[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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