Re: [PATCH v2] led: core: Use atomic bit-field for the blink-flags

From: Hans de Goede
Date: Wed Nov 09 2016 - 06:51:45 EST

Hi,

On 08-11-16 14:58, Jacek Anaszewski wrote:
From: Hans de Goede <hdegoede@xxxxxxxxxx>

All the LED_BLINK* flags are accessed read-modify-write from e.g.
led_set_brightness and led_blink_set_oneshot while both
set_brightness_work and the blink_timer may be running.

If these race then the modify step done by one of them may be lost,
switch the LED_BLINK* flags to a new atomic work_flags bit-field
to avoid this race.

Signed-off-by: Hans de Goede <hdegoede@xxxxxxxxxx>
Signed-off-by: Jacek Anaszewski <j.anaszewski@xxxxxxxxxxx>
---
Changes since v1:
- keep set_brightness_work in linux/leds.h

Thank you.

Patch looks good to me:

Reviewed-by: Hans de Goede <hdegoede@xxxxxxxxxx>

Regards,

Hans




drivers/leds/led-class.c | 1 +
drivers/leds/led-core.c | 52 +++++++++++++++++++++++++-----------------------
include/linux/leds.h | 24 ++++++++++++----------
3 files changed, 42 insertions(+), 35 deletions(-)

diff --git a/drivers/leds/led-class.c b/drivers/leds/led-class.c
index c8d2d67..b12f861 100644
--- a/drivers/leds/led-class.c
+++ b/drivers/leds/led-class.c
@@ -212,6 +212,7 @@ int led_classdev_register(struct device *parent, struct led_classdev *led_cdev)
return -ENODEV;
}

+ led_cdev->work_flags = 0;
#ifdef CONFIG_LEDS_TRIGGERS
init_rwsem(&led_cdev->trigger_lock);
#endif
diff --git a/drivers/leds/led-core.c b/drivers/leds/led-core.c
index e2e5cc7..620257a 100644
--- a/drivers/leds/led-core.c
+++ b/drivers/leds/led-core.c
@@ -61,12 +61,13 @@ static void led_timer_function(unsigned long data)

if (!led_cdev->blink_delay_on || !led_cdev->blink_delay_off) {
led_set_brightness_nosleep(led_cdev, LED_OFF);
- led_cdev->flags &= ~LED_BLINK_SW;
+ clear_bit(LED_BLINK_SW, &led_cdev->work_flags);
return;
}

- if (led_cdev->flags & LED_BLINK_ONESHOT_STOP) {
- led_cdev->flags &= ~(LED_BLINK_ONESHOT_STOP | LED_BLINK_SW);
+ if (test_and_clear_bit(LED_BLINK_ONESHOT_STOP,
+ &led_cdev->work_flags)) {
+ clear_bit(LED_BLINK_SW, &led_cdev->work_flags);
return;
}

@@ -81,10 +82,9 @@ static void led_timer_function(unsigned long data)
* Do it only if there is no pending blink brightness
* change, to avoid overwriting the new value.
*/
- if (!(led_cdev->flags & LED_BLINK_BRIGHTNESS_CHANGE))
+ if (!test_and_clear_bit(LED_BLINK_BRIGHTNESS_CHANGE,
+ &led_cdev->work_flags))
led_cdev->blink_brightness = brightness;
- else
- led_cdev->flags &= ~LED_BLINK_BRIGHTNESS_CHANGE;
brightness = LED_OFF;
delay = led_cdev->blink_delay_off;
}
@@ -95,13 +95,15 @@ static void led_timer_function(unsigned long data)
* the final blink state so that the led is toggled each delay_on +
* delay_off milliseconds in worst case.
*/
- if (led_cdev->flags & LED_BLINK_ONESHOT) {
- if (led_cdev->flags & LED_BLINK_INVERT) {
+ if (test_bit(LED_BLINK_ONESHOT, &led_cdev->work_flags)) {
+ if (test_bit(LED_BLINK_INVERT, &led_cdev->work_flags)) {
if (brightness)
- led_cdev->flags |= LED_BLINK_ONESHOT_STOP;
+ set_bit(LED_BLINK_ONESHOT_STOP,
+ &led_cdev->work_flags);
} else {
if (!brightness)
- led_cdev->flags |= LED_BLINK_ONESHOT_STOP;
+ set_bit(LED_BLINK_ONESHOT_STOP,
+ &led_cdev->work_flags);
}
}

@@ -114,10 +116,9 @@ static void set_brightness_delayed(struct work_struct *ws)
container_of(ws, struct led_classdev, set_brightness_work);
int ret = 0;

- if (led_cdev->flags & LED_BLINK_DISABLE) {
+ if (test_and_clear_bit(LED_BLINK_DISABLE, &led_cdev->work_flags)) {
led_cdev->delayed_set_value = LED_OFF;
led_stop_software_blink(led_cdev);
- led_cdev->flags &= ~LED_BLINK_DISABLE;
}

ret = __led_set_brightness(led_cdev, led_cdev->delayed_set_value);
@@ -160,7 +161,7 @@ static void led_set_software_blink(struct led_classdev *led_cdev,
return;
}

- led_cdev->flags |= LED_BLINK_SW;
+ set_bit(LED_BLINK_SW, &led_cdev->work_flags);
mod_timer(&led_cdev->blink_timer, jiffies + 1);
}

