Re: kldunload DIAGNOSTIC idea...

From: Brian Fundakowski Feldman (green_at_freebsd.org)
Date: 07/20/04

  • Next message: Willem Jan Withagen: "Re: kldunload DIAGNOSTIC idea..." 
    Date: Tue, 20 Jul 2004 14:52:36 -0400
To: Poul-Henning Kamp <phk@phk.freebsd.dk>

    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. 

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