From mboxrd@z Thu Jan 1 00:00:00 1970 Received: from NAM02-DM3-obe.outbound.protection.outlook.com (mail-dm3nam02on2069.outbound.protection.outlook.com [40.107.95.69]) (using TLSv1.2 with cipher ECDHE-RSA-AES256-GCM-SHA384 (256/256 bits)) (No client certificate requested) by smtp.subspace.kernel.org (Postfix) with ESMTPS id 2BDB41DFCB for ; Fri, 6 Jun 2025 18:21:41 +0000 (UTC) Authentication-Results: smtp.subspace.kernel.org; arc=fail smtp.client-ip=40.107.95.69 ARC-Seal:i=2; a=rsa-sha256; d=subspace.kernel.org; s=arc-20240116; t=1749234104; cv=fail; b=sWnTn3i//XHrBKOtrP+W+G3mPB1t+FkiJswWARg1kn0op59zN+r9f4ySCx35V0VYLB4Bq+39C0bfmNxHsPsPKC5TxkDhz2jJJCi0GflLwbSxu1DjEJbHT16IOpkJ8KZsLBgVBR/1wLPLrY6MD13zvyAxVfDI6N5nvA7DriRXdgw= ARC-Message-Signature:i=2; a=rsa-sha256; d=subspace.kernel.org; s=arc-20240116; t=1749234104; c=relaxed/simple; bh=lcMHYKhYXWu/vzSj57B6sqLPFaeSHskhktPOPQRAcVE=; h=Message-ID:Date:Subject:To:Cc:References:From:In-Reply-To: Content-Type:MIME-Version; b=ulJ8BsoTUrGaIEcfJVK4BiqadXcV7TobPU5VRzxA8hNUajr+hH6cSb8tkQqFcH1FMIjCiyXDTlsO2DHjflFpNQFzA4kydE5tE7Tez+2tETbpna9ONvz/D3bOoTbjc2eS3iG4HEr0UxFOy4CPrpwKz10AbebKY+lgXiKQFq+cyzI= ARC-Authentication-Results:i=2; smtp.subspace.kernel.org; dmarc=pass (p=reject dis=none) header.from=nvidia.com; spf=fail smtp.mailfrom=nvidia.com; dkim=pass (2048-bit key) header.d=Nvidia.com header.i=@Nvidia.com header.b=ZPSTvNsl; arc=fail smtp.client-ip=40.107.95.69 Authentication-Results: smtp.subspace.kernel.org; dmarc=pass (p=reject dis=none) header.from=nvidia.com Authentication-Results: smtp.subspace.kernel.org; spf=fail smtp.mailfrom=nvidia.com Authentication-Results: smtp.subspace.kernel.org; dkim=pass (2048-bit key) header.d=Nvidia.com header.i=@Nvidia.com header.b="ZPSTvNsl" ARC-Seal: i=1; a=rsa-sha256; s=arcselector10001; d=microsoft.com; cv=none; b=oGJyy/piO2FkXo4r5KQK3gERx7ipW44c+1Fm+62ruSH4pJcA42QjjTYeEdCQjo3ZHoM3Rkp8EblJZnJRD9XQuzdW0ce5U2e5nKFnGbwL4JHFR9vRxD5+KHYoZbwl67c7TVaBrj+W0EFxC2IvQmeWJ/kfKtdlV6+ch16YuxnbzDoHE9KkMCTzuIbtgJaGagNb+GxirEzuuik3u/x5prYy9TM7u6O6cOb2JLjIOvqpfO2ixe2soQUs9dPHVupSEu1LPVSHIw5meTI4P/2AfhTSmSKnsX8q+aw8nWWF4zh55Y3Wfp2qCBhUL30M6RHXjsPFqZbKgJi/uJcTFtr20bPFwQ== ARC-Message-Signature: