kernel: Warn when an IRQ's affinity notifier gets overwritten

An IRQ affinity notifier getting overwritten can point to some annoying
issues which need to be resolved, like multiple pm_qos objects being
registered to the same IRQ. Print out a warning when this happens to aid
debugging.

Signed-off-by: Sultan Alsawaf <sultan@kerneltoast.com>

kernel/irq/manage.c

@@ -330,6 +330,8 @@ irq_set_affinity_notifier(unsigned int irq, struct irq_affinity_notify *notify)
 	raw_spin_unlock_irqrestore(&desc->lock, flags);
 
 	if (old_notify) {
+		if (notify)
+			WARN(1, "overwriting previous IRQ affinity notifier\n");
 		if (cancel_work_sync(&old_notify->work)) {
 			/* Pending work had a ref, put that one too */
 			kref_put(&old_notify->kref, old_notify->release);