diff options
Diffstat (limited to 'kernel/smp.c')
| -rw-r--r-- | kernel/smp.c | 26 |
1 files changed, 17 insertions, 9 deletions
diff --git a/kernel/smp.c b/kernel/smp.c index c5e1da7a88da..4649fa4872ff 100644 --- a/kernel/smp.c +++ b/kernel/smp.c @@ -86,13 +86,15 @@ int smpcfd_dead_cpu(unsigned int cpu) int smpcfd_dying_cpu(unsigned int cpu) { /* - * The IPIs for the smp-call-function callbacks queued by other - * CPUs might arrive late, either due to hardware latencies or - * because this CPU disabled interrupts (inside stop-machine) - * before the IPIs were sent. So flush out any pending callbacks - * explicitly (without waiting for the IPIs to arrive), to - * ensure that the outgoing CPU doesn't go offline with work - * still pending. + * The IPIs for the smp-call-function callbacks queued by other CPUs + * might arrive late, either due to hardware latencies or because this + * CPU disabled interrupts (inside stop-machine) before the IPIs were + * sent. So flush out any pending callbacks explicitly (without waiting + * for the IPIs to arrive), to ensure that the outgoing CPU doesn't go + * offline with work still pending. + * + * This runs with interrupts disabled inside the stopper task invoked by + * stop_machine(), ensuring mutually exclusive CPU offlining and IPI flush. */ __flush_smp_call_function_queue(false); irq_work_run(); @@ -418,6 +420,10 @@ void __smp_call_single_queue(int cpu, struct llist_node *node) */ static int generic_exec_single(int cpu, call_single_data_t *csd) { + /* + * Preemption already disabled here so stopper cannot run on this CPU, + * ensuring mutually exclusive CPU offlining and last IPI flush. + */ if (cpu == smp_processor_id()) { smp_call_func_t func = csd->func; void *info = csd->info; @@ -638,8 +644,10 @@ int smp_call_function_single(int cpu, smp_call_func_t func, void *info, int err; /* - * prevent preemption and reschedule on another processor, - * as well as CPU removal + * Prevent preemption and reschedule on another CPU, as well as CPU + * removal. This prevents stopper from running on this CPU, thus + * providing mutual exclusion of the below cpu_online() check and + * IPI sending ensuring IPI are not missed by CPU going offline. */ this_cpu = get_cpu(); |