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    SubjectRe: Why can't we sleep in an ISR?
    Hi, Phillip,

    I have said the gap between you and me is the definition of context.
    In Robert's definition, *context* is used in a classification method
    and really something in higher-level. And I used that term to explain
    why ISR can not sleep.

    If you do not like the name, name it your way and substitute term
    *context* in my previous mail with what you name. But I believe my
    other explaination still hold, right?

    And again, if anyway I am forced to use your termnology system, I
    would also agree your other point regarding hardware.

    2007/5/18, Phillip Susi <>:
    > Dong Feng wrote:
    > > 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. ...
    > Yep, I disagree with that use of the term, because it is misleading and
    > caused your confusion. The context that the ISR executes in is not
    > associated with a _known_ process is more correct.
    > > 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.
    > Right, and that becomes more clear when you say that the ISR's is
    > executing in an indeterminate process context, rather than saying it
    > does not have any context at all, or has its own special context.
    > > Context has nothing to do with whether an ISR borrow any data
    > > structure of a process, instead, its something logical or related to
    > > causality.
    > No, it has everything to do with the data structures of the process.
    > When you are executing "in the same context" as you put it, as called
    > from the user mode code, you know you are using the task structure of
    > that process and so you can make use of that structure. For example,
    > you can look at the current uid to decide if you should allow an
    > operation to proceed. When you are in an ISR, there _is_ a task
    > structure there, but you shouldn't use it because you don't know which
    > task structure it is because you don't know which task you are
    > interrupting. Thus if you look at the current uid in an ISR, you have
    > no idea what you will see there and it will change from interrupt to
    > interrupt, depending on which task gets interrupted.
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