diff options
Diffstat (limited to 'kernel')
| -rw-r--r-- | kernel/events/core.c | 19 |
1 files changed, 19 insertions, 0 deletions
diff --git a/kernel/events/core.c b/kernel/events/core.c index 43e35faf576e..de24fbce5277 100644 --- a/kernel/events/core.c +++ b/kernel/events/core.c @@ -9449,10 +9449,29 @@ perf_cpu_notify(struct notifier_block *self, unsigned long action, void *hcpu) switch (action & ~CPU_TASKS_FROZEN) { case CPU_UP_PREPARE: + /* + * This must be done before the CPU comes alive, because the + * moment we can run tasks we can encounter (software) events. + * + * Specifically, someone can have inherited events on kthreadd + * or a pre-existing worker thread that gets re-bound. + */ perf_event_init_cpu(cpu); break; case CPU_DOWN_PREPARE: + /* + * This must be done before the CPU dies because after that an + * active event might want to IPI the CPU and that'll not work + * so great for dead CPUs. + * + * XXX smp_call_function_single() return -ENXIO without a warn + * so we could possibly deal with this. + * + * This is safe against new events arriving because + * sys_perf_event_open() serializes against hotplug using + * get_online_cpus(). + */ perf_event_exit_cpu(cpu); break; default: |