i=1; a=rsa-sha256; c=relaxed/relaxed; d=microsoft.com; s=arcselector10001; h=From:Date:Subject:Message-ID:Content-Type:MIME-Version:X-MS-Exchange-AntiSpam-MessageData-ChunkCount:X-MS-Exchange-AntiSpam-MessageData-0:X-MS-Exchange-AntiSpam-MessageData-1; bh=AEL16ELCWXBjkHkzn48i/Chb/D4lQa2N+DK5B4qXDvU=; b=THtbYKlFbsukCNPCJdcW50nf5zOqE+emrkxM322CGq1HjdrPKWaEwCgXYRBUGiVC+6bracyy6z/6CSTYKC5c4EHmqLmvlacoosuuUpuV5k9Bu8rVNiXqnjuV1NqD/HUm4lYk5mJyK51kYP3HBT/zBjRpE5v8wU+vxBQm6D4zev81rKrdk3x8JynRMcC7SLQk+dhQWiaJ+zNg+cS+PeYocP+LWR0irONb2tZcx9H8gaekYQwhMPvXdZKe8vZdF3LDCrql74gEtfiKficb8hUxSsJp+R+Qp19YAUdBYMGss0HB8o7c04j8szrSQLVC3c1kIGL4wxFT6l2FK6gAR22qJQ== ARC-Authentication-Results: i=1; mx.microsoft.com 1; spf=pass smtp.mailfrom=nvidia.com; dmarc=pass action=none header.from=nvidia.com; dkim=pass header.d=nvidia.com; arc=none DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/relaxed; d=Nvidia.com; s=selector2; h=From:Date:Subject:Message-ID:Content-Type:MIME-Version:X-MS-Exchange-SenderADCheck; bh=AEL16ELCWXBjkHkzn48i/Chb/D4lQa2N+DK5B4qXDvU=; b=ZPSTvNslp1qJDBpFn6/5JJOWIk89NS+XuTjNZuMEn3sMQF0KSB0TjL8hIs14A8X2wnN4VXlD/E4saeRcCwSGYTHHnr3BcdLKhuUyZQ9KWCUWIjBx+oA/faxr5/aZssjRahEc662t838rY/K7bOKDzat6E1Vcg4Eq3ru6JntaTqKRQ9W2K3WNBZG3JEWiPWUpfBaYVUXBRuhltOJeEC+nsBoF6aTDTRAxyzX8IlxCMNJxsaT0Z2BEp4Wgunj1PyDDMbg/MrevwsjVnJ7SVjYjxyCPe1GAtB2sdGju6eaj86sWNDsy4pjFASS7QWdooxQ8yfPAfxCFfcPwoRFuxBpvmQ== Authentication-Results: dkim=none (message not signed) header.d=none;dmarc=none action=none header.from=nvidia.com; Received: from LV2PR12MB5968.namprd12.prod.outlook.com (2603:10b6:408:14f::7) by DM4PR12MB7645.namprd12.prod.outlook.com (2603:10b6:8:107::16) with Microsoft SMTP Server (version=TLS1_2, cipher=TLS_ECDHE_RSA_WITH_AES_256_GCM_SHA384) id 15.20.8792.38; Fri, 6 Jun 2025 18:21:37 +0000 Received: from LV2PR12MB5968.namprd12.prod.outlook.com ([fe80::e6dd:1206:6677:f9c4]) by LV2PR12MB5968.namprd12.prod.outlook.com ([fe80::e6dd:1206:6677:f9c4%4]) with mapi id 15.20.8769.037; Fri, 6 Jun 2025 18:21:37 +0000 Message-ID: <3dfbbd63-697d-42aa-8906-539d74df9123@nvidia.com> Date: Fri, 6 Jun 2025 11:21:34 -0700 User-Agent: Mozilla Thunderbird Subject: Re: [PATCH v1] mm/gup: remove (VM_)BUG_ONs To: David Hildenbrand , Lorenzo Stoakes Cc: Michal Hocko , linux-kernel@vger.kernel.org, linux-mm@kvack.org, Andrew Morton , "Liam R. Howlett" , Vlastimil Babka , Mike Rapoport , Suren Baghdasaryan , Jason Gunthorpe , Peter Xu References: <20250604140544.688711-1-david@redhat.com> <1a65d0e6-6088-4a15-9c19-537203fe655c@redhat.com> <50ff9149-2824-4e57-8d74-d8d0c063c87e@lucifer.local> <1a7513cf-4a0a-4e58-b20d-31c1370b760f@lucifer.local> <72bb36f2-65b6-4785-af9d-5b1f8126fc78@lucifer.local> <2f866f12-2aa0-4456-b215-08ddc9b13b1e@redhat.com> Content-Language: en-US From: John Hubbard In-Reply-To: <2f866f12-2aa0-4456-b215-08ddc9b13b1e@redhat.com> Content-Type: text/plain; charset=UTF-8 Content-Transfer-Encoding: 7bit X-ClientProxiedBy: SJ0PR05CA0025.namprd05.prod.outlook.com (2603:10b6:a03:33b::30) To LV2PR12MB5968.namprd12.prod.outlook.com (2603:10b6:408:14f::7) Precedence: bulk X-Mailing-List: linux-kernel@vger.kernel.org List-Id: List-Subscribe: List-Unsubscribe: MIME-Version: 1.0 X-MS-PublicTrafficType: Email X-MS-TrafficTypeDiagnostic: LV2PR12MB5968:EE_|DM4PR12MB7645:EE_ X-MS-Office365-Filtering-Correlation-Id: b6c2eb77-f47d-4ff7-cb41-08dda526f988 X-MS-Exchange-SenderADCheck: 1 X-MS-Exchange-AntiSpam-Relay: 0 X-Microsoft-Antispam: BCL:0;ARA:13230040|1800799024|366016|376014|7416014; X-Microsoft-Antispam-Message-Info: =?utf-8?B?M1c2aE82T2Fma0hoWUprcXNJd1NST0g2SWNDV1BXc1FGNHQ4bXZUVlpCdFBy?= =?utf-8?B?WjA4UTExK1JjaTAra2hhcmo4b1NyazlMNEZuc2d0bEZldTVYa0N6R2ZVRHNE?= =?utf-8?B?U2JEZ0ZwWmdtM2dLZmJWSE92Ukk1TXJ1dHh1RmxBRHpLUWQzamluOU9ST3Nw?= =?utf-8?B?TFl3WFA4bkZKTWUrRW5Fc2puRERpTnM3S3VFQnRJbFZ3OFZxT3k5NnhadHpN?= =?utf-8?B?d29LUXhYRWljWjVEWmhaM01CcmNraXJGdHBUSWJYR3VlMk9TZkRkY3EwR3hS?= =?utf-8?B?aWlMNkpiZVNMdUZVR3NOQmVIOTZENlovbXFwa3J1KzByTjJUZXljMGY4dG1w?= =?utf-8?B?emF5SXRZWlIxOHNFRE5kNG8rZjRLMFdvakduM0RUNEZkNzEra3ZmbWk0NFRw?= =?utf-8?B?QzZXRlZKU3oyMkJrNk5WVDBDWlBIWGh3eGRwaW1SdWNCN2xxWmFSMXJXNk14?= =?utf-8?B?dUFDSUlJSEdJUFdZZ3VoejVpNUlOaHJKZk45VVI1cmQ3RWJDdXRhbDcyOXZP?= =?utf-8?B?M2NRSXpWOWJXalgwaFBsbUQvVDlXYmxoYXRIMU5pK0ZBTnhUVTZZWTRVamt6?= =?utf-8?B?TlhwSE5RYUFZYU1mNTA1OFpLeU5INmpLNjFoOVdraDI1TStST1FOYWJRWG5L?= =?utf-8?B?cHhmbHZGdllIYW5hVUl5d2VxNUFBOU10MEdqbjg5bWNzRkVralA0a0p1b2Fp?= =?utf-8?B?U05hWVAvVFVUNVZDUjQrUFV1dkxrWjEwbnczNkdKcUhSb0NmWjJBamUrNi9N?= =?utf-8?B?VFZkWUJxVUJ0NFFQV1p2bm1RMExJN2lkOW1SZUlkR3lnTVlnQ01zcFdWbE4v?= =?utf-8?B?YXJXOGMxVEhETWhISkgxS3E2UC9xK2ZkRnVDKyswcTladCsrendzd1Y5b3k0?= =?utf-8?B?dE1DaEd0ajZWc3VtYXJVdk9oS2dwRVhpZGVNc2JoNVpSK2RkZ0c3TmU5eWlK?= =?utf-8?B?bkQrMTRCWkpDT3U2MnNDZTVHZkRJczZQa3pCdGtZTFM2MWc0RzVzSUxZU1NB?