From mboxrd@z Thu Jan 1 00:00:00 1970 Received: from SN4PR2101CU001.outbound.protection.outlook.com (mail-southcentralusazon11012051.outbound.protection.outlook.com [40.93.195.51]) (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 64D2B576EDF; Tue, 22 Sep 2026 17:27:48 +0000 (UTC) Authentication-Results: smtp.subspace.kernel.org; arc=fail smtp.client-ip=40.93.195.51 ARC-Seal:i=2; a=rsa-sha256; d=subspace.kernel.org; s=arc-20240116; t=1790098069; cv=fail; b=twmKJyxklh+8vJ0HOpmPYH3reYy/8mM1d0Kpa3lBSkFpfW2al4V6U9rXvcON9ouFx7R40iv6eet+V7lX1zp/zRs4IotmbtqWcaAUKHj/memzT3wI6MY9x/PwaSXNrDuFMFNIgdy0rzzWgfPhrSpwijyqaSBQvia2yGs0G3RSbBs= ARC-Message-Signature:i=2; a=rsa-sha256; d=subspace.kernel.org; s=arc-20240116; t=1790098069; c=relaxed/simple; bh=ZL2nF69xuHOsFsv5e1BWAoXhN5uaPrPim05k+d+sTRM=; h=Content-Type:Date:Message-Id:From:Subject:Cc:To:References: In-Reply-To:MIME-Version; b=aryU5E6LXqEJC6/l2sGx1bAsoIAezZWqapIOnhCKfGnT53fExq+IC2ImBkAenNbGdfqS25UuYLckZxL/l+7BZjrkc5s+Pbgb1kPOoiZ7NwhzJ4pRyOQQvyJeyQmEbSecjXSS/qJAY7mxOEOPW2+0elRWYwGK6wPoAFmVIGRgIuE= 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=fnPII/u9; arc=fail smtp.client-ip=40.93.195.51 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="fnPII/u9" ARC-Seal: i=1; a=rsa-sha256; s=arcselector10001; d=microsoft.com; cv=none; b=vwiuYs5pe8YiYgwMfAFel3DgOJj0/Br+X6XOlyPqKDEZVdn3CPIxDJQ/h2YDmFEDDDbg4JlZQ5+wbz73MqACPkV8IgiZgfa9uGwu1L14fJhsAf4yg+xtoKIS0W970MUD9zZ25rsxBOiEnDi9LV35gsKAvM+lktdGy1b9xyCaAqBODbumVwHPLSN3MdaAPYpRVVI2wgoYt/I0/hl2XEqkzHj8oeD2oUBN/SRaDU0H5YE57l+0Fv/jvfovXFeK77REZ3n1nVrJgHe1zy+T1aqshffNAsJwIVKIarhqstByz2LmypUeUEp/ZsUlmujttaPcCM1HZ9ZwXHJDBPCKXrPcwA== 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=yhkKQiwoFz+jV1o03qDsg74RQDfyIbvIuJeRJWRx6NA=; b=Uu1LM5c5c0bcHYqE8sWL5LQ7/8LYmv003Yw/N7nqC2wYRDwuDyLAbMGg32+nPma9b4tClSV1slnh05qa7CRCHasSK4yAVnYIq02RX3whKINSdkbvjBkkZn3znSSxvziH8WizZuBM5kJv4+2zxN4d84WHgZWDhr+FGCzw9yRYyUUQpCQrNgPPrtAQUUBlAImkrvhFTnrCYqXkc87usMvgrC+RWvwPo7oQNLSOwJuJUrngZQd9YgHF1nhf+Ji8MDOtvGEx4+/iXl5GRrY4rKo4lr8DGW2+/xcBxa3TZdaTlMZIkkA5NsZ9ZaLbN7sT63Zu3tGYum9jfglNT82DGKw/cQ== 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=yhkKQiwoFz+jV1o03qDsg74RQDfyIbvIuJeRJWRx6NA=; b=fnPII/u9xvBeXiGIrhf/6uekLjHkkIZVOpmTfUPR2o7yNdTfVCDE7m9yjMw1/aA8dOM1NOVaftR3tEdF2ca99O9w8nu5Hf9JtyH93nUxefnT89GpixSk5yx2J0DoM7zD4nkMIBbJNmUWC7CRMuMoQ6MzXt+W/F0f0lsVIRAvyGV/iYb+n9xVtmPmJm98GzvEt9tA+hsQFByMnzCxMkk1+Hu/eLZHowm+YzNE2a0ctaC6/QA7/MmtCQOk5P63YG4a+zx1OyADCdZt09jNveHZTmKGfMcQxJXkLK3xQDbckOTzg3riQXTzX/AEew9x2U9O8VLwS034bz4YEa478DyDzg== Authentication-Results: