On Mon, Jun 13, 2022 at 07:28:25AM -1000, Tejun Heo <tj@kernel.org> wrote:
> I see. Is this part even necessary? All the .cpus files of the siblings are
> owned by the parent who's responsible for configuring both the mode that the
> cgroup subtree is gonna be in and their cpumasks. 

Do you mean such an example:

    parent	cpuset.cpus=SET (root)	cpuset.cpus.partition=isolated 
    `- child_1	cpuset.cpus=partition_of(SET) (root)	cpuset.cpus.partition=isolated
    `- ...
    `- child_n	cpuset.cpus=partition_of(SET) (root)	cpuset.cpus.partition=isolated
?

I don't think child_*/cpuset.cpus must be owned by root.
Actually, the root would only configure the parent, i.e.
parent/cpuset.cpus (whose changes would be disallowed to the
unprivileged tasks) and the distribution among siblings would up to the
whatever runs below.

> Given that all the other errors it can make are notified through
> "invalid (REASON)" in the mode file, wouldn't it fit better to notify
> cpus configuration error the same way too?

Do you suggest that a write into child_*/cpuset.cpus that'd not be
exclusive wrt a sibling would result in an error string in
parent/cpuset.cpus.partition?

Thanks,
Michal