Re: AGP bogosities

Dave Jones
2005-03-11T03:01:25Z

On Fri, Mar 11, 2005 at 01:40:24PM +1100, Benjamin Herrenschmidt wrote:
>
> > After it does that pci_dev_put on the from, it does another pci_dev_get
> > on 'dev', which is what my put was releasing.
> >
> > Or am I terribly confused ?
>
> Well, pci_get_class() put's the passed-in device and get's() the
> returned one. So if you run it in a loop, you should never have to
> either get or put. When you exit the loop with a valid pci_dev, though,
> you should definitely put() it after you're done with it, but this is
> something that should be done only for that specific instance and after
> you are finished with it...

Yeah. Makes perfect sense now I've had it spelled out for me :-)
I think Linus is right though that some extra bullet-proofing in kref_put
to BUG() if it goes negative would've caught this. I wonder if anyone
else has fallen into this trap.

Dave