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McKenney" , Phil Auld , Sebastian Andrzej Siewior , Shrikanth Hegde , Tejun Heo , Thomas =?iso-8859-1?Q?Wei=DFschuh?= , Valentin Schneider , Yury Norov , Bradley Morgan Subject: Re: [PATCH v2] stop_machine: Make stop_one_cpu_nowait() return void Message-ID: References: <20260729022355.325058-1-ynorov@nvidia.com> <20260729125133.GA751831@noisy.programming.kicks-ass.net> Content-Type: text/plain; charset=us-ascii Content-Disposition: inline In-Reply-To: <20260729125133.GA751831@noisy.programming.kicks-ass.net> X-ClientProxiedBy: IA4P220CA0001.NAMP220.PROD.OUTLOOK.COM (2603:10b6:208:558::14) To LV3PR12MB9356.namprd12.prod.outlook.com (2603:10b6:408:20c::21) 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: LV3PR12MB9356:EE_|PH7PR12MB5712:EE_ X-MS-Office365-Filtering-Correlation-Id: 3c8872c8-0c06-45a5-4f8a-08deed76e6af X-MS-Exchange-SenderADCheck: 1 X-MS-Exchange-AntiSpam-Relay: 0 X-Microsoft-Antispam: BCL:0;ARA:13230040|10070799003|7416014|376014|23010399003|366016|1800799024|18002099003|22082099003|56012099006|11063799006|4143699003|10067099003; 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X-MS-Exchange-AntiSpam-MessageData-ChunkCount: 2 X-MS-Exchange-AntiSpam-MessageData-0: =?us-ascii?Q?8GSd1P13BOIpCSdPZbM19+bTJMsp36uNo+0GYbFoyTFzybmFXKJX/q46kVQg?= =?us-ascii?Q?xE4hoR8QK5QSDG7j3rSFP0C/WVDVpgZkkX3XEMDk8X4wrxgQKB00ZZ8O6IYg?= =?us-ascii?Q?ZnolvAyhCq2LOO2CMqanG/7rW1Ll+AL4kVIdliNdWYY7n+AfbQf9n9qP81h/?= =?us-ascii?Q?/aE4TCm6MY1TTOSZjbOMCmKMqj+mAanJwihW+0voKiPNzsBeMnK4nQxOX1nA?= =?us-ascii?Q?iHwvLsDx6jLPmi51V4SQ4WqLNytYTQY9h1oJ8uknZiPvJnMhNUj/EjR7zK27?= =?us-ascii?Q?Cst2M1RyEprr4sLCnFwlt6YmtsjnfhxRu+zYVfxY/IyIsV4LFX2XCSrv8dmB?= =?us-ascii?Q?4AUAM3B8X6wye7FgRi54OzpnkFWOZfECTvhTaYoWe8Uf9KrE7CGBxqTfXm6J?= =?us-ascii?Q?cALFY92pcPRBZ7aWBhMX8E0C4WGXCgo/nzbl1QsbuFZqPVFDVK1x4KRTk75Y?= =?us-ascii?Q?wkgLKabhzft5WYgwNWGZhnJMOKCGeEMWgKJQ861zGSnkeYWTL6dNoRE7mDvE?= =?us-ascii?Q?sT+nU/I65TnfbWSxzbbRiaSczcCB9h+dJ1aJzLFIgoXVAsmiD+BbJbwfERSh?= =?us-ascii?Q?9fZNbMslh1ZH0WWFigE1F78ovZ6OJ08Xqo53qN4CwURZklAz4+WzHXV9sQRX?= =?us-ascii?Q?0BT51TpsP4WxK73zKpqDk7Hfo1Ri3jxVrcGmog7ofXEHA/lOLmD5T5bveGFn?= =?us-ascii?Q?g+5fC375+kcyyMpQwXDW54HaGE+dbZ8EJtbPp2mrf5wb+fdCiBp29MOPM0Y6?= =?us-ascii?Q?RwOdPK317L4EXG82x7X2YfS6Z54YHwLOfO3Sm8UC5BrSxa9WC3o5Ylb+LTW8?= =?us-ascii?Q?P0/RCCyVafMARxi5DTy++nUpS18EOlQrj9B7WyTPz5eAT5cgz+Nm+nvK/IWm?= =?us-ascii?Q?UFDZWve39wI3XqET4gmfcG05K7HweUFeWK189b7AFGpbK90BGlKOTuoUCb8e?= =?us-ascii?Q?8QAjpZpsY4xRad7jEMmDy9cUT/kSituvsJ3Fd5eVknZLMb5V9Z+t2Ewmjn+X?= =?us-ascii?Q?EFudbdk/nUHm6uPhDrM8hAQhq6PHyeONPihtHrmXEzSPdVSXgIOF3Et7+W93?= =?us-ascii?Q?knPPnL5XkveKYAoY8TzfVPktM+mrzLFLgUufeEiHZBuVnLJdrvJ9raNtALvx?