Re: [PATCH v2] acpi : acpi_bus_trim() stops removing devices whenfailing to remove the device

[Yasuaki Ishimatsu]

Hi Greg,

2012/10/27 0:25, Greg Kroah-Hartman wrote:
> On Fri, Oct 26, 2012 at 04:33:49PM +0900, Yasuaki Ishimatsu wrote:
> > 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@xxxxxxxxxxxxxx>
> > > >
> > > > 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.
>
> Why can't you check to find out if you can do the remove operation
> before you enter the driver core asking to actually remove the devices?
> That would allow you to "know" if you can do this before having to go
> through the whole operation.  What happens if you can complete half of
> the removal, and do that, but not the whole thing?  Don't you end up
> with half of the memory chunk gone from the system now?

> In other words, please solve this at a higher level than the driver
> core if at all possible.

O.K.
I'll check whether the problem is sloved at a higher level or not.

Thanks,
Yasuaki Ishimatsu

> greg k-h


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