@@ -169,7 +170,7 @@ static void led_blink_setup(struct led_classdev *led_cdev,
unsigned long *delay_on,
unsigned long *delay_off)
{
- if (!(led_cdev->flags & LED_BLINK_ONESHOT) &&
+ if (!test_bit(LED_BLINK_ONESHOT, &led_cdev->work_flags) &&
led_cdev->blink_set &&
!led_cdev->blink_set(led_cdev, delay_on, delay_off))
return;
@@ -196,8 +197,8 @@ void led_blink_set(struct led_classdev *led_cdev,
{
del_timer_sync(&led_cdev->blink_timer);

- led_cdev->flags &= ~LED_BLINK_ONESHOT;
- led_cdev->flags &= ~LED_BLINK_ONESHOT_STOP;
+ clear_bit(LED_BLINK_ONESHOT, &led_cdev->work_flags);
+ clear_bit(LED_BLINK_ONESHOT_STOP, &led_cdev->work_flags);

led_blink_setup(led_cdev, delay_on, delay_off);
}
@@ -208,17 +209,17 @@ void led_blink_set_oneshot(struct led_classdev *led_cdev,
unsigned long *delay_off,
int invert)
{
- if ((led_cdev->flags & LED_BLINK_ONESHOT) &&
+ if (test_bit(LED_BLINK_ONESHOT, &led_cdev->work_flags) &&
timer_pending(&led_cdev->blink_timer))
return;

- led_cdev->flags |= LED_BLINK_ONESHOT;
- led_cdev->flags &= ~LED_BLINK_ONESHOT_STOP;
+ set_bit(LED_BLINK_ONESHOT, &led_cdev->work_flags);
+ clear_bit(LED_BLINK_ONESHOT_STOP, &led_cdev->work_flags);

if (invert)
- led_cdev->flags |= LED_BLINK_INVERT;
+ set_bit(LED_BLINK_INVERT, &led_cdev->work_flags);
else
- led_cdev->flags &= ~LED_BLINK_INVERT;
+ clear_bit(LED_BLINK_INVERT, &led_cdev->work_flags);

led_blink_setup(led_cdev, delay_on, delay_off);
}
@@ -229,7 +230,7 @@ void led_stop_software_blink(struct led_classdev *led_cdev)
del_timer_sync(&led_cdev->blink_timer);
led_cdev->blink_delay_on = 0;
led_cdev->blink_delay_off = 0;
- led_cdev->flags &= ~LED_BLINK_SW;
+ clear_bit(LED_BLINK_SW, &led_cdev->work_flags);
}
EXPORT_SYMBOL_GPL(led_stop_software_blink);

@@ -240,17 +241,18 @@ void led_set_brightness(struct led_classdev *led_cdev,
* If software blink is active, delay brightness setting
* until the next timer tick.
*/
- if (led_cdev->flags & LED_BLINK_SW) {
+ if (test_bit(LED_BLINK_SW, &led_cdev->work_flags)) {
/*
* If we need to disable soft blinking delegate this to the
* work queue task to avoid problems in case we are called
* from hard irq context.
*/
if (brightness == LED_OFF) {
- led_cdev->flags |= LED_BLINK_DISABLE;
+ set_bit(LED_BLINK_DISABLE, &led_cdev->work_flags);
schedule_work(&led_cdev->set_brightness_work);
} else {
- led_cdev->flags |= LED_BLINK_BRIGHTNESS_CHANGE;
+ set_bit(LED_BLINK_BRIGHTNESS_CHANGE,
+ &led_cdev->work_flags);
led_cdev->blink_brightness = brightness;
}
return;
diff --git a/include/linux/leds.h b/include/linux/leds.h
index eebcd8c..1dc69df 100644
--- a/include/linux/leds.h
+++ b/include/linux/leds.h
@@ -43,16 +43,20 @@ struct led_classdev {
#define LED_UNREGISTERING (1 << 1)
/* Upper 16 bits reflect control information */
#define LED_CORE_SUSPENDRESUME (1 << 16)
-#define LED_BLINK_SW (1 << 17)
-#define LED_BLINK_ONESHOT (1 << 18)
-#define LED_BLINK_ONESHOT_STOP (1 << 19)
-#define LED_BLINK_INVERT (1 << 20)
-#define LED_BLINK_BRIGHTNESS_CHANGE (1 << 21)
-#define LED_BLINK_DISABLE (1 << 22)
-#define LED_SYSFS_DISABLE (1 << 23)
-#define LED_DEV_CAP_FLASH (1 << 24)
-#define LED_HW_PLUGGABLE (1 << 25)
-#define LED_PANIC_INDICATOR (1 << 26)
+#define LED_SYSFS_DISABLE (1 << 17)
+#define LED_DEV_CAP_FLASH (1 << 18)
+#define LED_HW_PLUGGABLE (1 << 19)
+#define LED_PANIC_INDICATOR (1 << 20)
+
+ /* set_brightness_work / blink_timer flags, atomic, private. */
+ unsigned long work_flags;
+
+#define LED_BLINK_SW 0
+#define LED_BLINK_ONESHOT 1
+#define LED_BLINK_ONESHOT_STOP 2
+#define LED_BLINK_INVERT 3
+#define LED_BLINK_BRIGHTNESS_CHANGE 4
+#define LED_BLINK_DISABLE 5

/* Set LED brightness level
* Must not sleep. Use brightness_set_blocking for drivers