Received-SPF: pass (google.com: domain of linux-kernel-owner@vger.kernel.org designates 2620:137:e000::1:20 as permitted sender) client-ip=2620:137:e000::1:20;
Message-ID: <1dd7e09f-e22d-0c32-e084-21cac2489d10@fujitsu.com>
Date:   Mon, 24 Oct 2022 11:15:22 +0800
MIME-Version: 1.0
User-Agent: Mozilla/5.0 (X11; Linux x86_64; rv:91.0) Gecko/20100101
 Thunderbird/91.11.0
Subject: Re: [for-next PATCH v2 1/2] RDMA/rxe: Remove unnecessary mr testing
Content-Language: en-US
To:     Zhu Yanjun <zyjzyj2000@gmail.com>,
        Bob Pearson <rpearsonhpe@gmail.com>
Cc:     jgg@ziepe.ca, leon@kernel.org, linux-rdma@vger.kernel.org,
        linux-kernel@vger.kernel.org
References: <1666338764-2-1-git-send-email-lizhijian@fujitsu.com>
 <1666338764-2-2-git-send-email-lizhijian@fujitsu.com>
 <CAD=hENeGMKri0nYMtcu98K2j3D+ZBkxO6fFX5cvvyJsEghrrmQ@mail.gmail.com>
 <1846f2e1-ff13-5fa2-240f-fd7749921ce2@fujitsu.com>
 <30ff25c4-ce66-eac4-eaa2-64c0db203a19@gmail.com>
 <CAD=hENeTnLGN5KKi_Cwni6FDb77prijHVjCjfdvhrjXdp7bdjQ@mail.gmail.com>
From:   Li Zhijian <lizhijian@fujitsu.com>
In-Reply-To: <CAD=hENeTnLGN5KKi_Cwni6FDb77prijHVjCjfdvhrjXdp7bdjQ@mail.gmail.com>
Content-Type: text/plain; charset=UTF-8; format=flowed
Content-Transfer-Encoding: 8bit
Precedence: bulk


On 24/10/2022 10:25, Zhu Yanjun wrote:
>>>>> +++ 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
>>>>>
>> Li is correct that the only way mr could be NULL is if qp->resp.mr == NULL. So the
> What I am concerned about is if "WARN_ON(!mr);" should be added or not.
> IMO, if the root cause remains unclear, this should be a problem.
> Currently this problem is not fixed. It is useless to send a debug
> statement to the maillist.

As per Bob's explanation,  no 'WARN_ON(!mr)' is needed.
I will update the patch soon.

> Zhu Yanjun
>
>> 'if (mr)' is not needed if that is the case. The read_reply subroutine is reached
>> from a new rdma read operation after going through check_rkey or from a previous
>> rdma read operations from get_req if qp->resp.res != NULL or from a duplicate request
>> where the previous responder resource is found. In all these cases the mr is set.
>> Initially in check_rkey where if it can't find the mr it causes an RKEY_VIOLATION.
>> Thereafter the rkey is stored in the responder resources and looked up for each
>> packet to get an mr or cause an RKEY_VIOLATION. So the mr can't be NULL. I think
>> you can leave out the WARN and just drop the if (mr).
Very thanks for your explanation

Thanks
Zhijian

>>
>> Bob
>>