On Tue, 21 Oct 2014, Paul E. McKenney wrote:
> > Looks like this indeed is something that lockdep *should* report (*),
> > although I would be suprised that stack unwinder would be so confused
> > by this -- there is no way for synchronize_sched_expedited() to be
> > inlined all the way to cpuidle_pause().
>
> I think that if synchronize_sched_expedited() was in fact called, it
> had already returned by the time we hit this problem. But I must confess
> that I am not seeing how cpuidle_uninstall_idle_handler() gets to
> synchronize_rcu().
Umm, it directly calls it? :-)
void cpuidle_uninstall_idle_handler(void)
{
if (enabled_devices) {
initialized = 0;
wake_up_all_idle_cpus();
}
/*
* Make sure external observers (such as the scheduler)
* are done looking at pointed idle states.
*/
synchronize_rcu();
}
> > (*) there are multiple places where cpu_hotplug.lock -> cpuidle_lock lock
> > dependency is assumed. The patch that Dave pointed out adds
> > cpuidle_lock -> cpu_hotplug.lock dependency.
> >
> > Still not clear whether this is what's happening here ... anyway, adding
> > Paul to CC.
>
> Hmmm...
>
> Both cpuidle_pause() and cpuidle_pause_and_lock() acquire cpuidle_lock,
> and are at the top of both stacks. Which was the original confusion. ;-)
Yup, they are, but lockdep is complaining about cpuidle_pause() acquiring
cpu_hotplug.lock ...
Thanks,
--
Jiri Kosina
SUSE Labs
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