Sync MySql Replication from Master2 to Master1 after failover
As Master2 is in read-only;
Master2: SHOW MASTER STATUS
Master1:
CHANGE MASTER TO
MASTER_HOST = 'host_name'
MASTER_USER = 'user_name'
MASTER_PASSWORD = 'password'
MASTER_LOG_FILE = 'master_log_name'
MASTER_LOG_POS = master_log_pos;

START SLAVE;

Where the master log file name/pos are from the Master2 SHOW MASTER STATUS
The rapidly changing master status isn't an issue as its binary logs are from Master1 anyway. Master1 won't write its own binary log message back again when received via replication.