Re: [PATCH] virtio: make PCI devices take a virtio_pci module ref

Greg KH
2008-12-05T18:47:31Z

On Fri, Dec 05, 2008 at 06:30:17PM +0000, Mark McLoughlin wrote:
> On Fri, 2008-12-05 at 07:26 -0800, Greg KH wrote:
> > On Fri, Dec 05, 2008 at 04:25:31PM +0100, Jiri Slaby wrote:
> > > Mark McLoughlin wrote:
> > > >> Fix the virtio bus instead.
> > > >
> > > > Yeah, the patch I posted wasn't meant as a fix for this traceback.
> > >
> > > So what's the module_get patch needed for?
> > >
> > > > Here's one that does fix it.
> > > ...
> > > > From: Mark McLoughlin <markmc@redhat.com>
> > > > Subject: [PATCH] virtio: add device release() function
> > > >
> > > > Add a release() function for virtio_pci devices so as to avoid:
> > > >
> > > > Device 'virtio0' does not have a release() function, it is broken and must be fixed
> >
> > Just providing an empty release function to the kernel is the complete
> > wrong thing. Do you not think the kernel is actually trying to tell you
> > something here? If it could test for an empty release function it would
> > complain about that as well, providing one is no "fix" at all.
> >
> > You need to free your memory in the release function that is owned by
> > the device/structure. Please read the file, Documentation/kobject.txt
> > for details as to what you need to do.
>
> Okay, consider me "mocked mercilessly by the kobject maintainer" :-)

Heh, prepare for some more mocking below...

> Does this version look a bit more reasonable?
>
> (The virtio_pci_root is statically allocated so I don't see how
> release() could be non-empty in this case, but let's debate whether we
> want to keep this dummy device at all)

You should NEVER declare a kobject statically. There should be a check
in the kernel that complains about this on some arches in the -mm and
-next trees, I'm supprised you didn't hit it.

To quote from the kobject.txt documentation file:
Because kobjects are dynamic, they must not be declared
statically or on the stack, but instead, always allocated
dynamically. Future versions of the kernel will contain a
run-time check for kobjects that are created statically and will
warn the developer of this improper usage.

That is why you need a "real" release function.

So, care to respin this again please?

thanks,

greg k-h