[dpdk-dev] [PATCH v3 2/5] bus/vdev: add lock on vdev device list

Tan, Jianfeng jianfeng.tan at intel.com
Fri Apr 20 17:23:53 CEST 2018



On 4/20/2018 11:16 PM, Burakov, Anatoly wrote:
> On 20-Apr-18 3:19 PM, Tan, Jianfeng wrote:
>>
>>
>> On 4/20/2018 4:26 PM, Burakov, Anatoly wrote:
>>> On 19-Apr-18 5:50 PM, Jianfeng Tan wrote:
>>>> As we could add virtual devices from different threads now, we
>>>> add a spin lock to protect the vdev device list.
>>>>
>>>> Suggested-by: Anatoly Burakov <anatoly.burakov at intel.com>
>>>> Signed-off-by: Jianfeng Tan <jianfeng.tan at intel.com>
>>>> Reviewed-by: Qi Zhang <qi.z.zhang at intel.com>
>>>> ---
>>>
>>> <...>
>>>
>>>> +/* The caller shall be responsible for thread-safe */
>>>>   static struct rte_vdev_device *
>>>>   find_vdev(const char *name)
>>>>   {
>>>> @@ -203,10 +206,6 @@ rte_vdev_init(const char *name, const char *args)
>>>>       if (name == NULL)
>>>>           return -EINVAL;
>>>>   -    dev = find_vdev(name);
>>>> -    if (dev)
>>>> -        return -EEXIST;
>>>> -
>>>>       devargs = alloc_devargs(name, args);
>>>>       if (!devargs)
>>>>           return -ENOMEM;
>>>> @@ -221,16 +220,28 @@ rte_vdev_init(const char *name, const char 
>>>> *args)
>>>>       dev->device.numa_node = SOCKET_ID_ANY;
>>>>       dev->device.name = devargs->name;
>>>>   +    rte_spinlock_lock(&vdev_device_list_lock);
>>>> +    if (find_vdev(name)) {
>>>> +        rte_spinlock_unlock(&vdev_device_list_lock);
>>>> +        ret = -EEXIST;
>>>> +        goto fail;
>>>> +    }
>>>> +    TAILQ_INSERT_TAIL(&vdev_device_list, dev, next);
>>>> +    rte_spinlock_unlock(&vdev_device_list_lock);
>>>> +
>>>
>>> I wonder if is possible to just leave the tailq locked until you 
>>> either insert the device into tailq, or figure out that it's not 
>>> possible? Seems like doing two locks here is unnecessary, unless 
>>> vdev_probe_all_drivers needs this tailq unlocked...
>>
>> My opinion is that we don't know what could be done in driver 
>> probe(). It could possibly insert a new vdev (it does not happen now, 
>> but could happen in future?). So here, we call this with tailq 
>> unlocked. Or we keep it as simple as possible as you say?
>
> I thought this code was responsible for inserting vdevs? I think it 
> would be generally bad design to insert vdev while inserting vdev :)

I might have mixed this with another case. I think it's a fair point.

>
> That said, it's a fair point, and i don't have a strong opinion on 
> this, so you can leave it as is if you want.

I'll change the implementation.

Thanks,
Jianfeng


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