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

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Message-ID: <71935de6-e3c1-c719-4e66-19242af51ab7@fujitsu.com>
Date:   Fri, 14 Apr 2023 10:09:53 +0000
From:   "Zhijian Li (Fujitsu)" <lizhijian@...itsu.com>
To:     Guoqing Jiang <guoqing.jiang@...ux.dev>,
        Leon Romanovsky <leon@...nel.org>
CC:     "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 14/04/2023 14:04, Guoqing Jiang wrote:
> 
> 
> On 4/14/23 13:37, Zhijian Li (Fujitsu) wrote:
>>
>> On 14/04/2023 11:40, Guoqing Jiang wrote:
>>>
>>> On 4/13/23 16:12, 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)
>>> The above can't be invoked, right?
>>>
>>>>> 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.
>>> I can see the path increase usecnt to 1.
>>>
>>> rtrs_cq_qp_create -> create_qp
>>>                       -> rdma_create_qp
>>>                           -> ib_create_qp
>>>                               -> create_qp
>>>                               -> ib_qp_usecnt_inc which increases pd->usecnt
>>>
>>> Where is another place to increase usecnt to 2?
>> It should be
>> ib_create_qp　...
>>     -> rxe_create_qp
>>       -> rxe_qp_from_init
>>          -> rxe_get(pd) <<< pd's refcnt will be increased.
> 
> Isn't rxe_get just increase elem->ref_cnt?

Yes, that's true.



> 
> https://elixir.bootlin.com/linux/v6.3-rc6/source/drivers/infiniband/sw/rxe/rxe_pool.c#L240
> 
>>>>> Then what is the appropriate time to call destroy_con_cq_qp for this scenario?
>>>>> Otherwise there could be memory leak.
>>>> we must ensure QP in con[0] is closed before destroying the PD.
>>>> Currently destroy_con_cq_qp() subroutine will close the opened QP first.
>>> Let me try another way, with below change, rtrs_ib_dev_put can't be called
>>> from destroy_con_cq_qp, right?
>> Not really, con[0]->has_dev is true, so con[0]'s cleanup will call rtrs_ib_dev_put()
>>
>> Without this patch, when con[1] failed, con[1]'s cleanup will be called first. then call con[0]'s cleanup.
>> After this change, con[1]'s cleanup will not call rtrs_ib_dev_put, but it will be called the later con[0]'s cleanup.
> 
> But rtrs_ib_dev_put relies on dev_ref, if con[1] returns earlier without decrease dev_ref
> (it is shared among connections), how rtrs_ib_dev_put can be called?
> 

we must ensure each connections that take dev_ref decrease dev_ref during its cleanup path.
So the new flag con->has_dev added to track if the con has taken the dev_ref.




> Thanks,
> Guoqing