tracing: Allow dumping traces without tracking trace started cpus

We don't init iter->started when dumping the ftrace buffer, and there's no
real need to do so - so allow skipping that check if the iter doesn't have
an initialized ->started cpumask.

Link: http://lkml.kernel.org/r/1441385156-27279-1-git-send-email-sasha.levin@oracle.com

Signed-off-by: Sasha Levin <sasha.levin@oracle.com>
Signed-off-by: Steven Rostedt <rostedt@goodmis.org>

kernel/trace/trace.c

@@ -2671,13 +2671,14 @@ static void test_cpu_buff_start(struct trace_iterator *iter)
 	if (!(iter->iter_flags & TRACE_FILE_ANNOTATE))
 		return;
 
-	if (cpumask_test_cpu(iter->cpu, iter->started))
+	if (iter->started && cpumask_test_cpu(iter->cpu, iter->started))
 		return;
 
 	if (per_cpu_ptr(iter->trace_buffer->data, iter->cpu)->skipped_entries)
 		return;
 
-	cpumask_set_cpu(iter->cpu, iter->started);
+	if (iter->started)
+		cpumask_set_cpu(iter->cpu, iter->started);
 
 	/* Don't print started cpu buffer for the first entry of the trace */
 	if (iter->idx > 1)