Hmmm.  IRQ4 is "PCI ExternalCommand Write"?  But I'm not using PCI.  
Here is the output:

# ./irqloop
NULL ->unmask handler, IRQ 4, chip <NULL>
Test mode:    user-space task
Port type:    serial
Port address: 0x3f8
Port IRQ:     4

Received IRQs:     0
Acknowledged IRQs: 0
Xenomai: POSIX: destroyed thread c0f80320


Philippe Gerum wrote:
> Steven A. Falco wrote:
>   
>> I am testing kernel 2.6.23 ARCH=powerpc with Xenomai 2.4-rc4.  The 
>> clocktest and cyclictest work perfectly with the uic/spinlock patches.  
>> However, the irqloop test fails with the Oops shown below.
>>
>>     
>
> Please try the patch below. It looks like the chip descriptor does not implement
> any unmask handler, which seems odd. This patch should tell us a bit more about
> this issue.
>
>