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Wysocki" , Tzung-Bi Shih , Linus Walleij , Jonathan Corbet , Shuah Khan , Laurent Pinchart , Simona Vetter , Dan Williams , linux-doc@vger.kernel.org, linux-kselftest@vger.kernel.org, linux-kernel@vger.kernel.org, Bartosz Golaszewski Subject: Re: [PATCH 0/3] Revert "revocable: Revocable resource management" Message-ID: <20260128150538.GA1134360@nvidia.com> References: <20260124170535.11756-1-johan@kernel.org> <2026012554-chatty-policy-42a1@gregkh> <20260127235232.GS1134360@nvidia.com> Content-Type: text/plain; charset=us-ascii Content-Disposition: inline In-Reply-To: X-ClientProxiedBy: BL1P222CA0024.NAMP222.PROD.OUTLOOK.COM (2603:10b6:208:2c7::29) To LV8PR12MB9620.namprd12.prod.outlook.com (2603:10b6:408:2a1::19) Precedence: bulk X-Mailing-List: linux-kernel@vger.kernel.org List-Id: List-Subscribe: List-Unsubscribe: MIME-Version: 1.0 X-MS-PublicTrafficType: Email X-MS-TrafficTypeDiagnostic: LV8PR12MB9620:EE_|BN3PR12MB9569:EE_ X-MS-Office365-Filtering-Correlation-Id: 77a576f4-2ef1-43a8-69c0-08de5e7eb283 X-MS-Exchange-SenderADCheck: 1 X-MS-Exchange-AntiSpam-Relay: 0 X-Microsoft-Antispam: BCL:0;ARA:13230040|1800799024|366016|7416014|376014; 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X-MS-Exchange-AntiSpam-MessageData-ChunkCount: 1 X-MS-Exchange-AntiSpam-MessageData-0: =?us-ascii?Q?pgTWqg1mtwTLIvRY5jF6rRzsYreqrTlEFhclXrDlmhhyqmjJN9sHKk21KEeu?= =?us-ascii?Q?8aha7yREY6nGJv0xkSjzkANCFNYz34DKhjGokCM/bMt6DYtt3siUrRHb4Ax2?= =?us-ascii?Q?lngI3oc4N3K2iw3Lc2dAZHmZYcDEYs7LoUZaJf4Sjq0hNkTsjIiS+9DXF1dU?= =?us-ascii?Q?X7gf+e1gFeKYzkmjAl12ABWEDrrGpIgj+F6YvMpyWSiKRJQBZqCldL4kggQD?= =?us-ascii?Q?VW8AZD3ZjYMPNzdzpvxaH15jCaEkCVEOTfiSTf8F/uoUctrdglZIMhDrmzvV?= =?us-ascii?Q?/7N/KrVpiVFF36lggkX2G4ydQowWFLDqXeaLAV9zvfqQmMmy8b5hiiHQXw7j?= =?us-ascii?Q?ZV/T9X36DBsv1ytxxdgKSa6llD0sx75BrbFPpOZM2XPzShQJfU2uZUai/3u/?= =?us-ascii?Q?XUSKzEToiO+sodei+6DLNzsNvpY5emcFAouhsgEoAAGP0Rpp+y/QyZ4mfsEy?= =?us-ascii?Q?AO4k0EXz9b6D6RHE4O7D04lbLUleJZ0zyDOLgnwdPhmzh+QKMDT+LB909Glz?= =?us-ascii?Q?A8CayNGP+LCYYKzuw+IQFD+E3AY7zI6+tHgaBRdw8aUts//vyyYS3pm0oTeZ?= =?us-ascii?Q?AfD6BRqnQgk4hFfRH+NsnzVjG1AksLOCEigjPOxfiY4mq2IkGTFf2TPnzX++?= =?us-ascii?Q?mJPko2N4CFGBTMb/AMz8ctxiKdK1ITGgnzFEelFMMl1Emao1R2DVJbMDmXis?= =?us-ascii?Q?PIKKsn3UeADx2vRZ5d7uiALnPIQXn0cjOYdl2vmZeqp+8EC+bIIyr0zonASW?= =?us-ascii?Q?MKqK1Keg2z795aqtBMteUwDn1LRUjbx1EG8uxIm/TdSePJ6faNVMCYmJ0vfW?= =?us-ascii?Q?XlqCmFrGBwxYQVZhv2PETyyAq1HNfw+er3DtaRfy6ypB+gvNyBve72sV7OAg?= =?us-ascii?Q?V/CXTKHkXVXcR5o3+wIF/WHYYxG0/O/rqINLVZFYxNWrJHLRvtV2cHTYZQQx?= =?us-ascii?Q?/sgrF9T91+nVUxgDW2nuckPjnAvA/E3id5GGRTtX2OogoKDJs8bM7vmH4j76?= =?us-ascii?Q?eMsKMNEML/O8FGW9eFVO87Va1zswQZVGRJsFNBSBvm+LzQR7oZccKa62zSDi?= =?us-ascii?Q?10MWAMBqwcKDy3BSO+oWWfDnXSe1Iskjl30Au4XRvxurEhiCQtzDlUw10aQL?