module context of execution

Question

I work on module for ipsec in linux. Look at two different situations when code from my module will be executed.

Executing from process context: application generate some traffic to transmit via network, application should call some syscall to transfer data, then process switch to kernel space and packet go through network subsystem of linux, somewere here will be executed my module, and all finished after affording task to network card. All these steps performed from process context and in any moment scheduler can switch process from one to another. Is as follows fist case of using my module - from process context.

Executing from softirq context: when network card receive packet it generate hardware interrupt, which "prepare" appropriate softirq to run. And packet go through network subsystem of linux (including my module) until some application got it. These steps performed from softirq context and could be interrupted only by hardware interrupt, but not by scheduler work.

The question is: How can I programmatically determine in module, from which context module is executing? It can be some element of struct task_struct or some syscall or something else. I couldn't find it by myself.

Answer 1

It is considered as a bad practice to make a function's control flow dependent from whether it is executed in interrupt context or not.

Citation from the Linux kernel developer (Andrew Morton):

The consistent pattern we use in the kernel is that callers keep track of whether they are running in a schedulable context and, if necessary, they will inform callees about that. Callees don't work it out for themselves.

---

However, there are several functions(macros) defined in linux/preempt.h for detect current scheduling context: in_atomic(), in_interrupt(). But see that LWN article about their usage.