Re: CLONE_INTO_CGROUP probably needs to call controller attach handlers

[Waiman Long <longman@redhat.com>]

On 3/28/23 11:39, Christian Brauner wrote:
> Hey,
>
> Giuseppe reported that the the affinity mask isn't updated when a
> process is spawned directly into the target cgroup via
> CLONE_INTO_CGROUP. However, migrating a process will cause the affinity
> mask to be updated (see the repro at [1].
>
> I took a quick look and the issue seems to be that we don't call the
> various attach handlers during CLONE_INTO_CGROUP whereas we do for
> migration. So the solution seems to roughly be that we need to call the
> various attach handlers during CLONE_INTO_CGROUP as well when the
> parent's cgroups is different from the child cgroup. I think we need to
> call all of them, can, cancel and attach.
>
> The plumbing here might be a bit intricate since the arguments that the
> fork handlers take are different from the attach handlers.
>
> Christian
>
> [1]: https://paste.centos.org/view/f434fa1a
>
I saw that the current cgroup code already have the can_fork, fork and 
cancel_fork callbacks. Unfortunately such callbacks are not defined for 
cpuset yet. That is why the cpu affinity isn't correctly updated. I can 
post a patch to add those callback functions to cpuset which should then 
able to correctly address this issue.

Cheers,
Longman