irq: clear kstat_irqs

Impact: get correct kstat_irqs [/proc/interrupts] for msi/msi-x etc

need to call clear_kstat_irqs(), so when we reuse that irq_desc,
we get correct kstat in /proc/interrupts.

This makes /proc/interrupts not have <NULL> entries.

Don't need to worry about arch that doesn't support genirq, because they
will not call dynamic_irq_cleanup().

v2: simplify and make clear_kstat_irqs more robust
Signed-off-by: Yinghai Lu <yinghai@kernel.org>
Signed-off-by: Ingo Molnar <mingo@elte.hu>

kernel/irq/chip.c

@@ -78,6 +78,7 @@ void dynamic_irq_cleanup(unsigned int irq)
 	desc->handle_irq = handle_bad_irq;
 	desc->chip = &no_irq_chip;
 	desc->name = NULL;
+	clear_kstat_irqs(desc);
 	spin_unlock_irqrestore(&desc->lock, flags);
 }
 

kernel/irq/handle.c

@@ -242,6 +242,11 @@ struct irq_desc *irq_to_desc_alloc_cpu(unsigned int irq, int cpu)
 }
 #endif /* !CONFIG_SPARSE_IRQ */
 
+void clear_kstat_irqs(struct irq_desc *desc)
+{
+	memset(desc->kstat_irqs, 0, nr_cpu_ids * sizeof(*(desc->kstat_irqs)));
+}
+
 /*
  * What should we do if we get a hw irq event on an illegal vector?
  * Each architecture has to answer this themself.

kernel/irq/internals.h

@@ -15,6 +15,7 @@ extern int __irq_set_trigger(struct irq_desc *desc, unsigned int irq,
 
 extern struct lock_class_key irq_desc_lock_class;
 extern void init_kstat_irqs(struct irq_desc *desc, int cpu, int nr);
+extern void clear_kstat_irqs(struct irq_desc *desc);
 extern spinlock_t sparse_irq_lock;
 extern struct irq_desc *irq_desc_ptrs[NR_IRQS];