Re: [v2 2/2] device-dax: "Hotremove" persistent memory that is used like normal RAM

[Pavel Tatashin]

>
> 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")
>
Hi David,

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.

https://soleen.com/source/xref/linux/arch/powerpc/platforms/powernv/memtrace.c?r=98fa15f3#248

Here we have a similar code:
lock_device_hotplug();
   online_mem_block();
    device_online()
     device_lock(dev);

Pasha