nfs41: fix session fore channel negotiation

If the rsize or wsize is not set on the mount command, negotiate the highest
supported rsize and wsize in session creation.

Fixes a bug where the client negotiated nfs41_maxwrite_overhead as
ca_maxrequestsize and nfs41_maxread_overhead as ca_maxresponsesize resulting
in NFS4ERR_REQ_TOO_BIG errors on writes.
Signed-off-by: Andy Adamson <andros@netapp.com>
Signed-off-by: Trond Myklebust <Trond.Myklebust@netapp.com>

fs/nfs/nfs4proc.c

@@ -4935,14 +4935,22 @@ int nfs4_init_session(struct nfs_server *server)
 {
 	struct nfs_client *clp = server->nfs_client;
 	struct nfs4_session *session;
+	unsigned int rsize, wsize;
 	int ret;
 
 	if (!nfs4_has_session(clp))
 		return 0;
 
+	rsize = server->rsize;
+	if (rsize == 0)
+		rsize = NFS_MAX_FILE_IO_SIZE;
+	wsize = server->wsize;
+	if (wsize == 0)
+		wsize = NFS_MAX_FILE_IO_SIZE;
+
 	session = clp->cl_session;
-	session->fc_attrs.max_rqst_sz = server->wsize + nfs41_maxwrite_overhead;
-	session->fc_attrs.max_resp_sz = server->rsize + nfs41_maxread_overhead;
+	session->fc_attrs.max_rqst_sz = wsize + nfs41_maxwrite_overhead;
+	session->fc_attrs.max_resp_sz = rsize + nfs41_maxread_overhead;
 
 	ret = nfs4_recover_expired_lease(server);
 	if (!ret)