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

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Date:	Wed, 17 Oct 2012 17:08:58 +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 10/17/2012 04:59 PM, KOSAKI Motohiro Wrote:
> On Wed, Oct 17, 2012 at 2:48 AM, Wen Congyang <wency@...fujitsu.com> wrote:
>> 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.
> 
> Heh, please explain why do you think so.
> 


We just introduce a function, and move codes from acpi_memory_disable_device() to the new
function. We call the new function in acpi_memory_disable_device(), so the function
acpi_memory_disable_device()'s behavior isn't changed.

Maybe I don't understand what do you want to say.

Thanks
Wen Congyang
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