首先摘一段网上的见解：

The enable_irq unbalanced messages are harmless. It just means that when the driver called disable_irq there were no devices already using the irq, and as such it was already disabled, so the call to disable_irq was forgotten by the kernel, so when we call enable_irq the core kernel code thinks it's unbalanced when it isn't.

我们再来跟一下这个unbalanced的代码：

void enable_irq(unsigned int irq)
{
 struct irqdesc *desc = irq_desc + irq;
 unsigned long flags;

 spin_lock_irqsave(&irq_controller_lock, flags);
 if (unlikely(!desc->disable_depth)) {
  printk("enable_irq(%u) unbalanced from %p/n", irq,
   __builtin_return_address(0));
 } else if (!--desc->disable_depth) {
  desc->probing = 0;
  desc->chip->unmask(irq);

  /*
   * If the interrupt is waiting to be processed,
   * try to re-run it.  We can't directly run it
   * from here since the caller might be in an
   * interrupt-protected region.
   */
  if (desc->pending && list_empty(&desc->pend)) {
   desc->pending = 0;
   if (!desc->chip->retrigger ||
       desc->chip->retrigger(irq))
    list_add(&desc->pend, &irq_pending);
  }
 }
 spin_unlock_irqrestore(&irq_controller_lock, flags);
}

可见unbalanced这个问题只会发生在enalbe_irq函数中，这里要提到一个变量disable_depth，这是一个标志中断禁止否的变量，如果调用disabled，这个变量会++，是正数，表示禁止中断，如果是enable，这个变量会--，是0，表示允许，一般都会一一对应。

而如果这个变量本身就是0，enable的时候，我们再去enable它的时候系统会去检查你这个是不是0，如果是0的话表示你这个中断本来就是打开的，你现在再去打开没有必要，这就是unbalanced了，所以可见这本身就是一个无害的信息。