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

From: Ingo Molnar <mingo@kernel.org>
To: Knut Petersen <Knut_Petersen@t-online.de>
Cc: "Linus Torvalds" <torvalds@linux-foundation.org>,
	"Thomas Gleixner" <tglx@linutronix.de>,
	"Paul McKenney" <paulmck@linux.vnet.ibm.com>,
	"Frédéric Weisbecker" <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
Date: Mon, 28 Oct 2013 16:16:37 +0100	[thread overview]
Message-ID: <20131028151637.GA13251@gmail.com> (raw)
In-Reply-To: <20131028150114.GA12905@gmail.com>

* 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.

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