Comment 9 for bug 1365095

OK, we tracked it down to a race between the fork in lightdm's session-child code and the cgroups being assigned to the process.

If it took too long for the cgroups to be assigned, the session would have already been spawned and only the "lightdm --session-child" process would have the right cgroups, but the session itself wouldn't. But if the cgroups got assigned before the fork, they would be inherited correctly.

The bug was in systemd-shim, which made an async call. Which meant that PAM might return before cgroups were assigned, which meant the race. desrt is going to fix it by just making that call sync.