Shutdown-time hangs in -next in locktorture

[Paul E. McKenney]

Hello, Peter,

I started hitting shutdown-time hangs in next-20251217 which persist
in next-20251219.  This hang happens on both x86 and arm64.  Once I
figured out that the failure is high probability, but not deterministic,
bisection converged here:

5d1f0b2f278e ("sched/core: Rework sched_class::wakeup_preempt() and rq_modified_*()")

This commit reverts cleanly, and doing so restores hang-free operation.

The reproducer is shown below.

Thoughts?

							Thanx, Paul

------------------------------------------------------------------------

for i in 1 2 3 4 5
do
	tools/testing/selftests/rcutorture/bin/torture.sh --duration 20 --do-none --do-normal --do-locktorture --do-kasan --configs-locktorture "LOCK09"
	ret=$?
	if test "$ret" -ne 0
	then
		exit "$ret"
	fi
	echo Test $i succeeded
done
exit 0