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McKenney" , Boqun Feng , Jonathan Corbet , Madadi Vineeth Reddy , K Prateek Nayak , Steven Rostedt , Sebastian Andrzej Siewior , Arnd Bergmann , "linux-arch@vger.kernel.org" References: <20251029125514.496134233@linutronix.de> <03687B00-0194-4707-ABCB-FB3CD5340F11@oracle.com> From: Mathieu Desnoyers Content-Language: en-US In-Reply-To: <03687B00-0194-4707-ABCB-FB3CD5340F11@oracle.com> Content-Type: text/plain; charset=UTF-8; format=flowed Content-Transfer-Encoding: 7bit X-ClientProxiedBy: YT2PR01CA0029.CANPRD01.PROD.OUTLOOK.COM (2603:10b6:b01:38::34) To YT2PR01MB9175.CANPRD01.PROD.OUTLOOK.COM (2603:10b6:b01:be::5) Precedence: bulk X-Mailing-List: linux-arch@vger.kernel.org List-Id: List-Subscribe: List-Unsubscribe: MIME-Version: 1.0 X-MS-PublicTrafficType: Email X-MS-TrafficTypeDiagnostic: YT2PR01MB9175:EE_|YT3PR01MB5552:EE_ X-MS-Office365-Filtering-Correlation-Id: 1294789e-89cb-4dbc-3991-08de2064b3cc X-MS-Exchange-SenderADCheck: 1 X-MS-Exchange-AntiSpam-Relay: 0 X-Microsoft-Antispam: BCL:0;ARA:13230040|1800799024|376014|7416014|366016; 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Assume this Is the latest. > https://git.kernel.org/pub/scm/linux/kernel/git/tglx/devel.git/ rseq/slice > > Appears to be spinning in mm_get_cid(). Must be the mm cid changes. > https://lore.kernel.org/all/20251029123717.886619142@linutronix.de/ When this happened during the development of the "complex" mm_cid scheme, this was typically caused by a stale "mm_cid" being kept around by a task even though it was not actually scheduled, thus causing over-reservation of concurrency IDs beyond the max_cids threshold. This ends up looping in: static inline unsigned int mm_get_cid(struct mm_struct *mm) { unsigned int cid = __mm_get_cid(mm, READ_ONCE(mm->mm_cid.max_cids)); while (cid == MM_CID_UNSET) { cpu_relax(); cid = __mm_get_cid(mm, num_possible_cpus()); } return cid; } Based on the stacktrace you provided, it seems to happen within sched_mm_cid_fork() within copy_process, so perhaps it's simply an initialization issue in fork, or an issue when cloning a new thread ? Thanks, Mathieu -- Mathieu Desnoyers EfficiOS Inc. https://www.efficios.com