linux-kernel - Re: lockdep splat in CPU hotplug

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Date:	Wed, 22 Oct 2014 16:45:01 +0200
From:	Daniel Lezcano <daniel.lezcano@...aro.org>
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>,
	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 10/22/2014 04:36 PM, Jiri Kosina wrote:
> 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).

Ok, thanks.


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