linux-kernel - Re: [PATCH 1/4] acpi,memory-hotplug : add memory offline code to acpi_memory_device

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Message-ID: <507E54AA.2080806@cn.fujitsu.com>
Date:	Wed, 17 Oct 2012 14:48:10 +0800
From:	Wen Congyang <wency@...fujitsu.com>
To:	KOSAKI Motohiro <kosaki.motohiro@...fujitsu.com>
CC:	Yasuaki Ishimatsu <isimatu.yasuaki@...fujitsu.com>, x86@...nel.org,
	linux-mm@...ck.org, linux-kernel@...r.kernel.org,
	linux-acpi@...r.kernel.org, rientjes@...gle.com, liuj97@...il.com,
	len.brown@...el.com, cl@...ux.com, minchan.kim@...il.com,
	akpm@...ux-foundation.org
Subject: Re: [PATCH 1/4] acpi,memory-hotplug : add memory offline code to
 acpi_memory_device_remove()

At 10/13/2012 03:10 AM, KOSAKI Motohiro Wrote:
>>>> -static int acpi_memory_disable_device(struct acpi_memory_device *mem_device)
>>>> +static int acpi_memory_remove_memory(struct acpi_memory_device *mem_device)
>>>>  {
>>>>         int result;
>>>>         struct acpi_memory_info *info, *n;
>>>>
>>>> +       list_for_each_entry_safe(info, n, &mem_device->res_list, list) {
>>>
>>> Which lock protect this loop?
>>
>> There is no any lock to protect it now...
> 
> When iterate an item removal list, you should use lock for protecting from
> memory corruption.
> 
> 
> 
> 
>>>> +static int acpi_memory_disable_device(struct acpi_memory_device *mem_device)
>>>> +{
>>>> +       int result;
>>>>
>>>>         /*
>>>>          * Ask the VM to offline this memory range.
>>>>          * Note: Assume that this function returns zero on success
>>>>          */
>>>
>>> Write function comment instead of this silly comment.
>>>
>>>> -       list_for_each_entry_safe(info, n, &mem_device->res_list, list) {
>>>> -               if (info->enabled) {
>>>> -                       result = remove_memory(info->start_addr, info->length);
>>>> -                       if (result)
>>>> -                               return result;
>>>> -               }
>>>> -               kfree(info);
>>>> -       }
>>>> +       result = acpi_memory_remove_memory(mem_device);
>>>> +       if (result)
>>>> +               return result;
>>>>
>>>>         /* Power-off and eject the device */
>>>>         result = acpi_memory_powerdown_device(mem_device);
>>>
>>> This patch move acpi_memory_powerdown_device() from ACPI_NOTIFY_EJECT_REQUEST
>>> to release callback, but don't explain why.
>>
>> Hmm, it doesn't move the code. It just reuse the code in acpi_memory_powerdown_device().
> 
> Even if reuse or not reuse, you changed the behavior. If any changes
> has no good rational, you cannot get an ack.

I don't understand this? IIRC, the behavior isn't changed.

Thanks
Wen Congyang

> 
> 
> 
> 
>>>> @@ -473,12 +486,23 @@ static int acpi_memory_device_add(struct
>>>>  static int acpi_memory_device_remove(struct acpi_device *device, int type)
>>>>  {
>>>>         struct acpi_memory_device *mem_device = NULL;
>>>> -
>>>> +       int result;
>>>>
>>>>         if (!device || !acpi_driver_data(device))
>>>>                 return -EINVAL;
>>>>
>>>>         mem_device = acpi_driver_data(device);
>>>> +
>>>> +       if (type == ACPI_BUS_REMOVAL_EJECT) {
>>>> +               /*
>>>> +                * offline and remove memory only when the memory device is
>>>> +                * ejected.
>>>> +                */
>>>
>>> This comment explain nothing. A comment should describe _why_ should we do.
>>> e.g. Why REMOVAL_NORMAL and REMOVEL_EJECT should be ignored. Why
>>> we need remove memory here instead of ACPI_NOTIFY_EJECT_REQUEST.
>>
>> Hmm, we have 2 ways to remove a memory:
>> 1. SCI
>> 2. echo 1 >/sys/bus/acpi/devices/PNP0C80:XX/eject
>>
>> In the 2nd case, there is no ACPI_NOTIFY_EJECT_REQUEST. We should offline
>> the memory and remove it from kernel in the release callback. We will poweroff
>> the memory device in acpi_bus_hot_remove_device(), so we must offline
>> and remove it if the type is ACPI_BUS_REMOVAL_EJECT.
>>
>> I guess we should not poweroff the memory device when we fail to offline it.
>> But device_release_driver() doesn't returns any error...
> 
> 1) I think /sys/bus/acpi/devices/PNP0C80:XX/eject should emulate acpi
> eject. Can't
> you make a pseudo acpi eject event and detach device by acpi regular path?
> 
> 2) Your explanation didn't explain why we should ignore REMOVAL_NORMAL
> and REMOVEL_EJECT. As far as reviewers can't track your intention, we
> can't maintain
> the code and can't ack them.
> 

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