About interrupt handler

[cheneydeng]

hi all,
     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?


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best regards！
  cheneydeng
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