Try using machine credentials for RENEW calls

Using user credentials for RENEW calls will fail when the user
credentials have expired.

To avoid this, try using the machine credentials when making RENEW
calls. If no machine credentials have been set, fall back to using user
credentials as before.
Signed-off-by: NSachin Prabhu <sprabhu@redhat.com>
Signed-off-by: NTrond Myklebust <Trond.Myklebust@netapp.com>

fs/nfs/nfs4state.c

@@ -146,6 +146,11 @@ struct rpc_cred *nfs4_get_renew_cred_locked(struct nfs_client *clp)
 	struct rpc_cred *cred = NULL;
 	struct nfs_server *server;
 
+	/* Use machine credentials if available */
+	cred = nfs4_get_machine_cred_locked(clp);
+	if (cred != NULL)
+		goto out;
+
 	rcu_read_lock();
 	list_for_each_entry_rcu(server, &clp->cl_superblocks, client_link) {
 		cred = nfs4_get_renew_cred_server_locked(server);
@@ -153,6 +158,8 @@ struct rpc_cred *nfs4_get_renew_cred_locked(struct nfs_client *clp)
 			break;
 	}
 	rcu_read_unlock();
+
+out:
 	return cred;
 }