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SubjectRe: Maybe a bug in kernel/irq/chip.c unmask_irq(), device IRQ masked unexpectedly. (re-formated the mail body, sorry)
Hi,

* Yi Zheng <goodmenzy@gmail.com> [191008 13:06]:
> NOTE: (1) My SoC is a single core ARM chip: TI-AM3352, so the raw
> spin-lock irq_desc->lock will be optimized to
> nothing. handle_level_irq() has no spin-lock protection, right?

Well not always, With CONFIG_SMP we modify only some of the SMP code on boot,
see arch/arm/kernel/head.S for smp_on_up and then the related macro usage.

> (2) In AM3352, INTC driver ACK the IRQ by write 0x01 into INTC Control
> Register(offset 0x48). The chip doc seems that bit[0] of
> INTC-Control Reg is only an enable/disable flag. The IRQ may
> generated even if no ACK action done. Any one can give me an
> clarification?

The TI INTC is probably better documented in dm3630 trm, it's the same
controller but with a different revision.

> (3) My analysis is not verified on the real machine. After some code
> change for debug(add counter to indicates the iteration level, save
> the IRQ mask status etc.), the device IRQ wrongly masked problem
> vanished. In fact, the original code can not re-produce the
> phenomena easily. In tens of machine, only one can get the bug. I
> have try my best to hacking the code, but the only verified result
> is here: when bug occur, the HW IRQ is masked, but the
> IRQD_IRQ_MASKED flag is cleared.
>
> My fixup is in the attachment, which remove the unexpected time window of
> IRQ iteration.

Let's see what Thomas has to say for that. Meanwhile, please take a
look at Documentation/process/submitting-patches.rst for getting things
right for sending out patches that can be applied without manual
editing :)

Cheers,

Tony

> --- kernel/irq/chip.c 2019-07-13 09:28:23.683787367 +0800
> +++ /tmp/chip.c 2019-10-08 11:32:35.082258572 +0800
> @@ -432,8 +432,8 @@ void unmask_irq(struct irq_desc *desc)
> return;
>
> if (desc->irq_data.chip->irq_unmask) {
> - desc->irq_data.chip->irq_unmask(&desc->irq_data);
> irq_state_clr_masked(desc);
> + desc->irq_data.chip->irq_unmask(&desc->irq_data);
> }
> }
>

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