Re: [PATCH 1/3] cgroup/cpuset: Protect is_in_v2_mode() in cpuset_num_cpus()

[Peter Zijlstra]

On Tue, Sep 29, 2026 at 03:46:23PM -0400, Waiman Long wrote:

> The cpuset_v2_mode mount option is only for making the cpuset.cpus and
> cpuset.mems behave like in v2. The cpu-cgroup and cpuset-cgroup can still be
> in separate hierarchies. If cross-cgroup transition is the main point, it
> won't work with the cpuset_v2_mode mount option. We should switch to use
> cpuset_v2().

Yes, the cross-cgroup transition is fundamental to how this works.
Without that you cannot reasonably talk about the CPUs of a cpu-cgroup,
you need to have cpu and cpuset aligned.