Re: [PATCH 1/2] mm: add private lock to serialize memory hotplug operations

From: Dan Williams
Date: Thu Mar 09 2017 - 17:38:04 EST

On Thu, Mar 9, 2017 at 2:22 PM, Rafael J. Wysocki <rjw@xxxxxxxxxxxxx> wrote:
> On Thursday, March 09, 2017 11:15:47 PM Rafael J. Wysocki wrote:
>> On Thursday, March 09, 2017 10:10:31 AM Dan Williams wrote:
>> > On Thu, Mar 9, 2017 at 5:39 AM, Rafael J. Wysocki <rjw@xxxxxxxxxxxxx> wrote:
>> > I *think* we're ok in this case because unplugging the CPU package
>> > that contains a persistent memory device will trigger
>> > devm_memremap_pages() to call arch_remove_memory(). Removing a pmem
>> > device can't fail. It may be held off while pages are pinned for DMA
>> > memory, but it will eventually complete.
>> What about the offlining, though? Is it guaranteed that no memory from those
>> ranges will go back online after the acpi_scan_try_to_offline() call in
>> acpi_scan_hot_remove()?
> My point is that after the acpi_evaluate_ej0() in acpi_scan_hot_remove() the
> hardware is physically gone, so if anything is still doing DMA to that memory at
> that point, then the user is going to be unhappy.

Hmm, ACPI 6.1 does not have any text about what _EJ0 means for ACPI0012.