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=-2.4 required=3.0 tests=DKIM_SIGNED,DKIM_VALID, DKIM_VALID_AU,HEADER_FROM_DIFFERENT_DOMAINS,MAILING_LIST_MULTI, MSGID_FROM_MTA_HEADER,SPF_HELO_NONE,SPF_PASS,USER_AGENT_SANE_1 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 55DDAC83009 for ; Tue, 28 Apr 2020 13:08:02 +0000 (UTC) Received: from vger.kernel.org (vger.kernel.org [23.128.96.18]) by mail.kernel.org (Postfix) with ESMTP id 2CBCB206A1 for ; Tue, 28 Apr 2020 13:08:02 +0000 (UTC) Authentication-Results: mail.kernel.org; dkim=pass (1024-bit key) header.d=prevas.dk header.i=@prevas.dk header.b="UV8SbGzE" Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1726975AbgD1NIB (ORCPT ); Tue, 28 Apr 2020 09:08:01 -0400 Received: from mail-eopbgr70095.outbound.protection.outlook.com ([40.107.7.95]:5156 "EHLO EUR04-HE1-obe.outbound.protection.outlook.com" rhost-flags-OK-OK-OK-FAIL) by vger.kernel.org with ESMTP id S1726785AbgD1NIA (ORCPT ); Tue, 28 Apr 2020 09:08:00 -0400 ARC-Seal: i=1; a=rsa-sha256; s=arcselector9901; d=microsoft.com; cv=none; b=EnW6/KHlCkMSusuFHFB6Eo7N90jhIJICCa+Lj8tlMdSVI1oYlc0xsJ3CJrvzm6lvRROooZwtqohKh5ose4v9F86CNv4rePtSVW7eDZq+MviTqrE9IKyUkt1wN31cYfIStgB2r28LTDERlDcMeT1saw3kwwlt3ubuiY6pCbU0qNbnv4GGqfJF4M2ZGoLXZNN+ClSfFtfc1sc4fAVOJYsYym4udfdKQ+Rzrv3VbIsLeuphQOQWeXe4KtYZK/g56nDQFCWI7Zi0CdJ1QDb/g1VBU0CCfl70psNC/Vtp8meGiVGPYMV10OLKJzApzjAn4EcBvSJM3WuCgpwdgqEOKy+MLA== ARC-Message-Signature: i=1; a=rsa-sha256; c=relaxed/relaxed; d=microsoft.com; s=arcselector9901; h=From:Date:Subject:Message-ID:Content-Type:MIME-Version:X-MS-Exchange-SenderADCheck; bh=UYgtue5ALmZyrZ0qSvjVDjS0jeWW1DvnFGoTKM/dvxo=; b=aFBsi00W7FAB3W82qxAIo+j0IEBNBaNkElVeAOYOXAhRJk8UPCQf9mJS5B8Si4/Dg/jT04MEir0xESTX5qIFCoYlzjGZY3SmzRllx6YlTtxrXS9CpiopXdNWS9V8Zdnipf/TtswRSKd6k105z5c7Nw3DmshO1oQHZIGeWe9OGNcM2HPsNr3iBW6k4KhCkCdHU2t2O6rJrLMHOkRc/ox+qkUmx+affcSZWuyywQF5GTO7nyv31gKpduvymU4Qxii+IPHee4+DjuE3HXkKnb/6ADMJSFLL7MAFh7mDvfYYlLBnTgc3PiiqLt/uv1KfNZ+a/kN8pX+MltSwLqIyMG3Dnw== ARC-Authentication-Results: i=1; mx.microsoft.com 1; spf=pass smtp.mailfrom=prevas.dk; dmarc=pass action=none header.from=prevas.dk; dkim=pass header.d=prevas.dk; arc=none DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/relaxed; d=prevas.dk; s=selector1; h=From:Date:Subject:Message-ID:Content-Type:MIME-Version:X-MS-Exchange-SenderADCheck; bh=UYgtue5ALmZyrZ0qSvjVDjS0jeWW1DvnFGoTKM/dvxo=; b=UV8SbGzExRDyCOO0lppk7O6oEleGNh6+kN6dZaGbB1+75QQfRY4yhPoc0WW4seF7mMlpyUGHZOsQgRuB8zwaNgVt/kxZO48B13yMnXYKE/FwjnSOePQ7lFlhvrrlsOXJWVcQVnzfvUXKl3Rb2ZERouzn0kkYxLSAnBC8Nq5FswA= Authentication-Results: arm.com; dkim=none (message not signed) header.d=none;arm.com; dmarc=none action=none header.from=prevas.dk; Received: from VI1PR10MB2765.EURPRD10.PROD.OUTLOOK.COM (2603:10a6:803:e1::21) by VI1PR10MB3664.EURPRD10.PROD.OUTLOOK.COM (2603:10a6:800:13f::14) with Microsoft SMTP Server (version=TLS1_2, cipher=TLS_ECDHE_RSA_WITH_AES_256_GCM_SHA384) id 15.20.2937.13; Tue, 28 Apr 2020 13:07:55 +0000 Received: from VI1PR10MB2765.EURPRD10.PROD.OUTLOOK.COM ([fe80::f0ac:4e97:2536:faa]) by VI1PR10MB2765.EURPRD10.PROD.OUTLOOK.COM ([fe80::f0ac:4e97:2536:faa%7]) with mapi id 15.20.2937.023; Tue, 28 Apr 2020 13:07:55 +0000 Subject: Re: [PATCH RT 10/30] hrtimer: Prevent using hrtimer_grab_expiry_lock() on migration_base To: Tom Zanussi , Steven Rostedt , linux-kernel@vger.kernel.org, linux-rt-users Cc: Thomas Gleixner , Carsten Emde , Sebastian Andrzej Siewior , John Kacur , Daniel Wagner , Julien Grall References: <20200123203930.646725253@goodmis.org> <20200123203943.749508731@goodmis.org> <1a5e52a6-39e4-ac9a-e11a-5df261e83068@prevas.dk> <7fce15e17cd3bef1216473386718e3cfd67349a4.camel@kernel.org> From: Rasmus Villemoes Message-ID: <049616fa-8908-e845-057f-d9482a483597@prevas.dk> Date: Tue, 28 Apr 2020 15:07:53 +0200 User-Agent: Mozilla/5.0 (X11; Linux x86_64; rv:68.0) Gecko/20100101 Thunderbird/68.7.0 In-Reply-To: <7fce15e17cd3bef1216473386718e3cfd67349a4.camel@kernel.org> Content-Type: text/plain; charset=utf-8 Content-Language: en-US Content-Transfer-Encoding: 7bit X-ClientProxiedBy: AM7PR02CA0018.eurprd02.prod.outlook.com (2603:10a6:20b:100::28) To VI1PR10MB2765.EURPRD10.PROD.OUTLOOK.COM (2603:10a6:803:e1::21) MIME-Version: 1.0 X-MS-Exchange-MessageSentRepresentingType: 1 Received: from [192.168.1.149] (5.186.116.45) by AM7PR02CA0018.eurprd02.prod.outlook.com (2603:10a6:20b:100::28) with Microsoft SMTP Server (version=TLS1_2, cipher=TLS_ECDHE_RSA_WITH_AES_256_GCM_SHA384) id 15.20.2937.13 via Frontend Transport; Tue, 28 Apr 2020 13:07:54 +0000 X-Originating-IP: [5.186.116.45] X-MS-PublicTrafficType: Email X-MS-Office365-Filtering-Correlation-Id: df3f89bb-932b-454e-6abd-08d7eb752aa7 X-MS-TrafficTypeDiagnostic: VI1PR10MB3664: X-Microsoft-Antispam-PRVS: X-MS-Oob-TLC-OOBClassifiers: OLM:9508; X-Forefront-PRVS: 0387D64A71 X-Forefront-Antispam-Report: CIP:255.255.255.255;CTRY:;LANG:en;SCL:1;SRV:;IPV:NLI;SFV:NSPM;H:VI1PR10MB2765.EURPRD10.PROD.OUTLOOK.COM;PTR:;CAT:NONE;SFTY:;SFS:(396003)(366004)(376002)(346002)(136003)(39850400004)(36756003)(44832011)(16576012)(186003)(7416002)(26005)(478600001)(8676002)(2616005)(956004)(316002)(4326008)(66556008)(16526019)(66476007)(81156014)(2906002)(52116002)(5660300002)(8976002)(31686004)(66946007)(86362001)(110136005)(8936002)(54906003)(6486002)(31696002);DIR:OUT;SFP:1102; X-MS-Exchange-SenderADCheck: 1 X-Microsoft-Antispam: BCL:0; X-Microsoft-Antispam-Message-Info: XQ+vRukWLkbOTcUJniu7VuHNZhz4sxUqQAhFqbYMLVF0+q6IBdjVOyqltFXYlmUlKkjUD2QXd3IG98bbE2/zknxkdIbTbNLKm3ZQ9SaEeeSCuxOi10Q1O48vA768ipxlLmWl/L+MpgVuUh1A7eB4DN9QY5e9zWHWA1MvVU5WtkBQ+v69hHHdmrVeWFh3/fIugFGayzpmFE87z6CYgyOVy96uwvF92gT9oJq27jxvdUkOvk9kcFN7dacieEghTRqZ12Q8dXOPkDNn5wMvc1PSsh/7Nb8Z0goB84N0+UWtiu8wVJYSqkyb6iep9u3ELesw5lKTBhsrWZJjb3HNVb6h3MlhnzNqAlYa5/2aHByIHBwJ6lv3AkGc9JE+gtqjkR924l11euXIhPVIs4ZzDM6HHTAmSfDAxTuuOYZ3/UckHWpwv/0VxfLp7IYtOE4/T7nT