update-manager hangs after click on technical description

[ThePhilips]

The GUI of update-manager to select updates to install keeps hanging for indefinite time with 100% CPU load (full single CPU core).

This is happening to me already since the 12.04 LTS times, and the behavior is more or less unchanged in 14.04 LTS.

Steps to reproduce:

0. There should be some updates available for update-manager to show the window with the update to be installed.
1. Click the "Details of updates" to display the list
2. Expand (for example) "*Ubuntu base" and click on some package in the list.
3. Click the "Technical description" to show the description.
4. Click again the "Technical description" to hide the description.
5. Click on some other package in the list.

Expected:
- The update manager reacts to the click and moves focus in the list to another package

Actual result:
- The update manager hangs (doesn't react to mouse/keyboard events) for indefinite time with 100% CPU load. Time of the blocking varies: from few seconds to up to a minute probably.

Just some general toggling of "Details of updates" and "Technical details", and clicking on different items in the list would cause the weird behavior to occur. (Eventually it would also cause the "Details of updates" to either stop showing the details or showing the details while making the update-manager window non-resizeable.)

[Mark (mark-k)]

Could this be the same issue as bug 1183672?

[TBeholder (turbobeholder)]

For me it doesn't hang completely, but freezes with 100% load on 1 CPU, often for minutes before showing details, and then does the same when another package is selected.
update-manager package v. 1:0.196.14

[Launchpad Janitor (janitor)]

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

[Mark (mark-k)]

Here's the comment I posted for bug 1183672:

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.