led_trigger_blink() calls led_blink_set() from a RCU read-side critical
section so led_blink_set() must not sleep. Note sleeping was not allowed
before the switch to RCU either because a spinlock was held before.
led_blink_set() does not sleep when sw-blinking is used, but
many LED controller drivers with hw blink support have a blink_set
function which may sleep, leading to an oops like this one:
[ 832.605062] ------------[ cut here ]------------
[ 832.605085] Voluntary context switch within RCU read-side critical section!
[ 832.605119] WARNING: CPU: 2 PID: 370 at kernel/rcu/tree_plugin.h:318 rcu_note_context_switch+0x4ee/0x690
<snip>
[ 832.606453] Call Trace:
[ 832.606466] <TASK>
[ 832.606487] __schedule+0x9f/0x1480
[ 832.606527] schedule+0x5d/0xe0
[ 832.606549] schedule_timeout+0x79/0x140
[ 832.606572] ? __pfx_process_timeout+0x10/0x10
[ 832.606599] wait_for_completion_timeout+0x6f/0x140
[ 832.606627] i2c_dw_xfer+0x101/0x460
[ 832.606659] ? psi_group_change+0x168/0x400
[ 832.606680] __i2c_transfer+0x172/0x6d0
[ 832.606709] i2c_smbus_xfer_emulated+0x27d/0x9c0
[ 832.606732] ? __schedule+0x430/0x1480
[ 832.606753] ? preempt_count_add+0x6a/0xa0
[ 832.606778] ? get_nohz_timer_target+0x18/0x190
[ 832.606796] ? lock_timer_base+0x61/0x80
[ 832.606817] ? preempt_count_add+0x6a/0xa0
[ 832.606842] __i2c_smbus_xfer+0xa2/0x3f0
[ 832.606862] i2c_smbus_xfer+0x66/0xf0
[ 832.606882] i2c_smbus_read_byte_data+0x41/0x70
[ 832.606901] ? _raw_spin_unlock_irqrestore+0x23/0x40
[ 832.606922] ? __pm_runtime_suspend+0x46/0xc0
[ 832.606946] cht_wc_byte_reg_read+0x2e/0x60
[ 832.606972] _regmap_read+0x5c/0x120
[ 832.606997] _regmap_update_bits+0x96/0xc0
[ 832.607023] regmap_update_bits_base+0x5b/0x90
[ 832.607053] cht_wc_leds_brightness_get+0x412/0x910 [leds_cht_wcove]
[ 832.607094] led_blink_setup+0x28/0x100
[ 832.607119] led_trigger_blink+0x40/0x70
[ 832.607145] power_supply_update_leds+0x1b7/0x1c0
[ 832.607174] power_supply_changed_work+0x67/0xe0
[ 832.607198] process_one_work+0x1c8/0x3c0
[ 832.607222] worker_thread+0x4d/0x380
[ 832.607243] ? __pfx_worker_thread+0x10/0x10
[ 832.607258] kthread+0xe9/0x110
[ 832.607279] ? __pfx_kthread+0x10/0x10
[ 832.607300] ret_from_fork+0x2c/0x50
[ 832.607337] </TASK>
[ 832.607344] ---[ end trace 0000000000000000 ]---
Add a new led_blink_set_nosleep() function which defers the actual
led_blink_set() call to a workqueue when necessary to fix this.
This also fixes an existing race where a pending led_set_brightness() has
been deferred to set_brightness_work and might then race with a later
led_cdev->blink_set() call. Note this race is only an issue with triggers
mixing led_trigger_event() and led_trigger_blink() calls, sysfs API
calls and led_trigger_blink_oneshot() are not affected.
Note rather then adding a separate blink_set_blocking callback this uses
the presence of the already existing brightness_set_blocking callback to
detect if the blinking call should be deferred to set_brightness_work.
