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=-7.3 required=3.0 tests=BAYES_00,DKIM_SIGNED, DKIM_VALID,DKIM_VALID_AU,HEADER_FROM_DIFFERENT_DOMAINS,MAILING_LIST_MULTI, MSGID_FROM_MTA_HEADER,NICE_REPLY_A,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 E8033C48BE5 for ; Tue, 15 Jun 2021 18:27:48 +0000 (UTC) Received: from kanga.kvack.org (kanga.kvack.org [205.233.56.17]) by mail.kernel.org (Postfix) with ESMTP id 73827610F7 for ; Tue, 15 Jun 2021 18:27:48 +0000 (UTC) DMARC-Filter: OpenDMARC Filter v1.3.2 mail.kernel.org 73827610F7 Authentication-Results: mail.kernel.org; dmarc=fail (p=none dis=none) header.from=oracle.com Authentication-Results: mail.kernel.org; spf=pass smtp.mailfrom=owner-linux-mm@kvack.org Received: by kanga.kvack.org (Postfix) id BF2696B0036; Tue, 15 Jun 2021 14:27:47 -0400 (EDT) Received: by kanga.kvack.org (Postfix, from userid 40) id BC9436B006C; Tue, 15 Jun 2021 14:27:47 -0400 (EDT) X-Delivered-To: int-list-linux-mm@kvack.org Received: by kanga.kvack.org (Postfix, from userid 63042) id 9F4F96B0072; Tue, 15 Jun 2021 14:27:47 -0400 (EDT) X-Delivered-To: linux-mm@kvack.org Received: from forelay.hostedemail.com (smtprelay0149.hostedemail.com [216.40.44.149]) by kanga.kvack.org (Postfix) with ESMTP id 6DDE06B0036 for ; Tue, 15 Jun 2021 14:27:47 -0400 (EDT) Received: from smtpin39.hostedemail.com (10.5.19.251.rfc1918.com [10.5.19.251]) by forelay02.hostedemail.com (Postfix) with ESMTP id 17CDF8798 for ; Tue, 15 Jun 2021 18:27:47 +0000 (UTC) X-FDA: 78256791774.39.5A95809 Received: from mx0a-00069f02.pphosted.com (mx0a-00069f02.pphosted.com [205.220.165.32]) by imf11.hostedemail.com (Postfix) with ESMTP id 34102200107A for ; Tue, 15 Jun 2021 18:27:34 +0000 (UTC) Received: from pps.filterd (m0246617.ppops.net [127.0.0.1]) by mx0b-00069f02.pphosted.com (8.16.0.43/8.16.0.43) with SMTP id 15FIMSup013418; Tue, 15 Jun 2021 18:27:20 GMT DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/relaxed; d=oracle.com; h=subject : to : cc : references : from : message-id : date : in-reply-to : content-type : content-transfer-encoding : mime-version; s=corp-2020-01-29; bh=QoHWPI66FWYWkK/5q3gau/qEKy/QAADkFCQT7r0QTjM=; b=ON4g2QJiCMqBXeIgslc61w21aZuRagqaTVg/8QVh+uMUwRTsA6mDe9GlsoMO554kGGhc 8F6GtYSYvYt5xjV7GYrE2sEjpM/XtxVLNHpfHYuiDZEdW5ohOt6iHSAA8hPPKveHwEmE wrkZ+y7kGPKpEySdJfqQ93eK4zgvScp5HBJwEfYOoyPtF5e8EzNrjN+n6ixLDIOh8pMK TrmYbVT9+LwoRs2JzoRNGaYZzWPJS+sIOac3Sdqk0MC3muGpveQFDaJjqoqy4qnoiTeA ZQ0bah4Epc/aqooelZrQyPm6viZwfI0srCNsKS3pqgx/hDSBuw2vMGU8Ubh3kzI1GTXy LA== Received: from userp3020.oracle.com (userp3020.oracle.com [156.151.31.79]) by mx0b-00069f02.pphosted.com with ESMTP id 