PCI: don't publish new root bus until it's fully initialized

When pci_create_root_bus() adds the new struct pci_bus to the global
pci_root_buses list, the bus becomes visible to other parts of the
kernel, so it should be fully initialized.

This patch delays adding the bus to the pci_root_buses list until after
all the struct pci_bus initialization is finished.
Signed-off-by: Bjorn Helgaas <bhelgaas@google.com>

drivers/pci/probe.c

@@ -1569,10 +1569,6 @@ struct pci_bus *pci_create_root_bus(struct device *parent, int bus,
 		goto err_out;
 	}
 
-	down_write(&pci_bus_sem);
-	list_add_tail(&b->node, &pci_root_buses);
-	up_write(&pci_bus_sem);
-
 	dev->parent = parent;
 	dev->release = pci_release_bus_bridge_dev;
 	dev_set_name(dev, "pci%04x:%02x", pci_domain_nr(b), bus);
@@ -1612,6 +1608,10 @@ struct pci_bus *pci_create_root_bus(struct device *parent, int bus,
 			dev_info(&b->dev, "root bus resource %pR\n", res);
 	}
 
+	down_write(&pci_bus_sem);
+	list_add_tail(&b->node, &pci_root_buses);
+	up_write(&pci_bus_sem);
+
 	return b;
 
 class_dev_reg_err: