selftests/ftrace: Fix eventfs ownership testcase to find mount point

Fix eventfs ownership testcase to find mount point if stat -c "%m" failed.
This can happen on the system based on busybox. In this case, this will
try to use the current working directory, which should be a tracefs top
directory (and eventfs is mounted as a part of tracefs.)
If it does not work, the test is skipped as UNRESOLVED because of
the environmental problem.

Fixes: ee9793b ("tracing/selftests: Add ownership modification tests for eventfs")
Signed-off-by: Masami Hiramatsu (Google) <mhiramat@kernel.org>
Acked-by: Steven Rostedt (Google) <rostedt@goodmis.org>
Signed-off-by: Shuah Khan <skhan@linuxfoundation.org>

tools/testing/selftests/ftrace/test.d/00basic/test_ownership.tc

@@ -6,6 +6,18 @@ original_group=`stat -c "%g" .`
 original_owner=`stat -c "%u" .`
 
 mount_point=`stat -c '%m' .`
+
+# If stat -c '%m' does not work (e.g. busybox) or failed, try to use the
+# current working directory (which should be a tracefs) as the mount point.
+if [ ! -d "$mount_point" ]; then
+	if mount | grep -qw $PWD ; then
+		mount_point=$PWD
+	else
+		# If PWD doesn't work, that is an environmental problem.
+		exit_unresolved
+	fi
+fi
+
 mount_options=`mount | grep "$mount_point" | sed -e 's/.*(\(.*\)).*/\1/'`
 
 # find another owner and group that is not the original