395y1ks694-1 (version=TLSv1.2 cipher=ECDHE-RSA-AES256-GCM-SHA384 bits=256 verify=OK); Tue, 15 Jun 2021 18:27:20 +0000 Received: from pps.filterd (userp3020.oracle.com [127.0.0.1]) by userp3020.oracle.com (8.16.0.42/8.16.0.42) with SMTP id 15FIFQP6055812; Tue, 15 Jun 2021 18:27:19 GMT Received: from nam11-dm6-obe.outbound.protection.outlook.com (mail-dm6nam11lp2175.outbound.protection.outlook.com [104.47.57.175]) by userp3020.oracle.com with ESMTP id 396wava5fx-1 (version=TLSv1.2 cipher=ECDHE-RSA-AES256-GCM-SHA384 bits=256 verify=OK); Tue, 15 Jun 2021 18:27:19 +0000 ARC-Seal: i=1; a=rsa-sha256; s=arcselector9901; d=microsoft.com; cv=none; b=hEuDAtExscYl5hR80NVjE5TZr2EOInLsmJkyyCKYEL8kElIGIMcGeWYxVtwltiJe6WbpMV3UL31PfIoMrKABvDNZFNXQpzTWVKDlHEMq9PpwNOmCroxL1PiGhz7CmsdTt4d3A+w8yKaFI/wxJFWrHr9fsWaaoh5hBlN8gYjgMXMe4Wm4Pi+o0yAsmG66wsiPkG+UHADt8yjK6nDd06kX3EK/R88+2AnPEf0PRQOTWcTGwsXMhtFFIlQHeTDtAy/8e+wl/r6y59l8WkAJqcxMwCWI/yBIcRbJTh5jp9xLsLIP1B80jgawY3uRmKHtvHGpBEZHMELF0f29oxLwAjOUuA== 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=QoHWPI66FWYWkK/5q3gau/qEKy/QAADkFCQT7r0QTjM=; b=LbQlcjKHQG7pCag7ibg49kwkOnINOifRxL6WqpthZEbaYtivOTyOtr7vHNnnsdmvk8Yny1OqBseV7fw9oYRaoOivxZVyhUq5XI9m+ezBCOhlH9p70PxlrhRgEZNAqiT67UZHGPVrwcigdsPQkwdhufnyAREfl2EDDs/MkUnGMI258XG9L9ZYO/5yX5U2Wg7LJ7beDVuRvXMeDB/gUcVJnU9FqC4cUgORiLA/bnXvLpgwDVAMGhEnxryIFtWdAhZ69e523elwO7/CyUsz0O8ga+4sWJftZBU5Nf7EfSwE8bzPmMNE0rosRTA8uqYcchgI14yyiw49I+oSb9KLTTsq6Q== ARC-Authentication-Results: i=1; mx.microsoft.com 1; spf=pass smtp.mailfrom=oracle.com; dmarc=pass action=none header.from=oracle.com; dkim=pass header.d=oracle.com; arc=none DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/relaxed; d=oracle.onmicrosoft.com; s=selector2-oracle-onmicrosoft-com; h=From:Date:Subject:Message-ID:Content-Type:MIME-Version:X-MS-Exchange-SenderADCheck; bh=QoHWPI66FWYWkK/5q3gau/qEKy/QAADkFCQT7r0QTjM=; b=OpUoh37CyTIA+6gRBvqJ/sDLIWQ9T0fI92iIgag2d2gYVT9STpWkd9PCVTdqRsc4vHFYsHXPtzIqXQhBwKVm9oNhD21iakxAhESXFFne6IdpwGoezYC9WtyZQgQaa/t8LpAXJ7/OjuSu1qly/K1Fq0ZdFSoKLt2WkbRlyQ2YYvM= Received: from BY5PR10MB4196.namprd10.prod.outlook.com (2603:10b6:a03:20d::23) by BY5PR10MB3761.namprd10.prod.outlook.com (2603:10b6:a03:1ff::33) with Microsoft SMTP Server (version=TLS1_2, cipher=TLS_ECDHE_RSA_WITH_AES_256_GCM_SHA384) id 15.20.4242.16; Tue, 15 Jun 2021 18:27:17 +0000 Received: from BY5PR10MB4196.namprd10.prod.outlook.com ([fe80::5d11:ae6d:24b6:e838]) by BY5PR10MB4196.namprd10.prod.outlook.com ([fe80::5d11:ae6d:24b6:e838%3]) with mapi id 15.20.4219.025; Tue, 15 Jun 2021 18:27:17 +0000 Subject: Re: page refcount race between prep_compound_gigantic_page() and __page_cache_add_speculative()? To: