kldunload DIAGNOSTIC idea...

[Willem Jan Withagen]

> On Tue, Jul 20, 2004 at 08:39:57PM +0200, Poul-Henning Kamp wrote:
> > In message <20040720183213.GC1009 at green.homeunix.org>, Brian Fundakowski
Feldma
> > n writes:
> > >On Tue, Jul 20, 2004 at 08:20:23PM +0200, Poul-Henning Kamp wrote:
> > >>
> > >> I'm pulling hair out trying to make it guaranteed safe to unload device
> > >> driver modules, and the major pain here is to make sure there is no
> > >> thread stuck somewhere inside the code.
> > >>
> > >> That gave me the idea for a simple little DIAGNOSTIC check for kldunload:
> > >> run through the proc/thread table and look for any thread with an
> > >> instruction counter inside the range of pages we are going to unload.
> > >>
> > >> Any takers ?

Sounds like a tantalizing task, which would match with my (old) compiler
knowledge. But I wonder if I know enough of the kernel internals to ever get it
doing something usefull.

> > >
> > >You mean any thread with a stack trace that includes an instruction
> > >counter inside those pages, don't you?
> >
> > That would require us to unwind the stack which I think is overkill
> > for the purpose.
> >
> > The most likely case is that the thread is sleeping on something
> > inside the kld so just checking the instruction pointer would be
> > fine.
> >
> > Looking for sleep addresses inside the module might make sense too.
>
> It's probably not overkill -- at least in my experience most of the
> time a driver is "doing something" it is sleeping, so the address
> will be in mi_switch() or somewhere way out there.  Sleep addresses
> on dynamic data addresses are also a lot more common than sleep
> addresses on static/code addresses.  If someone is interested in
> doign this, it would be very informative, especially if it could
> catch sleeps, pending timeouts, pending callouts, etc.

Ignorant, and without prejustice, I'd say:
The major problem here would be to get the framework in place.
Once that is available, it is glueing the principal code together, and whether
it is an address, or a series of addresses from a stack-unwind. The later is
only going to be more compute intensive.

--WjW