On Thu, Oct 20, 2016 at 11:04:16AM +0200, Peter Zijlstra wrote: > On Thu, Oct 20, 2016 at 10:58:03AM +0200, Jiri Olsa wrote: > > > @@ -8869,11 +8869,15 @@ void perf_pmu_unregister(struct pmu *pmu) > > free_percpu(pmu->pmu_disable_count); > > if (pmu->type >= PERF_TYPE_MAX) > > 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); > > + mutex_lock(&pmus_lock); > > + if (pmu_bus_running) { > > + if (pmu->nr_addr_filters) > > + device_remove_file(pmu->dev, &dev_attr_nr_addr_filters); > > + device_del(pmu->dev); > > + put_device(pmu->dev); > > + } > > free_pmu_context(pmu); > > + mutex_unlock(&pmus_lock); > > } > > EXPORT_SYMBOL_GPL(perf_pmu_unregister); > > I think that is still racy.. > > > unregister: sysfs_init: > > mutex_lock(&pmus_lock); > list_del_rcu(&pmu->entry); > mutex_unlock(&pmus_lock); > > synchronize_*rcu(); > > mutex_lock(&pmus_lock); > list_for_each_entry(pmu, &pmus, entry) { > /* add device muck */
ah, I thought this part would add the device back.. but it's already out of the pmu list.. right :-\ thanks, jirka > /* will _NOT_ see our PMU */ > } > pmus_bus_running = 1; > mutex_unlock(&pmus_lock); > > mutex_lock(&pmus_lock); > if (pmu_bus_running) { > device_del() /* OOPS */ > > > What you want is to read pmu_bus_running in the same pmus_lock section > as we do the list_del, and then use that local copy later.