From nobody Fri May 3 12:22:53 2024 Return-Path: X-Spam-Checker-Version: SpamAssassin 3.4.0 (2014-02-07) on aws-us-west-2-korg-lkml-1.web.codeaurora.org Received: from vger.kernel.org (vger.kernel.org [23.128.96.18]) by smtp.lore.kernel.org (Postfix) with ESMTP id 2B7F4C7EE2C for ; Fri, 2 Jun 2023 22:59:01 +0000 (UTC) Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S236753AbjFBW67 (ORCPT ); Fri, 2 Jun 2023 18:58:59 -0400 Received: from lindbergh.monkeyblade.net ([23.128.96.19]:42558 "EHLO lindbergh.monkeyblade.net" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S236467AbjFBW64 (ORCPT ); Fri, 2 Jun 2023 18:58:56 -0400 Received: from mx0a-00069f02.pphosted.com (mx0a-00069f02.pphosted.com [205.220.165.32]) by lindbergh.monkeyblade.net (Postfix) with ESMTPS id 758EA1B9; Fri, 2 Jun 2023 15:58:48 -0700 (PDT) Received: from pps.filterd (m0333521.ppops.net [127.0.0.1]) by mx0b-00069f02.pphosted.com (8.17.1.19/8.17.1.19) with ESMTP id 352Hf5WY008205; Fri, 2 Jun 2023 22:58:21 GMT DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/relaxed; d=oracle.com; h=from : to : cc : subject : date : message-id : in-reply-to : references : content-transfer-encoding : content-type : mime-version; s=corp-2023-03-30; bh=UX2zF7AAbNcFJFaE0l8xuRYwS+0ZT2DTAUgvTYkzDio=; b=xg1nOnnpTVS1yVnIUw+p0CnOQy6/21GwWinadd1I6zhq3NFEVG2ouEOYmEkQIF6Qw8uq PFEVqrwliw1QmNgn9uxgllZr4+K6DJGc5LbYcKFk/bFY3KxfUmAmRSgurCCoRe/jCx5D qeimUw+iVuZZVy38bIIm8i+Mvi+tk+usU4Jp5uBxdCDvwzYNB33ivE6Clhod+R+jSO9S Wm95hdPqH1K5FuVCsdae8WsK1ct2JIsntYAFigqTLHWukB5uJAvgFmO9HE16frExwZ2c r5s66HLuw10dGooRxFO5BwBWHq6MKLUWyYJZ5RerYZu2ilCJEAMWQtROF/2osVj4AaRS Dw== Received: from iadpaimrmta01.imrmtpd1.prodappiadaev1.oraclevcn.com (iadpaimrmta01.appoci.oracle.com [130.35.100.223]) by mx0b-00069f02.pphosted.com (PPS) with ESMTPS id 3qvhjhbxka-1 (version=TLSv1.2 cipher=ECDHE-RSA-AES256-GCM-SHA384 bits=256 verify=OK); Fri, 02 Jun 2023 22:58:21 +0000 Received: from pps.filterd (iadpaimrmta01.imrmtpd1.prodappiadaev1.oraclevcn.com [127.0.0.1]) by iadpaimrmta01.imrmtpd1.prodappiadaev1.oraclevcn.com (8.17.1.19/8.17.1.19) with ESMTP id 352MCUZI004640; Fri, 2 Jun 2023 22:58:20 GMT Received: from nam11-co1-obe.outbound.protection.outlook.com (mail-co1nam11lp2176.outbound.protection.outlook.com [104.47.56.176]) by iadpaimrmta01.imrmtpd1.prodappiadaev1.oraclevcn.com (PPS) with ESMTPS id 3qu8afrys7-1 (version=TLSv1.2 cipher=ECDHE-RSA-AES256-GCM-SHA384 bits=256 verify=OK); Fri, 