linux-kernel - Re: [Patch v4 1/7] acpi,memory-hotplug: introduce a mutex lock to protect the list in acpi_memory

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Message-ID: <1352754038.12509.16.camel@misato.fc.hp.com>
Date:	Mon, 12 Nov 2012 14:00:38 -0700
From:	Toshi Kani <toshi.kani@...com>
To:	Wen Congyang <wency@...fujitsu.com>
Cc:	linux-kernel@...r.kernel.org, linux-mm@...ck.org,
	linux-acpi@...r.kernel.org, Len Brown <len.brown@...el.com>,
	"Rafael J. Wysocki" <rjw@...k.pl>,
	Andrew Morton <akpm@...ux-foundation.org>,
	Yasuaki Ishimatsu <isimatu.yasuaki@...fujitsu.com>,
	Lai Jiangshan <laijs@...fujitsu.com>,
	Jiang Liu <jiang.liu@...wei.com>,
	KOSAKI Motohiro <kosaki.motohiro@...fujitsu.com>,
	Minchan Kim <minchan.kim@...il.com>,
	Mel Gorman <mgorman@...e.de>,
	David Rientjes <rientjes@...gle.com>,
	Konrad Rzeszutek Wilk <konrad.wilk@...cle.com>,
	Jiang Liu <liuj97@...il.com>,
	Benjamin Herrenschmidt <benh@...nel.crashing.org>,
	Paul Mackerras <paulus@...ba.org>,
	Christoph Lameter <cl@...ux.com>
Subject: Re: [Patch v4 1/7] acpi,memory-hotplug: introduce a mutex lock to
 protect the list in acpi_memory_device

On Thu, 2012-11-08 at 19:04 +0800, Wen Congyang wrote:
> The memory device can be removed by 2 ways:
> 1. send eject request by SCI
> 2. echo 1 >/sys/bus/pci/devices/PNP0C80:XX/eject
> 
> This 2 events may happen at the same time, so we may touch
> acpi_memory_device.res_list at the same time. This patch
> introduce a lock to protect this list.

Hi Wen,

This race condition is not unique in memory hot-remove as the sysfs
eject interface is created for all objects with _EJ0.  For CPU
hot-remove, I addressed this race condition by making the notify handler
to run the hot-remove operation on kacpi_hotplug_wq by calling
acpi_os_hotplug_execute().  This serializes the hot-remove operations
among the two events since the sysfs eject also runs on
kacpi_hotplug_wq.  This way is much simpler and is easy to maintain,
although it does not allow both operations to run simultaneously (which
I do not think we need).  Can it be used for memory hot-remove as well?

Thanks,
-Toshi

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