Comment 2 for bug 711635

I can confirm this behavior. To reproduce, I did:
 * launch ec2 instance (ami-fa01f193 us-east-1 ubuntu-lucid-10.04-amd64-server-20110201.1)
 * disable lucid-updates
 * sudo apt-get update && sudo apt-get install mysql-server-5.1
 * modify /etc/apparmor.d/usr.sbin.mysqld, adding hashes to the two lines below:
  # /var/lib/mysql/ r,
  # /var/lib/mysql/** rwk,
 * enable -updates
 * sudo apt-get update && sudo apt-get dist-upgrade
 * system hangs on:
   Setting up mysql-server-core-5.1 (5.1.41-3ubuntu12.9) ...
   Setting up mysql-server-5.1 (5.1.41-3ubuntu12.9) ...
   Installing new version of config file /etc/init/mysql.conf ...

These 4 processes are running:
 7476 pts/2 Ss+ 0:00 /usr/bin/dpkg --status-fd 14 --configure libmysqlclient16 mysql-client-core-5.1 mysql-client-5.1 mysql-server-core-5.1 mysql-server-5.1
 7486 pts/2 S+ 0:00 /usr/bin/perl -w /usr/share/debconf/frontend /var/lib/dpkg/info/mysql-server-5.1.postinst configure 5.1.41-3ubuntu12.7
 7496 pts/2 S+ 0:00 /bin/bash -e /var/lib/dpkg/info/mysql-server-5.1.postinst configure 5.1.41-3ubuntu12.7
 7703 pts/2 S+ 0:00 start mysql

because you commented out the lines in the config file, mysql cannot access /var/lib/mysql. I suspect you have app armour messages in your dmesg indicating this.

I'm not sure if I should call this bug invalid or confirmed.