spin_lock_irqsave.c

static inline unsigned long __raw_spin_lock_irqsave(raw_spinlock_t *lock)
 {
        unsigned long flags;

        local_irq_save(flags);     // local CPU 中斷關閉, 防ISR搶
         preempt_disable();         //  preemptive 也禁止, 防止process 也來互搶
         spin_acquire(&lock->dep_map, 0, 0, _RET_IP_);

         ....

        return flags;
 }


/*SMP, 於ISR內使用*/
static inline void __raw_spin_lock(raw_spinlock_t *lock)
 {
         preempt_disable();
         spin_acquire(&lock->dep_map, 0, 0, _RET_IP_);      // 要求獲得 lock (lock為一個記憶體變數),要不到就'spin'

         LOCK_CONTENDED(lock, do_raw_spin_trylock, do_raw_spin_lock);
}