Hi Bjorn,
Am 06.04.2016 um 16:01 schrieb David Engraf:
Hi Bjorn,
Am 06.04.2016 um 15:35 schrieb Bjorn Helgaas:
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?
With previous version, I mean reverting commit
2ba29e270e977b213a7d58ae1152c23a1c3074a3. This will check for bus->self
instead of using pci_is_root_bus().
I'm working on a driver which is basically based on drivers/pci/iov.c.
The code looks like this:
child = pci_add_new_bus(parent, NULL, busnr);
This will create child with child->parent = parent and child->self =
NULL. When the kernel calls __pci_bus_size_bridges(), accessing
bus->self->class crashes:
/* The root bus? */
if (pci_is_root_bus(bus))
return;
switch (bus->self->class >> 8) { <- crash here because of bus->self == NULL
With this patch the system no longer crashes and the virtual PCI bus
works. It returns on bus->self == NULL, thus the switch instruction does
not access a NULL pointer.
Best regards
- David
diff --git a/drivers/pci/setup-bus.c b/drivers/pci/setup-bus.c
index 55641a3..ddb3381 100644
--- a/drivers/pci/setup-bus.c
+++ b/drivers/pci/setup-bus.c
@@ -1245,6 +1245,10 @@ void __pci_bus_size_bridges(struct pci_bus *bus, struct list_head *realloc_head)
if (pci_is_root_bus(bus))
return;
+ /* bridge device available? */
+ if (!bus->self)
+ return;
+
switch (bus->self->class >> 8) {
case PCI_CLASS_BRIDGE_CARDBUS:
/* don't size cardbuses yet. */
