So far, we have learned how to use the mutex lock and, for the spinlock, the basic spin_[un]lock() APIs. A few other API variations on the spinlock exist, and we shall examine the more common ones here.
To understand exactly why you may need other APIs for spinlocks, let's go over a scenario: as a driver author, you find that the device you're working on asserts a hardware interrupt; accordingly, you write the interrupt handler for it (You can learn great detail about it in the Linux Kernel Programming (Part 2) book). Now, while implementing a read method for your driver, you find that you have a non-blocking critical section within it. This is easy to deal with: as you have learned, you should use a spinlock to protect it. Great! But what if, while in the read method's critical section, the device's hardware interrupt fires? As you're aware, hardware interrupts preempt anything and everything; thus, control will go to...
