On Tue, Oct 21, 2014 at 05:21:21PM +0200, Jiri Kosina wrote: > On Tue, 21 Oct 2014, Dave Jones wrote: > > > > I am seeing the lockdep report below when resuming from suspend-to-disk > > > with current Linus' tree (c2661b80609). > > > > > > The reason for CCing Ingo and Peter is that I can't make any sense of > > one > > > of the stacktraces lockdep is providing. > > > > > > Please have a look at the very first stacktrace in the dump, where > > lockdep > > > is trying to explain where cpu_hotplug.lock#2 has been acquired. It > > seems > > > to imply that cpuidle_pause() is taking cpu_hotplug.lock, but that's not > > > the case at all. > > > > Could inlining be confusing the trace here ? > > > > You can get from cpuidle_pause to cpuidle_uninstall_idle_handler -> > > synchronize_rcu > > -> synchronize_sched -> synchronize_sched_expedited which > > does a try_get_online_cpus which will take the cpu_hotplug.lock > > 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(). > (*) 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. ;-) Thanx, Paul -- To unsubscribe from this list: send the line "unsubscribe linux-kernel" in the body of a message to majord...@vger.kernel.org More majordomo info at http://vger.kernel.org/majordomo-info.html Please read the FAQ at http://www.tux.org/lkml/