linux-kernel - Re: [PATCH for-next 2/3] RDMA/rtrs: Fix rxe_dealloc

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Date:   Tue, 18 Apr 2023 07:04:00 +0000
From:   "Zhijian Li (Fujitsu)" <lizhijian@...itsu.com>
To:     Leon Romanovsky <leon@...nel.org>
CC:     Zhu Yanjun <yanjun.zhu@...ux.dev>,
        Guoqing Jiang <guoqing.jiang@...ux.dev>,
        "haris.iqbal@...os.com" <haris.iqbal@...os.com>,
        "jinpu.wang@...os.com" <jinpu.wang@...os.com>,
        "jgg@...pe.ca" <jgg@...pe.ca>,
        "linux-rdma@...r.kernel.org" <linux-rdma@...r.kernel.org>,
        "linux-kernel@...r.kernel.org" <linux-kernel@...r.kernel.org>
Subject: Re: [PATCH for-next 2/3] RDMA/rtrs: Fix rxe_dealloc_pd warning



On 18/04/2023 02:04, Leon Romanovsky wrote:
> On Mon, Apr 17, 2023 at 02:18:24AM +0000, Zhijian Li (Fujitsu) wrote:
>>
>>
>> On 14/04/2023 23:58, Zhu Yanjun wrote:
>>> 在 2023/4/13 21:24, Leon Romanovsky 写道:
>>>> On Thu, Apr 13, 2023 at 08:12:15AM +0000, Zhijian Li (Fujitsu) wrote:
>>>>>
>>>>>
>>>>> On 13/04/2023 15:35, Guoqing Jiang wrote:
>>>>>> Hi,
>>>>>>
>>>>>> I take a closer look today.
>>>>>>
>>>>>> On 4/12/23 09:15, Zhijian Li (Fujitsu) wrote:
>>>>>>>
>>>>>>> On 11/04/2023 20:26, Leon Romanovsky wrote:
>>>>>>>> On Tue, Apr 11, 2023 at 02:43:46AM +0000, Zhijian Li (Fujitsu) wrote:
>>>>>>>>>
>>>>>>>>> On 10/04/2023 21:10, Guoqing Jiang wrote:
>>>>>>>>>>
>>>>>>>>>> On 4/10/23 20:08, Leon Romanovsky wrote:
>>>>>>>>>>> On Mon, Apr 10, 2023 at 06:43:03AM +0000, Li Zhijian wrote:
>>>>>>>>>>>> The warning occurs when destroying PD whose reference count is not zero.
>>>>>>>>>>>>
>>>>>>>>>>>> Precodition: clt_path->s.con_num is 2.
>>>>>>>>>>>> So 2 cm connection will be created as below:
>>>>>>>>>>>> CPU0                                              CPU1
>>>>>>>>>>>> init_conns {                              |
>>>>>>>>>>>>        create_cm() // a. con[0] created        |
>>>>>>>>>>>>                                                |  a'. rtrs_clt_rdma_cm_handler() {
>>>>>>>>>>>>                                                |    rtrs_rdma_addr_resolved()
>>>>>>>>>>>>                                                |      create_con_cq_qp(con); << con[0]
>>>>>>>>>>>>                                                |  }
>>>>>>>>>>>>                                                | in this moment, refcnt of PD was increased to 2+
>>>>>>
>>>>>> What do you mean "refcnt of PD"? usecnt in struct ib_pd or dev_ref.
>>>>>
>>>>> I mean usecnt in struct ib_pd
>>>>>
>>>>>
>>>>>
>>>>>>
>>>>>>>>>>>>                                                |
>>>>>>>>>>>>        create_cm() // b. cid = 1, failed       |
>>>>>>>>>>>>          destroy_con_cq_qp()                   |
>>>>>>>>>>>>            rtrs_ib_dev_put()                   |
>>>>>>>>>>>>              dev_free()                        |
>>>>>>>>>>>>                ib_dealloc_pd(dev->ib_pd) << PD |
>>>>>>>>>>>>                 is destroyed, but refcnt is    |
>>>>>>>>>>>>                 still greater than 0           |
>>>>>>
>>>>>> Assuming you mean "pd->usecnt". We only allocate pd in con[0] by rtrs_ib_dev_find_or_add,
>>>>>> if con[1] failed to create cm, then alloc_path_reqs -> ib_alloc_mr -> atomic_inc(&pd->usecnt)
>>>>>> can't be triggered. Is there other places could increase the refcnt?
>>>>>
>>>>>
>>>>> Yes, when create a qp, it will also associate to this PD, that also mean refcnt of PD will be increased.
>>>>>
>>>>> When con[0](create_con_cq_qp) succeeded, refcnt of PD will be 2. and then when con[1] failed, since
>>>>> QP didn't create, refcnt of PD is still 2. con[1]'s cleanup will destroy the PD(ib_dealloc_pd) since dev_ref = 1, after that its
>>>>> refcnt is still 1.
>>>>
>>>> Why is refcnt 1 in con[1] destruction phase? It seems to me like a bug.
>>
>>
>>
>>> +	if (!con->has_dev)
>>> +		return;
>>>   	if (clt_path->s.dev_ref && !--clt_path->s.dev_ref) {
>>>   		rtrs_ib_dev_put(clt_path->s.dev);
>>>   		clt_path->s.dev = NULL;
>>
>> Currently, without this patch:
>> 1. PD and clt_path->s.dev are shared among connections.
>> 2. every con[n]'s cleanup phase will call destroy_con_cq_qp()
>> 3. clt_path->s.dev will be always decreased in destroy_con_cq_qp(), and when
>>      clt_path->s.dev become zero, it will destroy PD.
>> 4. when con[1] failed to create, con[1] will not take clt_path->s.dev, but it try to decreased clt_path->s.dev <<< it's wrong to do that.
> 
> So please fix it by making sure that failure to create con[1] will
> release resources which were allocated. If con[1] didn't increase
> s.dev_ref, it shouldn't decrease it either.

You are right, the current patch did exactly that.
It introduced a con owning flag 'has_dev' to indicate whether this con has taken s.dev.
so that its cleanup phase will only decrease its s.dev properly.

Thanks
Zhijian


> 
> Thanks
> 
>>
>>
>> Thanks
>> Zhijian
>>
>>> Agree. We should find out why refcnt 1 and fix this problem.
>>
>>
>>
>>
>>>
>>> Zhu Yanjun
>>>>
>>>> Thanks
>>>