Even though our configuration is different (we are using a 5.4.5-1~dotdeb.0 build of php5-fpm on Ubuntu 12.04 LTS that has been upgraded from previous LTS releases), we have been encountering this identical hang issue, same syscall, and other symptoms.
We were able to temporarily address the issue by removing the php5-imap module from our environment, so this looks like it could be a result of dependency issue. Happy to contribute if we find out more.
