NFS: File unlock needs to be a metadata synchronisation point

File unlock needs to update both data and metadata on the NFS server
in order to act as a synchronisation point for other clients.
Signed-off-by: Trond Myklebust <trond.myklebust@primarydata.com>

fs/nfs/file.c

@@ -780,7 +780,7 @@ do_unlk(struct file *filp, int cmd, struct file_lock *fl, int is_local)
 	 * Flush all pending writes before doing anything
 	 * with locks..
 	 */
-	nfs_sync_mapping(filp->f_mapping);
+	vfs_fsync(filp, 0);
 
 	l_ctx = nfs_get_lock_context(nfs_file_open_context(filp));
 	if (!IS_ERR(l_ctx)) {