Messages in this thread |  | | Date | Tue, 21 Oct 2014 17:21:21 +0200 (CEST) | From | Jiri Kosina <> | Subject | Re: lockdep splat in CPU hotplug |
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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().
(*) 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.
-- Jiri Kosina SUSE Labs
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