Re: [Xen-devel] DomU: kernel BUG at arch/x86/xen/enlighten.c:425

[James Sinclair <james.sinclair@xxxxxxxxxx>]

On 12/03/2013, at 6:45 PM, Jan Beulich <JBeulich@xxxxxxxx> wrote:

>>>> On 12.03.13 at 04:56, James Sinclair <james.sinclair@xxxxxxxxxx> wrote:
> 
> (re-adding xen-devel to Cc)
> 
>> I've done further testing and I have confirmed that I can trigger the bug 
>> pretty reliably on several Xen versions:
>> 
>>    * xen-3.4.4
>>    * xen-4.1.4
>>    * xen-4.1.5-pre
>> 
>> Dom0 kernels range between 2.6.18 & 3.7.7-1. I've also tried quite a few 
>> DomU 
>> kernels and I can trigger it in everything I've tried between 2.6.39.1 and 
>> 3.7.10. In the end, I haven't managed to find a combination of Xen, Dom0 & 
>> DomU where I cannot trigger it.
> 
> Partly because you apparently never tried non-pvops DomU kernels.
> But that's not the point here.
> 
>> As for the hypervisor log, I'm not seeing anything get logged at all. I 
>> suspect that I'm not capturing them correctly. Using Xen 4.1.4 I added the 
>> following to the command line:
>> 
>>    loglvl=all guest_loglvl=all sync_console console_to_ring earlyprintk=xen 
>> debug loglevel=8
> 
> Now, this mixture of hypervisor and kernel options already
> suggests that you don't look in the right place. Please put Xen
> options on the Xen command line, and kernel ones on the kernel
> line.

The documentation I found that mentioned using "earlyprintk=xen debug 
loglevel=8" did not make it clear those are kernel options. I've corrected that 
now:

    Hypervisor options: loglvl=all guest_loglvl=all sync_console console_to_ring
    Kernel options: earlyprintk=xen debug loglevel=8

> 
>> I'm seeing extra logs from Xen during boot, but nothing when the bug is 
>> triggered in the DomU. I'm assuming any extra logging will show up on the 
>> console or in /var/log/xen/xend.log - is there somewhere else I should be 
>> looking? Or something I'm not setting correctly?
> 
> They show up on the serial console (if in use) or in the output of
> "xl dmesg" (or "xm dmesg" if xend is in use). Without extra
> precautions, they _won't_ show up anywhere under /var/log.

I'm not seeing anything extra logged on the serial console nor in "xl dmesg" 
when the bug hits. The only log entry I'm getting is a warning from 
XendDomainInfo that the domain has crashed, and that's only logged when the bug 
hits a critical process (usually init) that causes the domU kernel to panic.

I'm working on building a hypervisor with "debug=y" enabled to see if that 
gives me anything extra.

James
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