based on testing log-slave-updates, however, there is a problem with the way they log.
In my setup, I only enabled it on M1. M2 does not have it because:
that flag will write to binlog all the master and slave changes. since M1 and M2 are both master and slave... both of them will keep logging each other in an endless cycle.
unless someone can share a way to not write to binlog those queries you already writted to the slave binlog
or maybe i did something wrong?