leds: avoid flush_work in atomic context

It turns out that various triggers use led_blink_setup() from atomic
context, so we can't do a flush_work there. Flush is still needed for
slow LEDs, but we can move it to sysfs code where it is safe.

    WARNING: inconsistent lock state
    5.2.0-rc1 #1 Tainted: G        W
    --------------------------------
    inconsistent {SOFTIRQ-ON-W} -> {IN-SOFTIRQ-W} usage.
    swapper/1/0 [HC0[0]:SC1[1]:HE1:SE0] takes:
    000000006e30541b
    ((work_completion)(&led_cdev->set_brightness_work)){+.?.}, at:
    +__flush_work+0x3b/0x38a
    {SOFTIRQ-ON-W} state was registered at:
      lock_acquire+0x146/0x1a1
     __flush_work+0x5b/0x38a
     flush_work+0xb/0xd
     led_blink_setup+0x1e/0xd3
     led_blink_set+0x3f/0x44
     tpt_trig_timer+0xdb/0x106
     ieee80211_mod_tpt_led_trig+0xed/0x112

Fixes: 0db37915 ("leds: avoid races with workqueue")
Signed-off-by: Pavel Machek <pavel@ucw.cz>
Tested-by: Hugh Dickins <hughd@google.com>
Signed-off-by: Jacek Anaszewski <jacek.anaszewski@gmail.com>

drivers/leds/led-core.c

@@ -164,11 +164,6 @@ static void led_blink_setup(struct led_classdev *led_cdev,
 		     unsigned long *delay_on,
 		     unsigned long *delay_off)
 {
-	/*
-	 * If "set brightness to 0" is pending in workqueue, we don't
-	 * want that to be reordered after blink_set()
-	 */
-	flush_work(&led_cdev->set_brightness_work);
 	if (!test_bit(LED_BLINK_ONESHOT, &led_cdev->work_flags) &&
 	    led_cdev->blink_set &&
 	    !led_cdev->blink_set(led_cdev, delay_on, delay_off))

drivers/leds/trigger/ledtrig-timer.c

@@ -113,6 +113,11 @@ static int timer_trig_activate(struct led_classdev *led_cdev)
 		led_cdev->flags &= ~LED_INIT_DEFAULT_TRIGGER;
 	}
 
+	/*
+	 * If "set brightness to 0" is pending in workqueue, we don't
+	 * want that to be reordered after blink_set()
+	 */
+	flush_work(&led_cdev->set_brightness_work);
 	led_blink_set(led_cdev, &led_cdev->blink_delay_on,
 		      &led_cdev->blink_delay_off);