linux-kernel - Re: CLONE_INTO_CGROUP probably needs to call controller attach handlers

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Message-ID: <c3d9cf24-1c3a-cda4-5063-6b7d27e9116f@redhat.com>
Date:   Tue, 28 Mar 2023 21:30:20 -0400
From:   Waiman Long <longman@...hat.com>
To:     Christian Brauner <brauner@...nel.org>, Tejun Heo <tj@...nel.org>,
        Johannes Weiner <hannes@...xchg.org>
Cc:     Zefan Li <lizefan.x@...edance.com>, cgroups@...r.kernel.org,
        linux-kernel@...r.kernel.org, gscrivan@...hat.com
Subject: Re: CLONE_INTO_CGROUP probably needs to call controller attach
 handlers

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