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Date:   Tue, 28 Mar 2023 17:39:43 +0200
From:   Christian Brauner <brauner@kernel.org>
To:     Tejun Heo <tj@kernel.org>, Johannes Weiner <hannes@cmpxchg.org>
Cc:     Zefan Li <lizefan.x@bytedance.com>, cgroups@vger.kernel.org,
        linux-kernel@vger.kernel.org, gscrivan@redhat.com
Subject: CLONE_INTO_CGROUP probably needs to call controller attach handlers
Message-ID: <20230328153943.op62j3sw7qaixdsq@wittgenstein>
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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