Messages in this thread | | | Date | Fri, 26 Oct 2012 16:33:49 +0900 | From | Yasuaki Ishimatsu <> | Subject | Re: [PATCH v2] acpi : acpi_bus_trim() stops removing devices when failing to remove the device |
| |
Hi Greg,
Sorry for late reply.
2012/10/20 2:59, Greg Kroah-Hartman wrote: > On Fri, Oct 19, 2012 at 06:29:52AM +0200, Rafael J. Wysocki wrote: >> On Thursday 11 of October 2012 19:12:28 Yasuaki Ishimatsu wrote: >>> acpi_bus_trim() stops removing devices, when acpi_bus_remove() return error >>> number. But acpi_bus_remove() cannot return error number correctly. >>> acpi_bus_remove() only return -EINVAL, when dev argument is NULL. Thus even if >>> device cannot be removed correctly, acpi_bus_trim() ignores and continues to >>> remove devices. acpi_bus_hot_remove_device() uses acpi_bus_trim() for removing >>> devices. Therefore acpi_bus_hot_remove_device() can send "_EJ0" to firmware, >>> even if the device is running on the system. In this case, the system cannot >>> work well. >>> >>> Vasilis hit the bug at memory hotplug and reported it as follow: >>> https://lkml.org/lkml/2012/9/26/318 >>> >>> So acpi_bus_trim() should check whether device was removed or not correctly. >>> The patch adds error check into some functions to remove the device. >>> >>> Applying the patch, acpi_bus_trim() stops removing devices when failing >>> to remove the device. But I think there is no impact with the >>> exceptionof CPU and Memory hotplug path. Because other device also fails >>> but the fail is an irregular case like device is NULL. >>> >>> v1->v2 >>> - add a rollback for reinstalling a notify handler. >>> >>> Signed-off-by: Yasuaki Ishimatsu <isimatu.yasuaki@jp.fujitsu.com> >> >> Greg, do you think there may be any problems with the changes in dd.c? > > Yes, I don't like it. > > remove should always work, just like the exit call in a module. It > means that the core wants to remove the driver, so it is going to > happen, a driver can't refuse it. > > Which brings me to the larger question, why would this solve anything?
Now we are developing physical memory hot plug.
https://lkml.org/lkml/2012/10/23/213
So if we aplly the patch-set, we can hot remove a physical memory by the following way.
"echo 1 > /sys/bus/acpi/devices/PNP/eject"
In this case, acpi_bus_hot_remove_device() tries to remove memory device by acpi_bus_trim(). But if the memory has irremovable memory, memory hot remove fails. And the memory remains in kernel. However acpi_bus_trim() cannot notice that memory hot remove fails and retruns 0. So acpi_bus_hot_remove_device() continues to remove memory devices and sends _EJ0 method to firmware. Thus the memory device cannot be used. But the memory remains in kernel yet. So if someone access the memory, kernel panic occurs.
Thanks, Yasuaki Ishimatsu
> If the kernel wants to unbind a device, why would we ever not want that > to happen? > > So, NAK on this patch, sorry. Fix up the ACPI core to handle this > properly, don't mess with the driver core here. > > greg k-h >
| |