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McKenney" Subject: Re: [Q] RCU usage in infiniband Message-ID: <20260708131727.GB674038@nvidia.com> References: <20260708092316.Qb39F_B0@linutronix.de> Content-Type: text/plain; charset=us-ascii Content-Disposition: inline In-Reply-To: <20260708092316.Qb39F_B0@linutronix.de> X-ClientProxiedBy: YT4PR01CA0252.CANPRD01.PROD.OUTLOOK.COM (2603:10b6:b01:10f::24) To LV8PR12MB9620.namprd12.prod.outlook.com (2603:10b6:408:2a1::19) Precedence: bulk X-Mailing-List: linux-rdma@vger.kernel.org List-Id: List-Subscribe: List-Unsubscribe: MIME-Version: 1.0 X-MS-PublicTrafficType: Email X-MS-TrafficTypeDiagnostic: LV8PR12MB9620:EE_|CY8PR12MB7682:EE_ X-MS-Office365-Filtering-Correlation-Id: a56b9de1-1b4e-411e-2de1-08dedcf3427e X-MS-Exchange-SenderADCheck: 1 X-MS-Exchange-AntiSpam-Relay: 0 X-Microsoft-Antispam: BCL:0;ARA:13230040|376014|1800799024|23010399003|366016|11063799006|18002099003|56012099006|22082099003|6133799003; X-Microsoft-Antispam-Message-Info: 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 X-Forefront-Antispam-Report: CIP:255.255.255.255;CTRY:;LANG:en;SCL:1;SRV:;IPV:NLI;SFV:NSPM;H:LV8PR12MB9620.namprd12.prod.outlook.com;PTR:;CAT:NONE;SFS:(13230040)(376014)(1800799024)(23010399003)(366016)(11063799006)(18002099003)(56012099006)(22082099003)(6133799003);DIR:OUT;SFP:1101; X-MS-Exchange-AntiSpam-MessageData-ChunkCount: 1 X-MS-Exchange-AntiSpam-MessageData-0: =?us-ascii?Q?z/tbwvkM6u/j3Rdi3NuuhgVmvOKE79Q55RFJznaCTF0LW8xPc5Nnt0NxBrw7?= =?us-ascii?Q?weAoqZGSlnEEi0qXgw5ECOdAy2Ji5vc/AbqPTTQzEgFEJBZewWvhHV99NMXu?= =?us-ascii?Q?jQwrGBQPFmLUIKspGJIc9tHpJKKbLadkP61vmdGjZcVr+n8KEkr7KeXKyeSU?= =?us-ascii?Q?YFGibuspFj1xBUN39TIIgyCb9VE667W2RilmQX0gyOyHaD+x0Q1HOhiSs2St?= =?us-ascii?Q?I0jJf0VsptUMKiS8AaOb+vfK8WWDc2YsGW9N0Y571qoMCWgF7WxkbVKX+wFc?= =?us-ascii?Q?b9puCiQEWRuBbUl52cewMnlVqB3vD9FujqjhvTTjOAzP3uA50nL8pYG9k81B?= =?us-ascii?Q?INLrGmHQ3UrujdCwXtacTGsPnRpWroI0KeYW4wAPKjPfawLfGwK7ASz/EbT9?= =?us-ascii?Q?p23GprkxVGYqG1N8tNDZWLiVm8P12UrlsG28bzw2g1hHlWHqbk8lhQVbGwof?= =?us-ascii?Q?NuGVcrZmwyFPaZXl1FxVB+ZT/F9EHKI3b3ShGri7wQDjytF7vi44tlWOMakp?= =?us-ascii?Q?ZKpFR1Lbi8cA8hVpR7iYEa1gqJRIvnbrExoI87KLyisjsyOiXPFU8xqlVOpt?= =?us-ascii?Q?x+W3BvNIdIk8BbZGmCJpl+bI69RPpx+Er2U56cRzuUrPI2gVE+qq7Dh1gMJ0?= =?us-ascii?Q?Sdpf24aoJ9zwDEbPkCzU0dRQwqXLdzp8dUL9FJDeuLRiJ3XrBbvwlzcknqSf?= =?us-ascii?Q?DGYKA+/CUgjhenJNR5E/DY5aFeda8wCU4aul0Njo8ttH0p7R+iOHMLBLe6fo?= =?us-ascii?Q?Ru8j6F+3XzDGaUIYfDQHSZbpIbSselyM2UfVyKbg3hyxsUGkazcW6Eam/GtB?= =?us-ascii?Q?Zo54dtvtQy/YDBcJ81s6OMXgpySOeUsWcsskPcc9ETKhkuzOzMRCRZ+xqVIG?