Update Linux to v5.4.2

Change-Id: Idf6911045d9d382da2cfe01b1edff026404ac8fd
diff --git a/arch/sparc/kernel/stacktrace.c b/arch/sparc/kernel/stacktrace.c
index be4c14c..d8eb1d1 100644
--- a/arch/sparc/kernel/stacktrace.c
+++ b/arch/sparc/kernel/stacktrace.c
@@ -1,3 +1,4 @@
+// SPDX-License-Identifier: GPL-2.0-only
 #include <linux/sched.h>
 #include <linux/sched/debug.h>
 #include <linux/stacktrace.h>
@@ -57,9 +58,11 @@
 			trace->entries[trace->nr_entries++] = pc;
 #ifdef CONFIG_FUNCTION_GRAPH_TRACER
 			if ((pc + 8UL) == (unsigned long) &return_to_handler) {
-				int index = t->curr_ret_stack;
-				if (t->ret_stack && index >= graph) {
-					pc = t->ret_stack[index - graph].ret;
+				struct ftrace_ret_stack *ret_stack;
+				ret_stack = ftrace_graph_get_ret_stack(t,
+								       graph);
+				if (ret_stack) {
+					pc = ret_stack->ret;
 					if (trace->nr_entries <
 					    trace->max_entries)
 						trace->entries[trace->nr_entries++] = pc;