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Date:   Thu, 13 Apr 2023 16:24:18 +0300
From:   Leon Romanovsky <leon@kernel.org>
To:     "Zhijian Li (Fujitsu)" <lizhijian@fujitsu.com>
Cc:     Guoqing Jiang <guoqing.jiang@linux.dev>,
        "haris.iqbal@ionos.com" <haris.iqbal@ionos.com>,
        "jinpu.wang@ionos.com" <jinpu.wang@ionos.com>,
        "jgg@ziepe.ca" <jgg@ziepe.ca>,
        "linux-rdma@vger.kernel.org" <linux-rdma@vger.kernel.org>,
        "linux-kernel@vger.kernel.org" <linux-kernel@vger.kernel.org>
Subject: Re: [PATCH for-next 2/3] RDMA/rtrs: Fix rxe_dealloc_pd warning
Message-ID: <20230413132418.GR17993@unreal>
References: <1681108984-2-1-git-send-email-lizhijian@fujitsu.com>
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 <0d9c57db-bca3-adb4-71fd-7362e4842917@linux.dev>
 <85323eb2-cfc7-d1b8-3a75-3fa63dde29db@fujitsu.com>
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 <aa43746f-77f9-8592-5370-2a5042506ee5@fujitsu.com>
 <8fe62e38-e43d-3d6c-624f-1c8ce5859788@linux.dev>
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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