= =?us-ascii?Q?Bpw0ds1xOHULgFG81C7gFmwl+erznoc2d5QWBzPhw6ifrITrYxW1ynLz9p+q?= =?us-ascii?Q?yS1cdFCjecBKi9ECoG9IkuHf8Ii7TV80OyFjT5NNYs99QtFOkthDw+WpqiMP?= =?us-ascii?Q?KclnA9U3YQ0y28ReCXqPUkarRPRWes8HoZlx9hhumC/qRlFQt26j66NxFVyQ?= =?us-ascii?Q?mgJts1PBj2qYO/btVt3xqmwI1dYpR8bbXD9aCqXe+Z+PCi+FziHMTjVWfFik?= =?us-ascii?Q?fO/8+VsRQ0ZayIAdFrVcG3c4EnHdPqEyMWEvJ5QMtGi6OZXvjcZiW8Rx/P4u?= =?us-ascii?Q?f9AOvOQdkyxD8GB97eo4NOMXIcGLxagr71/6BlpY6TSgwCO9I1DZ0pL7H1qp?= =?us-ascii?Q?HNOP9TRbCE68bYT2dIGOAewJA178Gk0vQavtRvjsaMeMMvIcM+cKAt5Fpg2o?= =?us-ascii?Q?b46A6gHYpua+HH+rDzd0IcsUj5TxI2D3S5cDiZnZRTb03Nj/s0Pb30C8PVko?= =?us-ascii?Q?ol7Og/99I4D6+EjXGCJkwuuWHeFnPSXJtJEkf6aSfHLFV08zx1BuVSOQ9dBd?= =?us-ascii?Q?JysUcfjmYwFnx7mvARvR6DAOxSpHYzXvfgZnXaI2u5bHYUf5jphUGPD6j2Z9?= =?us-ascii?Q?8gYnwUJWIg=3D=3D?= X-OriginatorOrg: Nvidia.com X-MS-Exchange-CrossTenant-Network-Message-Id: 77a576f4-2ef1-43a8-69c0-08de5e7eb283 X-MS-Exchange-CrossTenant-AuthSource: LV8PR12MB9620.namprd12.prod.outlook.com X-MS-Exchange-CrossTenant-AuthAs: Internal X-MS-Exchange-CrossTenant-OriginalArrivalTime: 28 Jan 2026 15:05:38.8715 (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: AwiyUBjbbf4bBQELxt1litUyPgzGA7R3Ax2/XgrnFkmL2qdo+Cn4GsYxUvF86EHl X-MS-Exchange-Transport-CrossTenantHeadersStamped: BN3PR12MB9569 On Wed, Jan 28, 2026 at 11:01:03AM +0100, Wolfram Sang wrote: > > > One exception is I2C where the logic is so broken we need to first > > rework a lot of drivers. > > Let's say "bitrotten" instead of broken. People used what was available > at that time and they prevented the kernel from crashing, at least. And > up to now, nobody had the bandwidth to improve that part in I2C. > > > Wolfram is on board with that though. > > Ack. I want to emphasize here that for I2C the SRCU part goes into the > subsystem, not into the drivers. I would just gently advise again that SRCU is not a pancea and should only be used if the read side sections are super performance critical. I'm not sure that describes I2C. rwsem is often a simpler and better choice. > > > The reason cdev keeps coming up is because there are few common ways a > > > typical driver can actually generate concurrent operations during and > > > after remove that would be problematic. > > Let me point out again that Dan Williams already had a PoC-patch for > handling the cdev issue generically [1]. Dunno if this fact is present > in the current discussion. > > [1] https://lkml.org/lkml/2021/1/20/999 Yeah, this was brought up a couple drafts of possible options were exchanged already but nothing was really focused on and polished. It is a tricky problem to find a storage location for the lock and revoke so that the fops shim can access it while not disturbing the actual driver. Jason