Re: [PATCH] irq: Resolve that mask_irq/unmask_irq may not be called in pairs

[xiongxin]

在 2023/12/13 22:59, Thomas Gleixner 写道:
> On Wed, Dec 13 2023 at 10:29, xiongxin wrote:
> > 在 2023/12/12 23:17, Thomas Gleixner 写道:
> > Sorry, the previous reply may not have clarified the BUG process. I
> > re-debugged and confirmed it yesterday. The current BUG execution
> > sequence is described as follows:
>
> It's the sequence how this works and it works correctly.
>
> Just because it does not work on your machine it does not mean that this
> is incorrect and a BUG.
>
> You are trying to fix a symptom and thereby violating guarantees of the
> core code.
>
> > That is, there is a time between the 1:handle_level_irq() and
> > 3:irq_thread_fn() calls for the 2:disable_irq() call to acquire the lock
> > and then implement the irq_state_set_disabled() operation. When finally
> > call irq_thread_fn()->irq_finalize_oneshot(), it cannot enter the
> > unmask_thread_irq() process.
>
> Correct, because the interrupt has been DISABLED in the mean time.
>
> > In this case, the gpio irq_chip irq_mask()/irq_unmask() callback pairs
> > are not called in pairs, so I think this is a BUG, but not necessarily
> > fixed from the irq core code layer.
>
> No. It is _NOT_ a BUG. unmask() is not allowed to be invoked when the
> interrupt is DISABLED. That's the last time I'm going to tell you that.
> Only enable_irq() can undo the effect of disable_irq(), period.
>
> > Next, when the gpio controller driver calls the suspend/resume process,
> > it is as follows:
> >
> > suspend process:
> > dwapb_gpio_suspend()
> >       ctx->int_mask   = dwapb_read(gpio, GPIO_INTMASK);
> >
> > resume process:
> > dwapb_gpio_resume()
> >       dwapb_write(gpio, GPIO_INTMASK, ctx->int_mask);
>
> 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?
>
> Thanks,
>
>          tglx

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.

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.