Re: runtimeimage of kernel module

[Joseph A Knapka <jknapka@earthlink.net>]

Eli Carter wrote:
> 
> Joseph A Knapka wrote:
> >
> > Anumula Venkat wrote:
> > >
> > > U are talking about stack used by kernel when a
> > > context switch takes place in a process. I am talking
> > > about Kernel Modules which completely runs in
> > > KERNEL MODE. If u have answer to this question please
> > > write to me.
> >
> > I answered it. Every time code in your kernel module
> > executes, it is doing so on behalf of some process.
> > Whether that process is a user-mode process that
> > has entered kernel mode for some reason, or is a
> > kernel thread, it is still a process in kernel mode
> > that executes on the current kernel stack. ALL CODE
> > in the Linux kernel, other than the boot code that
> > runs before init starts, is running in the context
> > of some process. The only difference between kernel
> > threads and user processes is that a kernel thread
> > -always- executes in kernel mode, using its kernel
> > stack and the kernel's pagetables.
> 
> Well, I'm not sure that's accurate... what about interrupt handlers?
> There is something called "interrupt context" where kernel code is
> executed, but _not_ on behalf of some process (think receive of a packet
> for instance).  There may be some random process that has been
> interrupted, but you don't know what process it is.  When something like
> read() or open() is called, then you are in a process context.

Even interrupt handlers are running in the context of
(though as you say, -not- on behalf of; I misspoke in
my earlier message) the current task. You're still, as
far as I know, running on the kernel stack of the current
process (of course, returning from the interrupt cleans the
stack, so the task never notices an interrupt handler has
used it). I don't think Linux implements a separate stack for
interrupt handlers to use, though I haven't looked at the
relevant code.

Cheers,

-- Joe
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