Validate GitLab CI/CD configuration times out with error 500

Summary

Validation of some GitLab CI/CD configurations can cause the API to return 500 errors after timing out. When visiting the validation page, the validation fails with:

Unable to validate CI/CD configuration. See the GitLab CI/CD troubleshooting guide for more details.

Steps to reproduce

Go to <some project with invalid config, see internal note below because path is sensitive>
The request will hang and timeout after 40s with a 500 response.

{
message: "500 Internal Server Error"
}

What is the current bug behavior?

500 error. This is new, as this API endpoint was fine last week (the CI/CD config was not valid though).

What is the expected correct behavior?

200 response with CI/CD linted config

Relevant logs and/or screenshots

Output of checks

This bug happens on GitLab.com

Results of GitLab environment info

Expand for output related to GitLab environment info


(For installations with omnibus-gitlab package run and paste the output of:
`sudo gitlab-rake gitlab:env:info`)

(For installations from source run and paste the output of:
`sudo -u git -H bundle exec rake gitlab:env:info RAILS_ENV=production`)

Results of GitLab application Check

Expand for output related to the GitLab application check

(For installations with omnibus-gitlab package run and paste the output of:
sudo gitlab-rake gitlab:check SANITIZE=true)
(For installations from source run and paste the output of:
sudo -u git -H bundle exec rake gitlab:check RAILS_ENV=production SANITIZE=true)
(we will only investigate if the tests are passing)