ring-buffer: do not swap if recording is disabled

If the ring buffer recording has been disabled. Do not let
swapping of ring buffers occur. Simply return -EAGAIN.

Signed-off-by: Steven Rostedt <srostedt@redhat.com>
Signed-off-by: Ingo Molnar <mingo@elte.hu>
diff --git a/kernel/trace/trace.c b/kernel/trace/trace.c
index 220c264..757ae6f 100644
--- a/kernel/trace/trace.c
+++ b/kernel/trace/trace.c
@@ -415,7 +415,7 @@
 
 	ftrace_enable_cpu();
 
-	WARN_ON_ONCE(ret);
+	WARN_ON_ONCE(ret && ret != -EAGAIN);
 
 	__update_max_tr(tr, tsk, cpu);
 	__raw_spin_unlock(&ftrace_max_lock);