problems with chained IRQ handlers

problems with chained IRQ handlers

[Brian Silverman]

Hi,

Chained IRQ handlers are always marked IRQ_NOTHREAD, which means
forced threading doesn't apply to them. I think this means they can't
safely use non-raw spinlocks under CONFIG_PREEMPT_RT_FULL. Is this
correct?

I have an ARM system with a CONFIG_PREEMPT_RT_FULL kernel which prints
lockdep warnings from many places because of this. It also locks up
under moderate load, which I think is related to this issue. Any
suggestions?

Thanks,
Brian Silverman

Re: problems with chained IRQ handlers

[Sebastian Andrzej Siewior]

* Brian Silverman | 2015-08-17 18:41:55 [-0700]:

>Chained IRQ handlers are always marked IRQ_NOTHREAD, which means
>forced threading doesn't apply to them. I think this means they can't
>safely use non-raw spinlocks under CONFIG_PREEMPT_RT_FULL. Is this
>correct?
yes,

>I have an ARM system with a CONFIG_PREEMPT_RT_FULL kernel which prints
>lockdep warnings from many places because of this. It also locks up
>under moderate load, which I think is related to this issue. Any
>suggestions?

Use raw locks there. The chain handler usually implement a irq chip
something like gpio controller which can also act as an interrupt
controller. If this is the case then the lock should be a raw-lock.
You should not do anything time consuming while holding the lock. It is
usually just held while masking/unmasking bits in the registers.

>Thanks,
>Brian Silverman

Sebastia