Hello Waiman.

On Tue, Jul 20, 2021 at 10:18:31AM -0400, Waiman Long <longman@redhat.com> wrote:
> @@ -2026,6 +2036,22 @@ static int update_prstate(struct cpuset *cs, int new_prs)
> [...]
> +	} else if (old_prs && new_prs) {

If an isolated root partition becomes invalid (new_prs == PRS_ERROR)...

> +		/*
> +		 * A change in load balance state only, no change in cpumasks.
> +		 */
> +		update_flag(CS_SCHED_LOAD_BALANCE, cs, (new_prs != PRS_ISOLATED));

...this seems to erase information about CS_SCHED_LOAD_BALANCE zeroness.

IOW, if there's an isolated partition that becomes invalid and later
valid again (a cpu is (re)added), it will be a normal root partition
without the requested isolation, which is IMO undesired.

I may have overlooked something in broader context but it seems to me
the invalidity should be saved independently of the root/isolated type.

Regards,
Michal