Re: [4.9-rc1+] intel_uncore builtin + CONFIG_DEBUG_TEST_DRIVER_REMOVE kernel panic

Jiri Olsa
2016-10-20T09:43:04Z

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.