Date:	Mon, 12 Nov 2012 18:20:47 +0100
From:	Vasilis Liaskovitis <vasilis.liaskovitis@...fitbricks.com>
To:	Wen Congyang <wency@...fujitsu.com>
Cc:	linux-acpi@...r.kernel.org, isimatu.yasuaki@...fujitsu.com,
	rjw@...k.pl, lenb@...nel.org, linux-kernel@...r.kernel.org,
	linux-pci@...r.kernel.org, linux-mm@...ck.org
Subject: Re: [RFC PATCH 0/3] acpi: Introduce prepare_remove device operation

On Mon, Nov 12, 2012 at 12:00:55PM +0800, Wen Congyang wrote:
> At 11/09/2012 02:29 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 (echo 1 > /sys/bus/acpi/devices/PNP/eject) of memory devices fails, since
> > the ACPI core goes ahead and ejects the device regardless of whether 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.
> > 
> > acpi_bus_hot_remove_device is changed to handle removal in 2 steps:
> > - preparation for removal i.e. perform part of removal that can fail outside of
> >   ACPI core. Should succeed for device and all its children.
> > - if above step was successfull, proceed to actual ACPI removal
> 
> If we unbind the device from the driver, we still need to do preparation. But
> you don't do it in your patch.

yes, driver_unbind breaks with the current patchset. I 'll try to fix and
repost. However, I think this will require a new driver-core wide prepare_remove
callback (not only acpi-specific). I am not sure that would be acceptable.

thanks,

- Vasilis

> 
> Thanks
> Wen Congyang
> > 
> > acpi_bus_trim is changed accordingly to handle preparation for removal and
> > actual 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.
> > 
> > Other ACPI devices (e.g. CPU) do not register prepare_remove callbacks, and
> > their OSPM-side eject should not be affected.
> > 
> > I am not happy with the name prepare_remove. Comments welcome. Let me know if I
> > should work more in this direction (I think Yasuaki might also look into this
> > and might have a simpler idea)
> > 
> > Patches are on top of Rafael's linux-pm/linux-next
> > 
> > Vasilis Liaskovitis (3):
> >   acpi: Introduce prepare_remove operation in acpi_device_ops
> >   acpi: Make acpi_bus_trim handle device removal preparation
> >   acpi_memhotplug: Add prepare_remove operation
> > 
> >  drivers/acpi/acpi_memhotplug.c     |   24 +++++++++++++++++++++---
> >  drivers/acpi/dock.c                |    2 +-
> >  drivers/acpi/scan.c                |   32 +++++++++++++++++++++++++++++---
> >  drivers/pci/hotplug/acpiphp_glue.c |    4 ++--
> >  drivers/pci/hotplug/sgi_hotplug.c  |    2 +-
> >  include/acpi/acpi_bus.h            |    4 +++-
> >  6 files changed, 57 insertions(+), 11 deletions(-)
> > 
> 
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