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

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Date:	Fri, 16 Nov 2012 16:14:44 -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 15:01 -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?

Thanks,
-Toshi


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