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Date: Mon, 28 Oct 2013 16:45:09 +0100
From: Knut Petersen <Knut_Petersen@t-online.de>
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To: Ingo Molnar <mingo@kernel.org>
CC: Linus Torvalds <torvalds@linux-foundation.org>,
        Thomas Gleixner <tglx@linutronix.de>,
        Paul McKenney <paulmck@linux.vnet.ibm.com>,
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	<fweisbec@gmail.com>,
        Greg KH <greg@kroah.com>, linux-kernel <linux-kernel@vger.kernel.org>
Subject: Re: [BUG 3.12.rc4] Oops: unable to handle kernel paging request during
 shutdown
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On 28.10.2013 16:16, Ingo Molnar wrote:
> * Ingo Molnar <mingo@kernel.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 thatīs true. On one machine it emits the old warning about the
videobuf_dvb_find_frontend() /  dvb_device_open() circular reference,
but thatīs definitely unrelated.

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

Weīll see ;-)
> Thanks,
>
> 	Ingo
>