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    SubjectRe: Why can't we sleep in an ISR?
    OK. I think the gap between you and me is the definition of term
    *context*. If you go to Linux Kernel Development, 2nd Edition (ISBN
    0-672-32720-1), Page 6, then you will read the following:

    .... in Linux, ... each processor is doing one of three things at any
    given moment:

    1. In kernel-space, in process context, ...
    2. In kernel-space, in interrupt context, not associated with a process, ...
    3. In user-space ...

    This list is inclusive. ...

    Maybe you prefer other terminology system, but I do like the above
    definition given by Robert Love. So maybe in your system *context*
    mean something at hardware level and you say ISR is in process
    context, but I think it is more like a logical level and agree with
    Rovert's definition.

    And in hardware level, Robert's *context* definition also mean
    something specific, that I started to be aware of. That is, *in the
    same context* means a kernel-code is triggered by a user-space code.
    *in different context* means a kernel-code is triggered by an external
    interrupt source other than a user-space code.

    Context has nothing to do with whether an ISR borrow any data
    structure of a process, instead, its something logical or related to

    2007/5/16, Phillip Susi <>:
    > Dong Feng wrote:
    > > If what you say were true, then an ISR would be running in the same
    > > context as the interrupted process.
    > Yes, and it is, as others have said in this thread, which is a good
    > reason why ISRs can't sleep.
    > > But please check any article or
    > > book, it will say ISR running in different context from any process.
    > > So ISR is considered in its own context, although it shares a lot of
    > > things with the interrupted process. I would only say *context* is a
    > > higher-level logical concept.
    > Depends on which book or article you are reading I suppose. The
    > generally accepted and often used thought is that ISRs technically are
    > running in the context of the interrupted process, but because that
    > context is unknown and therefore should not be used, it is often said
    > that they run in no context, or outside of any context. Sometimes
    > people then assume that because they run outside of any ( particular )
    > process context, they must be in their own context, but this is a mistake.
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