On Tue, Sep 03, 2019 at 12:15:24PM +0000, Salil Mehta wrote:

quoted

From: Linuxarm [mailto:linuxarm-bounces@huawei.com] On Behalf Of Peter Zijlstra
On Tue, Sep 03, 2019 at 02:19:04PM +0800, Yunsheng Lin wrote:

quoted

quoted

Is it possible that the node id set by device_add() become invalid
if the node is offlined, then dev_to_node() may return a invalid
node id.

In that case I would expect the device to go away too. Once the memory
controller goes away, the PCI bus connected to it cannot continue to
function.

I am not sure if this is *exactly* true on our system as NUMA nodes are
part of the SoCs and devices could still be used even if all the memory
and CPUs part of the node are turned off. Although, it is highly unlikely
anybody would do that(maybe could be debated for the Power Management case?) 

Cute; anyway, we never change nr_node_ids (after boot), so once a node
is deemed valid it always is.

The worst that can happen in the above case, is that cpumask_of_node()
returns an empty mask, which, if all CPUs (of said node) are offline, is
an accurate representation.