linux-kernel - Re: lockdep splat in CPU hotplug

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Message-ID: <20141021151043.GA11800@redhat.com>
Date:	Tue, 21 Oct 2014 11:10:43 -0400
From:	Dave Jones <davej@...hat.com>
To:	Jiri Kosina <jkosina@...e.cz>
Cc:	Peter Zijlstra <peterz@...radead.org>,
	Ingo Molnar <mingo@...hat.com>,
	"Rafael J. Wysocki" <rjw@...ysocki.net>,
	Pavel Machek <pavel@....cz>, linux-kernel@...r.kernel.org,
	linux-pm@...r.kernel.org
Subject: Re: lockdep splat in CPU hotplug

On Tue, Oct 21, 2014 at 01:09:04PM +0200, Jiri Kosina wrote:
 > Hi,
 > 
 > 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

	Dave

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