selftests/ftrace: Add max stack tracer testcase

Add a testcase for max stack tracer, which checks basic
max stack usage tracing and its filter feature.
Signed-off-by: Masami Hiramatsu <mhiramat@kernel.org>
Signed-off-by: Shuah Khan (Samsung OSG) <shuah@kernel.org>

tools/testing/selftests/ftrace/test.d/ftrace/func_stack_tracer.tc

+#!/bin/sh
+# SPDX-License-Identifier: GPL-2.0
+# description: ftrace - Max stack tracer
+# Test the basic function of max-stack usage tracing
+
+if [ ! -f stack_trace ]; then
+  echo "Max stack tracer is not supported - please make CONFIG_STACK_TRACER=y"
+  exit_unsupported
+fi
+
+echo > stack_trace_filter
+echo 0 > stack_max_size
+echo 1 > /proc/sys/kernel/stack_tracer_enabled
+
+: "Fork and wait for the first entry become !lock"
+timeout=10
+while [ $timeout -ne 0 ]; do
+  ( echo "forked" )
+  FL=`grep " 0)" stack_trace`
+  echo $FL | grep -q "lock" || break;
+  timeout=$((timeout - 1))
+done
+echo 0 > /proc/sys/kernel/stack_tracer_enabled
+
+echo '*lock*' > stack_trace_filter
+test `cat stack_trace_filter | wc -l` -eq `grep lock stack_trace_filter | wc -l`
+
+echo 0 > stack_max_size
+echo 1 > /proc/sys/kernel/stack_tracer_enabled
+
+: "Fork and always the first entry including lock"
+timeout=10
+while [ $timeout -ne 0 ]; do
+  ( echo "forked" )
+  FL=`grep " 0)" stack_trace`
+  echo $FL | grep -q "lock"
+  timeout=$((timeout - 1))
+done
+echo 0 > /proc/sys/kernel/stack_tracer_enabled