02 Jun 2023 22:58:19 +0000 ARC-Seal: i=1; a=rsa-sha256; s=arcselector9901; d=microsoft.com; cv=none; b=D6QLwCX+ovq97NPlYBzomOgM8BeNo89or4xut6LPM286ezWwxGxRliSwRmnkxvEeEs37G/obgiaVK4vGOtLIbUjplKCQRaNYn2BMPBdzrzBWLKg44ZTCPHtj+ka1+FE73mT8pWgH29mtinPpDhMxIpyd/+2r8qSUxy46qUgbnS6nQMXWl1wFDeny3zPwcHGysUqYC8fJ5dzwZYMHqgGX/4jjYZiLUbBk/SX/oC1uv19SScpCOK41UATtboAlSgAqMVjD2Iu1tWtkirWp2L+p3U3aB7g9G9Ev34xpn8Eg94N7IlWro/BTxptL7JwTWNYMgymJcsGd+YZFOYCCk66BkA== 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-AntiSpam-MessageData-ChunkCount:X-MS-Exchange-AntiSpam-MessageData-0:X-MS-Exchange-AntiSpam-MessageData-1; bh=UX2zF7AAbNcFJFaE0l8xuRYwS+0ZT2DTAUgvTYkzDio=; b=ZqiWPWeRliGysZJ50By4ob/lhCVTma2yL5PoyUp6RSe/kcp0qVBxKJx/baYHRq9FlIg+OyVScU8j8tqa59Dmzw38ZeZBDoV8iTcA3qqmfXt0lwUQSaiX5Xpwz78NaC7IJ/vy4D5ktqSKzOClqrvKKAdekxmLUM6u8RBlBDvx+PN0ANA/HTWxImTi5/+5sNs2UKbYP9e0V4Rz9dEUbfLUFe2IPzPMCXHViHUFDbKTdUZO/gjUWWJFlWWwiuAeJME5qr1OsTcJ9Vg0O5MNspYlp4t50y1IKQM6xA4T3V0BeGbs87eDfzYTEr+rySxyjQdYWpZSS/J2zP7MEaFUjcyvDg== 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=UX2zF7AAbNcFJFaE0l8xuRYwS+0ZT2DTAUgvTYkzDio=; b=djhC+iA4fFcEyAUH+oWChOoT4cZ8CFUz48GtoSX+y1gXMWhleQ+7a291ADiB+cpI0hen8+9z168AWH2ZrqctqmrWbs+qfZenHxzeHpuydrLeawzKVRmDhxrtjjunsfHV9gV0ENnG7mPemFkXEblQiqUqbdcw35Ra1XxU0Ciy1xo= Received: from BY5PR10MB4196.namprd10.prod.outlook.com (2603:10b6:a03:20d::23) by SA1PR10MB6519.namprd10.prod.outlook.com (2603:10b6:806:2b1::8) with Microsoft SMTP Server (version=TLS1_2, cipher=TLS_ECDHE_RSA_WITH_AES_256_GCM_SHA384) id 15.20.6433.23; Fri, 2 Jun 2023 22:57:56 +0000 Received: from BY5PR10MB4196.namprd10.prod.outlook.com ([fe80::4a17:13b0:2876:97f2]) by BY5PR10MB4196.namprd10.prod.outlook.com ([fe80::4a17:13b0:2876:97f2%6]) with mapi id 15.20.6455.027; Fri, 2 Jun 2023 22:57:56 +0000 From: Mike Kravetz To: linux-kernel@vger.kernel.org, linux-mm@kvack.org, linux-fsdevel@vger.kernel.org Cc: Matthew Wilcox , Ackerley Tng , Sidhartha Kumar , Muchun Song , vannapurve@google.com, erdemaktas@google.com, Andrew Morton , Mike Kravetz Subject: [PATCH 1/1] page cache: fix page_cache_next/prev_miss off by one Date: Fri, 2 Jun 2023 15:57:47 -0700 Message-Id: <20230602225747.103865-2-mike.kravetz@oracle.com> X-Mailer: git-send-email 2.40.1 In-Reply-To: <20230602225747.103865-1-mike.kravetz@oracle.com> References: <20230602225747.103865-1-mike.kravetz@oracle.com> Content-Transfer-Encoding: quoted-printable X-ClientProxiedBy: