From mboxrd@z Thu Jan  1 00:00:00 1970
Return-Path: <linux-kernel-owner@vger.kernel.org>
Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand
        id S1754265AbdCIWtF (ORCPT <rfc822;w@1wt.eu>);
        Thu, 9 Mar 2017 17:49:05 -0500
Received: from cloudserver094114.home.net.pl ([79.96.170.134]:44407 "EHLO
        cloudserver094114.home.net.pl" rhost-flags-OK-OK-OK-OK)
        by vger.kernel.org with ESMTP id S1753949AbdCIWtD (ORCPT
        <rfc822;linux-kernel@vger.kernel.org>);
        Thu, 9 Mar 2017 17:49:03 -0500
From: "Rafael J. Wysocki" <rjw@rjwysocki.net>
To: Dan Williams <dan.j.williams@intel.com>
Cc: Heiko Carstens <heiko.carstens@de.ibm.com>,
        Andrew Morton <akpm@linux-foundation.org>,
        Linux MM <linux-mm@kvack.org>,
        "linux-kernel@vger.kernel.org" <linux-kernel@vger.kernel.org>,
        linux-s390 <linux-s390@vger.kernel.org>,
        Michal Hocko <mhocko@suse.com>,
        Vladimir Davydov <vdavydov.dev@gmail.com>,
        Ben Hutchings <ben@decadent.org.uk>,
        Gerald Schaefer <gerald.schaefer@de.ibm.com>,
        Martin Schwidefsky <schwidefsky@de.ibm.com>,
        Sebastian Ott <sebott@linux.vnet.ibm.com>
Subject: Re: [PATCH 1/2] mm: add private lock to serialize memory hotplug operations
Date: Thu, 09 Mar 2017 23:43:42 +0100
Message-ID: <9260906.bxXFooPL9U@aspire.rjw.lan>
User-Agent: KMail/4.14.10 (Linux/4.10.0+; KDE/4.14.9; x86_64; ; )
In-Reply-To: <CAPcyv4gX-7BAZOEvi7UShZD0bo6JV1D7tiU5wQweauG0tx=Luw@mail.gmail.com>
References: <20170309130616.51286-1-heiko.carstens@de.ibm.com> <19605238.M7OFe3HAv5@aspire.rjw.lan> <CAPcyv4gX-7BAZOEvi7UShZD0bo6JV1D7tiU5wQweauG0tx=Luw@mail.gmail.com>
MIME-Version: 1.0
Content-Transfer-Encoding: 7Bit
Content-Type: text/plain; charset="us-ascii"
Sender: linux-kernel-owner@vger.kernel.org
List-ID: <linux-kernel.vger.kernel.org>
X-Mailing-List: linux-kernel@vger.kernel.org

On Thursday, March 09, 2017 02:37:55 PM Dan Williams wrote:
> On Thu, Mar 9, 2017 at 2:22 PM, Rafael J. Wysocki <rjw@rjwysocki.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@rjwysocki.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.

ACPI0012 is exceptional, but in general _EJ0 does not have to be present under
a particular device for it to be affected.  It can be under the device's parent, for
example, in which case the entire subtree under a device with _EJ0 goes away in
one go.  And that very well may mean disconnect at the physical level (voltage
goes away IOW).

Thanks,
Rafael