Yes, also I think you can let go of the device_lock in
check_memblocks_offline_cb, lock_device_hotplug() should take care of
this (see Documentation/core-api/memory-hotplug.rst - "locking internals")
Thank you for your comments. I went through memory-hotplug.rst, and I
still think that device_lock() is needed here. In this particular case
it can be replaced with something like READ_ONCE(), but for simplicity
it is better to have device_lock()/device_unlock() as this is not a
performance critical code.
I do not see any lock ordering issues with this code, as we are
holding lock_device_hotplug() first that prevents userland from
adding/removing memory during this check.
Here we have a similar code: