Re: [Qemu-devel] Unresponsive linux guest once migrated

[Marcin Gibuła]

> > Yes, that's where it gets weird. I've never seen this on fresh VM.
> > It needs to be idle for couple of hours at least. And even then it
> > doesn't always hang.
>
> So your OS is just sitting at a text console, running nothing special?
> When you reboot after the migration what's the last thing you see
> in the guests logs? Is there anything from after the migration?

Yes, it's completely idle. After reboot there is nothing in logs. I've 
dumped memory of one of hanged test VMs and found kernel message buffer. 
The last entries were:


init: failsafe main process (659) killed by TERM signal
init: plymouth-upstart-bridge main process (651) killed by TERM signal

<migration goes here, guest hangs>

Clocksource tsc unstable (delta = 470666274 ns)

<inject-nmi to test>

Uhhuh. NMI received for unknown reason 30 on CPU 0.
Do you have a strange power saving mode enabled?I:
Dazed and confused, but trying to continue
Uhhuh. NMI received for unknown reason 20 on CPU 0.
Do you have a strange power saving mode enabled?I:
Dazed and confused, but trying to continue
<0>Dazed and confused, but trying to continue



I've tried to disassemble where VM kernel (3.8.something from Ubuntu) is 
spinning (using qemu-monitor, registers info and symbols from guest 
kernel) and it was loop inside __run_timers function from kernel/timer.c:

while (time_after_eq(jiffies, base->timer_jiffies)) {
  ...
}

However my disassembly and qemu debugging skills are limited, would it 
help if I dump memory of broken VM and send it you somehow?

--
mg