Re: [v2 2/2] device-dax: "Hotremove" persistent memory that is used like normal RAM
On 25.04.19 14:30, Pavel Tatashin wrote:
>
> 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.
Yes, lock ordering is not an issue, I rather think that the device
hotplug lock will guard us in all situations. E.g. remove_memory() also
does not use it when checking if all blocks are offline. But you can
leave it in if you think it is needed.
https://soleen.com/source/xref/linux/arch/powerpc/platforms/powernv/memtr...
Here we have a similar code:
lock_device_hotplug();
online_mem_block();
device_online()
device_lock(dev);
Pasha
--
Thanks,
David / dhildenb