[PATCHv2][input-led] Defer input led work to workqueue

From: Samuel Thibault
Date: Tue Aug 26 2014 - 05:17:38 EST

When the kbd changes its led state (e.g. caps lock), this triggers
(led_trigger_event) the kbd-capsl trigger, which is by default
used by the vt::capsl LED, which triggers (led_trigger_event) the
vt-capsl trigger. These two nested led_trigger_event calls take a
trig->leddev_list_lock lock and thus lockdep complains.

Actually the user can make the vt::capsl LED use its own vt-capsl
trigger and thus build a loop. This produces an immediate oops.

This changeset defers the second led_trigger_event call into a
workqueue, which avoids the nested locking altogether. This does
not prevent the user from shooting himself in the foot by creating a
vt::capsl <-> vt-capsl loop, but the only consequence is the workqueue
threads eating some CPU until the user breaks the loop, which is not too

Signed-off-by: Samuel Thibault <samuel.thibault@xxxxxxxxxxxx>


Difference with v1: uses schedule_work instead of its own workqueue.

--- a/drivers/input/leds.c
+++ b/drivers/input/leds.c
@@ -100,13 +100,24 @@ static unsigned long vt_led_registered[B
/* Number of input devices having each LED */
static int vt_led_references[LED_CNT];

+static int vt_led_state[LED_CNT];
+static struct work_struct vt_led_work[LED_CNT];
+static void vt_led_cb(struct work_struct *work)
+ int led = work - vt_led_work;
+ led_trigger_event(&vt_led_triggers[led], vt_led_state[led]);
/* VT LED state change, tell the VT trigger. */
static void vt_led_set(struct led_classdev *cdev,
enum led_brightness brightness)
int led = cdev - vt_leds;

- led_trigger_event(&vt_led_triggers[led], !!brightness);
+ vt_led_state[led] = !!brightness;
+ schedule_work(&vt_led_work[led]);

/* LED state change for some keyboard, notify that keyboard. */
@@ -244,6 +255,22 @@ void input_led_disconnect(struct input_d

+static int __init input_led_init(void)
+ unsigned i;
+ for (i = 0; i < LED_CNT; i++)
+ INIT_WORK(&vt_led_work[i], vt_led_cb);
+ return 0;
+static void __exit input_led_exit(void)
MODULE_DESCRIPTION("User LED support for input layer");
MODULE_AUTHOR("Samuel Thibault <samuel.thibault@xxxxxxxxxxxx>");
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