Matthew Wilcox , Jann Horn Cc: Linux-MM , kernel list , Youquan Song , Andrea Arcangeli , Jan Kara , John Hubbard , "Kirill A. Shutemov" References: From: Mike Kravetz Message-ID: <41f698d6-a099-105d-e922-170fbb3e1798@oracle.com> Date: Tue, 15 Jun 2021 11:27:14 -0700 User-Agent: Mozilla/5.0 (X11; Linux x86_64; rv:68.0) Gecko/20100101 Thunderbird/68.1.1 In-Reply-To: Content-Type: text/plain; charset=utf-8 Content-Language: en-US Content-Transfer-Encoding: 7bit X-Originating-IP: [50.38.35.18] X-ClientProxiedBy: MWHPR20CA0017.namprd20.prod.outlook.com (2603:10b6:300:13d::27) To BY5PR10MB4196.namprd10.prod.outlook.com (2603:10b6:a03:20d::23) MIME-Version: 1.0 X-MS-Exchange-MessageSentRepresentingType: 1 Received: from [192.168.2.112] (50.38.35.18) by MWHPR20CA0017.namprd20.prod.outlook.com (2603:10b6:300:13d::27) with Microsoft SMTP Server (version=TLS1_2, cipher=TLS_ECDHE_RSA_WITH_AES_256_GCM_SHA384) id 15.20.4242.16 via Frontend Transport; Tue, 15 Jun 2021 18:27:16 +0000 X-MS-PublicTrafficType: Email X-MS-Office365-Filtering-Correlation-Id: 4fb75eea-05fb-47c8-b152-08d9302b3433 X-MS-TrafficTypeDiagnostic: BY5PR10MB3761: X-Microsoft-Antispam-PRVS: X-MS-Oob-TLC-OOBClassifiers: OLM:9508; X-MS-Exchange-SenderADCheck: 1 X-Microsoft-Antispam: BCL:0; X-Microsoft-Antispam-Message-Info: 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 X-Forefront-Antispam-Report: CIP:255.255.255.255;CTRY:;LANG:en;SCL:1;SRV:;IPV:NLI;SFV:NSPM;H:BY5PR10MB4196.namprd10.prod.outlook.com;PTR:;CAT:NONE;SFS:(376002)(366004)(136003)(346002)(39860400002)(396003)(6486002)(956004)(44832011)(2616005)(110136005)(16576012)(8936002)(4326008)(66946007)(5660300002)(16526019)(186003)(53546011)(26005)(31686004)(316002)(54906003)(2906002)(66556008)(8676002)(52116002)(66476007)(83380400001)(31696002)(86362001)(478600001)(36756003)(38350700002)(38100700002)(43740500002)(45980500001);DIR:OUT;SFP:1101; X-MS-Exchange-AntiSpam-MessageData-ChunkCount: 1 X-MS-Exchange-AntiSpam-MessageData-0: =?utf-8?B?VzdEU3lHTmdHenZKMVdaSE5JODNjZzdybk1tbEoxVGJIRU02Ym1POGJTdmZ5?= =?utf-8?B?ZVlhU3FCMis5SEF1OE5XK2RqWDNmbTBPa3lNZ1lnTDZJa05XdkVQUjZoMkdm?= =?utf-8?B?ZTZhazUyZUpGUU9hQUdpOEdJWldJLzkrbkwyQ3QrWkRsSHBmdGpqcGR2R1o5?= =?utf-8?B?blgzYld0VFM3MFhITk5lRnVVaHd2NG9GZUJZRG0vMG9yOUpValAxMjJ4MDFy?= =?utf-8?B?OGRBYUNlVjF5Wmd4Q0x0V0szbk9iUzh2ZjdnU1BEMndIWFNlUEQvbXdMb2NN?= =?utf-8?B?eGZpM1NIKzJpclZFSWJ4VVdmNFZCTmQ4TmFiRlZkT2VmWDJoSGE2eEFaWlJU?= =?utf-8?B?c1JWRkZzejBGa0tJaXo1NmpZMTRxaHpWcHZxa00xU2dRcXQxNStRcnRsMHhW?= =?utf-8?B?aHZjU1ZnMlNYVUo1UlpBbHNZek45bXdpR05nSTdKa3dlQnNJQmlmdWVwRVdB?= =?utf-8?B?bktkbys2TzVNdXB5RTA3NnRLdXNQU2haV3F1dGluRDF6bGZNVkRiVmswYlBF?