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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: Hans de Goede <hdegoede@redhat.com> Acked-by: Darren Hart <dvhart@linux.intel.com> Signed-off-by: Rafael J. Wysocki <rafael.j.wysocki@intel.com>
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7ee33baabc
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@ -82,6 +82,7 @@ static int disable_backlight_sysfs_if = -1;
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module_param(disable_backlight_sysfs_if, int, 0444);
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static int register_count;
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static DEFINE_MUTEX(register_count_mutex);
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static struct mutex video_list_lock;
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static struct list_head video_bus_head;
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static int acpi_video_bus_add(struct acpi_device *device);
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@ -1964,14 +1965,15 @@ static int __init intel_opregion_present(void)
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int acpi_video_register(void)
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{
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int ret;
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int ret = 0;
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mutex_lock(®ister_count_mutex);
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if (register_count) {
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/*
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* if the function of acpi_video_register is already called,
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* don't register the acpi_vide_bus again and return no error.
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*/
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return 0;
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goto leave;
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}
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mutex_init(&video_list_lock);
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@ -1981,7 +1983,7 @@ int acpi_video_register(void)
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ret = acpi_bus_register_driver(&acpi_video_bus);
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if (ret)
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return ret;
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goto leave;
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/*
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* When the acpi_video_bus is loaded successfully, increase
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@ -1989,24 +1991,20 @@ int acpi_video_register(void)
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*/
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register_count = 1;
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return 0;
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leave:
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mutex_unlock(®ister_count_mutex);
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return ret;
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}
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EXPORT_SYMBOL(acpi_video_register);
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void acpi_video_unregister(void)
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{
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if (!register_count) {
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/*
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* If the acpi video bus is already unloaded, don't
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* unload it again and return directly.
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*/
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return;
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mutex_lock(®ister_count_mutex);
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if (register_count) {
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acpi_bus_unregister_driver(&acpi_video_bus);
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register_count = 0;
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}
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acpi_bus_unregister_driver(&acpi_video_bus);
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register_count = 0;
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return;
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mutex_unlock(®ister_count_mutex);
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}
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EXPORT_SYMBOL(acpi_video_unregister);
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@ -2014,13 +2012,14 @@ void acpi_video_unregister_backlight(void)
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{
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struct acpi_video_bus *video;
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if (!register_count)
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return;
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mutex_lock(&video_list_lock);
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list_for_each_entry(video, &video_bus_head, entry)
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acpi_video_bus_unregister_backlight(video);
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mutex_unlock(&video_list_lock);
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mutex_lock(®ister_count_mutex);
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if (register_count) {
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mutex_lock(&video_list_lock);
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list_for_each_entry(video, &video_bus_head, entry)
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acpi_video_bus_unregister_backlight(video);
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mutex_unlock(&video_list_lock);
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}
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mutex_unlock(®ister_count_mutex);
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}
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EXPORT_SYMBOL(acpi_video_unregister_backlight);
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