MW4PR03CA0197.namprd03.prod.outlook.com (2603:10b6:303:b8::22) To BY5PR10MB4196.namprd10.prod.outlook.com (2603:10b6:a03:20d::23) MIME-Version: 1.0 X-MS-PublicTrafficType: Email X-MS-TrafficTypeDiagnostic: BY5PR10MB4196:EE_|SA1PR10MB6519:EE_ X-MS-Office365-Filtering-Correlation-Id: f10cd4d8-36a0-405c-591e-08db63bccdb9 X-MS-Exchange-SenderADCheck: 1 X-MS-Exchange-AntiSpam-Relay: 0 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:(13230028)(39860400002)(346002)(396003)(366004)(376002)(136003)(451199021)(41300700001)(316002)(5660300002)(54906003)(66556008)(4326008)(66476007)(26005)(44832011)(86362001)(66946007)(2906002)(8936002)(8676002)(478600001)(38100700002)(6666004)(966005)(107886003)(6486002)(1076003)(6506007)(6512007)(186003)(2616005)(36756003)(83380400001);DIR:OUT;SFP:1101; X-MS-Exchange-AntiSpam-MessageData-ChunkCount: 1 X-MS-Exchange-AntiSpam-MessageData-0: =?us-ascii?Q?8RrIQJig+8nQ+FsEd0UBTTVf9dxD5ZzicEpVocn3sLu9ZpdO3F8EkOh7e5UJ?= =?us-ascii?Q?R/PnVuUAOkhwH1d1o+462DCUKM7BT1jYPFi2T2Zjpmdseq1zx27MJxebi+Vp?= =?us-ascii?Q?ZVVnbtjyoUZToacIY5jk0QFgtwNOja7SPDHW7u2yyywA0tYBRYdoxu/HM4Pd?= =?us-ascii?Q?zaw39gl6ABFMvuFVuAnXZpdL/28gI04yj8fKjDdBpfZTAKYOrRRUKzFN2wnC?= =?us-ascii?Q?glQIXnK767g0VU/hcA/SDehcDKdOHYCO5KbTxs5k8l5/mxec3N+vVV+j0jYr?= =?us-ascii?Q?Utm4WjlPsFQP7NKZ0n83jD0hxbP+jlmxDRIAqmOobdtOPe9L0yVnKHbebN+c?= =?us-ascii?Q?iDO1aUKF0fMAmSlR90sd2Te20nZyvZid8Wn5D2gmt4GKZG69Gz+pPv5vVcWc?= =?us-ascii?Q?7aCe6gYz09KCaEecnyNoye9WRZ77WLSgKq783/uUyEkgeHcFGlf6+ph7a5DB?= =?us-ascii?Q?CrJJfRP/crgc6lhk97zC9Y3Cx2Cgy4VqucutY62BBVTF4DeQvjYl+UfgDsv4?= =?us-ascii?Q?ItnDfb+nHtFmpZviJr3d2OBUutVQuI24GfiIsrFXaDsxrQR1qLbpdE0Y5d9I?= =?us-ascii?Q?/i823cw3Jp/9ZccYhcL8L4ik85kk2gwclauDwOrLi1BQi3Stsc/N4rw9WxMW?= =?us-ascii?Q?FXpCmDY/UXHFXAYG7fYJlCrJr3+3ZMP25MBUWk7J/ZVzk2V07EqIzyg35VF3?= =?us-ascii?Q?5kj6IYREu/NdoszxrGHKb96enMqZCvMjOlY8TNBatWZSIIABGTQ/2TqI9iiu?= =?us-ascii?Q?YIv0oDY2XiMlqBv++XPFTsmsbT5pJtRhET6iiOOEiQUMwk67II2oJ5pxpkbg?= =?us-ascii?Q?nqaxw2Etobn9SGOzlJ8mmOqlvfBXeBCvZH5qD0nMhZy8su9idvxkl7jsuZqn?= =?us-ascii?Q?d4XyhhM6qkZkVVtzOJk4NuCXyMANJr2v9olMW9yUikJjQNHUr4QQcaPyLrMK?= =?us-ascii?Q?Wjw6fwqE+vOiQFTOpJ1IEuQ/15Xfe7YKysDfkeOW2tZ4S3EuZGUJMdqxWwSg?= =?us-ascii?Q?amkeW2EUtxm8pK3936PQO8aZr/3J6+nlA+YakTeiIwQZ7cUOEQWNXFfoW9gq?= =?us-ascii?Q?osEcsjnEeE4cfOLOGFzH0DOMW+fxbr0iJsIkc7Um8wGea4OmYlbX/MTN9YMO?= =?us-ascii?Q?0cDyUDGeqv3ezI87zvW0845wK8W2oCCyOLqc0vEG6BlPkabMC3lBwTZWrUqW?= =?us-ascii?Q?3/e73xUCz5xpFqoQkU3WzJF9puyPUzqdVnzHy7QxRIcsxy8o+th7OVEuVO0X?