From mboxrd@z Thu Jan 1 00:00:00 1970 Received: from BN8PR05CU002.outbound.protection.outlook.com (mail-eastus2azon11011056.outbound.protection.outlook.com [52.101.57.56]) (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 D575F30C147; Wed, 30 Sep 2026 05:39:04 +0000 (UTC) Authentication-Results: smtp.subspace.kernel.org; arc=fail smtp.client-ip=52.101.57.56 ARC-Seal:i=2; a=rsa-sha256; d=subspace.kernel.org; s=arc-20240116; t=1790746746; cv=fail; b=CLuoqbVFrbms1PPKe/nQ2A5J2JLrZtMLvVcv6+s5puofMw4H1HT6Hnmm7yJyPsBLb4kUkYsvZ6bwcrHP3MA7H8CQZN+I59wkSMo4t5f2ayc5b9fYdWkYOqv/6awC7iqRpMMX2UX+MgGZANKrshdMaiU2Gg+FzCpfMuBnLRGLxq8= ARC-Message-Signature:i=2; a=rsa-sha256; d=subspace.kernel.org; s=arc-20240116; t=1790746746; c=relaxed/simple; bh=ZU1mzj8jTyPXRt6osW9UBy0t6C1MLxHS+mriSIths9s=; h=Date:From:To:Cc:Subject:Message-ID:References:Content-Type: Content-Disposition:In-Reply-To:MIME-Version; b=TWO2z83ndjaIPd4q3p+qDq3VIeN5DJQ+ifuAvWB66TCOe4VrhG3TVqorGpeDtXHjlgoFr5WwfoBkUmkdcnL6x3j+UoVZSX+ZElOyZherzvnhei+kH1dAbsa2QWhHjIxMdldeqfrcMI42sgHNquyvOTHKC/PnO3ByD3d7qVW8iOc= 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=n3vrbbfn; arc=fail smtp.client-ip=52.101.57.56 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="n3vrbbfn" ARC-Seal: i=1; a=rsa-sha256; s=arcselector10001; d=microsoft.com; cv=none; b=yBbkP43sRD7ElAcwmFd8bhowfMw8uK4GP/5jqntPBxTq8RpF67hjSKiRByJ6ienHa4YOANcAOZC/XLsaY5axoxPFyk4we6XCIuTRb69F98cLASFllXhoS9Wa00rqjAkjj32xvwHQDdESkq92KTKh8fDed+eXTWr2VuzeSU5QLPF87YSDnorBaoIZWuqacJPJVOBHd3yazUw/L6ahdCKYolrjRLpk+n+U37ZAgVgsJkc+kzr1Y/9C4Wm71aHYEajZ9dgrW4ELzXMoSyMoo64XilyemuUY0IDKP1FpjmQZPVDcddWHON2tp61e5vH4A14HgyVgbmQ/MO8EhaZdxHqnQg== 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=vXSXrRY55bYTEE4Mhxd72otojqjKelUyD19Kjrq7C6A=; b=LbxvaCJJ/6Z3jcQ4HsHg9AS2PRcLR1+YDWoPjSWLDMUowlboDa9Br9Ghsls0xqnuzygI5SQuW5riGMlrdfP0pdUqpRUWRH3M3f31m0GcF3ume0FKe+VeYV5NWsvTt3KORYTPY/CrZUCRtYPbdjJDe2LxpRO2caLx63WI/KnPF8uOy1G4cE71jne51/bUPhqHz88Y0RgDSG2qr8g46hlmNMeNf39ou8VHzAuKijWbb5xumFAupgkk0629NLXIGhdlmUimJqwe1oLmBreVO1x18JYtCBJq+c3nG5clYxZvuYJDeSsUD6F1V/jAAhkXGArv1uiXE4Z5N5a1Tv84Giqtkg== 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=vXSXrRY55bYTEE4Mhxd72otojqjKelUyD19Kjrq7C6A=; b=n3vrbbfnKgwTfA1F7TJgVHfbdsOTPLhwCIpxUR670GOCqYaS+zaD85Z+MlceX9zVjzHq2hOgdcVqueitd283//HkQB2xlXvrpViNRhWu0zW+e164A/twwXMxGUgo+aY7miMvhy3lVgZNiDkDusvaC1MN0Hb1J2vYhrYOoiwr/b6aWGjh9+dJLx/GZ0jYStBd7yRFC1JIu0WqQSQoYiK+5tUKD/yF4exF9QaztuCdq+m/ODRV9uNAyOKQuB608vnxfVOrngte/v8MNjEHMTZdEeLMjFi4MJoXACZV1/lf9vC+3itBS8eMegaiqZWIYQMaC4K3CmdA/ZGquw8PaofaRA== Authentication-Results: