Re: Bug: linux/acpi may execute notify handler that has been removed

[Alexey Starikovskiy <astarikovskiy@suse.de>]

Shaohua Li wrote:
> On Thu, 2007-09-27 at 10:24 +0400, Alexey Starikovskiy wrote:
>> Shaohua Li wrote:
>>> On Thu, 2007-09-27 at 11:30 +0800, Zhang Rui wrote:
>>>> Hi, all,
>>>>
>>>> I found a bug that linux/acpi may execute notify handler that
>>>> has been removed.
>>>>
>>>> When a system notify(0~0x7f) is received, linux/acpi will
>>>> first invoke the generic system notify handler (acpi_bus_notify)
>>>> and then invoke the per-device notify handler if present.
>>>>
>>>> In my case, I add some code in acpi_bus_notify for battery
>>>> hotplug support, so that the generic system notify handler will
>>>> remove the battery device, including the per-device notify handler
>>>> acpi_battery_notify() when receiving notification
>>>> ACPI_NOTIFY_EJECT_REQUEST.
>>>> But linux/acpi invokes the per-device notify handler soon and
>>>> this breaks the system.
>>>>
>>>> Further more, device hot-removal is not the only case to encounter
>>>> this bug. For example, linux/acpi receives a notification and adds it
>>>> in the workqueue, and then the driver(notify handler) is removed
>>>> before kacpid_notify invoke it...
>>> For the non-hotplug case, adding a flush work queue just after notify
>>> handler is removed should be ok.
>> I think, the real problem with ACPI hotplug is that we know which devices might appear -- 
>> they are all enumerated in DSDT, but we don't add them until they appear.
>> If we do .add for all devices in DSDT, and then just .start/.stop them as they appear/disappear,
>> we will have to do much less work, and avoid a problem described above...
> If a device is not present, you can't access any method of it.
What is because you didn't call .add() yet, or already called .remove(), yes?
> 
> The real problem here is ACPICA will call some drivers routines
> (notification handler), but doesn't get a reference count of the driver
> module.
We just should be able to load drivers for declared, but physically absent devices.
> 
> Thanks,
> Shaohua