Re: CLONE_INTO_CGROUP probably needs to call controller attach handlers

[Christian Brauner <brauner@kernel.org>]

On Tue, Mar 28, 2023 at 05:39:52PM +0200, 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.

But note, as Johannes already pointed out somewhere else, that there's
probably a lot of code that doesn't apply to the CLONE_INTO_CGROUP case
so it might also make sense to just move the missing pieces into the
fork handlers.