= =?utf-8?B?OFdFUWNSYk1XbUlvcTBkZHJWM04xd0dkZmZrYjBETllkdTZFLzJZVkY0WXJH?= =?utf-8?B?QlFJb2Z0K2krNllacjBhbmd1TTRId21UcDFrMWpmcHZ4eWkwQzRCSW9wSlVo?= =?utf-8?B?SjBkQlEvWFlvK253TzJ3QkdnalRrTURiK1M2SysrRFY1bnJ3RGhlT1VHUGo2?= =?utf-8?B?TW9YRDd5MUFncitid3dnaFVGNHFIZFZyL1I2L21Dd3RHM1NiOHBYOHgrZTBa?= =?utf-8?B?UEhiaHJuSzFQcDAyZGZLRTRabXlSYTNqNFdIbzZLM2M4eHNLMDFCV0N5WVEx?= =?utf-8?B?blROVVE1QUNLdG81Y0hiTUZTcGVra3Y1blFlQ29MS1ZkYUdZUlhSUFM1amVk?= =?utf-8?B?T28zQy9yTkNYdkRvYnFmSGVOR1RTaGdhMjRhVFlmemk2L1Z2RVR3cjcvTHNC?= =?utf-8?B?Z1BZRjFFM2F0RjZXSDRzbTZHWUlEcXdIRkVTeXVLVEVZM0c4ckZPTlh5MVhx?= =?utf-8?B?NFI5VWNBRTFVWVFpSGVmMzFrMzRwUmo5aG5PcURhTmcxY3B6cWVkME1JS3Rz?= =?utf-8?B?OVloMHdIc0xjckIxWUdUY3FEMUhUM1lHWmlCWExWdU0zOWZTc2FqcUdYRlZ6?= =?utf-8?B?L0s4RXptWW15RCtYckJ3blNCbUE4MjBqZ2xKK29JMmdhVFVFeGxJOTgydXV4?= =?utf-8?B?bzZVQ3I5cjhmLzhSbVdVY25BemErK2RBZXgrRVNNaHVmN3pUYzVRaXpvS1ZM?= =?utf-8?B?YjR0Q3RXWHZvNVF4bFlsVlNxYldXQnFPK1N3T3JZZHlYS3VIOUVXcU1ScjE4?= =?utf-8?B?dGJtZWxvdTNjazdtY3VidUM0RmtFZFFhUFl1R0NSamVkZElzdDRkVEM4a25C?= =?utf-8?B?YWpkV1Y2dzJnOThMMGdCR1RmRTBsUEJtK0JSM09YU3k1bTVaRkZEYlZkRUVa?= =?utf-8?B?c05VWElYLzRkTHdVYUVCa2NoblRaSTJGOU5OWWRnLzhvQUhLSFFZY3Mwa1cw?= =?utf-8?B?ZklJM05XSG5DajZwL1ByV3gwMVlzVEh2ZGtQeWZ4VGl2WW9jTGgzOGJUY29T?= =?utf-8?B?bE5OYjNJVk9iSWtpdCtuSVZhamZqdGRSQXJXTk5vR2hsZ1pFOUVnSS9XMUlI?= =?utf-8?B?amg1ZlhLUlRSWE9lc0J5ZHN6YlFjL3k2dk42V1o5RFVJZVBmZGJKdHRkNldD?= =?utf-8?B?Q1BNbXJOQTQ1T21VZ2d2T2ZvVHpHWTc5ZVl1RzREYzFhNWZOeDZmVVppdFFy?= =?utf-8?Q?CrLDCMU7klUkQ9r+MLIN+AQbvLGKuGaq8ONNez7?= X-OriginatorOrg: oracle.com X-MS-Exchange-CrossTenant-Network-Message-Id: 4fb75eea-05fb-47c8-b152-08d9302b3433 X-MS-Exchange-CrossTenant-AuthSource: BY5PR10MB4196.namprd10.prod.outlook.com X-MS-Exchange-CrossTenant-AuthAs: Internal X-MS-Exchange-CrossTenant-OriginalArrivalTime: 15 Jun 2021 18:27:16.8908 (UTC) X-MS-Exchange-CrossTenant-FromEntityHeader: Hosted X-MS-Exchange-CrossTenant-Id: 4e2c6054-71cb-48f1-bd6c-3a9705aca71b X-MS-Exchange-CrossTenant-MailboxType: HOSTED X-MS-Exchange-CrossTenant-UserPrincipalName: 3T+EQJPw70SlwpJ2EDWYMc2hvCQcjAqFHvr6nGolOrkxNzIjdof4JiXfOpy/SgizdaUJgSTqFNFmfZmswz72rg== X-MS-Exchange-Transport-CrossTenantHeadersStamped: BY5PR10MB3761 X-Proofpoint-Virus-Version: vendor=nai engine=6200 definitions=10016 signatures=668682 X-Proofpoint-Spam-Details: rule=notspam policy=default score=0 adultscore=0 malwarescore=0 suspectscore=0 spamscore=0 bulkscore=0 mlxlogscore=999 mlxscore=0 phishscore=0 classifier=spam adjust=0 reason=mlx scancount=1 engine=8.12.0-2104190000 definitions=main-2106150114 X-Proofpoint-ORIG-GUID: kYz3TKMdVqd6COhkvbW2G8kJnSFV1-kp X-Proofpoint-GUID: kYz3TKMdVqd6COhkvbW2G8kJnSFV1-kp