PCI: Check for child busses which use more bus numbers than allocated

pci_scan_child_bus can (potentially) return a bus number higher than the
subordinate value of the child bus. Possible reasons are that bus numbers
are reserved for SR-IOV or for CardBus (SR-IOV is done without checks and
the CardBus checks are sketchy at best).

We clamp the returned value to the actual subordinate value and print a
warning if too many bus numbers are reserved.

[bhelgaas: whitespace]
Signed-off-by: Andreas Noever <andreas.noever@gmail.com>
Signed-off-by: Bjorn Helgaas <bhelgaas@google.com>

drivers/pci/probe.c

@@ -805,10 +805,12 @@ int pci_scan_bridge(struct pci_bus *bus, struct pci_dev *dev, int max, int pass)
 		}
 
 		cmax = pci_scan_child_bus(child);
-		if (cmax > max)
-			max = cmax;
-		if (child->busn_res.end > max)
-			max = child->busn_res.end;
+		if (cmax > subordinate)
+			dev_warn(&dev->dev, "bridge has subordinate %02x but max busn %02x\n",
+				 subordinate, cmax);
+		/* subordinate should equal child->busn_res.end */
+		if (subordinate > max)
+			max = subordinate;
 	} else {
 		/*
 		 * We need to assign a number to this bus which we always