dkim=none (message not signed) header.d=none;dmarc=none action=none header.from=nvidia.com; Received: from IA0PR12MB8374.namprd12.prod.outlook.com (2603:10b6:208:40e::7) by DS0PR12MB6415.namprd12.prod.outlook.com (2603:10b6:8:cc::14) with Microsoft SMTP Server (version=TLS1_2, cipher=TLS_ECDHE_RSA_WITH_AES_256_GCM_SHA384) id 15.21.428.16; Tue, 22 Sep 2026 17:27:33 +0000 Received: from IA0PR12MB8374.namprd12.prod.outlook.com ([fe80::d85f:4c87:ae84:3f16]) by IA0PR12MB8374.namprd12.prod.outlook.com ([fe80::d85f:4c87:ae84:3f16%6]) with mapi id 15.21.0451.014; Tue, 22 Sep 2026 17:27:32 +0000 Content-Transfer-Encoding: quoted-printable Content-Type: text/plain; charset=UTF-8 Date: Tue, 22 Sep 2026 13:27:30 -0400 Message-Id: From: "Zi Yan" Subject: Re: [PATCH v4 3/4] mm/truncate: fix data loss when splitting straddling large folios fails Cc: , , , , , , , , , , , , , , , , , , , , , , , To: "Zhang Yi" , X-Mailer: aerc 0.22.0 References: <20260922110703.468389-1-yi.zhang@huaweicloud.com> <20260922110703.468389-4-yi.zhang@huaweicloud.com> In-Reply-To: <20260922110703.468389-4-yi.zhang@huaweicloud.com> X-ClientProxiedBy: YQBPR0101CA0081.CANPRD01.PROD.OUTLOOK.COM (2603:10b6:c01:4::14) To IA0PR12MB8374.namprd12.prod.outlook.com (2603:10b6:208:40e::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: IA0PR12MB8374:EE_|DS0PR12MB6415:EE_ X-MS-Office365-Filtering-Correlation-Id: 910864c6-8c50-4bc3-5f4c-08df18cec92d X-MS-Exchange-SenderADCheck: 1 X-MS-Exchange-AntiSpam-Relay: 0 X-Microsoft-Antispam: BCL:0;ARA:13230040|376014|7416014|23010399003|366016|1800799024|6133799003|18002099003|22082099003|5023799004|11063799006|56012099006|4143699003|10067099003|3023799007; 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:IA0PR12MB8374.namprd12.prod.outlook.com;PTR:;CAT:NONE;SFS:(13230040)(376014)(7416014)(23010399003)(366016)(1800799024)(6133799003)(18002099003)(22082099003)(5023799004)(11063799006)(56012099006)(4143699003)(10067099003)(3023799007);DIR:OUT;SFP:1101; X-MS-Exchange-AntiSpam-MessageData-ChunkCount: 1 X-MS-Exchange-AntiSpam-MessageData-0: =?utf-8?B?QTlJbWRoNGlWR0w5bzVQcnhrWGVoODQwZmF2dXdBRXhqd3FNRUdlRDR6UkJh?= =?utf-8?B?Z0VpcWpwOGVTVkdLZGxoUUFheUdCdkE1QXM0UGlKc3dEMHNZS09ucmo4R1JM?= =?utf-8?B?TTRsNmY0Z252ZVp1SjJoSG9CRzV5SGpVVFhlRkZpTHVnWkJLZHh3bllscVZP?= =?utf-8?B?OTR4RitMVWNiTDVTVThNL3hhT05EM3FaLzRzSUhKRVBXbGJaZmxXTmh5b0hZ?= =?utf-8?B?aTdHcGdWVmhYWm9WOGJqL1ZCQW92QmZMaWs3dnRWRkRrdnppRHUvT2JRQVZB?= =?utf-8?B?S2dlMHA2UHgzSVRSL2JWVmZYb2NGYkRxaCtLbmNXL2VvNk9sTGoxWWc1dWI4?= =?utf-8?B?RTFHenhDamRKTE9tMmFsOElqUEQzckVlZGp3U2xzNWdRb0M4bHdiV3pZK0th?