How to setup a mysql slave server to works as a master for other servers

We can setup mysql server to be a slave and master at the same time.
However, slave updates will not be logged in master logs unless "log-slave-update" variable is set in my.cnf or via CHANGE MASTER TO statement

my.cnf:
[mysqld]
log-slave-update

or:
CHANGE MASTER TO --log-slave-update