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McKenney" , Metin Kaya , Xuewen Yan , Thomas Gleixner , "Daniel Lezcano" , Suleiman Souhlal , kuyo chang , hupu , References: <20251124223111.3616950-1-jstultz@google.com> <20251124223111.3616950-9-jstultz@google.com> Content-Language: en-US From: K Prateek Nayak In-Reply-To: <20251124223111.3616950-9-jstultz@google.com> Content-Type: text/plain; charset="UTF-8" Content-Transfer-Encoding: 7bit Received-SPF: None (SATLEXMB04.amd.com: kprateek.nayak@amd.com does not designate permitted sender hosts) X-EOPAttributedMessage: 0 X-MS-PublicTrafficType: Email X-MS-TrafficTypeDiagnostic: BL02EPF00021F6C:EE_|SJ2PR12MB8781:EE_ X-MS-Office365-Filtering-Correlation-Id: 81de087b-179d-434c-629e-08de4768ebaa X-MS-Exchange-SenderADCheck: 1 X-MS-Exchange-AntiSpam-Relay: 0 X-Microsoft-Antispam: BCL:0;ARA:13230040|36860700013|1800799024|82310400026|376014|7416014; X-Microsoft-Antispam-Message-Info: =?utf-8?B?UXBRZUVTL0xGSkhFZjFXTEVTRnB6RlYveVA3UFlKcUtxdXkvMngvcS9CbGt5?= =?utf-8?B?cmI3TXJwR0Jxdk9STFJnblE2Y2duMUZsaEdzZGpmSWRKemRFZzl6OTY5SnBQ?= =?utf-8?B?Um9nWGx3VGEvTVJ1aVU5YTJURC9Db1RCM0tsNUxVRDNGWUs0b0VTb2FZNGdD?= =?utf-8?B?WVl2cjBiZHhTd2JNN3Q1bzJ2Um1sQkdoczJFWHc3NUJIU0pxNi9vV0ZBMmQ1?= =?utf-8?B?SWFFaXRXYzFFR1R3Y1BRNFVuOGhPNEc3MDNqVHJBTlF2RE5IV2JJMVJRSHdv?= =?utf-8?B?OUkxZUZVMkZ2Vi9ybjF6cGM3dm1SVUdDMmdBU283Z1NKZEIyU3FqdGxDbmxr?= =?utf-8?B?cG9rOWhmUFJST1dqWThRQy9MLzNTemhsaDZRZkYrRFlLbEthL09ZNkxTNVU3?= =?utf-8?B?eWdKNXgvaWIvL0ovVnZKK2RUSXFLM1doTG9aZFM2L09xL2VRc0VHajZ4MDZ2?= =?utf-8?B?RVBZNy9FajFjNmxQRS8rRVAzNnBja2hrNkp6TzBsN0Y4bTNnUjhPRlkvbi9T?= =?utf-8?B?REZxaW9rNlVtU2pZbklSclBmc2srWG1tTGZxOUd2d2RyUU54QmVSZzc1bWxF?= =?utf-8?B?Z3ExZHg5aldRVGVlQXp4Y2EwT21IVFR2K0lybEpHMEM1QnhKdVNLOXdtMms3?= =?utf-8?B?ODdiY3k0SXFDaitmOWh4T1pNR1JDTzJQdW5MOGZmNndwQ0E2UktQQUFYY21w?= =?utf-8?B?dVdMV0x5MTZWeVE3TmI0OS9CWmdKakNjcnhWcUtDWHZMRnRjOEpjOU5ub0Fa?= =?utf-8?B?dFJ5WGY5bVRDZHNreElzZG5GcmdiQWxBRG5BejgrN1AwVzZRRHJwT0k1K2pW?= =?utf-8?B?STROcndUT3NWVGpKYnBNT1RWK2RsYXBmVGJmWmpCSGRMRUZDeHNoT3l6SXJo?= =?utf-8?B?ZzRoZm9wS1VLZzE4a253LzFrQTBieFNGaEVFU1NWK2lISGhab0hBMCsvbE81?= =?utf-8?B?bEJjS1hTVDc5Y3FINmFhRzVGQkdhUjJIMm1OQXNWemU3UVV2MkJxWmUxL2pV?= =?utf-8?B?QzNjVDBka3BnczJ3UG9TY0taMlBXQW9xR0ExZkNFbmhPZnJGSG53U2pOSXE0?= =?utf-8?B?SGVNM29HMUplQXZaMzlvUkdjY0NwU2RIM241STZPNFFINlJOWUwxKzdFZVZO?= =?utf-8?B?alF4ancraC9YOGg3VWUwMDRxbG5ON0JaME5iUGRWTWU2R1VMU1JvYW5rMEVr?= =?utf-8?B?eExBRENKV3ZLRTJRWXpyVkxSTUc3b0gvam1HUEd4M1ZpT21iMkVGQk5yVlRq?= =?utf-8?B?RXIrU05QSHlFam1LcUI0S1o3QmJUSkQwSmxlamg1NFpTZVdSZmZiRDdJbTdn?= =?utf-8?B?bnlvMUczL2lZUWV1VG9leENGMFk3SUFnZ3I5Q1Zzd1BsWDFEVGc2ZWpueGlP?