nfs: initialize the backing_dev_info when creating the server

NFS may free the server structure without ever having used the
bdi, so we either need to flag the bdi as being uninitialized or
initialize it up front. This does the latter.

This fixes a crash with mounting more than one NFS file system,
should people ever need that kind of obscure NFS functionality.
Tested-by: NPeter Zijlstra <a.p.zijlstra@chello.nl>
Acked-by: NTrond Myklebust <Trond.Myklebust@netapp.com>
Signed-off-by: NJens Axboe <jens.axboe@oracle.com>

fs/nfs/client.c

@@ -933,10 +933,6 @@ static int nfs_probe_fsinfo(struct nfs_server *server, struct nfs_fh *mntfh, str
 		goto out_error;
 
 	nfs_server_set_fsinfo(server, &fsinfo);
-	error = bdi_init(&server->backing_dev_info);
-	if (error)
-		goto out_error;
-
 
 	/* Get some general file system info */
 	if (server->namelen == 0) {
@@ -995,6 +991,12 @@ static struct nfs_server *nfs_alloc_server(void)
 		return NULL;
 	}
 
+	if (bdi_init(&server->backing_dev_info)) {
+		nfs_free_iostats(server->io_stats);
+		kfree(server);
+		return NULL;
+	}
+
 	return server;
 }