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

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Date:   Mon, 24 Oct 2022 11:15:22 +0800
From:   Li Zhijian <lizhijian@...itsu.com>
To:     Zhu Yanjun <zyjzyj2000@...il.com>,
        Bob Pearson <rpearsonhpe@...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 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
>>