On Wed, Oct 19, 2016 at 09:19:43PM +0200, Jiri Olsa wrote: > I think the reason here is that presume pmu devices are always added, > but we add them only if pmu_bus_running (in perf_event_sysfs_init) > is set which might happen after uncore initcall > > attached patch fixes the issue for me
Right, we never expected to be unloaded before userspace runs. Strictly speaking we should only read pmu_bus_running while holding pmus_lock, that way we're serialized against perf_event_sysfs_init() flipping it while we're being removed etc.. With the current setup the introduced race is harmless, but who knows what other crazy these device people will come up with ;-) > --- > diff --git a/kernel/events/core.c b/kernel/events/core.c > index c6e47e97b33f..c2099b799d16 100644 > --- a/kernel/events/core.c > +++ b/kernel/events/core.c > @@ -8871,8 +8871,10 @@ void perf_pmu_unregister(struct pmu *pmu) > idr_remove(&pmu_idr, pmu->type); > if (pmu->nr_addr_filters) > device_remove_file(pmu->dev, &dev_attr_nr_addr_filters); > - device_del(pmu->dev); > - put_device(pmu->dev); > + if (pmu_bus_running) { > + device_del(pmu->dev); > + put_device(pmu->dev); > + } > free_pmu_context(pmu); > } > EXPORT_SYMBOL_GPL(perf_pmu_unregister);