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

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Date:	Fri, 16 Nov 2012 16:02:50 -0800
From:	Greg Kroah-Hartman <gregkh@...uxfoundation.org>
To:	Toshi Kani <toshi.kani@...com>
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, Nov 16, 2012 at 04:35:06PM -0700, Toshi Kani wrote:
> 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.

Then handle that in the ACPI bus code, it isn't anything that the driver
core should care about, right?

And odds are, eventually you will have to handle surprise removal, it's
only a matter of time :)

greg k-h
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