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

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Date:   Fri, 14 Apr 2023 11:40:35 +0800
From:   Guoqing Jiang <guoqing.jiang@...ux.dev>
To:     "Zhijian Li (Fujitsu)" <lizhijian@...itsu.com>,
        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 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?

>> 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?

+	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;

Then when will you dealloc pd and free rtrs_ib_dev?

Thanks,
Guoqing