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

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Date:   Fri, 14 Apr 2023 23:58:26 +0800
From:   Zhu Yanjun <yanjun.zhu@...ux.dev>
To:     Leon Romanovsky <leon@...nel.org>,
        "Zhijian Li (Fujitsu)" <lizhijian@...itsu.com>
Cc:     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

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.
Agree. We should find out why refcnt 1 and fix this problem.

Zhu Yanjun
> 
> Thanks