mx.microsoft.com 1; dkim=none (message not signed) header.d=none;dmarc=none action=none header.from=nvidia.com; Received: from DM6PR12MB4827.namprd12.prod.outlook.com (2603:10b6:5:1d6::14) by PH9PR12MB409658.namprd12.prod.outlook.com (2603:10b6:510:412::13) with Microsoft SMTP Server (version=TLS1_2, cipher=TLS_ECDHE_RSA_WITH_AES_256_GCM_SHA384) id 15.21.472.15; Wed, 30 Sep 2026 05:38:59 +0000 Received: from DM6PR12MB4827.namprd12.prod.outlook.com ([fe80::6261:3040:864b:159c]) by DM6PR12MB4827.namprd12.prod.outlook.com ([fe80::6261:3040:864b:159c%6]) with mapi id 15.21.0451.022; Wed, 30 Sep 2026 05:38:59 +0000 Date: Wed, 30 Sep 2026 07:38:48 +0200 From: Andrea Righi To: Waiman Long Cc: Ridong Chen , Tejun Heo , Johannes Weiner , Michal =?iso-8859-1?Q?Koutn=FD?= , cgroups@vger.kernel.org, linux-kernel@vger.kernel.org Subject: Re: [PATCH v2] cgroup/cpuset: Don't access cpuset_cgrp_subsys.root in is_in_v2_mode() Message-ID: References: <20260930031833.660267-1-longman@redhat.com> Content-Type: text/plain; charset=us-ascii Content-Disposition: inline In-Reply-To: <20260930031833.660267-1-longman@redhat.com> X-ClientProxiedBy: MI1P293CA0030.ITAP293.PROD.OUTLOOK.COM (2603:10a6:290:3::17) To DM6PR12MB4827.namprd12.prod.outlook.com (2603:10b6:5:1d6::14) 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: DM6PR12MB4827:EE_|PH9PR12MB409658:EE_ X-MS-Office365-Filtering-Correlation-Id: 42bb6e0b-ad26-45a0-b0ae-08df1eb52057 X-MS-Exchange-SenderADCheck: 1 X-MS-Exchange-AntiSpam-Relay: 0 X-Microsoft-Antispam: BCL:0;ARA:13230040|376014|366016|1800799024|23010399003|11063799006|10067099003|56012099006|18002099003|22082099003; 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:DM6PR12MB4827.namprd12.prod.outlook.com;PTR:;CAT:NONE;SFS:(13230040)(376014)(366016)(1800799024)(23010399003)(11063799006)(10067099003)(56012099006)(18002099003)(22082099003);DIR:OUT;SFP:1101; X-MS-Exchange-AntiSpam-MessageData-ChunkCount: 1 X-MS-Exchange-AntiSpam-MessageData-0: =?us-ascii?Q?mR6BmfJ7D+3Y6a91rPZHNHAyOKRM+aFdxbEUpqOa81ZSfPVdlMJgReAwcOMI?= =?us-ascii?Q?JCJUkXJiGcq+/mVbdFSoUwVKKrJMWRd85eYwoaQVXS0ZFfDASVkBAyBrVhTh?= =?us-ascii?Q?GPtXeMB4Ib5HpBJ9Bwk0WmyGJxOg4cYiAfS1MHqIz7Mpt5uP3se1qikxzpkZ?