V4L/DVB (6276): V4L: videobuf-core.c lock before streaming check

The reading/streaming fields are used for mutual exclusion of the queue and
should be protected by the queue lock.

Signed-off-by: Brandon Philips <bphilips@suse.de>
Signed-off-by: Mauro Carvalho Chehab <mchehab@infradead.org>
http://thread.gmane.org/gmane.comp.video.video4linux/34978/focus=34981
Reviewed-by: Ricardo Cerqueira <v4l@cerqueira.org>

drivers/media/video/videobuf-core.c

@@ -289,16 +289,18 @@ int videobuf_reqbufs(struct videobuf_queue *q,
 		return -EINVAL;
 	}
 
+	mutex_lock(&q->lock);
 	if (q->streaming) {
 		dprintk(1,"reqbufs: streaming already exists\n");
-		return -EBUSY;
+		retval = -EBUSY;
+		goto done;
 	}
 	if (!list_empty(&q->stream)) {
 		dprintk(1,"reqbufs: stream running\n");
-		return -EBUSY;
+		retval = -EBUSY;
+		goto done;
 	}
 
-	mutex_lock(&q->lock);
 	count = req->count;
 	if (count > VIDEO_MAX_FRAME)
 		count = VIDEO_MAX_FRAME;