Update Linux to v5.4.2

Change-Id: Idf6911045d9d382da2cfe01b1edff026404ac8fd
diff --git a/samples/bpf/trace_event_user.c b/samples/bpf/trace_event_user.c
index d08046a..16a16ea 100644
--- a/samples/bpf/trace_event_user.c
+++ b/samples/bpf/trace_event_user.c
@@ -1,8 +1,5 @@
+// SPDX-License-Identifier: GPL-2.0-only
 /* Copyright (c) 2016 Facebook
- *
- * This program is free software; you can redistribute it and/or
- * modify it under the terms of version 2 of the GNU General Public
- * License as published by the Free Software Foundation.
  */
 #include <stdio.h>
 #include <unistd.h>
@@ -34,6 +31,11 @@
 	if (!addr)
 		return;
 	sym = ksym_search(addr);
+	if (!sym) {
+		printf("ksym not found. Is kallsyms loaded?\n");
+		return;
+	}
+
 	printf("%s;", sym->name);
 	if (!strcmp(sym->name, "sys_read"))
 		sys_read_seen = true;