[PATCH v2 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 a boolean flag to mark already unregistered battery
hooks as "dead" 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 | 11 ++++++++++-
 include/acpi/battery.h |  1 +
 2 files changed, 11 insertions(+), 1 deletion(-)

diff --git a/drivers/acpi/battery.c b/drivers/acpi/battery.c
index 10e9136897a7..b31a6183a082 100644
--- a/drivers/acpi/battery.c
+++ b/drivers/acpi/battery.c
@@ -719,6 +719,7 @@ static void battery_hook_unregister_unlocked(struct acpi_battery_hook *hook)
 			power_supply_changed(battery->bat);
 	}
 	list_del(&hook->list);
+	hook->dead = true;

 	pr_info("extension unregistered: %s\n", hook->name);
 }
@@ -726,7 +727,14 @@ 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 (!hook->dead)
+		battery_hook_unregister_unlocked(hook);
+
 	mutex_unlock(&hook_mutex);
 }
 EXPORT_SYMBOL_GPL(battery_hook_unregister);
@@ -737,6 +745,7 @@ void battery_hook_register(struct acpi_battery_hook *hook)

 	mutex_lock(&hook_mutex);
 	INIT_LIST_HEAD(&hook->list);
+	hook->dead = false;
 	list_add(&hook->list, &battery_hook_list);
 	/*
 	 * Now that the driver is registered, we need
diff --git a/include/acpi/battery.h b/include/acpi/battery.h
index c93f16dfb944..5cfe132bb7f5 100644
--- a/include/acpi/battery.h
+++ b/include/acpi/battery.h
@@ -16,6 +16,7 @@ struct acpi_battery_hook {
 	int (*add_battery)(struct power_supply *battery, struct acpi_battery_hook *hook);
 	int (*remove_battery)(struct power_supply *battery, struct acpi_battery_hook *hook);
 	struct list_head list;
+	bool dead;
 };

 void battery_hook_register(struct acpi_battery_hook *hook);
--
2.39.5