http://blog.csdn.net/myleeming/archive/2009/06/02/4235224.aspx
首先摘一段網上的見解：
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.
我們再來跟一下這個unbalanced的代碼：
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);
}
可見unbalanced這個問題只會發生在enalbe_irq函數中，這裏要提到一個變量disable_depth，這是一個標誌中斷禁止否 的變量，如果調用disabled，這個變量會++，是正數，表示禁止中斷，如果是enable，這個變量會--，是0，表示允許，一般都會一一對應。
而如果這個變量本身就是0，enable的時候，我們再去enable它的時候系統會去檢查你這個是不是0，如果是0的話表示你這個中斷本來就是打開的，你現在再去打開沒有必要，這就是unbalanced了，所以可見這本身就是一個無害的信息。