Alexey Klimov [off-list ref] writes:

The first section of comment seems problematic to me with regards to such move:

                 * As this needs to hold the cpu maps lock it's impossible
                 * to call device_offline() because that ends up calling
                 * cpu_down() which takes cpu maps lock. cpu maps lock
                 * needs to be held as this might race against in kernel
                 * abusers of the hotplug machinery (thermal management).

Cpu maps lock is released in cpu_maps_update_done() hence we will move
dev->offline out of cpu maps lock. Maybe I misunderstood the comment
and it relates to calling cpu_down_maps_locked() under lock to avoid
race?

Yes, that's what I take from the comment, the cpu maps lock protects
against racing hotplug operations.