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 15:50:10 +0100
From:	Knut Petersen <Knut_Petersen@...nline.de>
To:	Ingo Molnar <mingo@...nel.org>,
	Linus Torvalds <torvalds@...ux-foundation.org>
CC:	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 26.10.2013 13:43, Ingo Molnar wrote:
> * Linus Torvalds <torvalds@...ux-foundation.org> wrote:
>
>> On Fri, Oct 25, 2013 at 11:23 AM, Thomas Gleixner <tglx@...utronix.de> wrote:
>>> Enable DEBUG_OBJECTS, DEBUG_OBJECTS_FREE, DEBUG_OBJECTS_TIMERS
>> Yes, but nobody has actually been able to trigger it with those.
>> It's pretty rare, and the debug options are so expensive that they
>> aren't reasonable to enable generally...
>>
>> So we need to try to figure out how to trigger it, or narrow
>> things down some way..
> If it's timing then maybe the 1 seconds delay isn't enough
> (especially if it's boot related, where we have a couple of delays
> already) - the patch below triples it.
>
> (If the bug goes away due to some other side effect then this patch
> won't make a difference to reproducability.)

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 ;-(

Knut

> Thanks,
>
> 	Ingo
>
> diff --git a/lib/kobject.c b/lib/kobject.c
> index 084f7b1..124188f 100644
> --- a/lib/kobject.c
> +++ b/lib/kobject.c
> @@ -595,7 +595,7 @@ static void kobject_release(struct kref *kref)
>   	pr_info("kobject: '%s' (%p): %s, parent %p (delayed)\n",
>   		 kobject_name(kobj), kobj, __func__, kobj->parent);
>   	INIT_DELAYED_WORK(&kobj->release, kobject_delayed_cleanup);
> -	schedule_delayed_work(&kobj->release, HZ);
> +	schedule_delayed_work(&kobj->release, 3*HZ);
>   #else
>   	kobject_cleanup(kobj);
>   #endif
>

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