= =?utf-8?B?bTFWbGZNajBTcWM1ODljSFBqZFZRWDRwUVpacWx4bEVuNVpFZWpHbFh6OFlj?= =?utf-8?B?bHp5N1ZFLzFoVmdFRyswQWJCYkE4M0tEdFMvcG1BZ2Y3WTBUaWtQNFFDQmto?= =?utf-8?B?T3dNTmg2Y2h1YlEvYlV0bG1wTVhvVTFGSjkvM2pZRmppUFFYWnNac25qU2k4?= =?utf-8?B?TGRDL1V1ZDJOWXlkNnc5ZXlZZGROd1ppZ29HM3E3NkdjdlZOcGhmS3owN0lI?= =?utf-8?B?SUR5c2JqZEsweSsxMHJVMjEwcWoyU0RSZk43d0EzSDFyRU9vL0hrOWVuWmZE?= =?utf-8?B?L1BOa09LeUVUaHNOYzhmdGo3VmUxcUhjY0lzWU15anBYTmtvN0Q2cUVPNlNl?= =?utf-8?B?REhJMzdycFdZMWRUZFlZTGo1QkgvL3Q1UXhJb2xzUDBydDRCMERYcmx4cHFE?= =?utf-8?B?N1Rib1Z1NU92Zm1sSEFYRm1SMXVvTjJDa0crVnBNWDZna2EySUZQUnR1ZkxF?= =?utf-8?B?SGo0QU0xZk4vUEEyS1FWWndjSUREWmxzVDlKcEdCbUYwUGs4MllzNnZjNkVQ?= =?utf-8?B?MHFLNjdBRXFYZ0ZCVDI0MjVHWVEvM1JLUFU5Qko1elQwUzViUi9hZEdMMmRM?= =?utf-8?B?L3M5bnZYMEhrSGJVMkVPS2JRUEtldWJDSHRqbjMxcFhheGlqYVVSMVpYL2d5?= =?utf-8?B?dUgwdExlRWtxQnJEUFBLc3Y0N3ZqZHR6T3ZyYXNuTkpNNWVhRFZEUWhIa3M3?= =?utf-8?B?WTNDcE81eTB6dTliTkU5L0FldEdPQzR1Z0NCMk1iU2w3V2FYSnNvUWxuK1J1?= =?utf-8?B?KzEvSDMxdU5wMzNCNFJMdXAvbEJLTVlONVNIUFM1TEFXUldBQmJiZVJ4Ulpx?= =?utf-8?B?UHNVR2o1RWtya3ZvRVFtWEViOXJ6VVZDOGFUaXNHbVhjS29TVTZhSm5jUWNv?= =?utf-8?B?a2phYUNMeXRITk85WTluYVFWalZ6QlVvQzFOZ09IWDQ5SU05Vk1hYzFEdVdT?= =?utf-8?B?V2ZvL3RKd3Rhclp2Tk94UmMxQWk5M3EydHFVOUpIRmVqWmNDbGwxMTVHS2U4?= =?utf-8?B?d3ZtalJSNG14ZlhMYWhuZmFCRTZiNUd0K2hEVkdpeDlTNlBkdi92TEgrS2hN?= =?utf-8?B?NWU1WEthcXlwWXdaZ3lYZFlTbDdhQ0pKRmxoaytkOEJyaDRQTmlqZ0hJMkFu?= =?utf-8?B?TC9kTzRHZUxwaFJMRFU3YWNuTXZodFZ0WnlLRkZieFlKdy84NHhwUGJJZ1Ux?= =?utf-8?B?U1dJT1RsMVVGNlpNOGVPa3VUd01ITXlBWDBHeXBjclk2YTV0M1diUytMcnpL?= =?utf-8?B?NU1FbW4wZWJ0d2gwOHZhbStUb1daYnc3Y1d6ZCtoaGNrVHZvUW1RRG1FMkwx?= =?utf-8?B?S29pVmdMZ0Ixa3hPemhtZFYydWl3Wk9pbTV2MStjQTRPakVhbnlVWDBSWkJD?= =?utf-8?B?b1kyR0tzYU5JamJlNXE5ZHE0TWpzY3BSZXV3c3hGTkZicndoVjZNbDA5YytE?= =?utf-8?B?bmdLS1FCdW1kTWJJemZ5NEVEalFXNUs1Q1hmRkNXZ1V4NElCTDMrM2hXUDdS?= =?utf-8?B?TmQ3OTUwTW5qNlpFN0JiOHBLQkxCbnVHSDZoNmxGcWp0b2xFTHJRK0xqTVVo?= =?utf-8?B?eG5ZMWQzRTEyZXVPUzRFZzRqZW55NmNQNlNnNDVlZWJSNE9jN1ZYL1ZFMytZ?= =?utf-8?B?eDBsL2ZSdEl6WUdTQytUN25NK3BsaFFOanJxS0lIZnBkM2JhY3hBRHpmZTlX?= =?utf-8?B?Z0E0cm1BUVRIYmJlNXNERDdSOWhKdWx1K0dDZjhnVW8wWHBwZDh2TjVJdloz?= =?utf-8?B?UmhDTWJOdTlBQ01zZTQ0RmpGYnRLbFBjWnljTTZ2WXh3WjM0WmtlMmx0QlRQ?= =?utf-8?B?L01RRFNKSW5QTDFNYTkwTGdsdGFUSFdXMHJNUFlveVpaaHBybUpMUTk2MTNL?= =?utf-8?Q?HR9e8ueGyugIoyl/A8?