leds: Fix oops about sleeping in led_trigger_blink()

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@redhat.com>
Reviewed-by: Jacek Anaszewski <jacek.anaszewski@gmail.com>
Tested-by: Yauhen Kharuzhy <jekhor@gmail.com>
Link: https://lore.kernel.org/r/20230510162234.291439-4-hdegoede@redhat.com
Signed-off-by: Lee Jones <lee@kernel.org>

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);
 	}
 

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();
 }

include/linux/leds.h

@@ -127,6 +127,7 @@ 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
@@ -150,6 +151,10 @@ 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,
@@ -173,6 +178,8 @@ 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 */
@@ -275,12 +282,27 @@ 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_set_brightness() 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
@@ -294,6 +316,8 @@ 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,