linux-kernel - Re: [BUG 3.12.rc4] Oops: unable to handle kernel paging request during shutdown

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Message-ID: <20131028151637.GA13251@gmail.com>
Date:	Mon, 28 Oct 2013 16:16:37 +0100
From:	Ingo Molnar <mingo@...nel.org>
To:	Knut Petersen <Knut_Petersen@...nline.de>
Cc:	Linus Torvalds <torvalds@...ux-foundation.org>,
	Thomas Gleixner <tglx@...utronix.de>,
	Paul McKenney <paulmck@...ux.vnet.ibm.com>,
	Frédéric Weisbecker <fweisbec@...il.com>,
	Greg KH <greg@...ah.com>,
	linux-kernel <linux-kernel@...r.kernel.org>
Subject: Re: [BUG 3.12.rc4] Oops: unable to handle kernel paging request
 during shutdown


* Ingo Molnar <mingo@...nel.org> wrote:

> > I tried that patch, together with all the kobj debug options 
> > enabled. With that kernel configuration I was unable to 
> > reproduce the problem during 500 typical workload / reboot 
> > cycles. Without the debug options I was able to reproduce the 
> > last reported panic after 91 cycles. The debug options seem to 
> > change timing sufficiently to mask the bug ;-(
> 
> Could you send me the kernel config please?

I got your .config off-list, thanks Knut!

It has all DEBUG_OBJECT options enabled:

 CONFIG_DEBUG_OBJECTS=y
 # CONFIG_DEBUG_OBJECTS_SELFTEST is not set
 CONFIG_DEBUG_OBJECTS_FREE=y
 CONFIG_DEBUG_OBJECTS_TIMERS=y
 CONFIG_DEBUG_OBJECTS_WORK=y
 CONFIG_DEBUG_OBJECTS_RCU_HEAD=y
 CONFIG_DEBUG_OBJECTS_PERCPU_COUNTER=y
 CONFIG_DEBUG_OBJECTS_ENABLE_DEFAULT=1

but it also has DEBUG_PAGEALLOC enabled:

 CONFIG_DEBUG_PAGEALLOC=y

I'd suggest disabling that one - it kind of overlaps debugobjects 
and it will definitely be a big slowdown.

I'd also suggest turning off lockdep for now:

 CONFIG_PROVE_LOCKING=y

because we know it does not trigger any useful warning. This too 
should speed up things a bit.

Whether this would make the crash reproducable again I don't know
:-/

Thanks,

	Ingo
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