= =?us-ascii?Q?Gl1REuqh+965P6WwQVDD3AiD69SRT9Fek+cgcC4hYfrFvNByYF6bM5fjqVf2?= =?us-ascii?Q?sncTsZ0CJBclgLDs8M7w1b+qddEGeGHr1dmzkN1/WtZiy1y2sKTZWw4oXt/I?= =?us-ascii?Q?ndz5Yey0VqNNQdT2gbkVhUQTrPC/ldtNqIpzk5K5xH9sE+5e7IXaDgqOPsFW?= =?us-ascii?Q?RRGKsFZp9124CjnRWuGGKMF0CCB+sp+r8EpHNy10dwHuHLJwyekPfjeClArj?= =?us-ascii?Q?NoPy8bDu+xaDuIVJ0zlBDbIoQ57b8fgrUNqv6HnmCwl++ByWWVY26MJkm5cG?= =?us-ascii?Q?YHfhr+WuiaJ0Xu5fChzd3jfIPZSqA24wt2MgBLT5kd9trTHD/UmHT3LkXliB?= =?us-ascii?Q?YsMTspAXzPYxlO09VwakldQivjjbdnPuHaJlyIVdvD9O40W4EKgkk2ssQnNu?= =?us-ascii?Q?AbZ0Ol88Jio6dBRDKxeyWSUJ9pfRF8aDPIFWbPiNJtrviiXNjS16iTWiXj1y?= =?us-ascii?Q?U+FCec0M0ouTWRjt6FAjgD5f99xyCoRMXCILnNqRDvnADml0ykxvul5EIFzU?= =?us-ascii?Q?OxOUcsfbS7Hf0AZaK6sqrVgPoY0CzPxr8Dq4dg28MUTN0+gdc+WxGWYgsKF1?= =?us-ascii?Q?CUYbwb+WCp2jv/DFuJ3m/+H1laVQchQcF+x4wC7iIuzPyiSudxjtHnWg5b9H?= =?us-ascii?Q?ENp7KNgIOu7MPm3M7NNZJ+QR0MS8+cZx4VYuwZuucflcpwOi5vc+rKW4XCLh?= =?us-ascii?Q?Ip2uYiOkt1UqkvZhxB+rWI1Kesyj9UUHTUYu0zJknWdB3oN9UZrH2AX6zZFp?= =?us-ascii?Q?F6OIFiz/G2lpTZuLzdzgEUSLA/SuNnrOnQWL70wPF6WuDMh4?= X-OriginatorOrg: Nvidia.com X-MS-Exchange-CrossTenant-Network-Message-Id: a56b9de1-1b4e-411e-2de1-08dedcf3427e X-MS-Exchange-CrossTenant-AuthSource: LV8PR12MB9620.namprd12.prod.outlook.com X-MS-Exchange-CrossTenant-AuthAs: Internal X-MS-Exchange-CrossTenant-OriginalArrivalTime: 08 Jul 2026 13:17:28.5937 (UTC) X-MS-Exchange-CrossTenant-FromEntityHeader: Hosted X-MS-Exchange-CrossTenant-Id: 43083d15-7273-40c1-b7db-39efd9ccc17a X-MS-Exchange-CrossTenant-MailboxType: HOSTED X-MS-Exchange-CrossTenant-UserPrincipalName: J1TpkFIb0X/AYsCuEREvOQjgf1hPl75CtvW+7OpJv0FY0njW41wrQTXiXgkRQapk X-MS-Exchange-Transport-CrossTenantHeadersStamped: CY8PR12MB7682 On Wed, Jul 08, 2026 at 11:23:16AM +0200, Sebastian Andrzej Siewior wrote: > Hi, > > I've been randomly starting at infiniband code and noticed it uses > call_rcu() with a callback from its module. > > | drivers/infiniband/hw/mlx5/devx.c: call_rcu(&event_sub->rcu, devx_free_subscription); > | drivers/infiniband/ulp/ipoib/ipoib_main.c: call_rcu(&neigh->rcu, ipoib_neigh_reclaim); > > I don't see synchronize_rcu() and rcu_barrier() there so I've been > asking myself what ensures that the callback completes before module is > gone (via rmmod)? I would expect a rcu_barrier() in > ipoib_cleanup_module() for instance. > > Is the unload path so "late" that the callbacks run before the module is > unmapped or is there something between the APIs that ensures this? It wouldn't hurt to have a more explicit unload synchronize call, but there are already some existing ones on the path to unload a module that would cover anyhow Jason