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Re: Why can't we sleep in an ISR?

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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
causality.



2007/5/16, Phillip Susi <psusi@xxxxxxxxxx>:
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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