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

[Guoqing Jiang]

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