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Tue, 3 Mar 2026 14:13:33 +0000 Message-ID: <9c4b7ff3-ec22-43d3-93fc-1c0cb7de0e65@amd.com> Date: Tue, 3 Mar 2026 19:43:28 +0530 User-Agent: Mozilla Thunderbird Subject: Re: [PATCH v4] drm/amdgpu/userq: refcount userqueues to avoid any race conditions To: =?UTF-8?Q?Christian_K=C3=B6nig?= , Sunil Khatri , Alex Deucher Cc: amd-gfx@lists.freedesktop.org References: <20260303120654.2582995-1-sunil.khatri@amd.com> <38ec1a98-d112-4345-9711-d023a3e10da9@amd.com> Content-Language: en-US From: "Khatri, Sunil" In-Reply-To: Content-Type: text/plain; charset=UTF-8; format=flowed Content-Transfer-Encoding: 8bit X-ClientProxiedBy: MA0PR01CA0089.INDPRD01.PROD.OUTLOOK.COM (2603:1096:a01:ae::15) To BL1PR12MB5753.namprd12.prod.outlook.com (2603:10b6:208:390::15) MIME-Version: 1.0 X-MS-PublicTrafficType: Email X-MS-TrafficTypeDiagnostic: BL1PR12MB5753:EE_|IA0PR12MB8352:EE_ X-MS-Office365-Filtering-Correlation-Id: 2eac8bcd-2ec3-4c4f-cf0d-08de792f0d9c X-MS-Exchange-SenderADCheck: 1 X-MS-Exchange-AntiSpam-Relay: 0 X-Microsoft-Antispam: BCL:0;ARA:13230040|366016|376014|1800799024; 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>>>>           break; >>>>   -    case AMDGPU_USERQ_OP_FREE: >>>> -        r = amdgpu_userq_destroy(filp, args->in.queue_id); >>>> -        if (r) >>>> -            drm_file_err(filp, "Failed to destroy usermode queue\n"); >>>> +    case AMDGPU_USERQ_OP_FREE: { >>>> +        queue = xa_erase(&fpriv->userq_mgr.userq_xa, args->in.queue_id); >>> You need to have xa_lock around that or otherwise xa_load/kref_get can race. >> __xa_erase is unlocked version, but xa_erase internally does have xa_lock, since there is nothing else but just erase here to it made more sense to have clear xa_erase. > No, that doesn't work like that. > > The problem is that xa_erase() takes the lock only optionally when it can't exchange the entry with NULL atomically (e.g. because a full page needs to be freed up or similar). > > But in our use case taking the lock is mandatory because kref_get otherwise doesn't work. Ok sure i would add explicit locks in that case. Thanks for that information. Regards Sunil Khatri > > Regards, > Christian. >