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

x86 disables all local interrupts (except NMI of course) before jumping to the interrupt vector. Linux normally masks the specific interrupt and re-enables the rest of the interrupts (which aren't masked), unless a specific flags is passed to the interrupt handler registration.

Note that while this means your interrupt handler will not race with itself on the same CPU, it can and will race with itself running on other CPUs in an SMP / SMT system.