nfsd4: allow space for final error return

This post-encoding check should be taking into account the need to
encode at least an out-of-space error to the following op (if any).

Reviewed-by: Christoph Hellwig <hch@lst.de>
Signed-off-by: J. Bruce Fields <bfields@redhat.com>

fs/nfsd/nfs4xdr.c

@@ -3636,6 +3636,7 @@ void
 nfsd4_encode_operation(struct nfsd4_compoundres *resp, struct nfsd4_op *op)
 {
 	struct nfs4_stateowner *so = resp->cstate.replay_owner;
+	struct svc_rqst *rqstp = resp->rqstp;
 	__be32 *statp;
 	nfsd4_enc encoder;
 	__be32 *p;
@@ -3652,8 +3653,12 @@ nfsd4_encode_operation(struct nfsd4_compoundres *resp, struct nfsd4_op *op)
 	encoder = nfsd4_enc_ops[op->opnum];
 	op->status = encoder(resp, op->status, &op->u);
 	/* nfsd4_check_resp_size guarantees enough room for error status */
-	if (!op->status)
-		op->status = nfsd4_check_resp_size(resp, 0);
+	if (!op->status) {
+		int space_needed = 0;
+		if (!nfsd4_last_compound_op(rqstp))
+			space_needed = COMPOUND_ERR_SLACK_SPACE;
+		op->status = nfsd4_check_resp_size(resp, space_needed);
+	}
 	if (op->status == nfserr_resource ||
 	    op->status == nfserr_rep_too_big ||
 	    op->status == nfserr_rep_too_big_to_cache) {