Re: [PATCH for-next 2/3] RDMA/rtrs: Fix rxe_dealloc_pd warning

["Zhijian Li (Fujitsu)" <lizhijian@fujitsu.com>]

On 17/04/2023 11:08, Guoqing Jiang wrote:
> 
> 
> On 4/14/23 18:09, Zhijian Li (Fujitsu) wrote:
>>
>> 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.
> 
> I am confused, does increase ref_cnt equal to increase usecnt?


I need to apologize for my mistake. I have been referring to the elem.ref_cnt of the rxe driver as the refcnt of PD.


> If not, then where is another place to increase usecnt to 2?
> 
> BTW, I traced with 6.3-rc5, seems pd's usecnt is only increase once
> after create one connection.

And the warning mentioned above it also pointed to the PD's elem.ref_cnt.

> 
> [ 6941.525088] in init_conns 2353 con_num=3
> [ 6941.525732] in create_con_cq_qp 1648
> [ 6941.525944] in rtrs_cq_qp_create 311 con->cid=0 path->dev->ib_pd->usecnt=1
> [ 6941.532460] in create_con_cq_qp 1648
> [ 6941.532746] in rtrs_cq_qp_create 311 con->cid=1 path->dev->ib_pd->usecnt=2
> [ 6941.533183] in create_con_cq_qp 1648
> [ 6941.533464] in rtrs_cq_qp_create 311 con->cid=2 path->dev->ib_pd->usecnt=3
> [ 6941.533685] in init_conns 2365, clt_path->s.dev->ib_pd->usecnt=3
> [ 6941.535680] in init_conns 2371, clt_path->s.dev->ib_pd->usecnt=515

Thanks
Zhijian

below is a piece of code that i used to debug this issue.

--- a/drivers/infiniband/ulp/rtrs/rtrs-clt.c
+++ b/drivers/infiniband/ulp/rtrs/rtrs-clt.c
@@ -1730,15 +1730,39 @@ static int create_con_cq_qp(struct rtrs_clt_con *con)
         return err;
  }
  
+struct rxe_pool;
+struct rxe_pool_elem {
+       struct rxe_pool         *pool;
+       void                    *obj;
+       struct kref             ref_cnt;
+       struct list_head        list;
+       struct completion       complete;
+       u32                     index;
+};
+
+struct rxe_pd {
+       struct ib_pd            ibpd;
+       struct rxe_pool_elem    elem;
+};
+
+static inline struct rxe_pd *to_rpd(struct ib_pd *pd)
+{
+       return pd ? container_of(pd, struct rxe_pd, ibpd) : NULL;
+}
+
+#define rxe_read(obj) kref_read(&(obj)->elem.ref_cnt)
  static void destroy_con_cq_qp(struct rtrs_clt_con *con)
  {
         struct rtrs_clt_path *clt_path = to_clt_path(con->c.path);
+       struct rtrs_ib_dev *dev = clt_path->s.dev;
+       struct rxe_pd *pd = to_rpd(dev->ib_pd);
  
         /*
          * Be careful here: destroy_con_cq_qp() can be called even
          * create_con_cq_qp() failed, see comments there.
          */
         lockdep_assert_held(&con->con_mutex);
+       rtrs_info(clt_path->clt, "%s: clt_path->s.dev_ref: %d, pd %px, ref: %d\n", __func__, clt_path->s.dev_ref, &pd->elem, rxe_read(pd));
         rtrs_cq_qp_destroy(&con->c);
         if (con->rsp_ius) {
                 rtrs_iu_free(con->rsp_ius, clt_path->s.dev->ib_dev,
@@ -1746,7 +1770,8 @@ static void destroy_con_cq_qp(struct rtrs_clt_con *con)
                 con->rsp_ius = NULL;
                 con->queue_num = 0;
         }
+       rtrs_info(clt_path->clt, "%s: clt_path->s.dev_ref: %d, pd %px, ref: %d\n", __func__, clt_path->s.dev_ref, &pd->elem, rxe_read(pd));
         if (clt_path->s.dev_ref && !--clt_path->s.dev_ref) {
                 rtrs_ib_dev_put(clt_path->s.dev);
                 clt_path->s.dev = NULL;



> 
> Thanks,
> Guoqing