Which context a given function is called in Linux Kernel

Question

Is there a straight forward mechanism to identify if a given function is called in an interrupt context or from process context. This is the first part to the question. The second part is: How do I synchronize 2 processes, one which is in interrupt context and the other which is in process context. If my understanding is right, We cannot use mutexes for the process in interrupt context since it is not allowed to sleep. On the other hand, if I use spinlocks,the other process will use CPU cycles. What is the best way to synchronize these 2 processes. Correct me if my understanding is totally wrong.

Answer 1

You can tell if function was run as IRQ handler using in_irq() function. But I don't think it's a good practice to use it. You should see just from code in which context your function is being run. Otherwise I'd say your code has bad design.

As for synchronization mechanism -- you are right, you have to use spinlock, because you need to do synchronization in atomic context (e.g. interrupt) -- not that you have much of choice here. You are also right that much CPU cycles will be wasted when waiting for spinlock, so you should try and minimize amount of your code under lock.