Re: [PATCH] ethdev: fix wrong memset

[Ferruh Yigit <ferruh.yigit@intel.com>]

On 1/23/2017 1:06 PM, Ananyev, Konstantin wrote:
> 
> 
>> -----Original Message-----
>> From: Yuanhan Liu [mailto:yuanhan.liu@linux.intel.com]
>> Sent: Monday, January 23, 2017 12:53 PM
>> To: Ananyev, Konstantin <konstantin.ananyev@intel.com>
>> Cc: Yigit, Ferruh <ferruh.yigit@intel.com>; dev@dpdk.org; Thomas Monjalon <thomas.monjalon@6wind.com>; Horton, Remy
>> <remy.horton@intel.com>
>> Subject: Re: [dpdk-dev] [PATCH] ethdev: fix wrong memset
>>
>> On Mon, Jan 23, 2017 at 12:44:11PM +0000, Ananyev, Konstantin wrote:
>>>> On Mon, Jan 23, 2017 at 07:40:50PM +0800, Yuanhan Liu wrote:
>>>>> On Mon, Jan 23, 2017 at 11:32:23AM +0000, Ferruh Yigit wrote:
>>>>>> On 1/23/2017 11:24 AM, Yuanhan Liu wrote:
>>>>>>> On Mon, Jan 23, 2017 at 11:05:25AM +0000, Ferruh Yigit wrote:
>>>>>>>>>>>>>>  lib/librte_ether/rte_ethdev.c | 2 +-
>>>>>>>>>>>>>>  1 file changed, 1 insertion(+), 1 deletion(-)
>>>>>>>>>>>>>>
>>>>>>>>>>>>>> diff --git a/lib/librte_ether/rte_ethdev.c b/lib/librte_ether/rte_ethdev.c
>>>>>>>>>>>>>> index 4790faf..61f44e2 100644
>>>>>>>>>>>>>> --- a/lib/librte_ether/rte_ethdev.c
>>>>>>>>>>>>>> +++ b/lib/librte_ether/rte_ethdev.c
>>>>>>>>>>>>>> @@ -225,7 +225,7 @@ struct rte_eth_dev *
>>>>>>>>>>>>>>  		return NULL;
>>>>>>>>>>>>>>  	}
>>>>>>>>>>>>>>
>>>>>>>>>>>>>> -	memset(&rte_eth_devices[port_id], 0, sizeof(*eth_dev->data));
>>>>>>>>>>>>>> +	memset(&rte_eth_dev_data[port_id], 0, sizeof(struct rte_eth_dev_data));
>>>>>>>>>>>>>
>>>>>>>>>>>>> Not directly related to the this issue, but, after fix, this may have
>>>>>>>>>>>>> issues with secondary process.
>>>>>>>>>>>>>
>>>>>>>>>>>>> There were patches sent to fix this.
>>>>>>>>>>>>
>>>>>>>>>>>> I mean this one:
>>>>>>>>>>>> http://dpdk.org/ml/archives/dev/2017-January/054422.html
>>>>>>>>>>>
>>>>>>>>>>> d948f596fee2 ("ethdev: fix port data mismatched in multiple process
>>>>>>>>>>> model") should have fixed it.
>>>>>>>>>>
>>>>>>>>>> Think about case, where secondary process uses a virtual PMD, which does
>>>>>>>>>> a rte_eth_dev_allocate() call, shouldn't this corrupt primary process
>>>>>>>>>> device data?
>>>>>>>>>
>>>>>>>>> Yes, it may. However, I doubt that's the typical usage.
>>>>>>>>
>>>>>>>> But this is a use case, and broken now,
>>>>>>>
>>>>>>> I thought it was broken since the beginning?
>>>>>>
>>>>>> No, memset(&rte_eth_dev_data[port_id], ...) breaks it.
>>>>>
>>>>> Oh, you were talking about that particular case Remy's patch meant to
>>>>> fix.
>>>>>
>>>>>>>> and fix is known.
>>>>>>>
>>>>>>> And there is already a fix?
>>>>>>
>>>>>> http://dpdk.org/ml/archives/dev/2017-January/054422.html
>>>>>
>>>>> Yes, it should fix that issue.
>>>>
>>>> Well, few more thoughts: it may fix the crash issue Remy saw, but it
>>>> looks like more a workaround to me. Basically, if primary and secondary
>>>> shares a same port id, they should point to same device. Otherwise,
>>>> primary process may use eth_dev->data for a device A, while the
>>>> secondary process may use it for another device, as you said, it
>>>> could be a vdev.
>>>>
>>>> In such case, there is no way we could continue safely. That said,
>>>> the given patch avoids the total reset of eth_dev->data, while it
>>>> continues reset the eth_dev->data->name, which is wrong.
>>>>
>>>> So it's not a proper fix.
>>>>
>>>> Again, I think it's more about the usage. If primary starts with
>>>> a nic device A, while the secondary starts with a nic device B,
>>>> there is no way they could work well (unless they use different
>>>> port id).
>>>
>>> Why not?
>>> I think this is possible.
>>
>> Yes, it's possible: find another port id if that one is already taken
>> by primary process (or even by secondary process: think that primary
>> process might attatch a port later).
>>
>>> They just need to be initialized properly,
>>> so each rte_eth_devices[port_id]->data, etc. point to the right place.
>>
>> My understanding is, as far as they use different port_id, it might
>> be fine. Just not sure it's enough or not.
> 
> As I understand, the main problem is that  rte_eth_devices[] is local,
> while rte_eth_dev_data points to the shared memory array.
> And rte_eth_dev_allocate() assumes that if rte_eth_devices[x] is free,
> then rte_eth_dev_data[port_id] is also free.
> Which is wrong in case when primary/secondary processes have different devices attached.
> Another problem is that inside rte_ethdev.c we manipulate rte_eth_dev_data[]
> contents without grabbing any lock.

> I think it was an attempt to fix that issue in 16.07 timeframe or so,
> but I don't remember what happened with that patch.

Same here, I remember this already discussed and even some patches sent,
by Reshma if I remember correctly, but I don't remember latest status.

> Konstantin 
> 
> 
> 
>