interrupt

prevent interrupt entering critical section 

method 1:

 local_irq_disable();  /* Disable Interrupts in local CPU */

  /* ... Critical Section ...  */

  local_irq_enable();   /* Enable Interrupts in local CPU */

method 2:

unsigned long flags;

Point A:

  local_irq_save(flags);     /* Disable Interrupts */

  /* ... Critical Section ... */

  local_irq_restore(flags);  /* Restore state to what it was at point A */