Re: Exception due to PCI: Use pci_is_root_bus() to check for root bus

[Bjorn Helgaas <helgaas@kernel.org>]

Hi David,

On Wed, Apr 06, 2016 at 01:51:55PM +0200, David Engraf wrote:
> Hi,
> 
> I have an exception in __pci_bus_size_bridges() when pci_is_root_bus
> returns false but bus->self == NULL. My driver registers a virtual
> bus, like virtfn_add_bus(). pci_add_new_bus() is called with a
> parent but without a pci_dev. Thus bus->parent is set but bus->self
> is NULL. When __pci_bus_size_bridges() is called I get an exception
> at:
> 
> switch (bus->self->class >> 8)
> 
> The previous version of the code, checking for bus->self != NULL
> worked for me. I think an additional check is required to make sure
> we're not accessing a NULL pointer.

When you say "previous version of the code," do you mean a previous
version of Linux worked correctly but a newer version does not?  What
versions are they?  Did you identify a commit that changed the
behavior?  I assume you're talking about an out-of-tree driver that
registers a virtual bus?  Can you point us to the code?  Can you share
the dmesg log, including the backtrace?

Bjorn