update-manager grabs major share of CPU&RAM when browsing list items

[TEN]

The moment e.g. "Header files to the Linux kernel version 3.2.0" or "Linux kernel headers vor version 3.2.0 on 32 bit x86 SMP" (-44 thereof, i.e. between second and subsequent kernel-related entries from the top today) is highlighted, update-manager 1:0.156.14.11 on Ubuntu 12.04.2 LTS deselects the item, reproducibly grabs 100% CPU, becomes barely responsive for minutes (on a 2.66 MHz Dual Core) and starts leaking memory (process had to be user-terminated when taking more than 30% of 2 GB). Neither delays nor excessive RAM consumption occur when moving the selection within the lower, non-kernel items of the update list.

[Launchpad Janitor (janitor)]

Status changed to 'Confirmed' because the bug affects multiple users.

[Mark (mark-k)]

I see this problem too. The amount of CPU time wasted seems to be proportional to the length of the package's changelog. A kernel package with very long changelog causes update-manager to hang using 100% CPU for a long time, whereas it only hangs very briefly if you click a package whose changelog is smaller.

This happens even if the user did not click "Technical description" so the changelog is not shown on-screen.

It's really annoying. Even if you're just un-checking boxes to deselect packages, you get the 100% CPU hang. (Try moving down the list un-checking several boxes quickly.)

To reproduce should be fairly easy:
- Run "top" (or some other load monitor) in a terminal.
- Run update-manager and wait until the list of available updates appears.
- Click the top item, then keep tapping cursor-down to move to the next one.
- If you hit an update with a long changelog (e.g. kernel package), notice that CPU usage goes to 100% for a long time.

[Marco B. (boro3k)]

Confirming this bug on Ubuntu 16.04, update-manager version 1:16.04.3.

The GUI hangs (greys out) for several seconds / a few minutes when selecting kernel items with a large changelog. Couldn't check the memory usage.