From 0cc44098451b87275958ad203826499e590826b4 Mon Sep 17 00:00:00 2001
From: Andrew Tridgell <andrew@tridgell.net>
Date: Sat, 13 Feb 2021 09:36:04 +1100
Subject: [PATCH] HAL_ChibiOS: fixed handling of invalid channel for LED write

this prevents a null ptr dereference when an invalid channel (such as
one on IOMCU) is used for LEDs
---
 libraries/AP_HAL_ChibiOS/RCOutput.cpp | 4 ++--
 1 file changed, 2 insertions(+), 2 deletions(-)

diff --git a/libraries/AP_HAL_ChibiOS/RCOutput.cpp b/libraries/AP_HAL_ChibiOS/RCOutput.cpp
index 39f48b5a91..0875a27309 100644
--- a/libraries/AP_HAL_ChibiOS/RCOutput.cpp
+++ b/libraries/AP_HAL_ChibiOS/RCOutput.cpp
@@ -1979,12 +1979,12 @@ void RCOutput::set_serial_led_rgb_data(const uint16_t chan, int8_t led, uint8_t
     uint8_t i = 0;
     pwm_group *grp = find_chan(chan, i);
 
-    WITH_SEMAPHORE(grp->serial_led_mutex);
-
     if (!grp || grp->serial_nleds == 0) {
         return;
     }
 
+    WITH_SEMAPHORE(grp->serial_led_mutex);
+
     if (led == -1) {
         grp->prepared_send = true;
         for (uint8_t n=0; n<grp->serial_nleds; n++) {