virtio/vhost: Use auto_rcu_read macros

Use RCU_READ_LOCK_GUARD instead of manual rcu_read_(un)lock

Signed-off-by: Dr. David Alan Gilbert <dgilbert@redhat.com>
Message-Id: <20191025103403.120616-2-dgilbert@redhat.com>
Reviewed-by: Michael S. Tsirkin <mst@redhat.com>
Signed-off-by: Michael S. Tsirkin <mst@redhat.com>

hw/virtio/vhost.c

@@ -924,7 +924,7 @@ int vhost_device_iotlb_miss(struct vhost_dev *dev, uint64_t iova, int write)
     uint64_t uaddr, len;
     int ret = -EFAULT;
 
-    rcu_read_lock();
+    RCU_READ_LOCK_GUARD();
 
     trace_vhost_iotlb_miss(dev, 1);
 
@@ -956,8 +956,6 @@ int vhost_device_iotlb_miss(struct vhost_dev *dev, uint64_t iova, int write)
     trace_vhost_iotlb_miss(dev, 2);
 
 out:
-    rcu_read_unlock();
-
     return ret;
 }