/VsoVhv+ZdY4wrGKGXBokE/YjqzP2cG4YiJIERvDKs8WdL+lPZJ0Taen2AElTCfWrI/0= SpamDiagnosticOutput: 1:99 SpamDiagnosticMetadata: NSPM X-Microsoft-Exchange-Diagnostics: 1;SN6PR08MB4944;7:/7bh4W1rqX0GSfCpYYXBLY1+ouFSTmwHuXcJfF1Rwr7WaQyogmhZL6CilFgLGCS59wHTkX5BxYE4TKbj9i0e44Nn4Vz/9tuQAoVETvqko9Xn1hf6uo9vs3P1niJWci63u9fYLU56s1mCl3cQtN0PNxHud2B1VvItX+Fy/oalGAgBD0ZuPnr9sDEeHjKByHprbBeRpwg2EME945KksTfHoIVjzWlkR1AV1OjDuXwvkmqtC1dhJeNQeSiUhMITfiOw X-OriginatorOrg: mips.com X-MS-Exchange-CrossTenant-OriginalArrivalTime: 09 Jul 2018 16:49:42.7259 (UTC) X-MS-Exchange-CrossTenant-Network-Message-Id: c4a7abb5-05a2-47d4-d5bd-08d5e5bbf839 X-MS-Exchange-CrossTenant-FromEntityHeader: Hosted X-MS-Exchange-CrossTenant-Id: 463607d3-1db3-40a0-8a29-970c56230104 X-MS-Exchange-Transport-CrossTenantHeadersStamped: SN6PR08MB4944 Sender: linux-kernel-owner@vger.kernel.org Precedence: bulk List-ID: X-Mailing-List: linux-kernel@vger.kernel.org Hi Huacai, On Mon, Jul 09, 2018 at 10:26:38AM +0800, Huacai Chen wrote: > After commit 7f56b58a92aaf2c ("locking/mcs: Use smp_cond_load_acquire() > in MCS spin loop") Loongson-3 fails to boot. This is because Loongson-3 > has SFB (Store Fill Buffer) and the weak-ordering may cause READ_ONCE() > to get an old value in a tight loop. So in smp_cond_load_acquire() we > need a __smp_rmb() before the READ_ONCE() loop. > > This patch introduce a Loongson-specific smp_cond_load_acquire(). And > it should be backported to as early as linux-4.5, in which release the > smp_cond_acquire() is introduced. > > There may be other cases where memory barriers is needed, we will fix > them one by one. > > Cc: stable@vger.kernel.org > Signed-off-by: Huacai Chen > --- > arch/mips/include/asm/barrier.h | 18 ++++++++++++++++++ > 1 file changed, 18 insertions(+) > > diff --git a/arch/mips/include/asm/barrier.h b/arch/mips/include/asm/barrier.h > index a5eb1bb..e8c4c63 100644 > --- a/arch/mips/include/asm/barrier.h > +++ b/arch/mips/include/asm/barrier.h > @@ -222,6 +222,24 @@ > #define __smp_mb__before_atomic() __smp_mb__before_llsc() > #define __smp_mb__after_atomic() smp_llsc_mb() > > +#ifdef CONFIG_CPU_LOONGSON3 > +/* Loongson-3 need a __smp_rmb() before READ_ONCE() loop */ > +#define smp_cond_load_acquire(ptr, cond_expr) \ > +({ \ > + typeof(ptr) __PTR = (ptr); \ > + typeof(*ptr) VAL; \ > + __smp_rmb(); \ > + for (;;) { \ > + VAL = READ_ONCE(*__PTR); \ > + if (cond_expr) \ > + break; \ > + cpu_relax(); \ > + } \ > + __smp_rmb(); \ > + VAL; \ > +}) > +#endif /* CONFIG_CPU_LOONGSON3 */ The discussion on v1 of this patch [1] seemed to converge on the view that Loongson suffers from the same problem as ARM platforms which enable the CONFIG_ARM_ERRATA_754327 workaround, and that we might require a similar workaround. Is there a reason you've not done that, and instead tweaked your patch that's specific to the smp_cond_load_acquire() case? I'm not comfortable with fixing just this one case when there could be many similar problematic pieces of code you just haven't hit yet. Please also keep the LKMM maintainers on copy for this - their feedback will be valuable & I'll be much more comfortable applying a workaround for Loongson's behavior here if it's one that they're OK with. Thanks, Paul [1] https://www.linux-mips.org/archives/linux-mips/2018-06/msg00139.html