Re: [tip:irq/irqdomain] irqdomain: Introduce helper function irq_domain_add_hierarchy()

Jiang Liu
2014-12-01T02:21:01Z

On 2014/11/30 4:42, Thomas Gleixner wrote:
> On Sat, 29 Nov 2014, Borislav Petkov wrote:
>> So I'm seeing the lockdep splat below really early on an IVB laptop.
>>
>> Basically we're not supposed to do __GFP_FS allocations with IRQs off:
>>
>> 2737 /* We're only interested __GFP_FS allocations for now */
>> 2738 if (!(gfp_mask & __GFP_FS))
>> 2739 return;
>> 2740
>> 2741 /*
>> 2742 * Oi! Can't be having __GFP_FS allocations with IRQs disabled.
>> 2743 */
>> 2744 if (DEBUG_LOCKS_WARN_ON(irqs_disabled_flags(flags))) <--- HERE!
>> 2745 return;
>> 2746
>> 2747 mark_held_locks(curr, RECLAIM_FS);
>> 2748 }
>>
>> Now, AFAICT, enable_IR_x2apic() disables interrupts and the whole init
>> is done with IRQs off but down that path intel_setup_irq_remapping()
>> calls irq_domain_add_hierarchy() and it does by default GFP_KERNEL
>> allocations.
>>
>> The obvious fix is this and the machine boots fine with it. I'm not sure
>> it is kosher though so I rather run it by people first:
>>
>> ---
>> diff --git a/kernel/irq/irqdomain.c b/kernel/irq/irqdomain.c
>> index 7fac311057b8..c21a003b996a 100644
>> --- a/kernel/irq/irqdomain.c
>> +++ b/kernel/irq/irqdomain.c
>> @@ -46,14 +46,18 @@ struct irq_domain *__irq_domain_add(struct device_node *of_node, int size,
>> void *host_data)
>> {
>> struct irq_domain *domain;
>> + gfp_t gfp_flags = GFP_KERNEL;
>> +
>> + if (irqs_disabled())
>> + gfp_flags = GFP_NOFS;
>
> We want to use GFP_ATOMIC for that, but I really hate to do so. There
> is no reason except for the early boot stage to call into this code
> with interrupts disabled. And there we are covered by gfp_allowed_mask,
> so that a GFP_KERNEL allocation can succeed.
>
> I have no idea, why enable_IR_x2apic() has been bolted into
> smp_prepare_cpus(). Probably just because.
>
> There is no reason WHY this cannot be done in the early irq setup path
> (at least nowadays with the allocators being available early), but
> that is another area which needs some care and cleanup, but definitely
> too late before the 3.19 merge window opens.
Hi Thomas,
I will have a look at this after 3.19 merge window:)

>
> So we have to bite the bullet and apply something like this along with
> a big fat comment WHY we are doing so and I'm tempted to wrap this
> into a #ifdef CONFIG_X86 so that noone else thinks that calling this
> code with interrupts disabled - except for the early boot stage - is a
> brilliant idea.
>
> Thanks,
>
> tglx
>