genirq/cpuhotplug: Add support for conditional masking

Interrupts which cannot be migrated in process context, need to be masked
before the affinity is changed forcefully.

Add support for that. Will be compiled out for architectures which do not
have this x86 specific issue.

Signed-off-by: Thomas Gleixner <tglx@linutronix.de>
Cc: Jens Axboe <axboe@kernel.dk>
Cc: Marc Zyngier <marc.zyngier@arm.com>
Cc: Michael Ellerman <mpe@ellerman.id.au>
Cc: Keith Busch <keith.busch@intel.com>
Cc: Peter Zijlstra <peterz@infradead.org>
Cc: Christoph Hellwig <hch@lst.de>
Link: http://lkml.kernel.org/r/20170619235445.604565591@linutronix.de

kernel/irq/cpuhotplug.c

@@ -18,6 +18,7 @@ static bool migrate_one_irq(struct irq_desc *desc)
 {
 	struct irq_data *d = irq_desc_get_irq_data(desc);
 	struct irq_chip *chip = irq_data_get_irq_chip(d);
+	bool maskchip = !irq_can_move_pcntxt(d) && !irqd_irq_masked(d);
 	const struct cpumask *affinity;
 	bool brokeaff = false;
 	int err;
@@ -69,6 +70,10 @@ static bool migrate_one_irq(struct irq_desc *desc)
 	if (irq_fixup_move_pending(desc, true))
 		affinity = irq_desc_get_pending_mask(desc);
 
+	/* Mask the chip for interrupts which cannot move in process context */
+	if (maskchip && chip->irq_mask)
+		chip->irq_mask(d);
+
 	if (cpumask_any_and(affinity, cpu_online_mask) >= nr_cpu_ids) {
 		affinity = cpu_online_mask;
 		brokeaff = true;
@@ -78,8 +83,12 @@ static bool migrate_one_irq(struct irq_desc *desc)
 	if (err) {
 		pr_warn_ratelimited("IRQ%u: set affinity failed(%d).\n",
 				    d->irq, err);
-		return false;
+		brokeaff = false;
 	}
+
+	if (maskchip && chip->irq_unmask)
+		chip->irq_unmask(d);
+
 	return brokeaff;
 }