[PATCH 2.6.24-rc4] PCI: refuse to re-add a device to a bus upon pci_scan_child_bus()

[Eran Liberty]

Dear Penguins,

As  a follow up on my own post ( http://lkml.org/lkml/2008/6/18/195 ), I 
have  solved a small bug/misbehavior within the pci_scan_single_device().

The misbehavior manifest itself upon calling pci_scan_child_bus() with a 
bus which already contain some devices. After scanning is done devices 
that already existed will be present twice in the PCI bus devise list. 
Once with is_added indication and once without. Trying to add this bus 
will cause a resource conflict as the same device is already present and 
initialized.

This patch will simply prevent a device to be added to a bus list if it 
is already there.

Points to consider:
1. I am not a PCI Guru and might have over looked the bigger picture. Is 
it OK to prevent a device of being re-added?
2. I have decided that two devices are, in fact, the same instance if it 
has the same: vendor, device, and devfn. Is there a finer test for a 
device identity?

p.s. As per http://www.kernel.org/pub/linux/docs/lkml/#s1-10 it is 
preferred for Mozilla Firefox clients to attach the patch, hence my 
patch is attached.

Liberty

Signed-off-by: Eran Liberty <liberty@xxxxxxxxxxxxx>
---
Index: drivers/pci/probe.c
===================================================================
--- drivers/pci/probe.c	(revision 102)
+++ drivers/pci/probe.c	(revision 103)
@@ -996,11 +996,21 @@
 struct pci_dev *__ref pci_scan_single_device(struct pci_bus *bus, int devfn)
 {
 	struct pci_dev *dev;
+	struct list_head *ln;
 
 	dev = pci_scan_device(bus, devfn);
 	if (!dev)
 		return NULL;
 
+	/* refuse to re-add a device */
+	list_for_each(ln, &bus->devices) {
+		struct pci_dev *d = pci_dev_b(ln);
+		if ((d->vendor == dev->vendor) &&
+		    (d->device == dev->device) &&
+		    (d->devfn == dev->devfn))
+			return NULL;
+	}
+
 	pci_device_add(dev, bus);
 
 	return dev;