= =?utf-8?B?L0dhTUIxV08ybnpiOWtIVlZkQjVVUFN6VStqVjJEWHRXTFpXTC9DV29xSkxY?= =?utf-8?B?UUVxTWVnK2ZIMm9zbFR6VUtSVHdnUjVYeU5zcy92YTdkQXNJQ0JKeW1Takhq?= =?utf-8?B?Y0Ftd2RTbk9PbzBrSCtTRVR3NzZtYjNZT3EvS0hyUHJsZDRMZTc3MW95Q3d6?= =?utf-8?B?RWozdTc1cG12ZXo0RVVJNzd0eGFqMENSZlU5RkEzQVhVRTBRaUNNV051VDRD?= =?utf-8?B?MTdCR29vQjRtczErclBPRFJQSDhLd1dJWHc4YURJVlR6ajlCSFNGN253Mmpw?= =?utf-8?B?T3ZKWm5na25wNG45TmV4TG9BdDJCak5zb2lPVDZaQmIrUm5zVU1RMGZiam55?= =?utf-8?B?ekVNQjloWUV6UEVndUlOTndMRHkxZXpSMUJVL0E2ZHIvNW5Vb0x2bEFPV25k?= =?utf-8?B?VHpIWjNWVElWZUpmeHZ3S0duZmQvVVNoZys1KzlwbjBWZ1QwMkp0MURkZWZ6?= =?utf-8?B?c1FOaU0wcjZwemx6SzBKbkh0ekRqRGdFcEZSd1QzQzZtZlR5eXI5clZKbjc2?= =?utf-8?B?SDErUS9FOWkxSHVEVWdDRjZwWERmQXNpUm83R0RDeUVvaCs3ZjdZeXdFSVht?= =?utf-8?B?RGlwWXZtVmtQS3FDaklPNUFKVTFFV1BRaVdCd29Sa0dDUWIwZVRBNURFMWda?= =?utf-8?B?amEvaWlOcUxCU0pHZURHc2dEOTJNWldnZ1ZQYlZHSE9UblR6UTFjWFFIbXAy?= =?utf-8?B?dEt6YWJxOWZqTkhYQ1hHajZIZ2l4bDlQaVhJbjVHeWFsWklEcG54S1Fybjds?= =?utf-8?B?bS9TV21meWV0U2hBaVFiNFpSd2kzTHpMM1dWYWtEVVo1NyszZmQ2cXpKcmdY?= =?utf-8?B?WXFRSExHYlFCWmJqaWNFYlVZM0U2NDRCTWxkSzNFc0NpUlVFbDZzSFpuMng2?= =?utf-8?Q?s0lpsbqPfaU=3D?= X-Forefront-Antispam-Report: CIP:255.255.255.255;CTRY:;LANG:en;SCL:1;SRV:;IPV:NLI;SFV:NSPM;H:LV2PR12MB5968.namprd12.prod.outlook.com;PTR:;CAT:NONE;SFS:(13230040)(1800799024)(366016)(376014)(7416014);DIR:OUT;SFP:1101; X-MS-Exchange-AntiSpam-MessageData-ChunkCount: 1 X-MS-Exchange-AntiSpam-MessageData-0: =?utf-8?B?UEQ2VnpLOFpGWTUxQk5ZeTU3ZE9qeXl2TkZER01LMy85SHRzUVNEZEo2aUFh?= =?utf-8?B?N0lCcnRVaUN0RkVsRnpoNEZlOEF1a2hYaisvUzZUNjJVQ0pZYzB3TkNxSGt5?= =?utf-8?B?UWNvS2ZmUmlKR0pxRGVkWE9GNkloT085WnNOaU1kWWpscmJld0orUUdvVE5H?= =?utf-8?B?R0RUa0kvRG9nOEdhN0lRZVVsai9xYWN6cC9pYktFMlJ6amtEVGpqNUlleXNq?= =?utf-8?B?Z1U0bHFGUUtLeUpRU1p0MmlGOFZPWlJXOGEzdFFRWHZZSk9kR2NuajZPRWNs?= =?utf-8?B?RCtqZ0VMaTB4cFNta3JLNTN3eHdMRVIvQmJkSXljakFGeHc5ZHBvWmFhTG1W?= =?utf-8?B?SXNCMC9payt1VXZicWJUNmZqWEdOZ0hCbk1ybGFrenlwUHYybEhiVDJzdXBk?= =?utf-8?B?bUZ0Um80b2pDZmhOOTZZc3FiRUdVWXJ0aXdLWFdRK0lQR2o4YUUyd0x4T0F1?= =?utf-8?B?T3NweHNPQmxkNUh3SFNPTG1lZmxFbXpxbVJ0R0VUdXQ1SXE2MlpRUzZpelFu?= =?utf-8?B?NkwxODVDK1ZPVWlidk9zMEZtODlvNUt2dHVNNTQ1SVM4VkxjUDVuL0dEakM3?= =?utf-8?B?Y2dkTGU2MEpMM1luYkZDNXYvcktrTU1NSmZSYUhLYXErUGczT3BiK1NRbkF0?= =?utf-8?B?N3hsSWRCYVorZmFDVjgxdll1QzdValBiSlZ6ZUZEUFFwK1FBZEJqQUh4ZzI3?