= =?us-ascii?Q?cwv0iT++ewlBiLqEn8n2LxtkTw8gllqvWMDH3p2f5WrYHEqGRmKMv8DuD5dx?= =?us-ascii?Q?8YCR7J94P0F+82yHdb1UDhi+m5E1IYYflpPPAWS5p0wpKF3lu9MmumWpLwWk?= =?us-ascii?Q?MPexpNBHfd2Ypkh35LvXe05s1sF5jHhgiJ3lNNQ4H0L/WLKLPGQOLd2Ko1MB?= =?us-ascii?Q?gZ3NU6Putw7p2+7kc2k/39QmrowhA6IzK2Wj7VVxP+ZOTW0Ay7onzag4Xm3v?= =?us-ascii?Q?QQZ0cbagcxlhqPjoBM32f2VYxSnC4J+cjl66QI3CJxDmCuRFqbH+WaghCpzF?= =?us-ascii?Q?CIqvsfMzCjucmrNdwKgKelWt4LZ5NGs2P6mGkuf8UY0UOh7j40772eK4Z7EC?= =?us-ascii?Q?Bw=3D=3D?= X-MS-Exchange-AntiSpam-ExternalHop-MessageData-ChunkCount: 1 X-MS-Exchange-AntiSpam-ExternalHop-MessageData-0: =?us-ascii?Q?n9WBZ+lS/sBg63e8wTzw1ZZqxn1z4ntdzf0GS4e8ERNm1NdBIWzaO4J8V1ZZ?= =?us-ascii?Q?MgZsUiAl0WGSgzJ16P5UFPcRPoYhy2hFhZ6WPfXhg3Fh3VjfpkKgOsKDuEB9?= =?us-ascii?Q?Q+Kd08AClGLiNTdKWc1kJlMQmN9bLaTyGgfJRZN2GAx1h16B3ui6UYF+PplP?= =?us-ascii?Q?vbwBKq3TqjQQboIplENr+0WN9Nfo+wB0x0gWeV8OJ8f7cXfYBaU9pIiXdOhJ?= =?us-ascii?Q?rNa9ayvieaZhnVjZA8d+ur/ifttuou4CmOJEJDi3Gu7VL4MpaQVlkFh9XeWY?= =?us-ascii?Q?nFn81UWNf18si2zkAPjm4XFGkq4xeljPrj3N7X8t6W9m+oQkoFzhRREODa1d?= =?us-ascii?Q?YReC58STdpF4F/NBJ2Vh73Gg8aJmM9E96ajFe8A4YnHOhFPfHm5weENdSlJL?= =?us-ascii?Q?InVyq1IQPDFi00acQYgDJKRmFOlVDlevDUCp6mGMygBxse0IgppVi+JT+8YO?= =?us-ascii?Q?O3GgVPuCtZbB6DwzoVpvGamHqZBhpo04YbGgBDPfZcCK3iOYoXCnqrxUb8xx?= =?us-ascii?Q?vX+/EhCORj8WKbfee+ATp0FVX0OEoSKzVsQocMetTWvlH93XvplQ3pztHAOJ?= =?us-ascii?Q?qOentZ0XEvbI8rwsFaPVGfNijkH5mBZMGsiO43cAfgh80cPUk/lpIC6K2I/S?= =?us-ascii?Q?x7MP7a7XvtXMh82DDNyaXKhIoebCAvuHb470Ph48E8G2tPnwJ7vKwJ3ByIUz?= =?us-ascii?Q?CFEvw/DeFn+x0zRuh/gO+FxyGk/Ts6G3Bl9zW4NzhzhOQrKiXpNHXW4sJRmK?= =?us-ascii?Q?1qXXunBPDtvCNbbOkwEb/kDxTQ+tmkggnHA05aztytDuKZRl+l75Q0lgh7ko?= =?us-ascii?Q?IeSknIdPhT4lKDvxzj/tooLbl8k1pYuFcKdmDAXppkoDB/O0vuSV4yffWL0Y?= =?us-ascii?Q?E2ChMGGVazxhR+UR4s+C2U6P6eL75SZuUVhCBiALsekeIshfaeyTVMMFZH/w?= X-OriginatorOrg: oracle.com X-MS-Exchange-CrossTenant-Network-Message-Id: f10cd4d8-36a0-405c-591e-08db63bccdb9 X-MS-Exchange-CrossTenant-AuthSource: BY5PR10MB4196.namprd10.prod.outlook.com X-MS-Exchange-CrossTenant-AuthAs: Internal X-MS-Exchange-CrossTenant-OriginalArrivalTime: 02 Jun 2023 22:57:56.1045 (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: H5Q/3ofeT6U82SbO/v8U4r7cHpC1xf/226v5A7vE0hfTFB5hIZ2JOL/2E5DnRBDEL2Z0PSe0O837NE47g61hlw== X-MS-Exchange-Transport-CrossTenantHeadersStamped: SA1PR10MB6519 X-Proofpoint-Virus-Version: vendor=baseguard engine=ICAP:2.0.254,Aquarius:18.0.957,Hydra:6.0.573,FMLib:17.11.176.26 