[PATCH kernel v2] powerpc/xive: Drop deregistered irqs

[Michael Ellerman]

Cédric Le Goater <clg at kaod.org> writes:
> On 16/07/2019 11:10, Alexey Kardashevskiy wrote:
>> On 16/07/2019 18:59, Cédric Le Goater wrote:
>>> On 15/07/2019 09:11, Alexey Kardashevskiy wrote:
>>>> There is a race between releasing an irq on one cpu and fetching it
>>>> from XIVE on another cpu as there does not seem to be any locking between
>>>> these, probably because xive_irq_chip::irq_shutdown() is supposed to
>>>> remove the irq from all queues in the system which it does not do.
>>>>
>>>> As a result, when such released irq appears in a queue, we take it
>>>> from the queue but we do not change the current priority on that cpu and
>>>> since there is no handler for the irq, EOI is never called and the cpu
>>>> current priority remains elevated (7 vs. 0xff==unmasked). If another irq
>>>> is assigned to the same cpu, then that device stops working until irq
>>>> is moved to another cpu or the device is reset.
>>>>
>>>> This adds a new ppc_md.orphan_irq callback which is called if no irq
>>>> descriptor is found. The XIVE implementation drops the current priority
>>>> to 0xff which effectively unmasks interrupts in a current CPU.
>>>
>>>
>>> The test on generic_handle_irq() catches interrupt events that
>>> were served on a target CPU while the source interrupt was being
>>> shutdown on another CPU.
>>>
>>> The orphan_irq() handler restores the CPPR in such cases.
>>>
>>> This looks OK to me. I would have added some more comments in the
>>> code.
>> 
>> Which and where? Thanks,
>
> Above xive_orphan_irq() explaining the complete problem that we are 
> addressing. XIVE is not super obvious when looking at the code ...

Yes adding a comment would be good, thanks.

This will also need a Fixes: tag.

cheers