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

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Date:   Thu, 9 Mar 2017 14:37:55 -0800
From:   Dan Williams <dan.j.williams@...el.com>
To:     "Rafael J. Wysocki" <rjw@...ysocki.net>
Cc:     Heiko Carstens <heiko.carstens@...ibm.com>,
        Andrew Morton <akpm@...ux-foundation.org>,
        Linux MM <linux-mm@...ck.org>,
        "linux-kernel@...r.kernel.org" <linux-kernel@...r.kernel.org>,
        linux-s390 <linux-s390@...r.kernel.org>,
        Michal Hocko <mhocko@...e.com>,
        Vladimir Davydov <vdavydov.dev@...il.com>,
        Ben Hutchings <ben@...adent.org.uk>,
        Gerald Schaefer <gerald.schaefer@...ibm.com>,
        Martin Schwidefsky <schwidefsky@...ibm.com>,
        Sebastian Ott <sebott@...ux.vnet.ibm.com>
Subject: Re: [PATCH 1/2] mm: add private lock to serialize memory hotplug operations

On Thu, Mar 9, 2017 at 2:22 PM, Rafael J. Wysocki <rjw@...ysocki.net> 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@...ysocki.net> 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.