= =?utf-8?B?dGs1aFllbkxLaFMwN3BTbE9qRHpMNGdlT0RmVjBrNjNMc0dFZ3Z6empTdWpa?= =?utf-8?B?L1RMOVRMZllNZVNva2ZoMElmN0drcDluazRwOHZNN3JDYlRhbmYrN0V5NDF4?= =?utf-8?B?dFNab1R2a2R1TXNqSTFWUUpwL1hQK3M1cUhvVnliK3BXZFpzVm5udU9Pbk5K?= =?utf-8?B?SHFOTDhxVmx3bTcxUWNkT3Y5MWRuWFRzVlF3MU5XbFZER0xSSEFUMEZTOU43?= =?utf-8?B?YkRpd1pPVW1mVis0eU5jZ2pHNlQrNXlRbVp4azJtd3BEWFVxdkFnZXdhYVFn?= =?utf-8?B?ZFc0K2RUY3lRaE8vNmhic1RybHBTYVlwVE93WDNGL0lSNFhmUnNWNGFQc2N3?= =?utf-8?B?ZEt5ekVjUkV2WG9LbFp6VVhkaEwvd0dKQU52cG1ZYkNJUGlvckRTb3VYWnFM?= =?utf-8?B?OXRRY3M5RzNrb3YrNHo2V0hTcDZScjBUeDRSTVF0TGRJUjNnVXlPVm1pcVRs?= =?utf-8?B?dm1XWlNUb0dyRUtMQkNqVS9MUi84dzN3N2NDYjRhS1lNVmRMNWdWZkFXYUFp?= =?utf-8?B?K3JHQTA4Um90SXFhVllLdm5lalpaTDk5R2d4OFd6S2VEMVo1SDVLU0xZeDFl?= =?utf-8?B?dE1SYjIxMDVCcUtGRFVSL3BSMVhQQmJESzYrR3pabXVMNmNCZGMvOXRXNWVu?= =?utf-8?B?VjBjVDk4OW9vQVZ4OEE1and5ZG55MzFuTkJMUUhPaDdSQWJFTmlJNUt0VUhz?= =?utf-8?Q?Zuvw=3D?= X-Forefront-Antispam-Report: CIP:165.204.84.17;CTRY:US;LANG:en;SCL:1;SRV:;IPV:NLI;SFV:NSPM;H:satlexmb08.amd.com;PTR:InfoDomainNonexistent;CAT:NONE;SFS:(13230040)(36860700013)(1800799024)(82310400026)(376014)(7416014);DIR:OUT;SFP:1101; X-OriginatorOrg: amd.com X-MS-Exchange-CrossTenant-OriginalArrivalTime: 30 Dec 2025 06:01:48.8813 (UTC) X-MS-Exchange-CrossTenant-Network-Message-Id: 81de087b-179d-434c-629e-08de4768ebaa X-MS-Exchange-CrossTenant-Id: 3dd8961f-e488-4e60-8e11-a82d994e183d X-MS-Exchange-CrossTenant-OriginalAttributedTenantConnectingIp: TenantId=3dd8961f-e488-4e60-8e11-a82d994e183d;Ip=[165.204.84.17];Helo=[satlexmb08.amd.com] X-MS-Exchange-CrossTenant-AuthSource: BL02EPF00021F6C.namprd02.prod.outlook.com X-MS-Exchange-CrossTenant-AuthAs: Anonymous X-MS-Exchange-CrossTenant-FromEntityHeader: HybridOnPrem X-MS-Exchange-Transport-CrossTenantHeadersStamped: SJ2PR12MB8781 Hello John, On 11/25/2025 4:01 AM, John Stultz wrote: > With proxy-exec once we do return migration from ttwu(), if a > task is proxying for a waiting donor, and the donor is woken up, > we switch the rq->donor to point to idle briefly until we can > re-enter __schedule(). > > However, if a task that was acting as a proxy calls into > yield() right after the donor is switched to idle, it may > trip a null pointer traversal, because the idle task doesn't > have a yield_task() pointer. I thought that was a transient state that should not be observed by the running task. Since NEED_RESCHED is retained, we'll just go though another pass of __schedule() loop and the task should not observe rq->donor as idle in do_sched_yield() as only the current task can yield on the local CPU. Do we have a splat that suggests this happens? -- Thanks and Regards, Prateek