17.10->18.04 LTS hangs, CPU stalls in apt-pkg cache

When I do as root:

do-release-upgrade

The bionic tarball is downloaded and the python based "bionic" process is forked. On the screen I see the first "Reading cache..." message and then the process spikes the CPU to 100% where it stays there forever (I waited 15-20 minutes and there was no change in CPU state).

Here is the dist-upgrade log file:
2018-05-14 07:17:19,308 INFO uname information: 'Linux kitt 4.13.0-41-generic #46-Ubuntu SMP Wed May 2 13:38:30 UTC 2018 x86_64'
2018-05-14 07:17:19,594 INFO apt version: '1.5.1'
2018-05-14 07:17:19,594 INFO python version: '3.6.3 (default, Oct 3 2017, 21:45:48)
[GCC 7.2.0]'
2018-05-14 07:17:19,596 INFO release-upgrader version '18.04.17' started
2018-05-14 07:17:19,600 INFO locale: 'en_US' 'UTF-8'
2018-05-14 07:17:19,605 INFO screen could not be run
2018-05-14 07:17:19,744 DEBUG Using 'DistUpgradeViewText' view
2018-05-14 07:17:19,788 DEBUG enable dpkg --force-overwrite
2018-05-14 07:17:19,817 DEBUG creating statefile: '/var/log/dist-upgrade/apt-clone_system_state.tar.gz'

strace output of the "bionic" process:

$ sudo strace -f -p 6469
strace: Process 6469 attached with 3 threads
[pid 6546] restart_syscall(<... resuming interrupted poll ...> <unfinished ...>
[pid 6547] restart_syscall(<... resuming interrupted poll ...>strace: [ Process PID=6469 runs in x32 mode. ]

top output:
   PID USER PR NI VIRT RES SHR S %CPU %MEM TIME+ COMMAND
  6469 root 20 0 270048 33108 15728 R 99.7 0.1 0:38.85 bionic
  6555 pisymbol 20 0 46736 4376 3344 R 0.7 0.0 0:00.04 top

Looking at this further, it seems that the installer sets the the "rootdir=/" when it initiates the python-apt's Cache class. This hangs. I can reproduce this by simply changing it's test code to pass rootdir="/" and it hangs. It sorta smells like a deadlock issue though deep in the C++ module (apt_pkg) that backs the python one (GetLock?). But I'm not 100% sure.

This behavior is seen on my 32-core Threadripper machine (AMD64).

This is 17.10 latest with:

$ dpkg -l python-apt libapt-pkg5.0
Desired=Unknown/Install/Remove/Purge/Hold
| Status=Not/Inst/Conf-files/Unpacked/halF-conf/Half-inst/trig-aWait/Trig-pend
|/ Err?=(none)/Reinst-required (Status,Err: uppercase=bad)
||/ Name Version Architecture Description
+++-==============================================-============================-============================-=================================================================================================
ii libapt-pkg5.0:amd64 1.5.1 amd64 package management runtime library
ii python-apt 1.4.0~beta3build2 amd64 Python interface to libapt-pkg