definitions=2023-06-02_16,2023-06-02_02,2023-05-22_02 X-Proofpoint-Spam-Details: rule=notspam policy=default score=0 suspectscore=0 phishscore=0 spamscore=0 adultscore=0 mlxlogscore=999 bulkscore=0 malwarescore=0 mlxscore=0 classifier=spam adjust=0 reason=mlx scancount=1 engine=8.12.0-2304280000 definitions=main-2306020181 X-Proofpoint-GUID: -lqIgs5IfhyMUgG4BmkCOZm1ml9_72Gf X-Proofpoint-ORIG-GUID: -lqIgs5IfhyMUgG4BmkCOZm1ml9_72Gf Precedence: bulk List-ID: X-Mailing-List: linux-kernel@vger.kernel.org Content-Type: text/plain; charset="utf-8" Ackerley Tng reported an issue with hugetlbfs fallocate here[1]. The issue showed up after the conversion of hugetlb page cache lookup code to use page_cache_next_miss. Code in hugetlb fallocate, userfaultfd and GUP is now using page_cache_next_miss to determine if a page is present the page cache. The following statement is used. present =3D page_cache_next_miss(mapping, index, 1) !=3D index; There are two issues with page_cache_next_miss when used in this way. 1) If the passed value for index is equal to the 'wrap-around' value, the same index will always be returned. This wrap-around value is 0, so 0 will be returned even if page is present at index 0. 2) If there is no gap in the range passed, the last index in the range will be returned. When passed a range of 1 as above, the passed index value will be returned even if the page is present. The end result is the statement above will NEVER indicate a page is present in the cache, even if it is. As noted by Ackerley in [1], users can see this by hugetlb fallocate incorrectly returning EEXIST if pages are already present in the file. In addition, hugetlb pages will not be included in core dumps if they need to be brought in via GUP. userfaultfd UFFDIO_COPY also uses this code and will not notice pages already present in the cache. It may try to allocate a new page and potentially return ENOMEM as opposed to EEXIST. Both page_cache_next_miss and page_cache_prev_miss have similar issues. Fix by: - Check for index equal to 'wrap-around' value and do not exit early. - If no gap is found in range, return index outside range. - Update function description to say 'wrap-around' value could be returned if passed as index. [1] https://lore.kernel.org/linux-mm/cover.1683069252.git.ackerleytng@googl= e.com/ Reported-by: Ackerley Tng Signed-off-by: Mike Kravetz Reviewed-by: Ackerley Tng Tested-by: Ackerley