linux-kernel - Re: Re : [PATCH] acpi: Fix hot cpu remove problem on acpi subsystem

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Date:	Tue, 6 Sep 2011 11:38:39 -0700
From:	Bjorn Helgaas <bhelgaas@...gle.com>
To:	"canquan.shen" <shencanquan@...wei.com>
Cc:	"lenb@...nel.org" <lenb@...nel.org>,
	"rui.zhao@...el.com" <rui.zhao@...el.com>,
	"shemminger@...tta.com" <shemminger@...tta.com>,
	"yakui.zhao@...el.com" <yakui.zhao@...el.com>,
	"xiaowei.yang@...wei.com" <xiaowei.yang@...wei.com>,
	hanweidong <hanweidong@...wei.com>,
	"linux-kernel@...r.kernel.org" <linux-kernel@...r.kernel.org>,
	"linux-acpi@...r.kernel.org" <linux-acpi@...r.kernel.org>
Subject: Re: Re : [PATCH] acpi: Fix hot cpu remove problem on acpi subsystem

On Mon, Sep 5, 2011 at 11:48 PM, canquan.shen <shencanquan@...wei.com> wrote:
> On 2011/9/6 12:19, Bjorn Helgaas wrote:
>>>
>>> 主题: [PATCH] acpi: Fix hot cpu remove problem on acpi subsystem
>>>
>>> In Xen virtualization environment, When I used xen tools (xm vcpu-set
>>> vcpu_number ) to test the vcpu add and remove, I found it is failure on vcpu
>>> remove, I found the reason is that nothing to do when cpu remove in
>>> acpi_processor_hotplug_notify function, so I add the code of send the
>>> OFFLINE message to udev and add the rule of udev. it is ok on vcpu remove.
>>> Signed-off-by: Shen canquan<shencanquan@...wei.com>
>>> ---
>>>  drivers/acpi/processor_driver.c |    2 ++
>>>  1 files changed, 2 insertions(+), 0 deletions(-)
>>> diff --git a/drivers/acpi/processor_driver.c
>>> b/drivers/acpi/processor_driver.c
>>> index a4e0f1b..a1c564f 100644
>>> --- a/drivers/acpi/processor_driver.c
>>> +++ b/drivers/acpi/processor_driver.c
>>> @@ -677,6 +677,8 @@ static void acpi_processor_hotplug_notify(acpi_handle
>>> handle,
>>>                                     "Driver data is NULL, dropping
>>> EJECT\n");
>>>                         return;
>>>                 }
>>> +
>>> +               kobject_uevent(&device->dev.kobj, KOBJ_OFFLINE);
>>>                 break;
>>>         default:
>>>                 ACPI_DEBUG_PRINT((ACPI_DB_INFO,
>>
>> The processor driver used to generate ONLINE and OFFLINE messages.  I
>> removed them with c1815e0740.  According to the changelog, the driver
>> core still generates KOBJ_ADD and KOBJ_REMOVE events.
>
> Thanks for your answer.
> When I used xen tools (xm vcpu-set vcpu_numer) to reduce the cpu number. I
> don't found any event . I use the following tool to capture the event:
> udevadm monitor --env --kernel --udev.
>
> If I used xen tools to add the cpu number , udev module will receive the
> KOBJ_ADD event.
>
> In my patch ,It is more fine to replace KOBJ_OFFLINE to KOBJ_REMOVE event .

I don't think we should emit KOBJ_REMOVE from the ACPI processor
driver.  KOBJ_ADD is emitted by the driver model core
(device_register() -> device_add() path), and I think KOBJ_REMOVE
should also be emitted from the driver model core.

Is acpi_processor_remove() called when you remove a processor?  I see
a path where it will be called via acpi_eject_store():

    acpi_eject_store
      acpi_os_hotplug_execute(acpi_bus_hot_remove_device)
      acpi_bus_hot_remove_device
        acpi_bus_trim
          acpi_bus_remove
            device_release_driver
              dev->driver->remove (acpi_processor_remove())
            acpi_device_unregister
              device_unregister
                device_del
                  kobject_uevent(KOBJ_REMOVE)

but as far as I can tell, this path is only used when we write
something to the "eject" sysfs file.  I would think we'd want to use
most of this same path when we hot remove a CPU via the ACPI SCI
mechanism.

If you change acpi_processor_hotplug_notify() to use acpi_bus_trim()
for the removal case, you should get KOBJ_REMOVE events.  Would that
be enough to make the xen vcpu remove work, or at least get you
closer?

> btw: how to find changelog of the c1815e0740.

git show c1815e0740

Bjorn
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