Re: kldunload DIAGNOSTIC idea...

From: Doug Rabson (dfr_at_nlsystems.com)
Date: 07/21/04

  • Next message: Poul-Henning Kamp: "Re: kldunload DIAGNOSTIC idea..." 
    To: freebsd-arch@freebsd.org
Date: Wed, 21 Jul 2004 10:10:07 +0100

    On Tuesday 20 July 2004 20:10, Scott Long wrote:
    > Brian Fundakowski Feldman wrote:
    > > On Tue, Jul 20, 2004 at 08:39:57PM +0200, Poul-Henning Kamp wrote:
    > >>In message <20040720183213.GC1009@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.
    >
    > busdma callbacks, cam callbacks, netisr callbacks, and on and on and
    > on.

    The original intention was that drivers use the
    device_busy()/device_unbusy() counter to handle these things. In some
    cases, just calling device_busy() from fooopen() and device_unbusy()
    from fooclose() is sufficient.
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