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

[John Stultz <john.stultz@linaro.org>]

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