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Commit 2a8b18e9 authored by Hans de Goede's avatar Hans de Goede Committed by Rafael J. Wysocki
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ACPI / video: Fix acpi_video _register vs _unregister_backlight race 



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: default avatarHans de Goede <hdegoede@redhat.com>
Acked-by: default avatarDarren Hart <dvhart@linux.intel.com>
Signed-off-by: default avatarRafael J. Wysocki <rafael.j.wysocki@intel.com>
parent 7ee33baa

drivers/acpi/acpi_video.c

+21 −22
Original line number Diff line number Diff line
@@ -82,6 +82,7 @@ static int disable_backlight_sysfs_if = -1; 
module_param(disable_backlight_sysfs_if, int, 0444);



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);
@@ -1964,14 +1965,15 @@ static int __init intel_opregion_present(void) 


int acpi_video_register(void)

{

	int ret;

	int ret = 0;



	mutex_lock(&register_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);
@@ -1981,7 +1983,7 @@ 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
@@ -1989,24 +1991,20 @@ int acpi_video_register(void) 
	 */

	register_count = 1;



	return 0;

leave:

	mutex_unlock(&register_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(&register_count_mutex);

	if (register_count) {

		acpi_bus_unregister_driver(&acpi_video_bus);



		register_count = 0;



	return;

	}

	mutex_unlock(&register_count_mutex);

}

EXPORT_SYMBOL(acpi_video_unregister);
@@ -2014,14 +2012,15 @@ void acpi_video_unregister_backlight(void) 
{

	struct acpi_video_bus *video;



	if (!register_count)

		return;



	mutex_lock(&register_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(&register_count_mutex);

}

EXPORT_SYMBOL(acpi_video_unregister_backlight);



/*