Re: [RFC Dovetail 6.16]: Lockdep warning, IRQ while holding pci_config_lock

[Philippe Gerum <rpm@xenomai.org>]

Philippe Gerum <rpm@xenomai.org> writes:

> Philippe Gerum <rpm@xenomai.org> writes:
>
>> Florian Bezdeka <florian.bezdeka@siemens.com> writes:
>>
>>> Hi Philippe,
>>>
>>> from time to time I can see the following lockdep warning when testing
>>> on qemu.
>>>
>>> I'm not sure if my interpretation is correct. Should we convert
>>> pci_config_lock into a hard_spin_lock_t?
>>>
>>
>> No, we can't convert this lock. This would be a massive trauma, both
>> with respect to the PCI locking model and latency figures.
>
> Besides, that would not fix the core issue since the deadlock would
> still be there, and lockdep would still notice anyway (Dovetail locks
> are lockdep-tracked too).

However, that one should be turned into an hybrid lock. Not nice because
then we are going to disable hard irqs while fiddling with CPU masks,
but this would happen at irq startup exclusively. This said, that hidden
global lock looks pretty weird.

int irq_setup_affinity(struct irq_desc *desc)
{
	struct cpumask *set = irq_default_affinity;
	int node = irq_desc_get_node(desc);

	static DEFINE_RAW_SPINLOCK(mask_lock);

-- 
Philippe.