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

[Leon Romanovsky <leon@kernel.org>]

On Mon, Apr 17, 2023 at 02:18:24AM +0000, Zhijian Li (Fujitsu) wrote:
> 
> 
> On 14/04/2023 23:58, Zhu Yanjun wrote:
> > 在 2023/4/13 21:24, Leon Romanovsky 写道:
> >> 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.
> 
> 
> 
> > +	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;
> 
> Currently, without this patch:
> 1. PD and clt_path->s.dev are shared among connections.
> 2. every con[n]'s cleanup phase will call destroy_con_cq_qp()
> 3. clt_path->s.dev will be always decreased in destroy_con_cq_qp(), and when
>     clt_path->s.dev become zero, it will destroy PD.
> 4. when con[1] failed to create, con[1] will not take clt_path->s.dev, but it try to decreased clt_path->s.dev <<< it's wrong to do that.

So please fix it by making sure that failure to create con[1] will
release resources which were allocated. If con[1] didn't increase
s.dev_ref, it shouldn't decrease it either.

Thanks

> 
> 
> Thanks
> Zhijian
> 
> > Agree. We should find out why refcnt 1 and fix this problem.
> 
> 
> 
> 
> > 
> > Zhu Yanjun
> >>
> >> Thanks
> >