mate-appearance-properties segfaults on font-tab in certain cases (Ambience + Terminus)

[RichardNeill]

Under certain circumstances, the Mate-Control-Center Appearance window simply segfaults when the font-tab is chosen.
Here is how to reproduce it (and work-around it).

1. Always open mate-appearance-properties from the CLI, rather than the control-center - just to see the error message. When it does crash, it always gives this line:

mate-appearance-properties: ../../../../src/cairo-scaled-font.c:459: _cairo_scaled_glyph_page_destroy: Assertion `!scaled_font->cache_frozen' failed.
Aborted (core dumped)

2. To get back into a good state, (i.e. so that opening the font control allows us to use it, rather than crash), do the following:

- Open appearance-properties
- Select one of the "good" themes. Experimentally, these include BlueMenta, Quid, Fog, AlaDelta
- Go to the fonts tab (it doesn't now crash)
- Close appearance-properties window.

3. To make it crash:

- Open appearance-properties
- Select one of the "bad" themes. Experimentally, these include Ambiance, Ambiant-Mate, Radiance, Radiant-Mate
- Go to the fonts tab (it doesn't (usually) crash this time)
- Close appearance-properties window.
- Open the appearance-properties window again
- Go to the fonts tab (it doesn't (usually) crash this time)
- It will segfault instantly.

I looked into specific cases that upset it, and the crash only happens on certain choices of Fixed-width font:

- Terminus (my favourite for years) causes the crash (various font sizes: 6,9,17 all do)
- The others, don't seem to: I tried: Ubuntu Mono, Ubuntu Condensed, Monospaced, Courier, Courier 10 Pitch, Courier New,

in other words, the following will cause a segfault: all conditions are necessary

* One of the Ambience-derived themes
* The monospace-font being set to Terminus
* Opening the font-tab of mate-appearance-properties for the second time after setting the theme.

I have these packages, running under Ubuntu Mate, on Wily 64-bit:
libfreetype6:amd64 2.5.2-4ubuntu1
mate-control-center 1.8.3+dfsg1-2
xfonts-terminus 4.39-1
libcairo2:amd64 1.14.2-2ubuntu1 (this is also the latest release from upstream)

This is perhaps the weirdest bug I've ever tracked down... so I hope I've given enough info to get this fixed.

[RichardNeill (ubuntu-richardneill)]

Still present as of latest update in Wily, on 6/Aug/2015.

I noticed that when reading my instructions to replicate this bug, I copy-pasted a line which doesn't make sense. The paragraph 3 should read:

3. To make it crash:
- Open appearance-properties
- Select one of the "bad" themes. Experimentally, these include Ambiance, Ambiant-Mate, Radiance, Radiant-Mate
- Go to the fonts tab (it doesn't (usually) crash this time)
- Close appearance-properties window.
- Open the appearance-properties window again
- Go to the fonts tab
- It will segfault instantly.

Perhaps this should have been filed upstream, as nobody has reacted to this report, so I've re-filed it here:
https://github.com/mate-desktop/mate-control-center/issues/175

[Stephen Boddy (stephen-j-boddy)]

See https://bugs.launchpad.net/ubuntu/+source/terminator/+bug/1294699 for an earlier instance of this same issue, and details of an upstream (cairo) bug report that is getting no attention for now.

[Launchpad Janitor (janitor)]

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

[Martin Wimpress  (flexiondotorg)]

Please can you test this in Ubuntu MATE 16.04 Beta 2, this issue should be resolved.

[Launchpad Janitor (janitor)]

[Expired for mate-control-center (Ubuntu) because there has been no activity for 60 days.]