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

["pradeep singh" <2500.pradeep@gmail.com>]

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On 5/14/07, Helge Hafting <helge.hafting@aitel.hist.no> wrote:
>
> Learning Linux wrote:
> > I have a very basic doubt here ... what makes it impossible to sleep
> > in an ISR? I mean, I know that the kernel preemption is disabled and
> > the kernel will panic, but I could not understand why?
> First: an ISR is meant to be very quick. It is supposed to do only a
> minimum of work needed to service the interrupt, then exit.
> This is important, as other interrupts might be blocked during your ISR.
> Sleeping is out of question, even a long-running loop in no-no.
>
> Second: You don't ever need to sleep in an ISR anyway.
> Complicated work that might take time or might need to sleep
> is not supposed to be in an ISR.  If you think you have a need,
> tell us what you're up to and hopefully someone will explain
> how do do things properly.
>
> When an interrupt happens that needs complicated servicing, the
> ISR don't do the whole job.  It just acknowledges the interrupt,
> perhaps does a few things with the device in question, then it
> exits. It leaves the rest of the work for a bottom half or kernel
> thread or something like that.  Kernel threads may sleep . . .


Helge, i think the Original poster wants to know why *exactly*
cannot you sleep?
What prevents me from sleeping?

What is this complicated processing which force an ISR not to sleep?

Thanks

Helge Hafting
>
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