Re: node-hotplug: is memset 0 safe in try_offline_node()?

[Xie XiuQi <xiexiuqi@huawei.com>]

On 2015/3/11 9:12, Gu Zheng wrote:
> Hi Xishi,
> 
> What is the condition of this problem now?

Hi Gu,

I have no machine to do this test now. But I've tested the
patch "just remove memset 0" more than 20 hours last week,
it's OK.

Thanks,
	Xie XiuQi

> 
> Regards,
> Gu
> On 03/05/2015 05:39 PM, Xishi Qiu wrote:
> 
>> On 2015/3/5 16:26, Gu Zheng wrote:
>>
>>> Hi Xishi,
>>> Could you please try the following one?
>>> It postpones the reset of obsolete pgdat from try_offline_node() to
>>> hotadd_new_pgdat(), and just resetting pgdat->nr_zones and
>>> pgdat->classzone_idx to be 0 rather than the whole reset by memset()
>>> as Kame suggested.
>>>
>>> Regards,
>>> Gu
>>>
>>> ---
>>>  mm/memory_hotplug.c |   13 ++++---------
>>>  1 files changed, 4 insertions(+), 9 deletions(-)
>>>
>>> diff --git a/mm/memory_hotplug.c b/mm/memory_hotplug.c
>>> index 1778628..c17eebf 100644
>>> --- a/mm/memory_hotplug.c
>>> +++ b/mm/memory_hotplug.c
>>> @@ -1092,6 +1092,10 @@ static pg_data_t __ref *hotadd_new_pgdat(int nid, u64 start)
>>>  			return NULL;
>>>  
>>>  		arch_refresh_nodedata(nid, pgdat);
>>> +	} else {
>>> +		/* Reset the nr_zones and classzone_idx to 0 before reuse */
>>> +		pgdat->nr_zones = 0;
>>> +		pgdat->classzone_idx = 0;
>>
>> Hi Gu,
>>
>> This is just to avoid the warning, I think it's no meaning.
>> Here is the changlog from the original patch:
>>
>> commit 88fdf75d1bb51d85ba00c466391770056d44bc03
>>     ...
>>     Warn if memory-hotplug/boot code doesn't initialize pg_data_t with zero
>>     when it is allocated.  Arch code and memory hotplug already initiailize
>>     pg_data_t.  So this warning should never happen.  I select fields *randomly*
>>     near the beginning, middle and end of pg_data_t for checking.
>>     ...
>>
>> Thanks,
>> Xishi Qiu
>>
>>>  	}
>>>  
>>>  	/* we can use NODE_DATA(nid) from here */
>>> @@ -2021,15 +2025,6 @@ void try_offline_node(int nid)
>>>  
>>>  	/* notify that the node is down */
>>>  	call_node_notify(NODE_DOWN, (void *)(long)nid);
>>> -
>>> -	/*
>>> -	 * Since there is no way to guarentee the address of pgdat/zone is not
>>> -	 * on stack of any kernel threads or used by other kernel objects
>>> -	 * without reference counting or other symchronizing method, do not
>>> -	 * reset node_data and free pgdat here. Just reset it to 0 and reuse
>>> -	 * the memory when the node is online again.
>>> -	 */
>>> -	memset(pgdat, 0, sizeof(*pgdat));
>>>  }
>>>  EXPORT_SYMBOL(try_offline_node);
>>>  
>>
>>
>>
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> 
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