On RHEL5.7: XFS filesystem causes machine to hang with 'INFO: task pdflush:XXX blocked for more than 120 seconds.'

Issue

• Periodically a system will crash with the following INFO message in /var/log/messages:

Feb 16 00:04:03 hostname kernel: INFO: task pdflush:442 blocked for more than 120 seconds.
Feb 16 00:04:03 hostname kernel: "echo 0 > /proc/sys/kernel/hung_task_timeout_secs" disables this message.
Feb 16 00:04:03 hostname kernel: pdflush       D ffffffff80154dc2     0   442    147           443   440 (L-TLB)

• The machine will then begin to exhaust memory and hang until a forced reboot temporarily clears the issue. All I/O on the machine will come to a halt during the hang.