nfsd: fix error handling in __write_ports_addxprt

__write_ports_addxprt calls nfsd_create_serv. That increases the
refcount of nfsd_serv (which is tracked in sv_nrthreads). The service
only decrements the thread count on error, not on success like
__write_ports_addfd does, so using this interface leaves the nfsd
thread count high.

Fix this by having this function call svc_destroy() on error to release
the reference (and possibly to tear down the service) and simply
decrement the refcount without tearing down the service on success.

This makes the sv_threads handling work basically the same in both
__write_ports_addxprt and __write_ports_addfd.
Signed-off-by: Jeff Layton <jlayton@redhat.com>
Signed-off-by: J. Bruce Fields <bfields@redhat.com>

fs/nfsd/nfsctl.c

@@ -1018,6 +1018,9 @@ static ssize_t __write_ports_addxprt(char *buf)
 				PF_INET6, port, SVC_SOCK_ANONYMOUS);
 	if (err < 0 && err != -EAFNOSUPPORT)
 		goto out_close;
+
+	/* Decrease the count, but don't shut down the service */
+	nfsd_serv->sv_nrthreads--;
 	return 0;
 out_close:
 	xprt = svc_find_xprt(nfsd_serv, transport, PF_INET, port);
@@ -1026,8 +1029,7 @@ static ssize_t __write_ports_addxprt(char *buf)
 		svc_xprt_put(xprt);
 	}
 out_err:
-	/* Decrease the count, but don't shut down the service */
-	nfsd_serv->sv_nrthreads--;
+	svc_destroy(nfsd_serv);
 	return err;
 }