Comment 10 for bug 571682

It was not fixed for me as of 6/18/10 with the latest updates.
The following script seems to fix the tmp issue for me. It is a workaround though and not a fix. I've rebooted 10 times in a row and it is still mounting /dev/mapper/crypttmp on /tmp without hanging up the system.
I changed the stock /etc/init/mountall.conf script by commenting out the emits filesystem line. This is on Ubuntu 10.04 LTS.
My custom script called cryptdisks-tmp.conf, placed under /etc/init, has the following lines:
# cryptdisks-tmp - setup encrypted /tmp/device
#
# This is designed simply to setup and encrypted tmp device under
# /dev/mapper called crypttmp and then mount it on tmp.
# This requires a noauto entry in the fstab for the /tmp mount

# Also no crypttab entry is required to setup /dev/mapper/crypttmp
# as all that is taken care of in this script.
# Basically I commented out the "emit filesystem" section in
# /etc/init/mountall.conf, then created this script.
# This script will start once mountall is started and it will emit
# the filesystem emitter
# This will cause most other upstart jobs, which look for the filesystem
# emmitter not to start until this script is done.
# So I think it may fix the /tmp issue
# Also since the code is in a script, I think that the script must finish
# before the filesystem event is emitted. Someone please correct me if I
# am wrong about this.
#
description "script to setup encrypted /tmp to try to bypass race condition"

start on started mountall
emits filesystem
console output
task

script
  if [ -e /dev/mapper/crypttmp ]; then
    echo "For some reason /dev/mapper/crypttmp exists. Bailing out."
    exit 1
  fi
  if mount | grep /tmp > /dev/null 2>&1; then
    echo "/tmp directory is already mounted. Bailing out."
    exit 1
  fi
  ## Now we can proceed to create the /dev/mapper/crypttmp device and mount it.
  if ! cryptsetup create crypttmp /dev/sda3 --key-file=/dev/urandom > /dev/null 2>&1; then
    echo "Failed to create /dev/mapper/crypttmp on /dev/sda3. Bailing out."
    exit 1
  fi
  # Now we need to make the ext2 filesystem on /dev/mapper/crypttmp
  if ! mkfs.ext2 /dev/mapper/crypttmp > /dev/null 2>&1; then
    echo "Create ext2 filesystem on /dev/mapper/crypttmp failed. Bailing out."
    exit 1
  fi
  # We have an fstab entry with noauto in it, so mount /dev/mapper/crypttmp
  if ! mount /dev/mapper/crypttmp > /dev/null 2>&1; then
    echo "Failed to mount /dev/mapper/crypttmp on /tmp. Bailing out."
    exit 1
  else
    echo "/dev/mapper/crypttmp is mounted"
  fi
end script