This happened on Centos for no apparent reason with no obvious issue in the logs. Data could be read fine but not written (possibly due to some corruption or out of memory issue in the OpenVZ container is the best guess).
All mysql update and insert queries failed freezing without any error log on any database and table.
Tried to restart:
service mysqld restart
Timeout error occurred trying to stop MySQL........
# Disabling symbolic-links is recommended to prevent assorted security risks
The key is "bind-address", set that to 127.0.0.1 and no one from outside the server can connect.........