Ubuntu – Firefox freezing with 100% CPU usage for 30 seconds when launching Chromium

chromiumfirefoxfontsperformance

Recently I started to observe this very confusing and annoying, not to say worrying behaviour when having Firefox open and then launching Chromium:

For around 30 seconds, Firefox' child processes would consume all available CPU resources, causing websites to stop render (already displayed page freezes, new pages show a white page with grey spinning circle) while the overall window is still responsive (menus, page scrolling, switching tabs, even internal pages like about:config or about:preferences work…). Chromium itself does not show any symptoms. Terminating Chromium again immediately, while Firefox is spinning, does not stop the behaviour any faster.

The same happens with my regular Firefox profile, a brand new, untouched Firefox profile without any add-ons etc., Firefox started in safe mode with add-ons disabled, and Firefox started in private mode. Similar for Chromium, I can launch it with my regular profile, in incognito mode or with a temporary profile, always generating the same results.

There is nothing odd happening when Chromium is running and I open Firefox.

When launching Firefox from a terminal, I sometimes get messages like these when I quit it while it is spinning (note the pipe error line mentioning some chromium ipc…):

ExceptionHandler::GenerateDump cloned child 32165
ExceptionHandler::SendContinueSignalToChild sent continue signal to child
ExceptionHandler::WaitForContinueSignal waiting for continue signal...
[Parent 26520, Gecko_IOThread] WARNING: pipe error (52): Connection reset by peer: file /build/firefox-8oo9jx/firefox-62.0+build2/ipc/chromium/src/chrome/common/ipc_channel_posix.cc, line 353
ExceptionHandler::GenerateDump cloned child 32274
ExceptionHandler::WaitForContinueSignal waiting for continue signal...
ExceptionHandler::SendContinueSignalToChild sent continue signal to child

Strangely I could not reproduce that behaviour in a guest account or a newly created regular (admin) account.

Some system specs (updated):

  • Ubuntu 16.04 (64 bit)
  • Firefox 62.0+build2-0ubuntu0.16.04.5 63.0+build2-0ubuntu0.16.04.2
  • Chromium 69.0.3497.81-0ubuntu0.16.04.1 70.0.3538.77-0ubuntu0.16.04.1
  • fontconfig 2.11.94-0ubuntu1.1
  • Graphics hardware: Intel SkyLake integrated graphics (i5-6200U) + Nvidia GeForce 940M
    Currently I have the nvidia-410 driver installed, but switched to the Intel prime profile.
    How can I further troubleshoot and fix this issue?

I made a performance profile with the Gecko Profiler Extension, installed to a clean fresh Firefox profile on my regular Ubuntu account. It can be found here: https://perfht.ml/2zpTWsh – The unresponsive time frame with 100% CPU usage should roughly correspond to the highlighted area on the Content Proc timelines, from roughly 18s – 56s.

I created a Mozilla bug report for this issue: https://bugzilla.mozilla.org/show_bug.cgi?id=1504461

Important update: Apparently my bug report was a duplicate of https://bugzilla.mozilla.org/show_bug.cgi?id=1495900, which points out fontconfig as the culprit. Seems like starting Chromium is making a change in the font configuration somehow, which triggers a complete reload in Firefox. This fits the performance profiling report, and also aligns with how former updates to font packages have triggered the same kind of freeze.

Any ideas how I can make the three (Firefox, Chromium, fontconfig) behave nicely along each other?

Best Answer

TL;DR: It's an issue with fontconfig before version 2.13. It can be fixed by upgrading the package to 2.13 or higher (though I couldn't find a suitable provider). Alternatively, examine all your fonts-related folders and config files in your home directory and test if removing any of them resolves your issue. For me, renaming ~/.fonts did the trick.

After learning about the bug reports https://bugzilla.mozilla.org/show_bug.cgi?id=1495900 and https://bugzilla.mozilla.org/show_bug.cgi?id=1411338 it becomes rather clear that the problem must be caused by fontconfig.

Somehow when Chromium starts, it triggers a change in the fonts database (???), which causes Firefox - if currently running - to re-scan the file system for fonts somehow, resulting in the CPU usage and temporary freeze.

Apparently updating the fontconfig package from version 2.11 to 2.13 (the version shipped e.g. in Ubuntu 18.10) should fix the issue, but I found no easy way to get that version on 16.04, without breaking dependencies of lots of other packages I have installed.

So as the issue is limited to my user account, I examined my user's local font configuration and folders. There's quite a mess of different font-related directories to be honest, including ~/.fonts, ~/.local/share/fonts, ~/.local/share-font-manager, ~/.config/font-manager, ~/.cache/font-manager, ~/.cache/fontconfig and a few more config files and application-specific font stuff.

I started by removing (renaming) the ~/.fonts folder, as it didn't seem to contain anything useful anyway, and a simple touch ~/.fonts/Library/ before that triggered the Firefox misbehaviour. After that folder was gone, so was the issue when launching Chromium. \o/

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