[PATCH RESEND v3 2/3] ACPI: battery: Fix possible crash when unregistering a battery hook

[Armin Wolf <W_Armin@gmx.de>]

When a battery hook returns an error when adding a new battery, then
the battery hook is automatically unregistered.
However the battery hook provider cannot know that, so it will later
call battery_hook_unregister() on the already unregistered battery
hook, resulting in a crash.

Fix this by using the list head to mark already unregistered battery
hooks as already being unregistered so that they can be ignored by
battery_hook_unregister().

Fixes: fa93854f7a7e ("battery: Add the battery hooking API")
Signed-off-by: Armin Wolf <W_Armin@gmx.de>
---
 drivers/acpi/battery.c | 12 +++++++++---
 1 file changed, 9 insertions(+), 3 deletions(-)

diff --git a/drivers/acpi/battery.c b/drivers/acpi/battery.c
index dda59ee5a11e..1c45ff6dbb83 100644
--- a/drivers/acpi/battery.c
+++ b/drivers/acpi/battery.c
@@ -715,7 +715,7 @@ static void battery_hook_unregister_unlocked(struct acpi_battery_hook *hook)
 		if (!hook->remove_battery(battery->bat, hook))
 			power_supply_changed(battery->bat);
 	}
-	list_del(&hook->list);
+	list_del_init(&hook->list);

 	pr_info("extension unregistered: %s\n", hook->name);
 }
@@ -723,7 +723,14 @@ static void battery_hook_unregister_unlocked(struct acpi_battery_hook *hook)
 void battery_hook_unregister(struct acpi_battery_hook *hook)
 {
 	mutex_lock(&hook_mutex);
-	battery_hook_unregister_unlocked(hook);
+	/*
+	 * Ignore already unregistered battery hooks. This might happen
+	 * if a battery hook was previously unloaded due to an error when
+	 * adding a new battery.
+	 */
+	if (!list_empty(&hook->list))
+		battery_hook_unregister_unlocked(hook);
+
 	mutex_unlock(&hook_mutex);
 }
 EXPORT_SYMBOL_GPL(battery_hook_unregister);
@@ -733,7 +740,6 @@ void battery_hook_register(struct acpi_battery_hook *hook)
 	struct acpi_battery *battery;

 	mutex_lock(&hook_mutex);
-	INIT_LIST_HEAD(&hook->list);
 	list_add(&hook->list, &battery_hook_list);
 	/*
 	 * Now that the driver is registered, we need
--
2.39.5