Re: [PATCH 1/2] genirq: Introduce a new flag IRQ_IS_CHAINED for chained interrupts

[Thomas Gleixner]

On Fri, 2 Oct 2015, Mika Westerberg wrote:

> In some cases it is useful to know if the interrupt in question has chained
> handler installed. For example when a cpu is offlined the architecture code
> needs to know if it has any users so that it can fixup affinity
> accordingly.
> 
> To make this possible we introduce a new flag IRQ_IS_CHAINED that is set by
> the core code when chained interrupt handler is installed. We also make it
> possible for core and architecture code to check the flag by introducing
> function irq_has_chained_handler() for this.

While looking at that patch it occured to me, that we can solve this
in a different way, which does not require any changes to the
migration code.

When we install the chained handler, we set the action of that irq
descriptor to a statically allocated chained_action which provides a
handler which emits a fat warning. chained handlers should never end
up calling an action and if they do, it's clearly a bug.

The availability of an action makes the migration code just pick it
and move it along. And that fixes all architectures in one go without
touching them.

Sorry, that I didn't think about this right away.

Thanks,

	tglx

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