1 files changed, 37 insertions, 1 deletions

diff --git a/kernel/trace/trace_selftest.c b/kernel/trace/trace_selftest.c
index 38856ba78a92..b56dcf7d3566 100644
--- a/kernel/trace/trace_selftest.c
+++ b/kernel/trace/trace_selftest.c
@@ -248,6 +248,28 @@ trace_selftest_startup_function(struct tracer *trace, struct trace_array *tr)
 
 
 #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.
@@ -259,15 +281,29 @@ trace_selftest_startup_function_graph(struct tracer *trace,
         int ret;
         unsigned long count;
 
-        ret = tracer_init(trace, tr);
+        /*
+         * 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) {
+                trace->reset(tr);
+                ret = -1;
+                goto out;
+        }
+
         tracing_stop();
 
         /* check the trace buffer */