+
+#ifdef CONFIG_FUNCTION_GRAPH_TRACER
+
+/* Maximum number of functions to trace before diagnosing a hang */
+#define GRAPH_MAX_FUNC_TEST 100000000
+
+static void __ftrace_dump(bool disable_tracing);
+static unsigned int graph_hang_thresh;
+
+/* Wrap the real function entry probe to avoid possible hanging */
+static int trace_graph_entry_watchdog(struct ftrace_graph_ent *trace)
+{
+ /* This is harmlessly racy, we want to approximately detect a hang */
+ if (unlikely(++graph_hang_thresh > GRAPH_MAX_FUNC_TEST)) {
+ ftrace_graph_stop();
+ printk(KERN_WARNING "BUG: Function graph tracer hang!\n");
+ if (ftrace_dump_on_oops)
+ __ftrace_dump(false);
+ return 0;
+ }
+
+ return trace_graph_entry(trace);
+}
+
+/*
+ * Pretty much the same than for the function tracer from which the selftest
+ * has been borrowed.
+ */
+int
+trace_selftest_startup_function_graph(struct tracer *trace,
+ struct trace_array *tr)
+{
+ int ret;
+ unsigned long count;
+
+ /*
+ * Simulate the init() callback but we attach a watchdog callback
+ * to detect and recover from possible hangs
+ */
+ tracing_reset_online_cpus(tr);
+ ret = register_ftrace_graph(&trace_graph_return,
+ &trace_graph_entry_watchdog);
+ if (ret) {
+ warn_failed_init_tracer(trace, ret);
+ goto out;
+ }
+ tracing_start_cmdline_record();
+
+ /* Sleep for a 1/10 of a second */
+ msleep(100);
+
+ /* Have we just recovered from a hang? */
+ if (graph_hang_thresh > GRAPH_MAX_FUNC_TEST) {
+ tracing_selftest_disabled = true;
+ ret = -1;
+ goto out;
+ }
+
+ tracing_stop();
+
+ /* check the trace buffer */
+ ret = trace_test_buffer(tr, &count);
+
+ trace->reset(tr);
+ tracing_start();
+
+ if (!ret && !count) {
+ printk(KERN_CONT ".. no entries found ..");
+ ret = -1;
+ goto out;
+ }
+
+ /* Don't test dynamic tracing, the function tracer already did */
+
+out:
+ /* Stop it if we failed */
+ if (ret)
+ ftrace_graph_stop();
+
+ return ret;
+}
+#endif /* CONFIG_FUNCTION_GRAPH_TRACER */
+
+