Re: [Xen-devel] Using debug-key 'o: Dump IOMMU p2m table, locks up machine

[Keir Fraser <keir.xen@xxxxxxxxx>]

On 31/08/2012 22:45, "Sander Eikelenboom" <linux@xxxxxxxxxxxxxx> wrote:

> 
> I was trying to use the 'o' debug key to make a bug report about an "AMD-Vi:
> IO_PAGE_FAULT".
> 
> The result:
> - When using "xl debug-keys o", the machine seems in a infinite loop, can
> hardly login, eventually resulting in a kernel RCU stall and complete lockup.

We don't defer the key handler to tasklet context in this case (because of
'if !in_irq()' check in keyhandler.c:handle_keypress()). Hence the dom0 vCPU
gets 'stuck' while the handler executes. Possibly we should always defer
non-irq keyhandlers to tasklet context, even when executed via sysctl.

> - When using serial console: I get a infinite stream of "gfn:  mfn: " lines,
> mean while on the normal console, S-ATA devices are starting to give errors.

In this case the handler must be running in tasklet context. Not sure why
SATA interrupts would be affected as hardirq and softirq work will still be
carried out during execution of the keyhandler (the handler voluntarily
preempts itself for softirq work).

Would need more investigation. :)

 -- Keir

> So either option trashes the machine, other debug-keys work fine.
> 
> Machine has a 890-fx chipset and AMD phenom x6 proc.
> 
> xl dmesg with bootup and output from some other debug-keys is attached.
> 
> --
> 
> Sander
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