On 11/17/2012 08:25 AM, Toshi Kani wrote: > On Fri, 2012-11-16 at 16:22 -0800, Greg Kroah-Hartman wrote: >> On Fri, Nov 16, 2012 at 05:08:53PM -0700, Toshi Kani wrote: >>>>>>>>>> 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? >>> >>> Unfortunately not. Please take a look at the function flow for the >>> unbind case in my first email. This request directly goes to >>> driver_unbind(), which is a driver core function. >> >> Yes, and as the user asked for the driver to be unbound from the device, >> it can not fail. >> >> And that is WAY different from removing the memory from the system >> itself. Don't think that this is the "normal" way that memory should be >> removed, that is what stuff like "eject" was created for the PCI slots. >> >> Don't confuse the two things here, unbinding a driver from a device >> should not remove the memory from the system, it doesn't do that for any >> other type of 'unbind' call for any other bus. The device is still >> present, just that specific driver isn't controlling it anymore. >> >> In other words, you should NEVER have a normal userspace flow that is >> trying to do unbind. unbind is only for radical things like >> disconnecting a driver from a device if a userspace driver wants to >> control it, or a hacked up way to implement revoke() for a device. >> >> Again, no driver core changes are needed here. > > Okay, we might be able to make the eject case to fail if an ACPI driver > is not bound to a device. This way, the unbind case may be harmless to > proceed. Let us think about this further on this (but we may come up > again :). Hi all, The ACPI based system device hotplug framework project I'm working on has already provided a solution for this issue. We have added several callbacks to struct acpi_device_ops to support ACPI system device hotplug. By that way, we could guarantee unbinding ACPI CPU/memory/PCI host bridge drivers will always success. And we have a plan to implement the existing "eject" interface with the new hotplug framework. For more information, please take a look at: http://www.spinics.net/lists/linux-acpi/msg39487.html http://www.spinics.net/lists/linux-acpi/msg39490.html Thanks! Gerry > > Thanks, > -Toshi > > > > > > -- > To unsubscribe from this list: send the line "unsubscribe linux-acpi" in > the body of a message to majordomo@xxxxxxxxxxxxxxx > More majordomo info at http://vger.kernel.org/majordomo-info.html > -- To unsubscribe, send a message with 'unsubscribe linux-mm' in the body to majordomo@xxxxxxxxx. For more info on Linux MM, see: http://www.linux-mm.org/ . Don't email: <a href=mailto:"dont@xxxxxxxxx";> email@xxxxxxxxx </a>