vhost: check owner before we overwrite ubuf_info

If device has an owner, we shouldn't touch ubuf_info
since it might be in use.
Signed-off-by: Michael S. Tsirkin <mst@redhat.com>
Signed-off-by: David S. Miller <davem@davemloft.net>

drivers/vhost/net.c

@@ -1054,6 +1054,10 @@ static long vhost_net_set_owner(struct vhost_net *n)
 	int r;
 
 	mutex_lock(&n->dev.mutex);
+	if (vhost_dev_has_owner(&n->dev)) {
+		r = -EBUSY;
+		goto out;
+	}
 	r = vhost_net_set_ubuf_info(n);
 	if (r)
 		goto out;

drivers/vhost/vhost.c

@@ -343,6 +343,12 @@ static int vhost_attach_cgroups(struct vhost_dev *dev)
 	return attach.ret;
 }
 
+/* Caller should have device mutex */
+bool vhost_dev_has_owner(struct vhost_dev *dev)
+{
+	return dev->mm;
+}
+
 /* Caller should have device mutex */
 long vhost_dev_set_owner(struct vhost_dev *dev)
 {
@@ -350,7 +356,7 @@ long vhost_dev_set_owner(struct vhost_dev *dev)
 	int err;
 
 	/* Is there an owner already? */
-	if (dev->mm) {
+	if (vhost_dev_has_owner(dev)) {
 		err = -EBUSY;
 		goto err_mm;
 	}

drivers/vhost/vhost.h

@@ -133,6 +133,7 @@ struct vhost_dev {
 
 long vhost_dev_init(struct vhost_dev *, struct vhost_virtqueue **vqs, int nvqs);
 long vhost_dev_set_owner(struct vhost_dev *dev);
+bool vhost_dev_has_owner(struct vhost_dev *dev);
 long vhost_dev_check_owner(struct vhost_dev *);
 struct vhost_memory *vhost_dev_reset_owner_prepare(void);
 void vhost_dev_reset_owner(struct vhost_dev *, struct vhost_memory *);