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

From: Guoqing Jiang
Date: Sun Apr 16 2023 - 23:10:50 EST



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?
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.

[ 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,
Guoqing