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McKenney" , Peter Zijlstra , Phil Auld , Sebastian Andrzej Siewior , Shrikanth Hegde , Tejun Heo , =?UTF-8?q?Thomas=20Wei=C3=9Fschuh?= , Valentin Schneider Cc: Yury Norov , Yury Norov , Bradley Morgan Subject: [PATCH v2] stop_machine: Make stop_one_cpu_nowait() return void Date: Tue, 28 Jul 2026 22:23:54 -0400 Message-ID: <20260729022355.325058-1-ynorov@nvidia.com> X-Mailer: git-send-email 2.53.0 Content-Transfer-Encoding: 8bit Content-Type: text/plain X-ClientProxiedBy: SJ0PR03CA0155.namprd03.prod.outlook.com (2603:10b6:a03:338::10) To DM3PR12MB9349.namprd12.prod.outlook.com (2603:10b6:0:49::12) 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: DM3PR12MB9349:EE_|LV8PR12MB9689:EE_ X-MS-Office365-Filtering-Correlation-Id: d632ef08-798d-4670-a8ba-08deed1871f2 X-MS-Exchange-SenderADCheck: 1 X-MS-Exchange-AntiSpam-Relay: 0 X-Microsoft-Antispam: BCL:0;ARA:13230040|23010399003|376014|7416014|10070799003|366016|1800799024|56012099006|11063799006|10067099003|921020|18002099003; 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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 --- v1: https://lore.kernel.org/all/20260724232325.594212-1-ynorov@nvidia.com/ v2: - carefully include linux/bug.h (Bradley); - update the CONTEXT section (Bradley). include/linux/stop_machine.h | 21 ++++++++++----------- kernel/stop_machine.c | 14 ++++++-------- 2 files changed, 16 insertions(+), 19 deletions(-) diff --git a/include/linux/stop_machine.h b/include/linux/stop_machine.h index 01011113d226..84e7fb627ba4 100644 --- a/include/linux/stop_machine.h +++ b/include/linux/stop_machine.h @@ -2,6 +2,7 @@ #ifndef _LINUX_STOP_MACHINE #define _LINUX_STOP_MACHINE +#include #include #include #include @@ -31,7 +32,7 @@ struct cpu_stop_work { int stop_one_cpu(unsigned int cpu, cpu_stop_fn_t fn, void *arg); int stop_two_cpus(unsigned int cpu1, unsigned int cpu2, cpu_stop_fn_t fn, void *arg); -bool stop_one_cpu_nowait(unsigned int cpu, cpu_stop_fn_t fn, void *arg, +void stop_one_cpu_nowait(unsigned int cpu, cpu_stop_fn_t fn, void *arg, struct cpu_stop_work *work_buf); void stop_machine_park(int cpu); void stop_machine_unpark(int cpu); @@ -68,19 +69,17 @@ static void stop_one_cpu_nowait_workfn(struct work_struct *work) preempt_enable(); } -static inline bool stop_one_cpu_nowait(unsigned int cpu, +static inline void stop_one_cpu_nowait(unsigned int cpu, cpu_stop_fn_t fn, void *arg, struct cpu_stop_work *work_buf) { - if (cpu == smp_processor_id()) { - INIT_WORK(&work_buf->work, stop_one_cpu_nowait_workfn); - work_buf->fn = fn; - work_buf->arg = arg; - schedule_work(&work_buf->work); - return true; - } - - return false; + if (WARN_ON_ONCE(cpu != smp_processor_id())) + return; + + INIT_WORK(&work_buf->work, stop_one_cpu_nowait_workfn); + work_buf->fn = fn; + work_buf->arg = arg; + schedule_work(&work_buf->work); } static inline void print_stop_info(const char *log_lvl, struct task_struct *task) { } diff --git a/kernel/stop_machine.c b/kernel/stop_machine.c index 773d8e9ae30c..d085ba1f4b44 100644 --- a/kernel/stop_machine.c +++ b/kernel/stop_machine.c @@ -7,6 +7,7 @@ * Copyright (C) 2010 SUSE Linux Products GmbH * Copyright (C) 2010 Tejun Heo */ +#include #include #include #include @@ -376,17 +377,14 @@ int stop_two_cpus(unsigned int cpu1, unsigned int cpu2, cpu_stop_fn_t fn, void * * and will remain untouched until stopper starts executing @fn. * * CONTEXT: - * Don't care. - * - * RETURNS: - * true if cpu_stop_work was queued successfully and @fn will be called, - * false otherwise. + * Don't care, but the caller must ensure @cpu's stopper stays enabled + * until the work is queued, e.g. by preempt_disable(). */ -bool stop_one_cpu_nowait(unsigned int cpu, cpu_stop_fn_t fn, void *arg, - struct cpu_stop_work *work_buf) +void stop_one_cpu_nowait(unsigned int cpu, cpu_stop_fn_t fn, void *arg, + struct cpu_stop_work *work_buf) { *work_buf = (struct cpu_stop_work){ .fn = fn, .arg = arg, .caller = _RET_IP_, }; - return cpu_stop_queue_work(cpu, work_buf); + WARN_ON_ONCE(!cpu_stop_queue_work(cpu, work_buf)); } static bool queue_stop_cpus_work(const struct cpumask *cpumask, -- 2.53.0