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Wysocki" , Danilo Krummrich , Jonathan Corbet , Shuah Khan , linux-doc@vger.kernel.org, linux-kernel@vger.kernel.org, chrome-platform@lists.linux.dev, linux-kselftest@vger.kernel.org, Laurent Pinchart , Bartosz Golaszewski , Wolfram Sang , Simona Vetter , Dan Williams Subject: Re: [PATCH v6 2/2] platform/chrome: cros_ec_chardev: Consume cros_ec_device via revocable Message-ID: <20251106155951.GC1732817@nvidia.com> References: <20251106152602.11814-1-tzungbi@kernel.org> <20251106152602.11814-3-tzungbi@kernel.org> Content-Type: text/plain; charset=us-ascii Content-Disposition: inline In-Reply-To: <20251106152602.11814-3-tzungbi@kernel.org> X-ClientProxiedBy: BN9PR03CA0891.namprd03.prod.outlook.com (2603:10b6:408:13c::26) To MN2PR12MB3613.namprd12.prod.outlook.com (2603:10b6:208:c1::17) Precedence: bulk X-Mailing-List: linux-doc@vger.kernel.org List-Id: List-Subscribe: List-Unsubscribe: MIME-Version: 1.0 X-MS-PublicTrafficType: Email X-MS-TrafficTypeDiagnostic: MN2PR12MB3613:EE_|PH8PR12MB7277:EE_ X-MS-Office365-Filtering-Correlation-Id: 359e2239-caa0-40df-c24c-08de1d4d8551 X-MS-Exchange-SenderADCheck: 1 X-MS-Exchange-AntiSpam-Relay: 0 X-Microsoft-Antispam: BCL:0;ARA:13230040|1800799024|376014|7416014|366016; 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> > - priv->ec_dev = ec_dev; > + priv->ec_dev_rev = revocable_alloc(ec_dev->revocable_provider); > + if (!priv->ec_dev_rev) { > + ret = -ENOMEM; > + goto free_priv; > + } The lifecyle of ec_dev->ec_dev->revocable_provider memory is controlled by dev: + ec_dev->revocable_provider = devm_revocable_provider_alloc(dev, ec_dev); Under the lifecycle of some other driver. The above only works because misc calls open under the misc_mtx so it open has "sync" behavior during misc_unregister, and other rules ensure that ec_dev is valid during the full lifecycle of this driver. So, I think this cross-driver design an abusive use of the revocable idea. It should not be allocated by the parent driver, it should be fully contained to this driver alone and used only to synchronize the fops. This would make it clear that the ec_dev pointer must be valid during the *entire* lifecycle of this driver. What you have here by putting the providing in another driver is too magic and obfuscates what the actual lifetime rules are while providing a giant foot gun for someone to think that just because it is marked revocable it is fully safe to touch revocable_provider at any time. Broadly I think embedding a revocable in the memory that it is trying to protect is probably an anti-pattern as you must somehow already have a valid pointer to thing to get the revocable in the first place. This severely muddies the whole notion of when it can actually be revoked nor not. Jason