Calling schedule() inside Linux IRQ

Question

I'm making an emulation driver that requires me to call schedule() in ATOMIC contexts in order to make the emulation part work. For now I have this hack that allows me to call schedule() inside ATOMIC (e.g. spinlock) context:

int p_count = current_thread_info()->preempt_count;

current_thread_info()->preempt_count = 0;
schedule();
current_thread_info()->preempt_count = p_count;

But that doesn't work inside IRQs, the system just stops afer calling schedule().

Is there any way to hack the kernel in a way to allow me to do it? I'm using Linux kernel 4.2.1 with User Mode Linux

Answer 1

In kernel code you can be either in interrupt context or in process context. When you are in interrupt context, you cannot call any blocking function (e.g., schedule()) or access the current pointer. That's related to how the kernel is designed and there is no way for having such functionalities in interrupt context. See also this answer.

Depending on what is your purpose, you can find some strategy that allows you to reach your goal. To me, it sounds strange that you have to call schedule() explicitly instead of relying on the natural kernel flow.

One possible approach follows (but, again, it depends on your specific goal). Form the IRQ you can schedule the work on a work queue through schedule_work(). The work queue, in fact, by design, executes kernel code in process context. From there, you are allowed to call blocking functions and access the current process data.