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(-)
diff --git a/drivers/acpi/video.c b/drivers/acpi/video.c index b8053a8..fcc7c2e 100644 --- a/drivers/acpi/video.c +++ b/drivers/acpi/video.c @@ -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);