ring-buffer: do not swap buffers during a commit

If a commit is taking place on a CPU ring buffer, do not allow it to
be swapped. Return -EBUSY when this is detected instead.
Signed-off-by: Steven Rostedt <rostedt@goodmis.org>

kernel/trace/ring_buffer.c

@@ -3519,16 +3519,23 @@ int ring_buffer_swap_cpu(struct ring_buffer *buffer_a,
 	atomic_inc(&cpu_buffer_a->record_disabled);
 	atomic_inc(&cpu_buffer_b->record_disabled);
 
+	ret = -EBUSY;
+	if (local_read(&cpu_buffer_a->committing))
+		goto out_dec;
+	if (local_read(&cpu_buffer_b->committing))
+		goto out_dec;
+
 	buffer_a->buffers[cpu] = cpu_buffer_b;
 	buffer_b->buffers[cpu] = cpu_buffer_a;
 
 	cpu_buffer_b->buffer = buffer_a;
 	cpu_buffer_a->buffer = buffer_b;
 
+	ret = 0;
+
+out_dec:
 	atomic_dec(&cpu_buffer_a->record_disabled);
 	atomic_dec(&cpu_buffer_b->record_disabled);
-
-	ret = 0;
 out:
 	return ret;
 }