Re: [PATCH V5 1/6] vhost: introduce vhost_vring_call

[Jason Wang <jasowang@redhat.com>]

On 2020/8/5 下午1:49, Zhu, Lingshan wrote:
>
>
> On 8/5/2020 10:16 AM, Jason Wang wrote:
>>
>> On 2020/8/4 下午5:21, Michael S. Tsirkin wrote:
>>>>>>>    +struct vhost_vring_call {
>>>>>>> +    struct eventfd_ctx *ctx;
>>>>>>> +    struct irq_bypass_producer producer;
>>>>>>> +    spinlock_t ctx_lock;
>>>>>> It's not clear to me why we need ctx_lock here.
>>>>>>
>>>>>> Thanks
>>>>> Hi Jason,
>>>>>
>>>>> we use this lock to protect the eventfd_ctx and irq from race 
>>>>> conditions,
>>>> We don't support irq notification from vDPA device driver in this 
>>>> version,
>>>> do we still have race condition?
>>>>
>>>> Thanks
>>> Jason I'm not sure what you are trying to say here.
>>
>>
>> I meant we change the API from V4 so driver won't notify us if irq is 
>> changed.
>>
>> Then it looks to me there's no need for the ctx_lock, everyhing could 
>> be synchronized with vq mutex.
>>
>> Thanks
> from V4 to V5, there are only some minor improvements and bug fix, get_vq_irq() almost stays untouched, mutex can work for this, however I see the vq mutex is used in many scenarios.
> We only use this lock to protect the producer information, can this help to get less coupling, defensive code for less bugs?


I think not, vq mutex is used to protect all vq related data structure, 
introducing another one will increase the complexity.

Thanks


>
> Thanks
>>
>>>
>>>
>>