linux-kernel - Re: [for-next PATCH v2 1/2] RDMA/rxe: Remove unnecessary mr testing

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Message-ID: <1846f2e1-ff13-5fa2-240f-fd7749921ce2@fujitsu.com>
Date:   Sat, 22 Oct 2022 09:09:39 +0800
From:   Li Zhijian <lizhijian@...itsu.com>
To:     Zhu Yanjun <zyjzyj2000@...il.com>
Cc:     jgg@...pe.ca, leon@...nel.org, linux-rdma@...r.kernel.org,
        linux-kernel@...r.kernel.org
Subject: Re: [for-next PATCH v2 1/2] RDMA/rxe: Remove unnecessary mr testing



On 21/10/2022 22:39, Zhu Yanjun wrote:
> On Fri, Oct 21, 2022 at 3:53 PM Li Zhijian <lizhijian@...itsu.com> wrote:
>> Before the testing, we already passed it to rxe_mr_copy() where mr could
>> be dereferenced. so this checking is not exactly correct.
>>
>> I tried to figure out the details how/when mr could be NULL, but failed
>> at last. Add a WARN_ON(!mr) to that path to tell us more when it
>> happends.
> If I get you correctly, you confronted a problem,
Not exactly,  I removed the mr checking since i think this checking is not correct.
the newly added WARN_ON(!mr) is the only once place where the mr can be NULL but not handled correctly.
At least with/without this patch, once WARN_ON(!mr) is triggered, kernel will go something wrong.

so i want to place this  WARN_ON(!mr) to point to the problem.

Thanks
Zhijian

>   but you can not figure it out.
> So you send it upstream as a patch?
>
> I am not sure if it is a good idea.
>
> Zhu Yanjun
>
>> Signed-off-by: Li Zhijian <lizhijian@...itsu.com>
>> ---
>>   drivers/infiniband/sw/rxe/rxe_resp.c | 4 ++--
>>   1 file changed, 2 insertions(+), 2 deletions(-)
>>
>> diff --git a/drivers/infiniband/sw/rxe/rxe_resp.c b/drivers/infiniband/sw/rxe/rxe_resp.c
>> index ed5a09e86417..218c14fb07c6 100644
>> --- a/drivers/infiniband/sw/rxe/rxe_resp.c
>> +++ b/drivers/infiniband/sw/rxe/rxe_resp.c
>> @@ -778,6 +778,7 @@ static enum resp_states read_reply(struct rxe_qp *qp,
>>          if (res->state == rdatm_res_state_new) {
>>                  if (!res->replay) {
>>                          mr = qp->resp.mr;
>> +                       WARN_ON(!mr);
>>                          qp->resp.mr = NULL;
>>                  } else {
>>                          mr = rxe_recheck_mr(qp, res->read.rkey);
>> @@ -811,8 +812,7 @@ static enum resp_states read_reply(struct rxe_qp *qp,
>>
>>          rxe_mr_copy(mr, res->read.va, payload_addr(&ack_pkt),
>>                      payload, RXE_FROM_MR_OBJ);
>> -       if (mr)
>> -               rxe_put(mr);
>> +       rxe_put(mr);
>>
>>          if (bth_pad(&ack_pkt)) {
>>                  u8 *pad = payload_addr(&ack_pkt) + payload;
>> --
>> 2.31.1
>>