Possible deadlock when using Puma
@theoretick encountered a 4:Deadline Exceeded error while using the web file editor. This might have been caused by a Puma deadlock.
This has also been discussed previously in https://gitlab.com/gitlab-org/gitlab-ce/issues/3592#note_38402981
https://github.com/puma/puma/issues/1433#issuecomment-376705628 describes a scenario where Puma may run into deadlocks. This looks similar to what we do with requests that call the internal API for git hooks. Somewhat related to: https://gitlab.com/gitlab-org/gitlab-ce/issues/18771