tracing: keep the tracing buffer after self-test failure

Instead of using ftrace_dump_on_oops, it's far more convenient
to have the trace leading up to a self-test failure available
in /debug/tracing/trace.

Signed-off-by: Frederic Weisbecker <fweisbec@gmail.com>
Cc: Steven Rostedt <rostedt@goodmis.org>
LKML-Reference: <1237694675-23509-1-git-send-email-fweisbec@gmail.com>
Signed-off-by: Ingo Molnar <mingo@elte.hu>

kernel/trace/trace_selftest.c

@@ -299,7 +299,7 @@ trace_selftest_startup_function_graph(struct tracer *trace,
 
 	/* Have we just recovered from a hang? */
 	if (graph_hang_thresh > GRAPH_MAX_FUNC_TEST) {
-		trace->reset(tr);
+		tracing_selftest_disabled = true;
 		ret = -1;
 		goto out;
 	}