Tng --- mm/filemap.c | 26 ++++++++++++++++---------- 1 file changed, 16 insertions(+), 10 deletions(-) diff --git a/mm/filemap.c b/mm/filemap.c index 71dc90f64e43..123540c7ba45 100644 --- a/mm/filemap.c +++ b/mm/filemap.c @@ -1733,7 +1733,9 @@ bool __folio_lock_or_retry(struct folio *folio, struc= t mm_struct *mm, * * Return: The index of the gap if found, otherwise an index outside the * range specified (in which case 'return - index >=3D max_scan' will be t= rue). - * In the rare case of index wrap-around, 0 will be returned. + * In the rare case of index wrap-around, 0 will be returned. 0 will also + * be returned if index =3D=3D 0 and there is a gap at the index. We can = not + * wrap-around if passed index =3D=3D 0. */ pgoff_t page_cache_next_miss(struct address_space *mapping, pgoff_t index, unsigned long max_scan) @@ -1743,12 +1745,13 @@ pgoff_t page_cache_next_miss(struct address_space *= mapping, while (max_scan--) { void *entry =3D xas_next(&xas); if (!entry || xa_is_value(entry)) - break; - if (xas.xa_index =3D=3D 0) - break; + return xas.xa_index; + if (xas.xa_index =3D=3D 0 && index !=3D 0) + return xas.xa_index; } =20 - return xas.xa_index; + /* No gaps in range and no wrap-around, return index beyond range */ + return xas.xa_index + 1; } EXPORT_SYMBOL(page_cache_next_miss); =20 @@ -1769,7 +1772,9 @@ EXPORT_SYMBOL(page_cache_next_miss); * * Return: The index of the gap if found, otherwise an index outside the * range specified (in which case 'index - return >=3D max_scan' will be t= rue). - * In the rare case of wrap-around, ULONG_MAX will be returned. + * In the rare case of wrap-around, ULONG_MAX will be returned. ULONG_MAX + * will also be returned if index =3D=3D ULONG_MAX and there is a gap at t= he + * index. We can not wrap-around if passed index =3D=3D ULONG_MAX. */ pgoff_t page_cache_prev_miss(struct address_space *mapping, pgoff_t index, unsigned long max_scan) @@ -1779,12 +1784,13 @@ pgoff_t page_cache_prev_miss(struct address_space *= mapping, while (max_scan--) { void *entry =3D xas_prev(&xas); if (!entry || xa_is_value(entry)) - break; - if (xas.xa_index =3D=3D ULONG_MAX) - break; + return xas.xa_index; + if (xas.xa_index =3D=3D ULONG_MAX && index !=3D ULONG_MAX) + return xas.xa_index; } =20 - return xas.xa_index; + /* No gaps in range and no wrap-around, return index beyond range */ + return xas.xa_index - 1; } EXPORT_SYMBOL(page_cache_prev_miss); =20 --=20 2.40.1