This post does not discuss mutexes or latches. I wrote it under the impression of recent escalation due to database corruption.
This was Oracle 10.2.0.4 database on HP-UX. Database files underwent recurrent corruption. Most commonly blocks were corrupted in system and undo tablespaces. This resulted in corrupted dictionary tables and indexes. Neither db_block_checking/db_block_checksum nor installation of latest PSU and OS patches helped. SCNs showed that these dictionary blocks were not changed for years. It looks likes some program other than DBWR overwrites the blocks. Corruptions caused downtimes to restore and recover datafiles.