virtio: fix suspend when using virtio_balloon

Break out of wait_event_interruptible() if freezing has been requested,
in the vballoon thread. Without this change vballoon refuses to stop and
the system can't suspend.
Signed-off-by: NMarcelo Tosatti <mtosatti@redhat.com>
Signed-off-by: NRusty Russell <rusty@rustcorp.com.au>
Cc: stable@kernel.org

drivers/virtio/virtio_balloon.c

@@ -190,7 +190,8 @@ static int balloon(void *_vballoon)
 		try_to_freeze();
 		wait_event_interruptible(vb->config_change,
 					 (diff = towards_target(vb)) != 0
-					 || kthread_should_stop());
+					 || kthread_should_stop()
+					 || freezing(current));
 		if (diff > 0)
 			fill_balloon(vb, diff);
 		else if (diff < 0)