Can an interrupt handler be preempted by the same interrupt handler?

Question

Does the CPU disable all interrupts on local CPU before calling the interrupt handler? Or does it only disable that particular interrupt line, which is being served?

Answer 1

Yes, that's fine. I'd like to also add what I think might be relevant.

In many real-world drivers/kernel code, "bottom-half" (bh) handlers are used pretty often- tasklets, softirqs. These bh's run in interrupt context and can run in parallel with their top-half (th) handlers on SMP (esp softirq's).

Of course, recently there's a move (mainly code migrated from the PREEMPT_RT project) towards mainline, that essentially gets rid of the 'bh' mechanism- all interrupt handlers will run with all interrupts disabled. Not only that, handlers are (can be) converted to kernel threads- these are the so-called "threaded" interrupt handlers.

As of today, the choice is still left to the developer- you can use the 'traditional' th/bh style or the threaded style.

Ref and Details:

http://lwn.net/Articles/380931/

http://lwn.net/Articles/302043/