Re: [PATCH for-next] RDMA/hns: Bugfix for flush cqe in case softirq and multi-process

["Liuyixian (Eason)" <liuyixian@huawei.com>]

On 2019/11/5 22:37, Leon Romanovsky wrote:
> On Tue, Nov 05, 2019 at 10:06:20AM +0800, Liuyixian (Eason) wrote:
>>
>>
>> On 2019/10/28 17:34, Liuyixian (Eason) wrote:
>>>
>>>
>>> On 2019/10/15 16:00, Leon Romanovsky wrote:
>>>> On Sat, Oct 12, 2019 at 11:53:36AM +0800, Liuyixian (Eason) wrote:
>>>>>
>>>>>
>>>>> On 2019/9/24 11:54, Liuyixian (Eason) wrote:
>>>>>>
>>>>>>
>>>>>> On 2019/9/23 13:01, Leon Romanovsky wrote:
>>>>>>> On Fri, Sep 20, 2019 at 11:55:56AM +0800, Liuyixian (Eason) wrote:
>>>>>>>>
>>>>>>>>
>>>>>>>> On 2019/9/11 21:17, Liuyixian (Eason) wrote:
>>>>>>>>>
>>>>>>>>>
>>>>>>>>> On 2019/9/10 15:52, Leon Romanovsky wrote:
>>>>>>>>>> On Tue, Sep 10, 2019 at 02:40:20PM +0800, Liuyixian (Eason) wrote:
>>>>>>>>>>>
>>>>>>>>>>>
>>>>>>>>>>> On 2019/9/8 16:03, Leon Romanovsky wrote:
>>>>>>>>>>>> On Thu, Sep 05, 2019 at 08:31:11PM +0800, Weihang Li wrote:
>>>>>>>>>>>>> From: Yixian Liu <liuyixian@huawei.com>
>>>>>>>>>>>>>
>>>>>>>>>>>>> Hip08 has the feature flush cqe, which help to flush wqe in workqueue
>>>>>>>>>>>>> (sq and rq) when error happened by transmitting producer index with
>>>>>>>>>>>>> mailbox to hardware. Flush cqe is emplemented in post send and recv
>>>>>>>>>>>>> verbs. However, under NVMe cases, these verbs will be called under
>>>>>>>>>>>>> softirq context, and it will lead to following calltrace with
>>>>>>>>>>>>> current driver as mailbox used by flush cqe can go to sleep.
>>>>>>>>>>>>>
>>>>>>>>>>>>> This patch solves this problem by using workqueue to do flush cqe,
>>>>>>>>>>>>
>>>>>>>>>>>> Unbelievable, almost every bug in this driver is solved by introducing
>>>>>>>>>>>> workqueue. You should fix "sleep in flush path" issue and not by adding
>>>>>>>>>>>> new workqueue.
>>>>>>>>>>>>
>>>>>>>>>>> Hi Leon,
>>>>>>>>>>>
>>>>>>>>>>> Thanks for the comment.
>>>>>>>>>>> Up to now, for hip08, only one place use workqueue in hns_roce_hw_v2.c
>>>>>>>>>>> where for irq prints.
>>>>>>>>>>
>>>>>>>>>> Thanks to our lack of desire to add more workqueues and previous patches
>>>>>>>>>> which removed extra workqueues from the driver.
>>>>>>>>>>
>>>>>>>>> Thanks, I see.
>>>>>>>>>
>>>>>>>>>>>
>>>>>>>>>>> The solution for flush cqe in this patch is as follow:
>>>>>>>>>>> While flush cqe should be implement, the driver should modify qp to error state
>>>>>>>>>>> through mailbox with the newest product index of sq and rq, the hardware then
>>>>>>>>>>> can flush all outstanding wqes in sq and rq.
>>>>>>>>>>>
>>>>>>>>>>> That's the whole mechanism of flush cqe, also is the flush path. We can't
>>>>>>>>>>> change neither mailbox sleep attribute or flush cqe occurred in post send/recv.
>>>>>>>>>>> To avoid the calltrace of flush cqe in post verbs under NVMe softirq,
>>>>>>>>>>> use workqueue for flush cqe seems reasonable.
>>>>>>>>>>>
>>>>>>>>>>> As far as I know, there is no other alternative solution for this situation.
>>>>>>>>>>> I will be very grateful if you reminder me more information.
>>>>>>>>>>
>>>>>>>>>> ib_drain_rq/ib_drain_sq/ib_drain_qp????
>>>>>>>>>>
>>>>>>>>> Hi Leon,
>>>>>>>>>
>>>>>>>>> I think these interfaces are designed for application to check that all wqes
>>>>>>>>> have been processed by hardware, so called drain or flush. However, it is not
>>>>>>>>> the same as the flush in this patch. The solution in this patch is used
>>>>>>>>> to help the hardware generate flush cqes for outstanding wqes while qp error.
>>>>>>>>>
>>>>>>>> Hi Leon,
>>>>>>>>
>>>>>>>> What's your opinion about above? Do you have any further comments?
>>>>>>>
>>>>>>> My opinion didn't change, you need to read discussions about ib_drain_*()
>>>>>>> functions, how and why they were introduced. It is a way to go.
>>>>>>>
>>>>>>> Thanks
>>>>>>
>>>>>> Hi Leon,
>>>>>>
>>>>>> Thanks a lot! I will dig those functions for my problem.
>>>>>>
>>>>>
>>>>> Hi Leon,
>>>>>
>>>>> I have analysis the mechanism of ib_drain_(qp, sq, rq), that's okay to use
>>>>> it instead of our flush cqe as both of them are calling modify qp to error
>>>>> state in flush path.
>>>>>
>>>>> However, both ib_drain_* and flush cqe will face the same problem as declared
>>>>> in previous emails, that is, in NVME case, post verbs will be called under
>>>>> **softirq**, which will result to calltrace as mailbox used in modify qp
>>>>> (flush path) can sleep, this is not allowed under softirq.
>>>>>
>>>>> Thus, to resolve above calltrace (sleep in softirq), using workqueue as in
>>>>> this patch seems is a reasonable solution regardless of ib_drain_qp or
>>>>> flush cqe is called in the workqueue.
>>>>>
>>>>> I think it is not a good idea to fix sleep in flush path (actually referred
>>>>> to mailbox used in modify qp) as the mailbox is such a mature mechanism.
>>>>
>>>> No, it is not reasonable solution.
>>>>
>>>
>>> Hi Leon,
>>>
>>>      I have explained this issue better in another patch set and pruned other logic.
>>>      Thanks a lot for your review!
>>>
>>> Best regards.
>>> Eason
>>>
>>
>> Hi Doug and Loen,
>>
>> I just want to make sure that you know the above mentioned patch set is on:
>> https://patchwork.kernel.org/project/linux-rdma/list/?series=194423
>>
>> Sorry to reply your last comment so late as I analyzed all possible solutions with
>> your comment, and found that I haven't describe our problem clear enough and accurate,
>> thus, I made this new patch set with simple logic and detailed commit message. I hope
>> I have clearly explained this problem .
> 
> Hi,
> 
> I'm confident that Doug and/or Jason will review it very soon.
> 
> Thanks

Thanks a lot!

> 
>>
>> Thanks.
>>
>>
>>
>>
> 
> .
>