quoted

I'm begin to learn the Kernel and i'm reading <<Linux kernel
development>>.It says "This is an important point, always keep in mind that
all interrupt handler has interrupted other code(possibly even another
interrupt handler on a different line)".What i am not able to understand is
how a interrupt handler be interrupted ? DID NOT it uninterrupted?

It depends on the architecture and the interrupt controller being
used, and the driver code itself.

Normally, when an interrupt fires, that particular interrupt will be
masked and your own handler won't interrupt itself, but you may very
well be interrupted by other interrupts.

Can you please point out some code for explanation?

--- KostaZ