Re: [dpdk-dev] [PATCH] net/vhost: fix segfault when creating vdev dynamically

["Tan, Jianfeng" <jianfeng.tan@intel.com>]

On 3/27/2018 7:28 PM, Maxime Coquelin wrote:
>
>
> On 03/27/2018 11:42 AM, Tan, Jianfeng wrote:
>>
>>
>> On 3/27/2018 5:24 PM, Chen, Junjie J wrote:
>>>>>> On 3/28/2018 12:05 AM, Junjie Chen wrote:
>>>>>>> when creating vdev dynamically, vhost pmd driver start directly
>>>>>>> without checking TX/RX queues ready or not, and thus cause
>>>>>>> segmentation fault when vhost library accessing queues. This patch
>>>>>>> add flag to check whether queues setup or not, and add driver start
>>>>>>> call into dev_start to allow user start it after setting up queue.
>>>>>> The issue is clear now. But this patch just puts the situation 
>>>>>> before below
>>>> fix:
>>>>>> "it doesn't create the actual datagram socket until you call 
>>>>>> .dev_start()."
>>>>> No, if the queue exist, the datagram socket still get created in 
>>>>> vhost_create
>>>> API, since the vhost_driver_register still exist in vhost_create.
>>>>
>>>> The queue can never be created, as it's still not probed.
>>> I think we need to separate this into two cases:
>>>     Statically create vdev, the datagram recreate logical is still 
>>> there since queues are exist already, this patch doesn't change 
>>> anything.
>>>     Dynamic create vdev, as you pointed out, queue can never be 
>>> created, while this should be not valid since In normal process of 
>>> creating vdev dynamically, we always need to config queues. Correct 
>>> me if I'm wrong.
>>
>> My point is, either vdev is created statically or dynamically, when 
>> probe(), queues are not setup yet definitely, then *the unix socket 
>> will not be created* until we set up the queues and do dev_start(). 
>> If the unix socket is not created, then VM cannot connect to it.
>
> FYI, I think I reproduced such an issue with the vdev statically created
> in the past, while doing some experiments. I didn't went further into 
> the analysis at that time, but it looks like the issue Junjie is trying
> to address with this patch for dynamically created vdev.

Yes, I have noticed that this issue mostly happens at dynamic case. Just 
try to suggest a proper way to fix. Please check if my suggestion in 
another email makes sense.

Thanks,
Jianfeng

>
> Cheers,
> Maxime