= =?us-ascii?Q?z05HxW+cl2Tx1oBNlXf/GFB1Gxps3UB3J4MtxcmxdbFzspr2imSMDELY5pUl?= =?us-ascii?Q?yBHW9WzanGRjCcIyNpwtx8n5m27ZkYyxytEiC8+eaXBrg2NeCGdld0B5a5y8?= =?us-ascii?Q?5Hl8jei2/Q+qrF9gZm/3WXpDQVPHzkPrkK4MElkgQFXhpypnkRdhWFOQ04iK?= =?us-ascii?Q?P2Io0FKsgbKgnKzJCbN9DDtQI6oqEEFwOLERb2hzja6dO0ZawzzO8OBJOS9A?= =?us-ascii?Q?NsDIjYhZbU7Mhd97ywqIwnU7wZI4I9M4TAm+bYOB42v22k95NTAPeP6MDMpo?= =?us-ascii?Q?okzSUEBX4Y7rqV0nvuD353D09WLoyHc2Qf0bveTKpSb/tyk/42zMzEcbHulg?= =?us-ascii?Q?IWLXit3tv/9DuhaqMLNG9W9/+3Nt2LcfEZvCZRduU07DFklc1Mu8uawW/DvV?= =?us-ascii?Q?2kQCfE7OfEZViSqxwmojFjNlMFW2ZWR1t75Q4MdPh3LyAX+5BKlhMugSPPvb?= =?us-ascii?Q?x0bS9hV5hkfQnqADHUZcSI15amkIaNqtQe7rB3bQV2dL2QbbZ1HDZmgOhSK1?= =?us-ascii?Q?VYDGnNVMd7wsaPYI8yJyHpNVNW+4VRqzErVcJjdO3+NNAYF9h4wSGEeDIfv4?= =?us-ascii?Q?UM3qTY9ebHBZMNcW4QWjTuX5iTeQ4Jl3AAtfWng8/HuV9w+KdUK3dOGxrTDi?= =?us-ascii?Q?XkEtf9ysh6boAmHxmV1byyMTRPuf5q+pkDv0ZpRZqVYSJf+qEIMRjooeJkbD?= =?us-ascii?Q?/9wzgEq1pXqwTN3OMl6rcWvyzaSAaxzSCfhK5VZ5AYNjiXZqUXo1Wb36c+H+?= =?us-ascii?Q?xiwdm2GDX5x4W3kFJEgGVIXFngOnRSKtP0KcEstjhaNgEwGZxUFZ1AAOvvmK?= =?us-ascii?Q?aMN+cOZ8gjrgpX9F68VrnKf5O10klZpZjimJSotvN+OXh0CmBgldD127gg0y?= =?us-ascii?Q?B9gVMrWl7m2WYcb6AvjrMiDKi9XUpq13OARs/7FA45G4Y27rVLQGHN49AyWa?= =?us-ascii?Q?ntSuSKriDupxksX9iXxtr+oWINb60C6azLfWlUmKouy7asWG4Ac4S2fQNSjX?= =?us-ascii?Q?2zGo+zThwnfY4oVBDDQ00vw+mRiMgsxhcj86rxsktR7VwhjY10G32o1nu+Np?= =?us-ascii?Q?AK+QCANQEOvDpyYp9aOlD331fHLhlYHNHZiNNoA42m8EjzCFZO65VNh5sXY8?= =?us-ascii?Q?FIYUTOZq3V593M7Da3St3lfdIHvwJuk5PTFCa/NQAgyWXsaia+bs0uQoSaPq?= =?us-ascii?Q?nVddinuttWA08zQlMB4ECjDR8PmBE39r966LrZXA6ccx+PAnbX4vtWbGUVwe?= =?us-ascii?Q?phqeTIFrYZ77ERyQTRKV3xCRZ1rm1+YUNite/hS1PSHe+trLnuv7P7gu6DOW?= =?us-ascii?Q?6fYapWODthAN2ovfbqymkE6wbATqFd6LjNE1YA2Dw+TAXOMHawIeyRbFtQ1e?= =?us-ascii?Q?nhm73GorrwoMstDH4KdUDyo9E4EHoxMSgBR7S+QTYOKlMobshuiag3Uapnlw?= =?us-ascii?Q?i1XpWYbRWpzuLVJsfzTqBV/t1+SD/zx3l2OSMOmW/DMr7zV8RSFpS/ikRO1U?= =?us-ascii?Q?ix52xFlWaBnQrFF5LfjKOXn2p4lqqLcXNF1K999QVzNKzjQYsaX8sIqRQZ+j?= =?us-ascii?Q?Mk1rBUD2aQ=3D=3D?= X-OriginatorOrg: Nvidia.com X-MS-Exchange-CrossTenant-Network-Message-Id: 42bb6e0b-ad26-45a0-b0ae-08df1eb52057 X-MS-Exchange-CrossTenant-AuthSource: DM6PR12MB4827.namprd12.prod.outlook.com X-MS-Exchange-CrossTenant-AuthAs: Internal X-MS-Exchange-CrossTenant-OriginalArrivalTime: 30 Sep 2026 05:38:59.2094 (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: