Does the Linux kernel interrupt any running code to call the __exit function when unloading a kernel module?

The source code for the kernel is available, ask the LLM to point you to the code that does "checks if the instruction pointer is in the module's memory" and the alleged global lock. I don't think either is a thing.

If a process is currently using the module, it should have a non-zero reference count.

if my cleanup function is mid-execution (not using kthreads, directly on the CPU)

What's the context here? How did it get to be executed, what triggered its execution then?

will it just interrupt

Fairly sure there is no interruption going on. That would be extremely dangerous to do. The kernel just calls your module_exit function and that's it. It is up to you to ensure your module stops doing things before that functione exits.

I think you need to either bump your reference count or mutex out your cleanup routine to make sure it us not called simultaneously by two different threads of execution (whether they are managed by kthreads or not). Pretty sure there's no interruption. LLMs seem to be on some hard drugs. Program counter? Come on. What if you call some function that is not in your module? Will the kernel unroll the stack? This is ridiculous.