disable_irq關閉中斷並等待中斷處理完後返回, 而disable_irq_nosync立即返回. 那麼在中斷處理程序中應該使用哪一個函數來關閉中斷呢?
在<linux設備驅動開發詳解>中的按鍵驅動中, 使用disable_irq來關閉中斷, 但是我在測試時進入中斷後系統會死在中斷處理程序, 而改爲disable_irq_nosync則能正常退出中斷處理程序.下面從內核代碼來找一下原因:
先看一下disable_irq_nosync,內核代碼中是這樣解釋的:
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/**
* disable_irq_nosync - disable an irq without waiting
* @irq: Interrupt to disable
*
* Disable the selected interrupt line. Disables and Enables are
* nested.
* Unlike disable_irq(), this function does not ensure existing
* instances of the IRQ handler have completed before returning.
*
* This function may be called from IRQ context.
*/
void disable_irq_nosync(unsigned int irq)
{
struct irq_desc *desc = irq_to_desc(irq);
unsigned long flags;
if (!desc)
return;
chip_bus_lock(irq, desc);
spin_lock_irqsave(&desc->lock, flags);
__disable_irq(desc, irq, false);
spin_unlock_irqrestore(&desc->lock, flags);
chip_bus_sync_unlock(irq, desc);
}
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關閉中斷後程序返回, 如果在中斷處理程序中, 那麼會繼續將中斷處理程序執行完.
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/**
* disable_irq - disable an irq and wait for completion
* @irq: Interrupt to disable
*
* Disable the selected interrupt line. Enables and Disables are
* nested.
* This function waits for any pending IRQ handlers for this interrupt
* to complete before returning. If you use this function while
* holding a resource the IRQ handler may need you will deadlock.
*
* This function may be called - with care - from IRQ context.
*/
void disable_irq(unsigned int irq)
{
struct irq_desc *desc = irq_desc + irq;
if (irq >= NR_IRQS)
return;
disable_irq_nosync(irq);
if (desc->action)
synchronize_irq(irq);
}
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關閉中斷並等待中斷處理完後返回.從代碼中可以看到, disable_irq先是調用了disable_irq_nosync, 然後檢測desc->action是否爲1. 在中斷處理程序中, action是置1的, 所以進入synchronize_irq函數中.
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/**
* synchronize_irq - wait for pending IRQ handlers (on other CPUs)
* @irq: interrupt number to wait for
*
* This function waits for any pending IRQ handlers for this interrupt
* to complete before returning. If you use this function while
* holding a resource the IRQ handler may need you will deadlock.
*
* This function may be called - with care - from IRQ context.
*/
void synchronize_irq(unsigned int irq)
{
struct irq_desc *desc = irq_to_desc(irq);
unsigned int status;
if (!desc)
return;
do {
unsigned long flags;
/*
* Wait until we're out of the critical section. This might
* give the wrong answer due to the lack of memory barriers.
*/
while (desc->status & IRQ_INPROGRESS)
cpu_relax();
/* Ok, that indicated we're done: double-check carefully. */
spin_lock_irqsave(&desc->lock, flags);
status = desc->status;
spin_unlock_irqrestore(&desc->lock, flags);
/* Oops, that failed? */
} while (status & IRQ_INPROGRESS);
/*
* We made sure that no hardirq handler is running. Now verify
* that no threaded handlers are active.
*/
wait_event(desc->wait_for_threads, !atomic_read(&desc->threads_active));
}
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註釋中說明該函數是在等待中斷處理程序的結束, 這也是disable_irq與disable_irq_nosync不同的主要所在. 但是在中斷處理函數中調用會發生什麼情況呢? 進入中斷處理函數前IRQ_INPROGRESS會被__setup_irq設置, 所以程序會一直陷在while循環中, 而此時內核以經被獨佔, 這就導致系統死掉.
總結:
由於在disable_irq中會調用synchronize_irq函數等待中斷返回, 所以在中斷處理程序中不能使用disable_irq, 否則會導致cpu被synchronize_irq獨佔而發生系統崩潰.
