virtio_console: verify if queue is broken after virtqueue_get_buf()

If virtqueue_get_buf() returns with a NULL pointer it should be verified
if the virtqueue is broken, in order to avoid loop calling cpu_relax().

Signed-off-by: Heinz Graalfs <graalfs@linux.vnet.ibm.com>
Signed-off-by: Rusty Russell <rusty@rustcorp.com.au>

drivers/char/virtio_console.c

@@ -577,7 +577,8 @@ static ssize_t __send_control_msg(struct ports_device *portdev, u32 port_id,
 	spin_lock(&portdev->c_ovq_lock);
 	if (virtqueue_add_outbuf(vq, sg, 1, &cpkt, GFP_ATOMIC) == 0) {
 		virtqueue_kick(vq);
-		while (!virtqueue_get_buf(vq, &len))
+		while (!virtqueue_get_buf(vq, &len)
+			&& !virtqueue_is_broken(vq))
 			cpu_relax();
 	}
 	spin_unlock(&portdev->c_ovq_lock);
@@ -650,7 +651,8 @@ static ssize_t __send_to_port(struct port *port, struct scatterlist *sg,
 	 * we need to kmalloc a GFP_ATOMIC buffer each time the
 	 * console driver writes something out.
 	 */
-	while (!virtqueue_get_buf(out_vq, &len))
+	while (!virtqueue_get_buf(out_vq, &len)
+		&& !virtqueue_is_broken(out_vq))
 		cpu_relax();
 done:
 	spin_unlock_irqrestore(&port->outvq_lock, flags);