Authentication-Results: imf11.hostedemail.com; dkim=pass header.d=oracle.com header.s=corp-2020-01-29 header.b=ON4g2QJi; dkim=pass header.d=oracle.onmicrosoft.com header.s=selector2-oracle-onmicrosoft-com header.b=OpUoh37C; dmarc=pass (policy=none) header.from=oracle.com; spf=none (imf11.hostedemail.com: domain of mike.kravetz@oracle.com has no SPF policy when checking 205.220.165.32) smtp.mailfrom=mike.kravetz@oracle.com X-Stat-Signature: hemoxwj5o4ridtjkq75gcn6ps7u9p8jw X-Rspamd-Server: rspam04 X-Rspamd-Queue-Id: 34102200107A X-HE-Tag: 1623781654-165547 X-Bogosity: Ham, tests=bogofilter, spamicity=0.000003, version=1.2.4 Sender: owner-linux-mm@kvack.org Precedence: bulk X-Loop: owner-majordomo@kvack.org List-ID: On 6/15/21 5:40 AM, Matthew Wilcox wrote: > On Tue, Jun 15, 2021 at 01:03:53PM +0200, Jann Horn wrote: >> The messier path, as the original commit describes, is "gigantic" page >> allocation. In that case, we'll go through the following path (if we >> ignore CMA): >> >> alloc_fresh_huge_page(): >> alloc_gigantic_page() >> alloc_contig_pages() >> __alloc_contig_pages() >> alloc_contig_range() >> isolate_freepages_range() >> split_map_pages() >> post_alloc_hook() [FOR EVERY PAGE] >> set_page_refcounted() >> set_page_count(page, 1) >> prep_compound_gigantic_page() >> set_page_count(p, 0) [FOR EVERY TAIL PAGE] >> >> so all the tail pages are initially allocated with refcount 1 by the >> page allocator, and then we overwrite those refcounts with zeroes. >> >> >> Luckily, the only non-__init codepath that can get here is >> __nr_hugepages_store_common(), which is only invoked from privileged >> writes to sysfs/sysctls. Thanks for spotting this Jann! > Argh. What if we passed __GFP_COMP into alloc_contig_pages()? > The current callers of alloc_contig_range() do not pass __GFP_COMP, > so it's no behaviour change for them, and __GFP_COMP implies this > kind of behaviour. I think that would imply _not_ calling > split_map_pages(), which implies not calling post_alloc_hook(), > which means we probably need to do a lot of the parts of > post_alloc_hook() in alloc_gigantic_page(). Yuck. That might work. We would need to do something 'like' split_map_pages to split the compound free pages in the allocated range. Then, stitch them together into one big compound page. We 'should' be able to call post_alloc_hook on the resulting big compound page. Of course, that is all theory without digging into the details. Note that in the general case alloc_contig_range/alloc_contig_pages can be called to request a non-power of two number of pages. In such cases __GFP_COMP would make little sense. -- Mike Kravetz