Message-ID: <53E1F96C.2030307@arm.com>
Date:	Wed, 06 Aug 2014 10:46:20 +0100
From:	Marc Zyngier <marc.zyngier@....com>
To:	Liu hua <sdu.liu@...wei.com>
CC:	Will Deacon <Will.Deacon@....com>,
	"nicolas.pitre@...aro.org" <nicolas.pitre@...aro.org>,
	"linux@....linux.org.uk" <linux@....linux.org.uk>,
	"linux-arm-kernel@...ts.infradead.org" 
	<linux-arm-kernel@...ts.infradead.org>,
	"linux-kernel@...r.kernel.org" <linux-kernel@...r.kernel.org>,
	"peifeiyue@...wei.com" <peifeiyue@...wei.com>,
	"liusdu@....com" <liusdu@....com>,
	"wangnan0@...wei.com" <wangnan0@...wei.com>,
	"ebiederm@...ssion.com" <ebiederm@...ssion.com>
Subject: Re: [PATCH V2 1/1] GIC: introduce method to deactive interupts

Hi Liu,

On 06/08/14 09:43, Liu hua wrote:
> 于 2014/8/4 17:43, Marc Zyngier 写道:
>> Hi Liu,
>>
>> On 04/08/14 05:17, Liu Hua wrote:
>>> When using kdump on ARM platform, if kernel panics in interrupt handler
>>> (maybe PPI), the capture kernel can not recive certain interrupt, and 
>>> fails to boot.
>>>
>>> On this situation, We have read register GICC_IAR. But we have no chance
>>> to write relative bit to register GICC_EOIR (kernel paniced before). So
>>> the state of this type interrupt remains active. And that makes gic not
>>> deliver this type interrupt to cpu interface.
>>>
>>> So we should not assume that all interrut states of GIC are inactive when
>>> kernel inittailize the GIC. This patch will identify these type interrupts
>>> and deactive them
>>>
>>> Signed-off-by: Liu Hua <sdu.liu@...wei.com>
>>> ---
>>>  drivers/irqchip/irq-gic.c | 26 ++++++++++++++++++++++++++
>>>  1 file changed, 26 insertions(+)
>>>
>>> diff --git a/drivers/irqchip/irq-gic.c b/drivers/irqchip/irq-gic.c
>>> index b2648fc..7708df1 100644
>>> --- a/drivers/irqchip/irq-gic.c
>>> +++ b/drivers/irqchip/irq-gic.c
>>> @@ -351,12 +351,37 @@ static u8 gic_get_cpumask(struct gic_chip_data *gic)
>>>  	return mask;
>>>  }
>>>  
>>> +void gic_eois(u32 active, int irq_off, void __iomem *cpu_base)
>>> +{
>>> +	int bit = -1;
>>> +
>>> +	for_each_set_bit(bit, (unsigned long *)&active, 32)
>>> +		writel_relaxed(bit + irq_off, cpu_base + GIC_CPU_EOI);
>>> +}
>>> +
>>> +void gic_dist_clear_active(void __iomem *dist_base,
>>> +			void __iomem *cpu_base, int gic_irqs)
>>> +{
>>> +	int irq, offset;
>>> +	u32 active;
>>> +
>>> +	for (irq = 0; irq < gic_irqs; irq += 32) {
>>> +		offset = GIC_DIST_ACTIVE_SET + irq * 4 / 32;
>>> +		active = readl_relaxed(dist_base + offset);
>>> +		if (!active)
>>> +			continue;
>>> +		gic_eois(active, irq, cpu_base);
>>> +	}
>>> +}
>>> +
>>> +
>>>  static void __init gic_dist_init(struct gic_chip_data *gic)
>>>  {
>>>  	unsigned int i;
>>>  	u32 cpumask;
>>>  	unsigned int gic_irqs = gic->gic_irqs;
>>>  	void __iomem *base = gic_data_dist_base(gic);
>>> +	void __iomem *cpu_base = gic_data_cpu_base(gic);
>>>  
>>>  	writel_relaxed(0, base + GIC_DIST_CTRL);
>>>  
>>> @@ -371,6 +396,7 @@ static void __init gic_dist_init(struct gic_chip_data *gic)
>>>  
>>>  	gic_dist_config(base, gic_irqs, NULL);
>>>  
>>> +	gic_dist_clear_active(base, cpu_base, gic_irqs);
>>>  	writel_relaxed(1, base + GIC_DIST_CTRL);
>>>  }
>>
>> So while this is solving a real issue, I don't think you can just fix it
>> for the UP case. You'll have to fix the same thing for secondary CPUs
>> (shouldn't be too hard to split things between local and global interrupts).
> Hi Marc,
> 
> Thanks very much for you reply!
> 
> when I tried to implement your ideas. I found that: when kdump is deployed
> and without my patch,
> 
> (1) panic in PPI, the capture kernel can not boot up.
> (2) panic in SPI, the capture kernel boot up regularly.
> 
> I was confused and there may be something I did not catch. I glanced the kdump
> code and found that function machine_kexec_mask_interrupts. It will clear the
> GIC active state only if the IRQD_IRQ_INPROGRESS bit in d->state_use_accessors
> is set.
> 
> And the PPI handler does not set this flag. So there are two ways to solve this
> problem.
> 
>  (1) consider this problem common, as you and I thought before. we should fix secondary CPUs issues;
> 
> 
>  (2)just set flag IRQD_IRQ_INPROGRESS in PPI. we need patch like this:
> 
> 	-------------(2) patch start-----------
> 	diff --git a/kernel/irq/chip.c b/kernel/irq/chip.c
> 	index a2b28a2..0a5dfe0 100644
> 	--- a/kernel/irq/chip.c
> 	+++ b/kernel/irq/chip.c
> 	@@ -677,10 +677,18 @@ void handle_percpu_devid_irq(unsigned int irq, struct irq_desc *desc)
>         	if (chip->irq_ack)
>                 	chip->irq_ack(&desc->irq_data);
> 
> 	+ raw_spin_lock(&desc->lock);
> 	+ irqd_set(&desc->irq_data, IRQD_IRQ_INPROGRESS);
> 	+ raw_spin_unlock(&desc->lock);
> 	+
>         trace_irq_handler_entry(irq, action);
>         res = action->handler(irq, dev_id);
>         trace_irq_handler_exit(irq, action, res);
> 
> 	+ raw_spin_lock(&desc->lock);
> 	+ irqd_clear(&desc->irq_data, IRQD_IRQ_INPROGRESS);
> 	+ raw_spin_unlock(&desc->lock);
> 	+
>         if (chip->irq_eoi)
>                 chip->irq_eoi(&desc->irq_data);
> 	 }
> 	-------------(2) patch end-----------
> 
> Way 2 seems to be needed anyway.
> For way 1, I do not find another situation that the gic interrupt states remains active when kernel booting.
> And for kdump process, Way 2 is enough.
> 
> What do you think about them?

Your second approach doesn't work, because you can have multiple CPUs
handling the same PPI at the same time. Remember these are per-processor
interrupts, despite having the same number. So you can't just have one
bit, you'd need one bit per CPU (and that's not going to happen).

I'm afraid that for PPIs, parsing the active bits is the only way.

Thanks,

	M.
-- 
Jazz is not dead. It just smells funny...
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