Child Git processes are not terminated cleanly, and keep piling up as zombie processes

Issue Summary

Multiple customers are seeing zombie (defunct) Git processes after an upgrade to 7.x (earliest affected version reported is 7.2.4). The parent process, as expected, is Bitbucket Server so the processes are cleaned only once Bitbucket Server is restarted.

Steps to Reproduce

Upgrade Bitbucket Server from a pre-7.x version to 7.x.

Expected Results

No zombie processes are seen, as they should be reaped by parent Bitbucket Server process on completion of the related Git operation/command.

Actual Results

Following type of processes are seen:

atlbitb+ 1523 3444 0 Nov28 ? 00:00:18 [git] <defunct>
atlbitb+ 1697 3444 0 Dec09 ? 00:00:37 [git] <defunct>
atlbitb+ 1807 3444 0 Nov28 ? 00:00:18 [git] <defunct>

Workaround

Only known workaround is to terminate the parent process. Hence, a restart of Bitbucket Server instance cleans up the zombie processes.