= X-OriginatorOrg: Nvidia.com X-MS-Exchange-CrossTenant-Network-Message-Id: 910864c6-8c50-4bc3-5f4c-08df18cec92d X-MS-Exchange-CrossTenant-AuthSource: IA0PR12MB8374.namprd12.prod.outlook.com X-MS-Exchange-CrossTenant-AuthAs: Internal X-MS-Exchange-CrossTenant-OriginalArrivalTime: 22 Sep 2026 17:27:32.8593 (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: DpRZhJYFGJD5bETNnhdfxl7MIKXaxUjXkGhynLIgQYlc0Z+/SyCGufJHgcBVHcVk X-MS-Exchange-Transport-CrossTenantHeadersStamped: DS0PR12MB6415 On Tue Sep 22, 2026 at 7:07 AM EDT, Zhang Yi wrote: > From: Zhang Yi > > truncate_inode_partial_folio() splits a large folio so that the caller's > truncate loop can drop the in-range sub-folios while keeping the > out-of-range tail. The first split at the punch start edge is > non-uniform, which leaves the sub-folio at the truncation end edge as > large as possible, this means it may still straddle the range, holding > both zeroed in-range and valid out-of-range data. The function then > attempts a second split at offset + length to isolate that tail. > > If the second split fails the straddling sub-folio stays merged. The > function returned true unconditionally on all exit paths of the success > block, telling the caller it was fully handled. The caller kept its > default end and the truncate loop truncated every sub-folio below it, > including the merged straddler, discarding the valid out-of-range tail. > > For example, a 4-page order-2 folio punched from offset 0 to the middle > of the last page: > > truncate_inode_pages_range() > truncate_inode_partial_folio() # same_folio =3D=3D true > 1st split at page0 -> [p0, p1, p2-3] # non-uniform, success > folio2 =3D p2-3 # straddles: p2 zeroed, p3 tail valid > 2nd split of folio2 fails / cannot lock > return true # BUG: caller keeps default end > end =3D 3 > loop truncates p0, p1, p2-3 # p3's valid tail is lost > > This became reachable after commit 7460b470a131 ("mm/truncate: use > folio_split() in truncate operation") replaced the atomic split_folio() > with folio_split(), whose non-uniform split can partially split a folio > and leave the end edge merged. > > It has gone unnoticed because a dirty large folio normally carries the > filesystem's private data, for example buffer_head, so > filemap_release_folio() fails on a dirty folio and folio_split() aborts > with -EBUSY before any split, leaving the straddler safely unsplit. The > bug is only reachable on paths that produce dirty large folios without > filesystem private data, and it was caught on the upcoming ext4 iomap > buffered I/O path when no ifs is attached. > > Rework the contract so the caller is told the folio range to discard: > > - Add pgoff_t *pstart and *pend out-parameters that receive the folio > range fully covered by [lstart, lend] after any split (or