Socialist Views on Religion?

What are the socialist views on religion itself, IE believing in Jesus, Muhammad, Abraham, Zeus, Jupiter, Odin, Quetzalcoatl, Brahma, Buddha, etc? The socialist views on traditions such as Easter, Yule, Hanukkah, Christmas, Eid Al-Adha, Lughsanadh, Disablot, Halloween, and so forth? From what I know the Soviet Union in particular kept some traditions but killed the beliefs; they moved Russian Christmas to New Years.