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ACPI / video: Fix circular lock dependency issue in the video-detect code

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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.

Fixes: 93a291dfaf (ACPI / video: Move backlight notifier to video_detect.c)
Signed-off-by: Hans de Goede <hdegoede@redhat.com>
Reported-and-tested-by: Sedat Dilek <sedat.dilek@gmail.com>
Signed-off-by: Rafael J. Wysocki <rafael.j.wysocki@intel.com>
This commit is contained in:
Hans de Goede 2015-08-13 18:53:37 +02:00 committed by Rafael J. Wysocki
parent f7644cbfcd
commit 7231ed1a81
1 changed files with 13 additions and 3 deletions
Show Stats Download Patch File Download Diff File Expand all files Collapse all files

16
drivers/acpi/video_detect.c
View File

@ -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)