linux-kernel - Re: [RFC PATCH v2 0/3] acpi: Introduce prepare

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Date:	Fri, 16 Nov 2012 16:35:06 -0700
From:	Toshi Kani <toshi.kani@...com>
To:	Greg Kroah-Hartman <gregkh@...uxfoundation.org>
Cc:	"Rafael J. Wysocki" <rjw@...k.pl>,
	Vasilis Liaskovitis <vasilis.liaskovitis@...fitbricks.com>,
	linux-acpi@...r.kernel.org, isimatu.yasuaki@...fujitsu.com,
	wency@...fujitsu.com, lenb@...nel.org,
	linux-kernel@...r.kernel.org, linux-mm@...ck.org
Subject: Re: [RFC PATCH v2 0/3] acpi: Introduce prepare_remove device
 operation

On Fri, 2012-11-16 at 15:33 -0800, Greg Kroah-Hartman wrote:
> On Fri, Nov 16, 2012 at 04:14:44PM -0700, Toshi Kani wrote:
> > On Fri, 2012-11-16 at 15:01 -0800, Greg Kroah-Hartman wrote:
> > > On Fri, Nov 16, 2012 at 03:45:43PM -0700, Toshi Kani wrote:
> > > > On Fri, 2012-11-16 at 22:43 +0100, Rafael J. Wysocki wrote:
> > > > > 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.
> > > > > 
> > > > > So the question is, does the ACPI core have to do that and if so, then why?
> > > > 
> > > > The problem is that acpi_memory_devcie_remove() can fail.  However,
> > > > device_release_driver() is a void function, so it cannot report its
> > > > error.  Here are function flows for SCI, sysfs eject and unbind.
> > > 
> > > Then don't ever let acpi_memory_device_remove() fail.  If the user wants
> > > it gone, it needs to go away.  Just like any other device in the system
> > > that can go away at any point in time, you can't "fail" that.
> > 
> > That would be ideal, but we cannot delete a memory device that contains
> > kernel memory.  I am curious, how do you deal with a USB device that is
> > being mounted in this case?
> 
> As the device is physically gone now, we deal with it and clean up
> properly.
> 
> And that's the point here, what happens if the memory really is gone?
> You will still have to handle it now being removed, you can't "fail" a
> physical removal of a device.
> 
> If you remove a memory device that has kernel memory on it, well, you
> better be able to somehow remap it before the kernel needs it :)

:)

Well, we are not trying to support surprise removal here.  All three
use-cases (SCI, eject, and unbind) are for graceful removal.  Therefore
they should fail if the removal operation cannot complete in graceful
way.

Thanks,
-Toshi





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