From mboxrd@z Thu Jan 1 00:00:00 1970 From: Greg Kroah-Hartman Subject: Re: [RFC PATCH v2 0/3] acpi: Introduce prepare_remove device operation Date: Fri, 16 Nov 2012 16:22:32 -0800 Message-ID: <20121117002232.GA22543@kroah.com> References: <1352974970-6643-1-git-send-email-vasilis.liaskovitis@profitbricks.com> <1446291.TgLDtXqY7q@vostro.rjw.lan> <1353105943.12509.60.camel@misato.fc.hp.com> <20121116230143.GA15338@kroah.com> <1353107684.12509.65.camel@misato.fc.hp.com> <20121116233355.GA21144@kroah.com> <1353108906.10624.5.camel@misato.fc.hp.com> <20121117000250.GA4425@kroah.com> <1353110933.10939.6.camel@misato.fc.hp.com> Mime-Version: 1.0 Content-Type: text/plain; charset=us-ascii Return-path: Received: from mail-da0-f46.google.com ([209.85.210.46]:63062 "EHLO mail-da0-f46.google.com" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1753687Ab2KQAWg (ORCPT ); Fri, 16 Nov 2012 19:22:36 -0500 Received: by mail-da0-f46.google.com with SMTP id n41so1350971dak.19 for ; Fri, 16 Nov 2012 16:22:36 -0800 (PST) Content-Disposition: inline In-Reply-To: <1353110933.10939.6.camel@misato.fc.hp.com> Sender: linux-acpi-owner@vger.kernel.org List-Id: linux-acpi@vger.kernel.org To: Toshi Kani Cc: "Rafael J. Wysocki" , Vasilis Liaskovitis , linux-acpi@vger.kernel.org, isimatu.yasuaki@jp.fujitsu.com, wency@cn.fujitsu.com, lenb@kernel.org, linux-kernel@vger.kernel.org, linux-mm@kvack.org 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. greg k-h From mboxrd@z Thu Jan 1 00:00:00 1970 Return-Path: Received: from psmtp.com (na3sys010amx164.postini.com [74.125.245.164]) by kanga.kvack.org (Postfix) with SMTP id D7D266B0071 for ; Fri, 16 Nov 2012 19:22:36 -0500 (EST) Received: by mail-pa0-f41.google.com with SMTP id fa10so2392931pad.14 for ; Fri, 16 Nov 2012 16:22:36 -0800 (PST) Date: Fri, 16 Nov 2012 16:22:32 -0800 From: Greg Kroah-Hartman Subject: Re: [RFC PATCH v2 0/3] acpi: Introduce prepare_remove device operation Message-ID: <20121117002232.GA22543@kroah.com> References: <1352974970-6643-1-git-send-email-vasilis.liaskovitis@profitbricks.com> <1446291.TgLDtXqY7q@vostro.rjw.lan> <1353105943.12509.60.camel@misato.fc.hp.com> <20121116230143.GA15338@kroah.com> <1353107684.12509.65.camel@misato.fc.hp.com> <20121116233355.GA21144@kroah.com> <1353108906.10624.5.camel@misato.fc.hp.com> <20121117000250.GA4425@kroah.com> <1353110933.10939.6.camel@misato.fc.hp.com> MIME-Version: 1.0 Content-Type: text/plain; charset=us-ascii Content-Disposition: inline In-Reply-To: <1353110933.10939.6.camel@misato.fc.hp.com> Sender: owner-linux-mm@kvack.org List-ID: To: Toshi Kani Cc: "Rafael J. Wysocki" , Vasilis Liaskovitis , linux-acpi@vger.kernel.org, isimatu.yasuaki@jp.fujitsu.com, wency@cn.fujitsu.com, lenb@kernel.org, linux-kernel@vger.kernel.org, linux-mm@kvack.org 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. 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: email@kvack.org