= =?us-ascii?Q?BDprBMxEEPcWzc7A6CAUSbaYkKz2Hu4SvTMuGxIVoYJBOxPp8aPrnaSR//mY?= =?us-ascii?Q?KAhl++kpOjkWmnhCAxOA1qUIG+jabxyvYs3wo74KUktpTJ/PzGPBVGM3zHnp?= =?us-ascii?Q?n6wk6zx316a0MOawo1/8ihfUykAcp5hy39DAtQS4OqJc7S97pLNZ8/x9Llhw?= =?us-ascii?Q?9y0pMCvtaMOjIVKctlVB+h4QZ14LHvliSAE0xgdZQqBXoUMKvVg+IAQJhPIE?= =?us-ascii?Q?1CcsknBsw2wYX2hpIXtQ4aFxdz4yFxz0cjBJ9G77Xkf1F76OsQNBOjrW8IWF?= =?us-ascii?Q?nL7qWDNy1HtIFh0eAC6MGltiOR6OJfJsainYevNs5N1cFF7bznpkZNY7s7pr?= =?us-ascii?Q?xFJBi2Qfh1+rBo2QY3rhGIUAsiarqmhstiza1ELaHPVF6Q0fJFFdxVwKld45?= =?us-ascii?Q?SR6HW27mX0Lhfc7VfmWCE9cXpNzEohHTmE8rtQw6oyU13GPWGy+9UMo2ywSs?= =?us-ascii?Q?cFHWSeUUrP4BObNT252Q3A3PjiXV7aUYkn6yIXFCevY3hB1aqgKqDOuSefzj?= =?us-ascii?Q?ImfmEKcrxcCOoCpf5hY7qF7KL3vnyH/UrjRZW18kDJcDXxAjtZRMUxN5Qz7x?= =?us-ascii?Q?nm09S7f6USF1DT8WBRy866BwkHCrg1X+5EmeedwitKSIxNk3K7mz7XjmTVDe?= X-MS-Exchange-AntiSpam-MessageData-1: VcY7BTNfLLBiTg== X-OriginatorOrg: Nvidia.com X-MS-Exchange-CrossTenant-Network-Message-Id: 3c8872c8-0c06-45a5-4f8a-08deed76e6af X-MS-Exchange-CrossTenant-AuthSource: LV3PR12MB9356.namprd12.prod.outlook.com X-MS-Exchange-CrossTenant-AuthAs: Internal X-MS-Exchange-CrossTenant-OriginalArrivalTime: 29 Jul 2026 13:40:06.6824 (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: dlkrjXtf9uVYAzhTb+eJkTmBXF2aKA10JfqxUXLpfKBSagiJU3KkQHjEa9pHKyssAg3Tqw2dUyPM9YBSi7PTdg== X-MS-Exchange-Transport-CrossTenantHeadersStamped: PH7PR12MB5712 On Wed, Jul 29, 2026 at 02:51:33PM +0200, Peter Zijlstra wrote: > On Tue, Jul 28, 2026 at 10:23:54PM -0400, Yury Norov wrote: > > No caller checks the return value from stop_one_cpu_nowait(). All > > callers require the callback to run and arrange for the target CPU's > > stopper to remain enabled while queuing the work. In particular, commit > > f0498d2a54e7 ("sched: Fix stop_one_cpu_nowait() vs hotplug") added > > preemption protection to the scheduler callers so that queuing must > > succeed once the target CPU has been observed online. > > > > Therefore, a failure is an unrecoverable violation rather than a condition > > individual callers can recover from. Diagnose it with WARN_ON_ONCE() in > > stop_one_cpu_nowait(). A check in the common helper covers current and > > future callers consistently, while individual checks would duplicate > > the same non-recoverable handling at every call site. > > > > Make the function return void because there is no longer a meaningful > > result for callers to consume. > > > > On UP, warn if the supplied CPU is not the current CPU because the work > > cannot be scheduled in that case. > > > > CC: Bradley Morgan > > Signed-off-by: Yury Norov > > I suppose; you want me to take this through the scheduler tree? Sure, thanks!