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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. Signed-off-by: Yury Norov --- include/linux/stop_machine.h | 20 +++++++++----------- kernel/stop_machine.c | 10 +++------- 2 files changed, 12 insertions(+), 18 deletions(-) diff --git a/include/linux/stop_machine.h b/include/linux/stop_machine.h index 01011113d226..604ab4d103a8 100644 --- a/include/linux/stop_machine.h +++ b/include/linux/stop_machine.h @@ -31,7 +31,7 @@ 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 +68,17 @@ 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..a8a91b1e62f1 100644 --- a/kernel/stop_machine.c +++ b/kernel/stop_machine.c @@ -377,16 +377,12 @@ int stop_two_cpus(unsigned int cpu1, unsigned int cpu2, cpu_stop_fn_t fn, void * * * CONTEXT: * Don't care. - * - * RETURNS: - * true if cpu_stop_work was queued successfully and @fn will be called, - * false otherwise. */ -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