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Tue, 19 May 2026 11:54:09 -0700 Date: Tue, 19 May 2026 11:54:08 -0700 From: Nicolin Chen To: Jason Gunthorpe CC: Will Deacon , Robin Murphy , "Joerg Roedel" , Bjorn Helgaas , "Rafael J . Wysocki" , Len Brown , "Pranjal Shrivastava" , Mostafa Saleh , Lu Baolu , Kevin Tian , , , , , , , Shuai Xue Subject: Re: [PATCH v4 06/24] iommu: Defer iommu_group free via kfree_rcu() Message-ID: References: <20260519113916.GO787748@nvidia.com> MIME-Version: 1.0 Content-Type: text/plain; charset="us-ascii" Content-Disposition: inline In-Reply-To: <20260519113916.GO787748@nvidia.com> X-NV-OnPremToCloud: ExternallySecured X-EOPAttributedMessage: 0 X-MS-PublicTrafficType: Email X-MS-TrafficTypeDiagnostic: BL6PEPF0001AB4A:EE_|DM4PR12MB8569:EE_ X-MS-Office365-Filtering-Correlation-Id: 490fd3f0-b7d7-4d70-f46e-08deb5d80dd1 X-MS-Exchange-SenderADCheck: 1 X-MS-Exchange-AntiSpam-Relay: 0 X-Microsoft-Antispam: BCL:0;ARA:13230040|82310400026|36860700016|376014|7416014|1800799024|11063799006|4143699003|18002099003|22082099003|56012099003; X-Microsoft-Antispam-Message-Info: h8mfqFHQ0XcremjlpsnYCdeH3CodQMgU/jVdfyHMGnyYIPI5udY+YaARQV4/gaZvWPRe3iXMvMub5wy7l5SlUBbLTiKNl4FPOSm/C0iMuzoyG21JISwzeHKEp6i2RdxQCqjXsAC5PNNPm+5V4VgUW84YQhfyK6egSlzzLCV8mcAYm5Z6hBJjCAGUv1ZX2WpLF6iwWQ92ldrRzO6pzCoJgE0vqhDhCYPxO7ZV1ISqWY+tNq7Bq83FwIQckopfXKYB1+pR2DYMVrANBY/1a0IILmXr15nFS0RpGu1Ku94W4BE7WJ3Xo45RqX6DvAgCT1mc6l054smSiaYp0A2xlWPnTS24jkbYUy5Pl5msMR4o6TMxRfcYjbdihTH8p66VJbciYdB18VSMotCHXAvZoY2DC9Y2aGjp2pQoA6JAOC9xVZZyGoQRBzVn6v0crEMW1tQoC2XLNGe/mv4SSBg5iWaLuQF3Qd6qg9P3A3bOKhKb0aJLQPZMSAdLrAfXWH5y/YTCcRHIVNziowQQz1FwkE3nDCT8e0+fw8ZbgblpFHTh7pOzk9u7jlk2IwjSQK5UYQqUeEqFj/0vBrDa/2pB/clEuPcXZIpP0Xfeqhz5uC/5LWNKBHxuOfzv/xAwbNlVzKpo3qmQtvuZznxGKgQzYdvJHO+TcEJVS1HVD/fJVBL6xjCHlM7ZepFlbblxXZb83qtF8z+l57lhEQXYeL5XF8yk/FTPddW61AHl8Z70X+1ZcR8= X-Forefront-Antispam-Report: CIP:216.228.118.233;CTRY:US;LANG:en;SCL:1;SRV:;IPV:NLI;SFV:NSPM;H:mail.nvidia.com;PTR:dc7edge2.nvidia.com;CAT:NONE;SFS:(13230040)(82310400026)(36860700016)(376014)(7416014)(1800799024)(11063799006)(4143699003)(18002099003)(22082099003)(56012099003);DIR:OUT;SFP:1101; X-MS-Exchange-AntiSpam-MessageData-ChunkCount: 1 X-MS-Exchange-AntiSpam-MessageData-0: hP5nLuCM2xfX7k4w9tC71WVPg+K1dqGm/gKPKM91pvKNvuSyrFdgNc+UuoFz+MGqdZJB0t5VxZdO+jt87VRWQ+umjedIDsJLXW0750+nM5U/eavNsTBWrg9l7ICr37UkYmNXJASEZzvdAhyDPrjgtZVEahqL236LG5PUyoOH9yZoIe4tm0Xw1cKhxOb7/zl6MeRF9nauDGp0kCvWGIz0QHgiHfLcra3F8+Pgrp9aiWdPfcJOve7ied3ZJlGg98DvDW8Pyph/XZVs5B6uZbmz0EwBfG1idNhWgA6iLlFvLjn4aKr/7SN5bCERVisi3RDZz2u5bFWzqvw5ILkJIflrbwscQkOOAdb3HJuVI8/q/GzWbTEv+edguGMsN0yhp9chR8b8j/fViEEGeJ4/kceVbIrUGR51zcwIrgoTiU6QGpbwOVEvhZn6a6JaP/aLjr1k