PCI: Hold pci_slot_mutex while searching bus->slots list

Previously, pci_setup_device() and similar functions searched the
pci_bus->slots list without any locking.  It was possible for another
thread to update the list while we searched it.

Add pci_dev_assign_slot() to search the list while holding pci_slot_mutex.

[bhelgaas: changelog, fold in CONFIG_SYSFS fix]
Tested-by: Guenter Roeck <linux@roeck-us.net>
Signed-off-by: Yijing Wang <wangyijing@huawei.com>
Signed-off-by: Bjorn Helgaas <bhelgaas@google.com>
diff --git a/drivers/pci/slot.c b/drivers/pci/slot.c
index 4bd3fce..429d34c 100644
--- a/drivers/pci/slot.c
+++ b/drivers/pci/slot.c
@@ -194,6 +194,17 @@
 	return result;
 }
 
+void pci_dev_assign_slot(struct pci_dev *dev)
+{
+	struct pci_slot *slot;
+
+	mutex_lock(&pci_slot_mutex);
+	list_for_each_entry(slot, &dev->bus->slots, list)
+		if (PCI_SLOT(dev->devfn) == slot->number)
+			dev->slot = slot;
+	mutex_unlock(&pci_slot_mutex);
+}
+
 static struct pci_slot *get_slot(struct pci_bus *parent, int slot_nr)
 {
 	struct pci_slot *slot;