At 15:56 +0100 on 14 Sep (1284479787), Roger Cruz wrote:
> I had a pretty good inkling that one of you hardcore developers would
> say that :-) Yes, it is pretty well wedged. I can cause the problem
> more rapidly by dropping to a single CPU. When the hang happens, the
> Xen console is completely dead. None of the special keys work.
If the 'd' key doesn't work then the serial irq isn't getting handled,
so the CPU is wedged at a higher TPR (at least). Usually in that case
the CPU is spinning so the NMI watchdog timer kicks in OK; possibly if
it was idle with a high TPR it wouldn't.
What version of Xen are you using?
It might be worth trying a boot with MSI disabled (there were reports at
one stage of MSIs not being EOI'd because the timer interupt that would
remind Xen to EOI them was at a lower priority than the MSI).
> I do have hopes a BIOS upgrade could fix this as a last resort but I
> want to see if at least I can understand the problem. We have a few
> different machines that are exhibiting similar symptoms so I have to
> see if I can find a work-around without requiring every user to
> upgrade their BIOS :-(
>
> Just in case, what debugger have you been using? Are there recent
> instructions on how to set it up that you can point me to?
I don't use a debugger on Xen. I usually find that by the time the
debugger kicks in it's too late to help, so I end up finding bugs by
code inspection and printks. :)
Mukesh Rathor at Oracle has done some debugger work, though, including
an in-Xen debugger. There's a gdb stub too but I suspect it's rotted
quite badly.
Cheers,
Tim.
> Thanks
> Roger
>
>
> -----Original Message-----
> From: Tim Deegan [mailto:Tim.Deegan@xxxxxxxxxx]
> Sent: Tue 9/14/2010 10:30 AM
> To: Roger Cruz
> Cc: xen-devel@xxxxxxxxxxxxxxxxxxx
> Subject: Re: [Xen-devel] State of current Xen debugger
>
> Hi,
>
> At 15:22 +0100 on 14 Sep (1284477779), Roger Cruz wrote:
> > I am trying to debug a problem where the hypervisor is hanging hard.
> > Not even the NMI watchdog is triggering a reboot. So I wanted to hook
> > up a debugger.
>
> Sorry to bring a counsel of despair but if the NMI watchdog isn't
> working then your chances of getting a working debugger are slim. It's
> likely that at least one CPU is very very stuck. Does the 'd' debug key
> work on the serial line when the machine is wedged?
>
> On a more cheerful note, I've twice seen hard hangs like this that
> turned out to be hardware issues, fixable with BIOS upgrades.
>
> Cheers,
>
> Tim.
>
> > What is the state of the current debuggers out there?
> > Any input on how I should set it up (kdb, gdb, etc) and pointers to a
> > good wiki page are much appreciated. I did perform a Google search
> > and found some links but I want to hear from the current developers as
> > to what is most stable and useful for debugging this type of hard
> > hang. I only have a serial port PCI-express card to use as the laptop
> > has no built in port.
>
> --
> Tim Deegan <Tim.Deegan@xxxxxxxxxx>
> Principal Software Engineer, XenServer Engineering
> Citrix Systems UK Ltd. (Company #02937203, SL9 0BG)
>
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--
Tim Deegan <Tim.Deegan@xxxxxxxxxx>
Principal Software Engineer, XenServer Engineering
Citrix Systems UK Ltd. (Company #02937203, SL9 0BG)
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