~90s reboot delay with v6.19 and PREEMPT_RT

[Bert Karwatzki <spasswolf@web.de>]

Since linux v6.19 I noticed that rebooting my MSI Alpha 15 Laptop
would hang for about ~90s before rebooting. I bisected this (from
v6.18 to v6.19) and got this as the first bad commit:
9311e6c29b34 ("cgroup: Fix sleeping from invalid context warning on PREEMPT_RT")

Reverting this commit fixes the reboot delay but introduces these error (which
also seem to make the system crash sometimes):
[    T0] BUG: scheduling while atomic: swapper/0/0/0x00000002

Compiling the kernel without PREEMPT_RT also fixes the issue.

I've test these commits from "git log --oneline v6.19 kernel/cgroup"

This commit shows the reboot delay:
9311e6c29b34 cgroup: Fix sleeping from invalid context warning on PREEMPT_RT
These commits show no reboot delay, but "scheduling while atomic" warnings
and instability:
be04e96ba911 cgroup/cpuset: Globally track isolated_cpus update
b1034a690129 cgroup/cpuset: Ensure domain isolated CPUs stay in root or isolated partition
6cfeddbf4ade cgroup/cpuset: Move up prstate_housekeeping_conflict() helper
103b08709e8a cgroup/cpuset: Fail if isolated and nohz_full don't leave any housekeeping
55939cf28a48 cgroup/cpuset: Rename update_unbound_workqueue_cpumask() to update_isolation_cpumasks()
b66c7af4d86d cgroup: use credential guards in cgroup_attach_permissions()
d245698d727a cgroup: Defer task cgroup unlink until after the task is done switching out
This commit shows neither the reboot delay nor the "scheduling while atomic" problem:
260fbcb92bbe cgroup: Move dying_tasks cleanup from cgroup_task_release() to cgroup_task_free()

Bert Karwatzki