@@ -32,6 +32,7 @@
#include <linux/module.h>
#include <linux/pci.h>
#include <linux/types.h>
+#include <linux/workqueue.h>
#include <acpi/video.h>
ACPI_MODULE_NAME("video");
@@ -41,6 +42,7 @@ void acpi_video_unregister_backlight(void);
static bool backlight_notifier_registered;
static struct notifier_block backlight_nb;
+static struct work_struct backlight_notify_work;
static enum acpi_backlight_type acpi_backlight_cmdline = acpi_backlight_undef;
static enum acpi_backlight_type acpi_backlight_dmi = acpi_backlight_undef;
@@ -262,6 +264,13 @@ static const struct dmi_system_id video_detect_dmi_table[] = {
{ },
};
+/* This uses a workqueue to avoid various locking ordering issues */
+static void acpi_video_backlight_notify_work(struct work_struct *work)
+{
+ if (acpi_video_get_backlight_type() != acpi_backlight_video)
+ acpi_video_unregister_backlight();
+}
+
static int acpi_video_backlight_notify(struct notifier_block *nb,
unsigned long val, void *bd)
{
@@ -269,9 +278,8 @@ static int acpi_video_backlight_notify(struct notifier_block *nb,
/* A raw bl registering may change video -> native */
if (backlight->props.type == BACKLIGHT_RAW &&
- val == BACKLIGHT_REGISTERED &&
- acpi_video_get_backlight_type() != acpi_backlight_video)
- acpi_video_unregister_backlight();
+ val == BACKLIGHT_REGISTERED)
+ schedule_work(&backlight_notify_work);
return NOTIFY_OK;
}
@@ -304,6 +312,8 @@ enum acpi_backlight_type acpi_video_get_backlight_type(void)
acpi_walk_namespace(ACPI_TYPE_DEVICE, ACPI_ROOT_OBJECT,
ACPI_UINT32_MAX, find_video, NULL,
&video_caps, NULL);
+ INIT_WORK(&backlight_notify_work,
+ acpi_video_backlight_notify_work);
backlight_nb.notifier_call = acpi_video_backlight_notify;
backlight_nb.priority = 0;
if (backlight_register_notifier(&backlight_nb) == 0)
Before this commit, the following would happen: a) acpi_video_get_backlight_type() gets called b) acpi_video_get_backlight_type() calls acpi_video_init_backlight_type() c) acpi_video_init_backlight_type() locks its function static init_mutex d) acpi_video_init_backlight_type() calls backlight_register_notifier() e) backlight_register_notifier() takes its notifier-chain lock And when the backlight notifier chain gets called we've: 1) blocking_notifier_call_chain() gets called 2) blocking_notifier_call_chain() takes the notifier-chain lock 3) blocking_notifier_call_chain() calls acpi_video_backlight_notify() 4) acpi_video_backlight_notify() calls acpi_video_get_backlight_type() 5) acpi_video_get_backlight_type() calls acpi_video_init_backlight_type() 6) acpi_video_init_backlight_type() locks its function static init_mutex So in the first call sequence we have: a) init_mutex gets locked b) notifier-chain gets locked and in the second call sequence we have: 1) notifier-chain gets locked 2) init_mutex gets locked And we've a circular locking dependency. This specific locking dependency is fixable without using the big hammer otherwise known as a workqueue, but further analysis shows a similar problem with the backlight notifier chain lock vs register_count_mutex from drivers/acpi/acpi_video.c, and fixing that becomes problematic. So this commit simply fixes this with the big hammer, performance wise this is a non issue as we expect the work to get scheduled exactly zero or one times during normal system use. Signed-off-by: Hans de Goede <hdegoede@redhat.com> --- drivers/acpi/video_detect.c | 16 +++++++++++++--- 1 file changed, 13 insertions(+), 3 deletions(-)