RE: [Xen-devel] Xen PANIC in MCE interrupt context : can global variable dom0 be NULL ?

["Jiang, Yunhong" <yunhong.jiang@xxxxxxxxx>]

Anshiwin and Jan, thanks for pointing this out.
As all our developer/test machine is off during the Chinese New Year Holiday. I 
can't access any system now ( not even run a vim )

Jan, as the error is quite straightfoward, can you please cook a patch for it 
(I can't even have a smoking testing if I cook a patch) ? If needed, I will 
verify it after the CNY.

Thanks
--jyh

>-----Original Message-----
>From: Jan Beulich [mailto:JBeulich@xxxxxxxxxx]
>Sent: Tuesday, February 16, 2010 5:06 PM
>To: Jiang, Yunhong; Ashwin Pankaj
>Cc: Xen-devel@xxxxxxxxxxxxxxxxxxx
>Subject: Re: [Xen-devel] Xen PANIC in MCE interrupt context : can global 
>variable
>dom0 be NULL ?
>
>>>> Ashwin Pankaj <ashwin.pankaj@xxxxxxx> 15.02.10 15:19 >>>
>>  After some digging, probable culprit seems to be smp_cmci_interrupt
>>
>>> if (bs.errcnt && mctc != NULL) {
>>>         if (guest_enabled_event(dom0->vcpu[0],
>>> <------------------------------------ here
>>>                      VIRQ_MCA)) {
>>>             mctelem_commit(mctc);
>>>             printk(KERN_DEBUG "CMCI: send CMCI to DOM0 through
>virq\n");
>>>             send_guest_global_virq(dom0, VIRQ_MCA);
>>>         } else {
>>>             x86_mcinfo_dump(mctelem_dataptr(mctc));
>>>             mctelem_dismiss(mctc);
>>>        }
>>
>>
>>Looks like dom0 is NULL here ( vcpu[0] offset is 0x468). Is this possible?
>
>Yes, your call trace confirms this.
>
>>Other functions like mce_softirq() perform a NULL check on dom0 before
>>accessing it's members ....
>
>The majority of uses doesn't seem to do that check, yet it is essential
>if CMCIs occur during boot of Xen. Even more, it should not only be
>dom0 that is checked against NULL, but also dom0->vcpu (or
>dom0->max_vcpus) and dom0->vcpu[0].
>
>Jan


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