Hang/Slow Test

The attached test case causes the browser to become unresponsive for more than a short period of time.

Why is this a problem?

Temporary unresponsiveness or complete hangs have a negative impact on the user experience. These issues also have a negative impact on the efficiency and effectiveness of test suites and fuzzers.

False Positive?

Fuzzers can generate unrealistic test cases which for example may pass large values to APIs leading to slow downs or hangs. Please review the code in question to verify no further optimizations can be made and reasonable limits are in place.

Details

To reproduce the issue with Grizzly:
python3 -m grizzly.replay <browser-bin> testcase.html --ignore memory -t 60

A Pernosco session is available here: https://pernos.co/debug/WycaIHsmnZ-JDTfiJ6xg2Q/index.html

In this trace SIGABRT is sent to the busiest process.

The performance problem seems to arise because the testcase has an extremely long dashed line, which cairo spends a lot of time processing even though most of it will be outside the rendered area of the page. So more of a Graphics than Layout issue, I think.

This reminds me of things we've seen before, actually; e.g. bug 1123019 (which was a Core Graphics-related version of a similar thing).

However, before considering possible mitigations, the first thing to check would be whether the issue still occurs with cairo 1.17.4, which we're hoping to take as an update to the very old version we have in the tree. It's possible the performance there may have changed.

This appears to have been fixed by bug 739096. Thanks Jonathan!