Re: [PATCH] pciehp: Handle interrupts that happen during initialization.

[Kenji Kaneshige <kaneshige.kenji@jp.fujitsu.com>]

Eric W. Biederman wrote:
> ebiederm@xmission.com (Eric W. Biederman) writes:
> 
>> And on the big gotcha's I have found one more I am tracking.
>>
>> I am seeing pci bridges with a NULL pointer for the subordinate bus.
>> Earlier I had thought that this was a symptom of the double remove
>> but I have been able to reproduce it without that.
>>
>> On just a little bit deeper investigation it looks like the cases
>> are dying are all coming when the nested bridge reappears.
>>
>> Which is wrong on so many levels as I am toggle power to the outer
>> slot, so the nested bridge should not even exist at that time.  Ugh.
>> More tracing to for me on that one.
> 
> Ok. Got it.  I was processing the interrupt for a device after it had
> been hot removed but before the device state had disappeared.
> 
> pcie_isr looks like it would be even worse in that situation.  Looping forever
> if pciehp_readw(ctrl, PCIE_EXPSLTA) always succeed sand returns 0xffff.
> 
> That loop in there appears impossibly misguided.  If the pending interrupt
> values change after you have received the interrupt another instance
> of the same interrupt should be pending so the loop should be completely
> unnecessary.
> 

For level-triggered interrupt, I think it's true.

But for edge-triggered interrupt, I don't think it's true. I think
only one interrupt is generated if the first hotplug event occurs
and the second hotplug event occurs before clearing the status of
first hotplug event.

Thanks,
Kenji Kaneshige