none), > aligned inwards to min_order, i.e. the folios wholly within the > range and safe to discard. > > - Report a reliable end position to the caller. The straddler is > looked up at an index aligned inwards to the mapping minimum folio > order, and *pend is set to that boundary on success. If nothing > covers the boundary, discarding up to it stays safe. If the > straddler is locked by someone else, fall back to folio->index. > This best-effort fallback may leave the in-range sub-folios to a > later pass but never discards the out-of-range tail. If the > straddler cannot be split, fall back to folio2->index so the caller > keeps the out-of-range tail. > > - Rename the byte-range parameters start/end to lstart/lend to better > express their semantics. > > Callers in truncate_inode_pages_range() and shmem_undo_range() pass > &pstart for the folio at the start edge and &pend for the folio at the > end edge, so the truncate loop drops exactly the fully covered pages and > never touches a straddling folio that still holds valid out-of-range > data. > > Suggested-by: Brian Foster > Link: https://lore.kernel.org/linux-fsdevel/anH-WKA1coW6wtfG@bfoster/ > Fixes: 7460b470a131 ("mm/truncate: use folio_split() in truncate operatio= n") > Signed-off-by: Zhang Yi > --- > mm/internal.h | 4 +-- > mm/shmem.c | 13 +++----- > mm/truncate.c | 88 +++++++++++++++++++++++++++++++++++---------------- > 3 files changed, 68 insertions(+), 37 deletions(-) > > @@ -251,6 +264,7 @@ bool truncate_inode_partial_folio(struct folio *folio= , loff_t start, loff_t end) Add more context: if (!folio_test_large(folio)) > return true; > =20 > min_order =3D mapping_min_folio_order(folio->mapping); > + min_nrbytes =3D mapping_min_folio_nrbytes(folio->mapping); > split_at =3D folio_page(folio, PAGE_ALIGN_DOWN(offset) / PAGE_SIZE); > if (!folio_split_or_unmap(folio, split_at, min_order)) { > /* > @@ -259,34 +273,57 @@ bool truncate_inode_partial_folio(struct folio *fol= io, loff_t start, loff_t end) > * for shmem truncate > */ > struct folio *folio2; > - pgoff_t end_idx; > + pgoff_t end, aligned_end =3D round_down(pos + offset + length, > + min_nrbytes) >> PAGE_SHIFT; > + /* Already at the minimum order, nothing to split */ > + if (folio_order(folio2) =3D=3D min_order) > + goto out_put; In the above, folio_test_large() is used to determine whether folio needs to be split or not, but here folio_order() =3D=3D min_order is used. Should the above "if (!folio_test_large(folio))" be changed to use min_order check to match the check here? --=20 Best Regards, Yan, Zi