ACPI / battery: Safe unregistering of hooks

A hooking API was implemented for 4.17 in fa93854 followed
by hooks for Thinkpad laptops in 2801b96. The Thinkpad
drivers did not support the Thinkpad 13 and the hooking API crashes
on unsupported batteries by altering a list of hooks during unsafe
iteration. Thus, Thinkpad 13 laptops could no longer boot.

Additionally, a lock was kept in place and debugging information was
printed out of order.

Fixes: fa93854 (battery: Add the battery hooking API)
Cc: 4.17+ <[email protected]> # 4.17+
Signed-off-by: Jouke Witteveen <[email protected]>
Signed-off-by: Rafael J. Wysocki <[email protected]>

Author: joukewitteveen

drivers/acpi/battery.c

@@ -717,10 +717,11 @@ void battery_hook_register(struct acpi_battery_hook *hook)
 			 */
 			pr_err("extension failed to load: %s", hook->name);
 			__battery_hook_unregister(hook, 0);
-			return;
+			goto end;
 		}
 	}
 	pr_info("new extension: %s\n", hook->name);
+end:
 	mutex_unlock(&hook_mutex);
 }
 EXPORT_SYMBOL_GPL(battery_hook_register);
@@ -732,7 +733,7 @@ EXPORT_SYMBOL_GPL(battery_hook_register);
 */
 static void battery_hook_add_battery(struct acpi_battery *battery)
 {
-	struct acpi_battery_hook *hook_node;
+	struct acpi_battery_hook *hook_node, *tmp;
 
 	mutex_lock(&hook_mutex);
 	INIT_LIST_HEAD(&battery->list);
@@ -744,15 +745,15 @@ static void battery_hook_add_battery(struct acpi_battery *battery)
 	 * when a battery gets hotplugged or initialized
 	 * during the battery module initialization.
 	 */
-	list_for_each_entry(hook_node, &battery_hook_list, list) {
+	list_for_each_entry_safe(hook_node, tmp, &battery_hook_list, list) {
 		if (hook_node->add_battery(battery->bat)) {
 			/*
 			 * The notification of the extensions has failed, to
 			 * prevent further errors we will unload the extension.
 			 */
-			__battery_hook_unregister(hook_node, 0);
 			pr_err("error in extension, unloading: %s",
 					hook_node->name);
+			__battery_hook_unregister(hook_node, 0);
 		}
 	}
 	mutex_unlock(&hook_mutex);