linux-kernel - Re: Regression: ONE CPU fails bootup at Re: [3.2.0-RC7] BUG: unable to handle kernel NULL pointer dereference at 0000000000000598 1.478005] IP: [<ffffffff8107a6c4>] queue_work

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Message-ID: <1325702212.3037.102.camel@work-vm>
Date:	Wed, 04 Jan 2012 10:36:52 -0800
From:	John Stultz <john.stultz@...aro.org>
To:	Stefan Bader <stefan.bader@...onical.com>
Cc:	NeilBrown <neilb@...e.de>,
	Konrad Rzeszutek Wilk <konrad.wilk@...cle.com>,
	Sander Eikelenboom <linux@...elenboom.it>, rjw@...k.pl,
	Thomas Gleixner <tglx@...utronix.de>,
	linux-kernel@...r.kernel.org
Subject: Re: Regression: ONE CPU fails bootup at Re: [3.2.0-RC7] BUG: unable
 to handle kernel NULL pointer dereference at 0000000000000598  1.478005]
 IP: [<ffffffff8107a6c4>] queue_work_on+0x4/0x30

On Wed, 2012-01-04 at 09:17 +0100, Stefan Bader wrote:
> Over night I had still be thinking on this and maybe one important fact I had
> been ignoring. This really has only been observed on paravirt guests on Xen as
> far as I know. And one thing that I should have pointed out is that
> 
> [    0.792634] rtc_cmos rtc_cmos: rtc core: registered rtc_cmos as rtc0
> [    0.792725] rtc_cmos: probe of rtc_cmos failed with error -38
> 
> So first the registration is done and the first line is the last thing printed
> in the registration function. Then, and that line always comes after, the probe,
> which looks like being done asynchronously, detects that the rtc is not
> implemented. I would assume that this causes the rtc to be unregistered again
> and that is probably the point where, under the right circumstances, the worker
> triggered by the initialize alarm is trying to set another alarm. Probably while
> some of the elements of the structure started to be torn down. I need to check
> on that code path, yet. So right now its more a guess.

Hrm. Do you see the same probe error with 3.1 kernels as well?  

Konrad: Is the probe failure a known issue on Xen? Any clues on whats
going on there?

thanks
-john


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