eBZEV6JVWy8nDIuNDTqGIbj/7HSpVKqw/nqoKp/ZAOgViF08ABaKH38d3h9a54p2n+oITWfqBNfYsN3I8zyt9A== X-MS-Exchange-Transport-CrossTenantHeadersStamped: PH9PR12MB409658 Hi Waiman, On Tue, Sep 29, 2026 at 11:18:33PM -0400, Waiman Long wrote: > After seeing the patch [1] to guard is_in_v2_mode() with RCU, it makes > me realize that is_in_v2_mode() may be called in a context where a new > cgroup filesystem is being rebound with stale cpuset_cgrp_subsys.root > pointer. Avoid this potential UaF situation by adding a new cpuset_v2_mode > flag which is set when the cpuset_v2_mode mount option is used. This > flag is written into only when cpuset_bind() is being called with a > stable cpuset_cgrp_subsys.root value. The is_in_v2_mode() helper is > modified to read the new cpuset_v2_mode flag instead of accessing > cpuset_cgrp_subsys.root directly. > > [1] https://lore.kernel.org/lkml/20260929084124.626693-2-arighi@nvidia.com > > Fixes: b8d1b8ee93df ("cpuset: Allow v2 behavior in v1 cgroup") > Signed-off-by: Waiman Long This works for me. Reviewed-by: Andrea Righi Thanks, -Andrea > --- > kernel/cgroup/cpuset.c | 11 +++++++++-- > 1 file changed, 9 insertions(+), 2 deletions(-) > > [v2] Update the comment as suggested by Ridong > > diff --git a/kernel/cgroup/cpuset.c b/kernel/cgroup/cpuset.c > index 19661df6244f..4a2b6f154609 100644 > --- a/kernel/cgroup/cpuset.c > +++ b/kernel/cgroup/cpuset.c > @@ -152,6 +152,12 @@ static cpumask_var_t isolated_cpus; /* CSCB */ > */ > static bool update_housekeeping; /* RWCS */ > > +/* > + * Set if "cpuset_v2_mode" mount option is used > + * Cached at bind time and not lock protected; accessed via {READ,WRITE}_ONCE > + */ > +static bool cpuset_v2_mode; > + > /* > * Copy of isolated_cpus to be passed to housekeeping_update() > */ > @@ -439,8 +445,7 @@ static inline bool cpuset_v2(void) > */ > static inline bool is_in_v2_mode(void) > { > - return cpuset_v2() || > - (cpuset_cgrp_subsys.root->flags & CGRP_ROOT_CPUSET_V2_MODE); > + return cpuset_v2() || READ_ONCE(cpuset_v2_mode); > } > > /** > @@ -3664,6 +3669,8 @@ static void cpuset_bind(struct cgroup_subsys_state *root_css) > mutex_lock(&cpuset_mutex); > spin_lock_irq(&callback_lock); > > + WRITE_ONCE(cpuset_v2_mode, > + !!(cpuset_cgrp_subsys.root->flags & CGRP_ROOT_CPUSET_V2_MODE)); > if (is_in_v2_mode()) { > cpumask_copy(top_cpuset.cpus_allowed, cpu_possible_mask); > cpumask_copy(top_cpuset.effective_xcpus, cpu_possible_mask); > -- > 2.55.0 >