ACPI / hotplug / PCI: Simplify disable_slot()

After recent PCI core changes related to the rescan/remove locking,
the ACPIPHP's disable_slot() function is only called under the
general PCI rescan/remove lock, so it doesn't have to use
dev_in_slot() any more to avoid race conditions.  Make it simply
walk the devices on the bus and drop the ones in the slot being
disabled and drop dev_in_slot() which has no more users.

Moreover, to avoid problems described in the changelog of commit
29ed1f29b68a (PCI: pciehp: Fix null pointer deref when hot-removing
SR-IOV device), make disable_slot() carry out the list walk in
reverse order.

Signed-off-by: Rafael J. Wysocki <rafael.j.wysocki@intel.com>
Tested-by: Mika Westerberg <mika.westerberg@linux.intel.com>

drivers/pci/hotplug/acpiphp_glue.c

@@ -625,32 +625,15 @@ static void __ref enable_slot(struct acpiphp_slot *slot)
 	}
 }
 
-/* return first device in slot, acquiring a reference on it */
-static struct pci_dev *dev_in_slot(struct acpiphp_slot *slot)
-{
-	struct pci_bus *bus = slot->bus;
-	struct pci_dev *dev;
-	struct pci_dev *ret = NULL;
-
-	down_read(&pci_bus_sem);
-	list_for_each_entry(dev, &bus->devices, bus_list)
-		if (PCI_SLOT(dev->devfn) == slot->device) {
-			ret = pci_dev_get(dev);
-			break;
-		}
-	up_read(&pci_bus_sem);
-
-	return ret;
-}
-
 /**
  * disable_slot - disable a slot
  * @slot: ACPI PHP slot
  */
 static void disable_slot(struct acpiphp_slot *slot)
 {
+	struct pci_bus *bus = slot->bus;
+	struct pci_dev *dev, *prev;
 	struct acpiphp_func *func;
-	struct pci_dev *pdev;
 
 	/*
 	 * enable_slot() enumerates all functions in this device via
@@ -658,10 +641,9 @@ static void disable_slot(struct acpiphp_slot *slot)
 	 * methods (_EJ0, etc.) or not.  Therefore, we remove all functions
 	 * here.
 	 */
-	while ((pdev = dev_in_slot(slot))) {
-		pci_stop_and_remove_bus_device(pdev);
-		pci_dev_put(pdev);
-	}
+	list_for_each_entry_safe_reverse(dev, prev, &bus->devices, bus_list)
+		if (PCI_SLOT(dev->devfn) == slot->device)
+			pci_stop_and_remove_bus_device(dev);
 
 	list_for_each_entry(func, &slot->funcs, sibling)
 		acpiphp_bus_trim(func_to_handle(func));