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

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Date:   Thu, 13 Apr 2023 16:24:18 +0300
From:   Leon Romanovsky <leon@...nel.org>
To:     "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

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.

Thanks