= =?utf-8?B?Q2lnTURtRTdGaW4xbEQ1cm9TTWVQYkhOOHZUeVEyV282MVhNcFdQckRRaEsw?= =?utf-8?B?R0JNVm00QnRNUFhxZFZmc2E4SkhTOE93ZjdoNUEwTG0vb3R3SVE1NzlpNllz?= =?utf-8?B?QlRUT0hCU3MrQnV4WVQzQ1pwcjlZK3JQV0FKbUdWUHEyeUkzK3hXZzRmbzMw?= =?utf-8?B?RjBVc3lDWWtBNU9aOGhWS21vMXZaMEFWcWxLdmoyQjFCWTJCOVRXMXRvdzF2?= =?utf-8?B?U3ZjdmRiRWh5cHltVklKOWtxUjhlcmdBMU9ZbHhqVzBCTzdmbUNHWXBrNlRv?= =?utf-8?B?T1h3aUM2NU1xUlErcmJSZHk4YTNZSmttSFEwblFZcUpvZHlOWDRsc1VzRHZX?= =?utf-8?B?VDViUkJaNHlSbG1CV3poajEzSnE2d1I3WExVVnBtektxVUdVTjlRNXEweVRx?= =?utf-8?B?WFNOK1pxczhBRUIyUDlZTHZoRks4ZHR4Mnk5Tzg0d08wb3JKZFlDRjR1aFgr?= =?utf-8?B?dW5xY3pyS2krN1FZaW82STIwUmYxdWo5cnRJVndXT25YK1R6ZkNMOXhVVzE0?= =?utf-8?B?R2d3b3Uvd2l6VGUwSGZLVGhwdFM5TzFaVHQ0RWJYc0NQc2s1NWplMDhydjdt?= =?utf-8?B?eWRHSmIvMlR1UWVmY2RkWXRNV0xTY3czdkwzTVFYYzB1OVdQVXo0bEVvaGNj?= =?utf-8?B?azNpQndwK2VyL1lON0lKZitBTUIyeDh2dFcyMjdIY1V6dExJMlVTOXkxbFFK?= =?utf-8?B?R3FaTE1QWXJ4VlhEU1lrMVZRdWM2a24vc05YQzBNeDFYMS9tZXhSb0doTUtm?= =?utf-8?B?YUsyOUFCUzRSSG5VeWNpYmZVaktDSUNRbzF3YTFyeFMzTGZEbitsZlF0RnpQ?= =?utf-8?B?NUJjd1hOWHBBMm41dCtGYlk1YkxCYkhiU1YzS1dicW5LVzlVQ214K3YxZXF6?= =?utf-8?B?R1MxSkhJZkhBRGxqSk4wUWs1cUVZN2xlVkM5eUZmelRyeXV4THJIbmVIY3Nw?= =?utf-8?B?TVNJS3F5UXBPaHpFWndJdGVkdkpWNVpyMUZia0JCL3BWRnB0QU1TSjZ5bm9o?= =?utf-8?B?UWNXdVFmZ2JDY3FubWtTWmJ1YWxwQ3FvamlocE1WSzVVa0RpRHVQZFBpQ2Qr?= =?utf-8?B?Qkh2WnhtRUxnZzVTSU9XWUpsSnpwWkFMU3VybnBiMGpRejJMUTFiNGJ4L3Ba?= =?utf-8?B?VkVWWUxZRVI5WVhwdURRWjFEaHBsTlRDMXJGNXhwdU9GMUtIMDkyc0VTSFRM?= =?utf-8?B?SnNhQ0RQdjVqbkZjd2d4YnR1Qkd1b2d3bTB4dUxodDRnVVVoMnc2ZW9EMzJQ?= =?utf-8?B?QVd0RnVqcEgyU0sxejY5eUhXZklRNTBPS2ZucnM5VTU1U2pwckVYZkYzNC82?= =?utf-8?B?eUlmamhuQVEzQy9LaE1QS1BTcm9uZ0QrOFpnMmhBZkw5SnVUU2pCcXRHc1NF?= =?utf-8?Q?CBI6h+eWIUhg3cSKfOS0lS1N+?= X-OriginatorOrg: Nvidia.com X-MS-Exchange-CrossTenant-Network-Message-Id: b6c2eb77-f47d-4ff7-cb41-08dda526f988 X-MS-Exchange-CrossTenant-AuthSource: LV2PR12MB5968.namprd12.prod.outlook.com X-MS-Exchange-CrossTenant-AuthAs: Internal X-MS-Exchange-CrossTenant-OriginalArrivalTime: 06 Jun 2025 18:21:37.1917 (UTC) X-MS-Exchange-CrossTenant-FromEntityHeader: Hosted X-MS-Exchange-CrossTenant-Id: 43083d15-7273-40c1-b7db-39efd9ccc17a X-MS-Exchange-CrossTenant-MailboxType: HOSTED X-MS-Exchange-CrossTenant-UserPrincipalName: /iVL41+XGxIkbLdNw7T3arXP/tZNZVQNamCzcYfST56wVYAjg3h7TNuobrEK01jbMVUwJ+8LBC+1QmaaeWqEIg== X-MS-Exchange-Transport-CrossTenantHeadersStamped: DM4PR12MB7645 On 6/6/25 11:15 AM, David Hildenbrand wrote: > On 06.06.25 20:06, Lorenzo Stoakes wrote: >> On Fri, Jun 06, 2025 at 10:57:44AM -0700, John Hubbard wrote: >>> On 6/6/25 4:04 AM, Lorenzo Stoakes wrote: >>>> On Fri, Jun 06, 2025 at 12:28:28PM +0200, David Hildenbrand wrote: >>>>> On 06.06.25 12:19, Lorenzo Stoakes wrote: >>>>>> On Fri, Jun 06, 2025 at 12:13:27PM +0200, Michal Hocko wrote: >>>>>>> On Fri 06-06-25 11:01:18, David Hildenbrand wrote: >>>>>>>> On 06.06.25 10:31, Michal Hocko wrote: >>>>>>> [...] >>>> So to me the only assessment needed is 'do we want to warn on this or not?'. >>>> >>>> And as you say, really WARN_ON_ONCE() seems appropriate, because nearly always >>>> we will get flooded with useless information. >>>> >>> >>> As yet another victim of such WARN_ON() floods at times, I've followed >>> this thread with great interest. And after reflecting on it a bit, I believe >>> that, surprisingly enough, WARN_ON() is a better replacement for VM_BUG_ON() >>> than WARN_ON_ONCE(), because: >> >> Right, these shouldn't be happening _at all_. > > > I'm easy on this point, I'd say in that case VM_WARN_ON() is the most >> _conservative_ approach, since these are things that must not happen, and >> so it's not unreasonable to fail to repress repetitions of the 'impossible' >> :) >> >> But I get the general point about ...WARN_ON_ONCE() avoiding floods. >> >> David, what do you think? > > Well, in this patch here I deliberately want _ONCE for the unpin sanity > checks. Because if they start happening (IOW, now after 5 years observed > for the first time?) I *absolutely don't* want to get flooded and > *really* figure out what is going on by seeing what else failed. > > And crashing on VM_BUG_ON() and not observing anything else was also not > particularly helpful :) > > Because ... they shouldn't be happening ... > > (well, it goes back to my initial point about requiring individual > decisions etc ...) > > Not sure what's best now in the general case, in the end I don't care > that much. > > Roll a dice? ;) One last data point: I've often logged onto systems that were running long enough that the dmesg had long since rolled over. And this makes the WARN_ON_ONCE() items disappear. > thanks, -- John Hubbard