linux-kernel - Re: lockdep splat in CPU hotplug

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Date:	Wed, 22 Oct 2014 16:36:14 +0200 (CEST)
From:	Jiri Kosina <jkosina@...e.cz>
To:	Daniel Lezcano <daniel.lezcano@...aro.org>
cc:	Peter Zijlstra <peterz@...radead.org>,
	Ingo Molnar <mingo@...hat.com>,
	"Rafael J. Wysocki" <rjw@...ysocki.net>,
	Pavel Machek <pavel@....cz>,
	Steven Rostedt <rostedt@...dmis.org>,
	Dave Jones <davej@...hat.com>,
	"Paul E. McKenney" <paulmck@...ux.vnet.ibm.com>,
	Nicolas Pitre <nico@...aro.org>, linux-kernel@...r.kernel.org,
	linux-pm@...r.kernel.org
Subject: Re: lockdep splat in CPU hotplug

On Wed, 22 Oct 2014, Daniel Lezcano 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.
> > > 
> > > What am I missing?
> > 
> > Okay, reverting 442bf3aaf55a ("sched: Let the scheduler see CPU idle
> > states") and followup 83a0a96a5f26 ("sched/fair: Leverage the idle state
> > info when choosing the "idlest" cpu") which depends on it makes the splat
> > go away.
> 
> Are you able to reproduce it by offlining the cpu and onlining it again ?

No, that doesn't trigger it (please note that all the relevant stacktraces 
from lockdep are going through hibernation).

-- 
Jiri Kosina
SUSE Labs
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