How to take mysql replication backup

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http://serverfault.com – I have a MySQL master-master replication setup with a slave for each master(only one master used for read/writes at a time) on Ubuntu server. Wondering what would be the best way to schedule backup of replication databases with mysqldump. I have following clarifications because of which could not proceed further. Scheduling mysqldump backup on masters safe for replication? Connecting masters with GUI applications(workbench) for database manipulations(read, writes.. by developers) is safe? Any inputs are welcome. (HowTos)