X-MS-Exchange-AntiSpam-MessageData: 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 X-OriginatorOrg: prevas.dk X-MS-Exchange-CrossTenant-Network-Message-Id: df3f89bb-932b-454e-6abd-08d7eb752aa7 X-MS-Exchange-CrossTenant-OriginalArrivalTime: 28 Apr 2020 13:07:55.7209 (UTC) X-MS-Exchange-CrossTenant-FromEntityHeader: Hosted X-MS-Exchange-CrossTenant-Id: d350cf71-778d-4780-88f5-071a4cb1ed61 X-MS-Exchange-CrossTenant-MailboxType: HOSTED X-MS-Exchange-CrossTenant-UserPrincipalName: qQzcumqelZ/pOGiqguznwXvXuO/BZjVWnkuI/6SyGGMT/neEYi+ft0wF914SeDRmaguB5W+LsvGvKf0hEhWbNFvX409tZL0TKZZifAulpmQ= X-MS-Exchange-Transport-CrossTenantHeadersStamped: VI1PR10MB3664 Sender: linux-kernel-owner@vger.kernel.org Precedence: bulk List-ID: X-Mailing-List: linux-kernel@vger.kernel.org On 28/04/2020 14.59, Tom Zanussi wrote: > On Tue, 2020-04-28 at 09:03 +0200, Rasmus Villemoes wrote: >> Hold on a second. This patch (hrtimer: Prevent using >> hrtimer_grab_expiry_lock() on migration_base) indeed seems to >> implement >> the optimization implied by the above, namely avoid the lock/unlock >> in >> case base == migration_base: >> >>> - if (timer->is_soft && base && base->cpu_base) { >>> + if (timer->is_soft && base != &migration_base) { >> >> But the followup patch (hrtimer: Add a missing bracket and hide >> `migration_base on !SMP) to fix the build on !SMP [the missing >> bracket >> part seems to have been fixed when backporting the above to 4.19-rt] >> replaces that logic by >> >> +static inline bool is_migration_base(struct hrtimer_clock_base >> *base) >> +{ >> + return base == &migration_base; >> +} >> + >> ... >> - if (timer->is_soft && base != &migration_base) { >> + if (timer->is_soft && is_migration_base(base)) { >> >> in the SMP case, i.e. the exact opposite condition. One of these >> can't >> be correct. >> >> Assuming the followup patch was wrong and the condition should have >> read >> >> timer->is_soft && !is_migration_base(base) >> >> while keeping is_migration_base() false on !SMP might explain the >> problem I see. But I'd like someone who knows this code to chime in. >> > > I don't know this code, but I think you're correct - the followup patch > reversed the condition by forgetting the !. > > So, does your problem go away when you make that change? Yes, it does. (I'll have to ask the customer to check in their setup whether the boot hang also vanishes). Essentially, adding that ! is equivalent to reverting the two patches on !SMP (which I also tested): Before, the condition was timer->is_soft && base && base->cpu_base and, assuming the NULL pointer checks are indeed redundant, that's the same as "timer->is_soft". Appending " && !is_migration_base()" to that, with is_migration_base() always false as on !SMP, doesn't change anything. Thanks, Rasmus