[PATCH] arm: use cpu_online_mask when using forced irq_set_affinity

[Thomas Gleixner]

On Thu, 17 Jul 2014, Sudeep Holla wrote:
> > > Any suggestions on this ? Since commit 01f8fa4f01d8 and ffde1de64012 are
> > > now in
> > > stable releases, CPU0 hotplug is broken there now.
> > 
> > Maybe we should ask Thomas, as he's (a) the maintainer of the irqchip
> > stuff, and (b) the author of the patch causing the breakage.
> > 
> >  From what I can see looking at the x86 code, the work-around in
> > ffde1de64012 is wrong.
> > 
> 
> Can provide your thoughts on how to solve this issue ?

ffde1de64012 is not about offlining a cpu, it's about onlining where
we need to make sure that we assign the affinity to a not yet online
marked cpu.
 
> Is it expected from all the irqchip implementation to use force flag in
> irq_set_affinity to ignore cpu_online_mask similar to GIC ?

No, it's only relevant for the cases where we need to route irqs to
not yet online cpus.

Now the wreckage of offlining was definitely not intended and I wonder
why set_affinity() is called there with force = true. This was
introduced in commit 1dbfa187dad. I acked it back then, but I have no
idea why, because the force argument did not have any effect at that
time.

Changing it to false should solve the issue.

Thanks,

	tglx

diff --git a/arch/arm/kernel/irq.c b/arch/arm/kernel/irq.c
index 2c4257604513..5c4d38e32a51 100644
--- a/arch/arm/kernel/irq.c
+++ b/arch/arm/kernel/irq.c
@@ -175,7 +175,7 @@ static bool migrate_one_irq(struct irq_desc *desc)
 	c = irq_data_get_irq_chip(d);
 	if (!c->irq_set_affinity)
 		pr_debug("IRQ%u: unable to set affinity\n", d->irq);
-	else if (c->irq_set_affinity(d, affinity, true) == IRQ_SET_MASK_OK && ret)
+	else if (c->irq_set_affinity(d, affinity, false) == IRQ_SET_MASK_OK && ret)
 		cpumask_copy(d->affinity, affinity);
 
 	return ret;