linux-kernel - Re: latest -git: hibernate: possible circular locking dependency detected

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Message-ID: <20080822091827.GC6542@atrey.karlin.mff.cuni.cz>
Date:	Fri, 22 Aug 2008 11:18:27 +0200
From:	Pavel Machek <pavel@...e.cz>
To:	Vegard Nossum <vegard.nossum@...il.com>
Cc:	Dmitry Adamushko <dmitry.adamushko@...il.com>,
	Oleg Nesterov <oleg@...sign.ru>,
	Peter Zijlstra <a.p.zijlstra@...llo.nl>,
	"Rafael J. Wysocki" <rjw@...k.pl>,
	Max Krasnyanskiy <maxk@...lcomm.com>,
	Linux Kernel Mailing List <linux-kernel@...r.kernel.org>
Subject: Re: latest -git: hibernate: possible circular locking dependency detected

Hi!

> > this path is triggered as a result of "echo disk > /sys/power/state"
> 
> Yes. That is what I typed.
> 
> >
> > disable_nonboot_cpus() calls cpu_maps_update_being() which takes
> > "cpu_add_remove_lock" (lock-1).
> >
> > If we go down the road cleanup_workqueue_thread() ->
> > flush_cpu_workqueue() will take "cwq->lock" (lock-2).
> > So this should be the second lock.
> >
> >
> [...]
> 
> > hmm, did you somehow hit "Sysrq + o"?
> >
> > 'cause I don't see any other places (say, with handle_sysrq(k,...)
> > where "k" migth be 'o') from where do_power_off() might have been
> > triggered...
> >
> 
> No. But in my logs I often saw SysRq triggered, even though I didn't
> do it any of these times:
> 
> log-20080821-104053.txt:SysRq : SysRq : Show State
> log-20080821-105541.txt:SysRq : Emergency Sync
> log-20080821-105541.txt:SysRq : Emergency Sync
> log-20080821-105541.txt:SysRq : Power Off
> log-20080821-110514.txt:SysRq : Terminate All Tasks
> log-20080821-111650.txt:SysRq : HELP : loglevel0-8 <6>serial 00:0d: activated
> log-20080821-111650.txt:SysRq : Power Off
> log-20080821-111650.txt:SysRq : Terminate All Tasks
> log-20080821-111650.txt:SysRq : SysRq : <6>serial 00:0d: activated
> log-20080821-120628.txt:SysRq : SysRq : HELP : HELP : <6>serial 00:0d: activated
> log-20080821-120628.txt:SysRq : SysRq : HELP : HELP : <6>serial 00:0d: activated
> 
> (And it seems to pick a random letter too. It even showed the "HELP:"
> line at one point!)
> 
> I have no idea why this happens. Is it possible to trigger SysRq by
> writing data on the other end of the serial console? (Maybe my cable
> is bad or something, but data seems to be going in both directions
> over my serial console.)

Serial break translates to sysrq, IIRC.

-- 
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(cesky, pictures) http://atrey.karlin.mff.cuni.cz/~pavel/picture/horses/blog.html
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