Interrupt sharing for percpu-devid interrupts is forbidden, and
for good reasons. These are interrupts generated *from* a CPU and
handled by itself (timer, for example). Nobody in their right mind
would put two devices on the same pin (and if they have, they get to
keep the pieces...).

But this also prevents more benign cases, where devices are connected
to groups of CPUs, and for which the affinities are not overlapping.
Effectively, the only thing they share is the interrupt number, and
nothing else.

Let's tweak the definition of IRQF_SHARED applied to percpu_devid
interrupts to allow this particular case. This results in extra
validation at the point of the interrupt being setup and freed,
as well as a tiny bit of extra complexity for interrupts at handling
time (to pick the correct irqaction).

Signed-off-by: Marc Zyngier <maz@kernel.org>
---
 kernel/irq/chip.c   |  8 ++++--
 kernel/irq/manage.c | 67 +++++++++++++++++++++++++++++++++++++--------
 2 files changed, 61 insertions(+), 14 deletions(-)

diff --git a/kernel/irq/chip.c b/kernel/irq/chip.c
index 0d0276378c707..af90dd440d5ee 100644
--- a/kernel/irq/chip.c
+++ b/kernel/irq/chip.c

@@ -897,8 +897,9 @@ void handle_percpu_irq(struct irq_desc *desc)
 void handle_percpu_devid_irq(struct irq_desc *desc)
 {
 	struct irq_chip *chip = irq_desc_get_chip(desc);
-	struct irqaction *action = desc->action;
 	unsigned int irq = irq_desc_get_irq(desc);
+	unsigned int cpu = smp_processor_id();
+	struct irqaction *action;
 	irqreturn_t res;
 
 	/*

@@ -910,12 +911,15 @@ void handle_percpu_devid_irq(struct irq_desc *desc)
 	if (chip->irq_ack)
 		chip->irq_ack(&desc->irq_data);
 
+	for (action = desc->action; action; action = action->next)
+		if (cpumask_test_cpu(cpu, action->affinity))
+			break;
+
 	if (likely(action)) {
 		trace_irq_handler_entry(irq, action);
 		res = action->handler(irq, raw_cpu_ptr(action->percpu_dev_id));
 		trace_irq_handler_exit(irq, action, res);
 	} else {
-		unsigned int cpu = smp_processor_id();
 		bool enabled = cpumask_test_cpu(cpu, desc->percpu_enabled);
 
 		if (enabled)