X-OriginatorOrg: Nvidia.com X-MS-Exchange-CrossTenant-OriginalArrivalTime: 19 May 2026 18:54:28.0653 (UTC) X-MS-Exchange-CrossTenant-Network-Message-Id: 490fd3f0-b7d7-4d70-f46e-08deb5d80dd1 X-MS-Exchange-CrossTenant-Id: 43083d15-7273-40c1-b7db-39efd9ccc17a X-MS-Exchange-CrossTenant-OriginalAttributedTenantConnectingIp: TenantId=43083d15-7273-40c1-b7db-39efd9ccc17a;Ip=[216.228.118.233];Helo=[mail.nvidia.com] X-MS-Exchange-CrossTenant-AuthSource: BL6PEPF0001AB4A.namprd04.prod.outlook.com X-MS-Exchange-CrossTenant-AuthAs: Anonymous X-MS-Exchange-CrossTenant-FromEntityHeader: HybridOnPrem X-MS-Exchange-Transport-CrossTenantHeadersStamped: DM4PR12MB8569 X-CRM114-Version: 20100106-BlameMichelson ( TRE 0.9.0 (BSD) ) MR-646709E3 X-CRM114-CacheID: sfid-20260519_115444_803481_5886CD46 X-CRM114-Status: GOOD ( 20.32 ) X-BeenThere: linux-arm-kernel@lists.infradead.org X-Mailman-Version: 2.1.34 Precedence: list List-Id: List-Unsubscribe: , List-Archive: List-Post: List-Help: List-Subscribe: , Sender: "linux-arm-kernel" Errors-To: linux-arm-kernel-bounces+linux-arm-kernel=archiver.kernel.org@lists.infradead.org On Tue, May 19, 2026 at 08:39:16AM -0300, Jason Gunthorpe wrote: > On Mon, May 18, 2026 at 08:38:49PM -0700, Nicolin Chen wrote: > > dev->iommu_group will be read in an ISR-context to look up a group_device > > for fault reporting, in which case mutex cannot be used. For that read to > > be safe, two things are needed: > > What driver does this? iommu_report_device_fault() has to be called in > a sleepable context - usually a threaded IRQ handler. So mutex is no > problem. It's used in an invalidation context, where mutex is a problem. > This seems like Sashiko slop - iommu_group does not change while a > driver is attached and a driver is not permitted to do any "fault > handling" after it has detached, it must flush and synchronize its > IRQ if it is using this from a hard IRQ for some bad reason. Oh, I probably picked a wrong word. "fault" here means "ATS broken". IOMMU driver sees ATC timeout during invalidation, and reports "ATS broken" in a lockless context where device could be detached. No? > You need to be alot more critical about the noise that Sashiko > generates, alot is useful, alot is not. It is a not a tool you want to > have 0 reports, complaining about hallucinations is expected. OK. I will be more aware of that in the future. Thanks Nicolin