We tried to upgrade mongodb components from 2.2.1 to 2.2.2. (simply by kill & upgrade & start one by one component)
Several minutes after we killed the first config server, one of mongod began to report "Too many open files", and it crashed several minutes later.

The system's limit had already been set:
Limit Soft Limit Hard Limit Units
Max open files 65535 65535 files

I guess in this situation, mongod opens too many files/sockets and forget to close them.
Please look into the attachement, it contains full log from the time we kill the config server to the end.