cgroups: handle the cgroup v1 release_agent race - #1058
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The asynchronous release agent may remove an empty service cgroup after mkdir succeeds but before openrc-run writes the current process to its tasks file. The write then fails with ENOENT or ENODEV, leaving the service outside its per-service cgroup. Retry the complete create-and-attach operation. Once the tasks write succeeds, the populated cgroup can no longer be removed by the release agent. Fixes: OpenRC#90
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While cgroup v1 support is not dropped, I think it's a good idea to fix the old-standing bug #90
The source for the problem is visible: release_agent works asynchronously and may remove an empty service cgroup after mkdir succeeds but before openrc-run writes the current process to its tasks file. The write then fails with ENOENT or ENODEV, leaving the service outside its per-service cgroup.
Retry the complete create-and-attach operation. Once the tasks write succeeds, the populated cgroup can no longer be removed by the release agent.