From: "Rafael J. Wysocki" <rjw@sisk.pl>
To: Vasilis Liaskovitis <vasilis.liaskovitis@profitbricks.com>
Cc: linux-acpi@vger.kernel.org, isimatu.yasuaki@jp.fujitsu.com,
        wency@cn.fujitsu.com, lenb@kernel.org, toshi.kani@hp.com,
        linux-kernel@vger.kernel.org, linux-mm@kvack.org,
        Greg Kroah-Hartman <gregkh@linuxfoundation.org>
Subject: Re: [RFC PATCH v2 0/3] acpi: Introduce prepare_remove device operation
Date: Fri, 16 Nov 2012 22:17:17 +0100
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On Thursday, November 15, 2012 11:22:47 AM Vasilis Liaskovitis wrote:
> As discussed in https://patchwork.kernel.org/patch/1581581/
> the driver core remove function needs to always succeed. This means we need
> to know that the device can be successfully removed before acpi_bus_trim / 
> acpi_bus_hot_remove_device are called. This can cause panics when OSPM-initiated
> eject or driver unbind of memory devices fails e.g with:
> 
> echo 1 >/sys/bus/pci/devices/PNP0C80:XX/eject
> echo "PNP0C80:XX" > /sys/bus/acpi/drivers/acpi_memhotplug/unbind
> 
> since the ACPI core goes ahead and ejects the device regardless of whether the
> the memory is still in use or not.
> 
> For this reason a new acpi_device operation called prepare_remove is introduced.
> This operation should be registered for acpi devices whose removal (from kernel
> perspective) can fail.  Memory devices fall in this category.
> A similar operation is introduced in bus_type to safely handle driver unbind
> from the device driver core.
> 
> acpi_bus_hot_remove_device and driver_unbind are changed to handle removal in 2
> steps:
> - preparation for removal i.e. perform part of removal that can fail. Should
>   succeed for device and all its children.
> - if above step was successfull, proceed to actual device removal
> 
> With this patchset, only acpi memory devices use the new prepare_remove
> device operation. The actual memory removal (VM-related offline and other memory
> cleanups) is moved to prepare_remove. The old remove operation just cleans up
> the acpi structures. Directly ejecting PNP0C80 memory devices works safely. I
> haven't tested yet with an ACPI container which contains memory devices.
> 
> v1->v2:
> - new patch to introduce bus_type prepare_remove callback. Needed to prepare
> removal on driver unbinding from device-driver core.
> - v1 patches 1 and 2 simplified and merged in one. acpi_bus_trim does not require
> argument changes.
> 
> Comments welcome.
> 
> Vasilis Liaskovitis (3):
>   driver core: Introduce prepare_remove in bus_type
>   acpi: Introduce prepare_remove operation in acpi_device_ops
>   acpi_memhotplug: Add prepare_remove operation
> 
>  drivers/acpi/acpi_memhotplug.c |   22 ++++++++++++++++++++--
>  drivers/acpi/scan.c            |   21 ++++++++++++++++++++-
>  drivers/base/bus.c             |   36 ++++++++++++++++++++++++++++++++++++
>  include/acpi/acpi_bus.h        |    2 ++
>  include/linux/device.h         |    2 ++
>  5 files changed, 80 insertions(+), 3 deletions(-)

CCs of all driver core patches have to go to Greg Kroah-Hartman.

Thanks,
Rafael


-- 
I speak only for myself.
Rafael J. Wysocki, Intel Open Source Technology Center.
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