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:

quoted

On Fri, Nov 16, 2012 at 04:14:44PM -0700, Toshi Kani wrote:

quoted

On Fri, 2012-11-16 at 15:01 -0800, Greg Kroah-Hartman wrote:

quoted

On Fri, Nov 16, 2012 at 03:45:43PM -0700, Toshi Kani wrote:

quoted

On Fri, 2012-11-16 at 22:43 +0100, Rafael J. Wysocki wrote:

quoted

On Thursday, November 15, 2012 11:22:47 AM Vasilis Liaskovitis wrote:

quoted

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

--
To unsubscribe, send a message with 'unsubscribe linux-mm' in
the body to majordomo@kvack.org.  For more info on Linux MM,
see: http://www.linux-mm.org/ .
Don't email: <a href=mailto:"dont@kvack.org"> email@kvack.org </a>