Signed-off-by: Hans de Goede <hdegoede@xxxxxxxxxx>
---
drivers/leds/led-core.c | 24 ++++++++++++++++++++++++
drivers/leds/led-triggers.c | 2 +-
include/linux/leds.h | 24 ++++++++++++++++++++++++
3 files changed, 49 insertions(+), 1 deletion(-)
diff --git a/drivers/leds/led-core.c b/drivers/leds/led-core.c
index e61acc785410..b9b1295833c9 100644
--- a/drivers/leds/led-core.c
+++ b/drivers/leds/led-core.c
@@ -152,6 +152,13 @@ static void set_brightness_delayed(struct work_struct *ws)
if (test_and_clear_bit(LED_SET_BRIGHTNESS, &led_cdev->work_flags))
set_brightness_delayed_set_brightness(led_cdev, led_cdev->delayed_set_value);
+
+ if (test_and_clear_bit(LED_SET_BLINK, &led_cdev->work_flags)) {
+ unsigned long delay_on = led_cdev->delayed_delay_on;
+ unsigned long delay_off = led_cdev->delayed_delay_off;
+
+ led_blink_set(led_cdev, &delay_on, &delay_off);
+ }
}
static void led_set_software_blink(struct led_classdev *led_cdev,
@@ -246,6 +253,22 @@ void led_blink_set_oneshot(struct led_classdev *led_cdev,
}
EXPORT_SYMBOL_GPL(led_blink_set_oneshot);
+void led_blink_set_nosleep(struct led_classdev *led_cdev, unsigned long delay_on,
+ unsigned long delay_off)
+{
+ /* If necessary delegate to a work queue task. */
+ if (led_cdev->blink_set && led_cdev->brightness_set_blocking) {
+ led_cdev->delayed_delay_on = delay_on;
+ led_cdev->delayed_delay_off = delay_off;
+ set_bit(LED_SET_BLINK, &led_cdev->work_flags);
+ schedule_work(&led_cdev->set_brightness_work);
+ return;
+ }
+
+ led_blink_set(led_cdev, &delay_on, &delay_off);
+}
+EXPORT_SYMBOL_GPL(led_blink_set_nosleep);
+
void led_stop_software_blink(struct led_classdev *led_cdev)
{
del_timer_sync(&led_cdev->blink_timer);
@@ -301,6 +324,7 @@ void led_set_brightness_nopm(struct led_classdev *led_cdev, unsigned int value)
set_bit(LED_SET_BRIGHTNESS, &led_cdev->work_flags);
} else {
clear_bit(LED_SET_BRIGHTNESS, &led_cdev->work_flags);
+ clear_bit(LED_SET_BLINK, &led_cdev->work_flags);
set_bit(LED_SET_BRIGHTNESS_OFF, &led_cdev->work_flags);
}
diff --git a/drivers/leds/led-triggers.c b/drivers/leds/led-triggers.c
index e06361165e9b..8214d3f7bc5f 100644
--- a/drivers/leds/led-triggers.c
+++ b/drivers/leds/led-triggers.c
@@ -409,7 +409,7 @@ static void led_trigger_blink_setup(struct led_trigger *trig,
led_blink_set_oneshot(led_cdev, &delay_on, &delay_off,
invert);
else
- led_blink_set(led_cdev, &delay_on, &delay_off);
+ led_blink_set_nosleep(led_cdev, delay_on, delay_off);
}
rcu_read_unlock();
}
diff --git a/include/linux/leds.h b/include/linux/leds.h
index eb68aea79c6d..3c93dec3f4e2 100644
--- a/include/linux/leds.h
+++ b/include/linux/leds.h
@@ -119,6 +119,7 @@ struct led_classdev {
/* Brightness off also disables hw-blinking so it is a separate action */
#define LED_SET_BRIGHTNESS_OFF 6
#define LED_SET_BRIGHTNESS 7
+#define LED_SET_BLINK 8
/* Set LED brightness level
* Must not sleep. Use brightness_set_blocking for drivers
@@ -142,6 +143,10 @@ struct led_classdev {
* match the values specified exactly.
* Deactivate blinking again when the brightness is set to LED_OFF
* via the brightness_set() callback.
+ * For led_blink_set_nosleep() the LED core assumes that blink_set
+ * implementations, of drivers which do not use brightness_set_blocking,
+ * will not sleep. Therefor if brightness_set_blocking is not set
+ * this function must not sleep!
*/
int (*blink_set)(struct led_classdev *led_cdev,
unsigned long *delay_on,
@@ -165,6 +170,8 @@ struct led_classdev {
struct work_struct set_brightness_work;
int delayed_set_value;
+ unsigned long delayed_delay_on;
+ unsigned long delayed_delay_off;
#ifdef CONFIG_LEDS_TRIGGERS
/* Protects the trigger data below */
@@ -257,12 +264,27 @@ struct led_classdev *__must_check devm_of_led_get(struct device *dev,
* software blinking if there is no hardware blinking or if
* the LED refuses the passed values.
*
+ * This function may sleep!
+ *
* Note that if software blinking is active, simply calling
* led_cdev->brightness_set() will not stop the blinking,
* use led_classdev_brightness_set() instead.
*/
void led_blink_set(struct led_classdev *led_cdev, unsigned long *delay_on,
unsigned long *delay_off);
+
+/**
+ * led_blink_set_nosleep - set blinking, guaranteed to not sleep
+ * @led_cdev: the LED to start blinking
+ * @delay_on: the time it should be on (in ms)
+ * @delay_off: the time it should ble off (in ms)
+ *
+ * This function makes the LED blink and is guaranteed to not sleep. Otherwise
+ * this is the same as led_blink_set(), see led_blink_set() for details.
+ */
+void led_blink_set_nosleep(struct led_classdev *led_cdev, unsigned long delay_on,
+ unsigned long delay_off);
+
/**
* led_blink_set_oneshot - do a oneshot software blink
* @led_cdev: the LED to start blinking
@@ -276,6 +298,8 @@ void led_blink_set(struct led_classdev *led_cdev, unsigned long *delay_on,
*
* If invert is set, led blinks for delay_off first, then for
* delay_on and leave the led on after the on-off cycle.
+ *
+ * This function is guaranteed not to sleep.
*/
void led_blink_set_oneshot(struct led_classdev *led_cdev,
unsigned long *delay_on, unsigned long *delay_off,
--
2.39.1
