@@ -79,6 +79,7 @@ static bool allow_duplicates;
module_param(allow_duplicates, bool, 0644);
static int register_count;
+static DEFINE_MUTEX(register_count_mutex);
static struct mutex video_list_lock;
static struct list_head video_bus_head;
static int acpi_video_bus_add(struct acpi_device *device);
@@ -1931,14 +1932,15 @@ static int __init intel_opregion_present(void)
int acpi_video_register(void)
{
- int ret;
+ int ret = 0;
+ mutex_lock(®ister_count_mutex);
if (register_count) {
/*
* if the function of acpi_video_register is already called,
* don't register the acpi_vide_bus again and return no error.
*/
- return 0;
+ goto leave;
}
mutex_init(&video_list_lock);
@@ -1948,7 +1950,7 @@ int acpi_video_register(void)
ret = acpi_bus_register_driver(&acpi_video_bus);
if (ret)
- return ret;
+ goto leave;
/*
* When the acpi_video_bus is loaded successfully, increase
@@ -1956,24 +1958,20 @@ int acpi_video_register(void)
*/
register_count = 1;
- return 0;
+leave:
+ mutex_unlock(®ister_count_mutex);
+ return ret;
}
EXPORT_SYMBOL(acpi_video_register);
void acpi_video_unregister(void)
{
- if (!register_count) {
- /*
- * If the acpi video bus is already unloaded, don't
- * unload it again and return directly.
- */
- return;
+ mutex_lock(®ister_count_mutex);
+ if (register_count) {
+ acpi_bus_unregister_driver(&acpi_video_bus);
+ register_count = 0;
}
- acpi_bus_unregister_driver(&acpi_video_bus);
-
- register_count = 0;
-
- return;
+ mutex_unlock(®ister_count_mutex);
}
EXPORT_SYMBOL(acpi_video_unregister);
@@ -1981,13 +1979,14 @@ void acpi_video_unregister_backlight(void)
{
struct acpi_video_bus *video;
- if (!register_count)
- return;
-
- mutex_lock(&video_list_lock);
- list_for_each_entry(video, &video_bus_head, entry)
- acpi_video_bus_unregister_backlight(video);
- mutex_unlock(&video_list_lock);
+ mutex_lock(®ister_count_mutex);
+ if (register_count) {
+ mutex_lock(&video_list_lock);
+ list_for_each_entry(video, &video_bus_head, entry)
+ acpi_video_bus_unregister_backlight(video);
+ mutex_unlock(&video_list_lock);
+ }
+ mutex_unlock(®ister_count_mutex);
}
EXPORT_SYMBOL(acpi_video_unregister_backlight);
It is possible for a native backlight driver to load while acpi_video_register is running, which may lead to acpi_video_unregister_backlight being called while acpi_video_register is running and the 2 racing against eachother. The register_count variable protects against this, but not in a thread safe manner, this commit adds locking to make this thread safe. Signed-off-by: Hans de Goede <hdegoede@redhat.com> --- drivers/acpi/video.c | 43 +++++++++++++++++++++---------------------- 1 file changed, 21 insertions(+), 22 deletions(-)