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Fri, 24 Apr 2026 17:51:38 -0700 Date: Fri, 24 Apr 2026 17:51:37 -0700 From: Nicolin Chen To: Jason Gunthorpe CC: Baolu Lu , Will Deacon , "Robin Murphy" , Joerg Roedel , Bjorn Helgaas , "Rafael J . Wysocki" , Len Brown , Pranjal Shrivastava , Mostafa Saleh , Kevin Tian , , , , , , , Shuai Xue Subject: Re: [PATCH v3 05/11] iommu: Change group->devices to RCU-protected list Message-ID: References: <12a224061de4fff9e0725909fd0ba4e14996ff08.1776381841.git.nicolinc@nvidia.com> <779dad61-d7e7-4ae0-83a9-8c5920222219@linux.intel.com> <20260424131148.GB3444440@nvidia.com> <20260424225820.GN3444440@nvidia.com> Precedence: bulk X-Mailing-List: linux-acpi@vger.kernel.org List-Id: List-Subscribe: List-Unsubscribe: MIME-Version: 1.0 Content-Type: text/plain; charset="us-ascii" Content-Disposition: inline In-Reply-To: <20260424225820.GN3444440@nvidia.com> X-NV-OnPremToCloud: ExternallySecured X-EOPAttributedMessage: 0 X-MS-PublicTrafficType: Email X-MS-TrafficTypeDiagnostic: DS1PEPF0001708F:EE_|DS0PR12MB8574:EE_ X-MS-Office365-Filtering-Correlation-Id: 008006bd-c31a-4f6e-f5ea-08dea264d582 X-MS-Exchange-SenderADCheck: 1 X-MS-Exchange-AntiSpam-Relay: 0 X-Microsoft-Antispam: BCL:0;ARA:13230040|7416014|36860700016|376014|1800799024|82310400026|56012099003|18002099003|22082099003; X-Microsoft-Antispam-Message-Info: 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 X-Forefront-Antispam-Report: CIP:216.228.117.161;CTRY:US;LANG:en;SCL:1;SRV:;IPV:NLI;SFV:NSPM;H:mail.nvidia.com;PTR:dc6edge2.nvidia.com;CAT:NONE;SFS:(13230040)(7416014)(36860700016)(376014)(1800799024)(82310400026)(56012099003)(18002099003)(22082099003);DIR:OUT;SFP:1101; X-MS-Exchange-AntiSpam-MessageData-ChunkCount: 1 X-MS-Exchange-AntiSpam-MessageData-0: FypL5IZRuEq7AP/ndOT6DTOQjqw/wd0yWkiUQn3yeFjMBMnJLITpu2vNEBP7tm4r0RXiJ5zTkuyqE2Mi+eIj55agZf8IOkUg3Yf4zQt4ELoEyyT45f35Cj53TqveCvyLdoPUgBYCIZ+43E1fydgtkU2uSjU3aV5a1a0hn1WWItSoWj4lsNCGqMviLywqBrMP58ig07qPRwxxBVtMmzSQGzZYDFTSdvgEq3tCgjaWIabgDI9PdSIwabR9JXBmMJ/erX6Tub1ziNqs/j1gn+mtQmH6r0b+aI15zGmN3g8N7f+RR59oH3XAhzthpIenMdF+lpQMJPkvzYpKOLtk1DWMbGHUKo84x7Y3T+E6mVVbJKo/tZHGI11GmJi/f4DnLpC1vNJsMp+QWUC6joYl8a1a05fql/6xsY0lvHzR2LkPQclwtK9QFEZKSaTLlJdbgrdj X-OriginatorOrg: Nvidia.com X-MS-Exchange-CrossTenant-OriginalArrivalTime: 25 Apr 2026 00:51:49.4537 (UTC) X-MS-Exchange-CrossTenant-Network-Message-Id: 008006bd-c31a-4f6e-f5ea-08dea264d582 X-MS-Exchange-CrossTenant-Id: 43083d15-7273-40c1-b7db-39efd9ccc17a X-MS-Exchange-CrossTenant-OriginalAttributedTenantConnectingIp: TenantId=43083d15-7273-40c1-b7db-39efd9ccc17a;Ip=[216.228.117.161];Helo=[mail.nvidia.com] X-MS-Exchange-CrossTenant-AuthSource: DS1PEPF0001708F.namprd03.prod.outlook.com X-MS-Exchange-CrossTenant-AuthAs: Anonymous X-MS-Exchange-CrossTenant-FromEntityHeader: HybridOnPrem X-MS-Exchange-Transport-CrossTenantHeadersStamped: DS0PR12MB8574 On Fri, Apr 24, 2026 at 07:58:20PM -0300, Jason Gunthorpe wrote: > On Fri, Apr 24, 2026 at 12:12:40PM -0700, Nicolin Chen wrote: > > On Fri, Apr 24, 2026 at 10:11:48AM -0300, Jason Gunthorpe wrote: > > > On Thu, Apr 23, 2026 at 08:08:59PM -0700, Nicolin Chen wrote: > > > > On Fri, Apr 24, 2026 at 10:53:49AM +0800, Baolu Lu wrote: > > > > > On 4/17/26 07:28, Nicolin Chen wrote: > > > > > mutex_unlock(&group->mutex); > > > > > /* > > > > > * FIXME: Mis-locked because the ops->probe_finalize() call-back > > > > > * of some IOMMU drivers calls arm_iommu_attach_device() which > > > > > * in-turn might call back into IOMMU core code, where it tries > > > > > * to take group->mutex, resulting in a deadlock. > > > > > */ > > > > > for_each_group_device(group, gdev) > > > > > iommu_group_do_probe_finalize(gdev->dev); > > > > > } > > > > > > > > > > return 0; > > > > > } > > > > > > > > > > Will the change above trigger a lockdep splat due to this "mis-locked" > > > > > case?" > > > > > > > > Oh, I missed this one. That's a good finding! > > > > > > > > Perhaps we can just change it to list_for_each_entry_rcu holding > > > > rcu_read_lock() and drop the FIXME. > > > > > > You can't hold rcu across that function IIRC > > > > Oh right. I didn't think too carefully... > > > > I tend to keep it as-is. So, maybe just list_for_each_entry? > > Does your series make this existing race materially worse? I think it would be a status quo. The only possible place is __iommu_group_remove_device() that this series touched by changing the kfree(gdev) within the mutex to the kfree_rcu(gdev, rcu) outside the mutex, which actually added small delay. Though that doesn't fix a potential race, it shouldn't make things worse. Nicolin