Re: [PATCH 7/10] ACPI / hotplug: Move container-specific code out of the core

[Yasuaki Ishimatsu <isimatu.yasuaki@jp.fujitsu.com>]

(2013/11/29 22:08), Rafael J. Wysocki wrote:
> On Friday, November 29, 2013 11:36:55 AM Yasuaki Ishimatsu wrote:
>> Hi Rafael,
>
> Hi,
>
>> Replying to this mail may be wrong.
>
> OK, so this particular patch doesn't break things any more?

Yes.

>
>> Do you remember following your patch?
>> http://lkml.org/lkml/2013/2/23/97
>>
>> I want to add autoeject variable in acpi_hotplug_profile structure and
>> set autoecjet of container device "false".
>
> Then after the series the $subject patch belongs to it will work almost the
> same way as /sys/firmware/acpi/container/enabled (hot add will still work after
> patch [4/10] if "enabled" is 0), but only for containers.
>
>> Currently, I have a problem on ejecting container device. Since linux-3.12,
>> container device is removed by acpi_scan_hot_remove.
>>
>> I think this has two problems.
>>
>>     1. easily fail
>>        My container device has CPU device and Memory device, and maximum size of
>>        memory is 3Tbyte. In my environment, hot removing container device fails
>>        on offlining memory if memory is used by application.
>>        I think if offlininig memory, we must retly to offline memory several
>>        times.
>
> Yes, that's correct.  But then you can try to offline the memory upfront
> and only remove the container after that has been successful.
>
>>     2. cannot work with userland's application
>>        Hot removing CPU and memory on container device, we need take care of
>>        userland application. Before linux-3.12, container device just notifies
>>        KOBJ_OFFLINE to udev. So by using udev, if application binds to removed
>>        CPU or node, applications can change them before hot removing container
>>        device.
>>        Currently, KOBJ_OFFLINE is notified to udev. But acpi_scan_hot_remove
>>        also runs simultaneously for hot removing container device. So when
>>        applications runs for corresponding to the deletion of the devices,
>>        the devices may have been deleted.
>

> So the expectation is that the container will refuse to offline, but instead
> it will emit KOBJ_OFFLINE so that user space can do some cleanup and offline
> it through the "eject" attribute, right?

Yes, that's right.

>
>> I don't know what devices are on hotpluggable conatainer device of other
>> vendors. At least, my container device cannot be hot removed correctly.
>> Then I want to add autoeject variable in acpi_hotplug_profile so that user
>> can change the parameter to "true" or "false".
>
> I have a different idea.
>
> Why don't we create a bus type for containers in analogy with CPUs and memory
> and make it support offline.  Then, the container scan handler will create a
> "physical" container device under that bus type and the new bus type code will
> implement the logic you need (that is, it will have a sysfs flag that will
> cause the offline to fail emitting a uevent of some sort if set and will allow
> the offline to happen when unset).  That "physical" container device will go
> away (again, via the container scan handler) during container removal.
>

> The eject work flow can be:
>    (1) an eject event occurs,
>    (2) the container "physical" device fails offline in acpi_scan_hot_remove()
>        emmitting, say, KOBJ_CHANGE for the "physical" device,
>    (3) user space notices the KOBJ_CHANGE and does the cleanup as needed,
>    (4) user space changes the "physical" container device flag controlling
>        offline to 0,
>    (5) user space uses the sysfs "eject" attribute of the ACPI container object
>        to finally eject the container,
>    (6) the offline in acpi_scan_hot_remove() is now successful, because the
>        flag controlling it has been set to 0 in step (4),
>    (7) the "physical" container device goes away before executing _EJ0,
>    (8) the container is ejected.
>
> Of course, if the flag controlling container offline is 0 to start with, step
> (6) will now occur directly after (1), so whoever wants containers to be
> hot-removed automatically may just clear that flag for all of them on boot.
>
> How does that sound?


The above ideas are almost O.K. I want kernel to notify user space of KOBJ_OFFLINE.
Even if user space catches "KOBJ_CHANGE", user doesn't know whether the notification
is offline or not.

Thanks,
Yasuaki Ishimatsu

> Rafael
>
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