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

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Date:	Mon, 28 Oct 2013 16:45:09 +0100
From:	Knut Petersen <Knut_Petersen@...nline.de>
To:	Ingo Molnar <mingo@...nel.org>
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

On 28.10.2013 16:16, Ingo Molnar wrote:
> * 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.

ACK
> 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.

Well, for now that´s true. On one machine it emits the old warning about the
videobuf_dvb_find_frontend() /  dvb_device_open() circular reference,
but that´s definitely unrelated.

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

We´ll see ;-)
> Thanks,
>
> 	Ingo
>

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