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SubjectRe: Disabling an interrupt in the handler locks the system up
On 25/10/2016 12:45, Marc Zyngier wrote:
> On 25/10/16 09:36, Mason wrote:
>> On 25/10/2016 10:29, Sebastian Frias wrote:
>>> On 10/24/2016 06:55 PM, Thomas Gleixner wrote:
>>>> On Mon, 24 Oct 2016, Mason wrote:
>>>>> For the record, setting the IRQ_DISABLE_UNLAZY flag for this device
>>>>> makes the system lock-up disappear.
>>>> The way how lazy irq disabling works is:
>>>> 1) Interrupt is marked disabled in software, but the hardware is not masked
>>>> 2) If the interrupt fires befor the interrupt is reenabled, then it's
>>>> masked at the hardware level in the low level interrupt flow handler.
>>> Would you mind explaining what is the intention behind?
>>> Because it does not seem obvious why there isn't a direct map between
>>> "disable_irq*()" and "mask_irq()"
>> I had a similar, but slightly different question:
>> What is the difference between struct irq_chip's
>> * @irq_shutdown: shut down the interrupt (defaults to ->disable if NULL)
>> * @irq_disable: disable the interrupt
>> * @irq_mask: mask an interrupt source
> One important difference between disable and mask is that disable is
> perfectly allowed not to care about pending signals, whereas mask must
> preserve an interrupt becoming pending whilst masked.

(For my information)

Is it correct to say that "mask" is supposed to defer any interrupt
until sometime later; while "disable" will simply discard incoming
interrupts, losing them forever.

Is the irq_mask() call-back exposed via some module-visible API?

include/linux/interrupt.h documents mostly enable/disable variants.

extern void disable_irq_nosync(unsigned int irq);
extern bool disable_hardirq(unsigned int irq);
extern void disable_irq(unsigned int irq);
extern void disable_percpu_irq(unsigned int irq);
extern void enable_irq(unsigned int irq);
extern void enable_percpu_irq(unsigned int irq, unsigned int type);
extern bool irq_percpu_is_enabled(unsigned int irq);
extern void irq_wake_thread(unsigned int irq, void *dev_id);


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