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Tue, 10 Mar 2026 19:54:23 +0000 From: Dan Williams Date: Tue, 10 Mar 2026 12:54:21 -0700 To: Li Ming , Greg Kroah-Hartman , "Rafael J. Wysocki" , "Danilo Krummrich" , Davidlohr Bueso , "Jonathan Cameron" , Dave Jiang , Alison Schofield , Vishal Verma , Ira Weiny , Dan Williams , Bjorn Helgaas , Ben Cheatham CC: , , , Jonathan Cameron , Li Ming Message-ID: <69b076eda4655_490a1000@dwillia2-mobl4.notmuch> In-Reply-To: <20260310-fix_access_endpoint_without_drv_check-v1-3-94fe919a0b87@zohomail.com> References: <20260310-fix_access_endpoint_without_drv_check-v1-0-94fe919a0b87@zohomail.com> <20260310-fix_access_endpoint_without_drv_check-v1-3-94fe919a0b87@zohomail.com> Subject: Re: [PATCH 3/7] cxl/region: Hold memdev lock during region poison injection/clear Content-Type: text/plain; charset="utf-8" Content-Transfer-Encoding: 7bit X-ClientProxiedBy: BY5PR03CA0016.namprd03.prod.outlook.com (2603:10b6:a03:1e0::26) To PH8PR11MB8107.namprd11.prod.outlook.com (2603:10b6:510:256::6) Precedence: bulk X-Mailing-List: linux-cxl@vger.kernel.org List-Id: List-Subscribe: List-Unsubscribe: MIME-Version: 1.0 X-MS-PublicTrafficType: Email X-MS-TrafficTypeDiagnostic: PH8PR11MB8107:EE_|BN9PR11MB5275:EE_ X-MS-Office365-Filtering-Correlation-Id: 02e5b55d-6176-45f5-ae83-08de7eded395 X-MS-Exchange-SenderADCheck: 1 X-MS-Exchange-AntiSpam-Relay: 0 X-Microsoft-Antispam: BCL:0;ARA:13230040|376014|7416014|1800799024|366016|18002099003|56012099003|22082099003|921020; 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So, the justification for this is not that cxl_dpa_to_region() is going to start enforcing lock holding, it is that cxl_dpa_to_region() has expectations that ->endpoint remains valid for the duration of the call. > To prepare > it, region poison injection/clearing debugfs interfaces need to ensure > the correct CXL memdev lock is held at the beginning. My RFC [1] suggestion was "if there is a problem, here is locking changes to fix it". That "if there is a problem" is what needed more thought and time. Before we act on that RFC I want to see some plausible analysis of how not holding this lock can cause a failure in theory (better in practice), or how it makes the code hard to reason about. In other words the justification is not "future patch adds a lockdep assert so all code paths need to get more complicated". The justification is identifying a theoretical race window and how the locking solves it, and how the previous fix [2] did not handle all the potential races. [1]: http://lore.kernel.org/69813ac070f79_55fa1005c@dwillia2-mobl4.notmuch [2]: 0066688dbcdc cxl/port: Hold port host lock during dport adding.