linux-kernel - Re: [PATCH] irq: Resolve that mask_irq/unmask

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Date:   Thu, 14 Dec 2023 11:13:12 +0100
From:   Thomas Gleixner <tglx@...utronix.de>
To:     xiongxin <xiongxin@...inos.cn>, jikos@...nel.org,
        benjamin.tissoires@...hat.com
Cc:     linux-input@...r.kernel.org, stable@...r.kernel.org,
        Riwen Lu <luriwen@...inos.cn>, hoan@...amperecomputing.com,
        fancer.lancer@...il.com, linus.walleij@...aro.org, brgl@...ev.pl,
        andy@...nel.org, linux-gpio@...r.kernel.org,
        linux-kernel@...r.kernel.org
Subject: Re: [PATCH] irq: Resolve that mask_irq/unmask_irq may not be called
 in pairs

On Thu, Dec 14 2023 at 09:54, xiongxin wrote:
> 在 2023/12/13 22:59, Thomas Gleixner 写道:
>> Did you actually look at the sequence I gave you?
>> 
>>     Suspend:
>> 
>> 	  i2c_hid_core_suspend()
>> 	     disable_irq();       <- Marks it disabled and eventually
>> 				     masks it.
>> 
>> 	  gpio_irq_suspend()
>> 	     save_registers();    <- Saves masked interrupt
>> 
>>     Resume:
>> 
>> 	  gpio_irq_resume()
>> 	     restore_registers(); <- Restores masked interrupt
>> 
>> 	  i2c_hid_core_resume()
>> 	     enable_irq();        <- Unmasks interrupt and removes the
>> 				     disabled marker
>> 
>> 
>> Have you verified that this order of invocations is what happens on
>> your machine?
>
> As described earlier, in the current situation, the irq_mask() callback 
> of gpio irq_chip is called in mask_irq(), followed by the disable_irq() 
> in i2c_hid_core_suspend(), unmask_irq() will not be executed.

Which is correct.

> Then call enable_irq() in i2c_hid_core_resume(). Since gpio irq_chip 
> does not implement the irq_startup() callback, it ends up calling 
> irq_enable().
>
> The irq_enable() function is then implemented as follows:
>
> irq_state_clr_disabled(desc);
> if (desc->irq_data.chip->irq_enable) {
> 	desc->irq_data.chip->irq_enable(&desc->irq_data);
> 	irq_state_clr_masked(desc);
> } else {
> 	unmask_irq(desc);
> }
>
> Because gpio irq_chip implements irq_enable(), unmask_irq() is not 
> executed, and gpio irq_chip's irq_unmask() callback is not called. 
> Instead, irq_state_clr_masked() was called to clear the masked flag.
>
> The irq masked behavior is actually controlled by the 
> irq_mask()/irq_unmask() callback function pairs in gpio irq_chip. When 
> the whole situation occurs, there is one more irq_mask() operation, or 
> one less irq_unmask() operation. This ends the i2c hid resume and the 
> gpio corresponding i2c hid interrupt is also masked.
>
> Please help confirm whether the current situation is a BUG, or suggest 
> other solutions to fix it.

Again, I already explained to you in great detail why the core code is
correct and does not have a bug.

But as you insist that the bug is in the core code you obviously failed
to validate what I asked you to validate:

>> 	  i2c_hid_core_resume()
>> 	     enable_irq();        <- Unmasks interrupt and removes the
>> 				     disabled marker

The keyword to validate here is 'Unmasks'.

As gpio_dwapb implements the irq_enable() callback enable_irq() is not
going to end up invoking the irq_unmask() callback. But the irq_enable()
callback is required to be a superset of irq_unmask(). I.e. the core
code expects it to do:

    1) Some preparatory work to enable the interrupt line

    2) Unmask the interrupt, which is why the masked state is cleared
       by the core after invoking the irq_enable() callback.

which is pretty obvious because if an interrupt chip does not implement
the irq_enable() callback the core defaults to irq_unmask()

Correspondingly the core expects from the irq_disable() callback:

    1) To mask the interrupt

    2) To do some extra work to disable the interrupt line

which is obvious again because the core defaults to irq_mask() if the
irq_disable() callback is not implemented by the interrupt chip.

I'm pretty sure that with the previous provided information and the
extra information above you can figure out yourself that:

  1) the core code is correct as is

  2) where exactly the problem is located and how to fix it

No?

Thanks,

        tglx