kldunload DIAGNOSTIC idea...

Brian Fundakowski Feldman green at freebsd.org
Tue Jul 20 11:52:38 PDT 2004


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 ?
> >
> >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.

-- 
Brian Fundakowski Feldman                           \'[ FreeBSD ]''''''''''\
  <> green at FreeBSD.org                               \  The Power to Serve! \
 Opinions expressed are my own.                       \,,,,,,,,,,,,,,,,,,,,,,\


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