Re: [PATCH] RDMA/rxe: fix retry forever when rnr_retry >= 7

[Zhu Yanjun <zyjzyj2000@gmail.com>]

On Thu, Jul 23, 2020 at 9:28 PM Fan Yang <yangfan.fan@bytedance.com> wrote:
>
> Currently when an error occurs and the completion state becomes
> COMPST_RNR_RETRY, qp->comp.rnr_retry is only decreased when
> qp->comp.rnr_retry != 7.
>
> If the user happens to config the rnr retry count to be >= 7, the
> driver will retry forever, instead of exposing IB_WC_RNR_RETRY_EXC_ERR.

Please read the following from IB specification

"

The RNR NAK retry counter is decremented each time the responder returns

an RNR NAK. If the requester’s RNR NAK retry counter is zero, and
an RNR NAK packet is received, an RNR NAK retry error occurs. Each
time an RNR NAK is cleared (i.e., an acknowledge message other than
an RNR NAK is returned), the retry counter is reloaded. An exception to
the following is if the RNR NAK retry counter is set to 7. This value indicates

infinite retry and the counter is not decremented.

"


>
> ---
>  drivers/infiniband/sw/rxe/rxe_comp.c | 3 +--
>  1 file changed, 1 insertion(+), 2 deletions(-)
>
> diff --git a/drivers/infiniband/sw/rxe/rxe_comp.c b/drivers/infiniband/sw/rxe/rxe_comp.c
> index 4bc88708b355..16c1870b6482 100644
> --- a/drivers/infiniband/sw/rxe/rxe_comp.c
> +++ b/drivers/infiniband/sw/rxe/rxe_comp.c
> @@ -745,8 +745,7 @@ int rxe_completer(void *arg)
>
>                 case COMPST_RNR_RETRY:
>                         if (qp->comp.rnr_retry > 0) {
> -                               if (qp->comp.rnr_retry != 7)
> -                                       qp->comp.rnr_retry--;
> +                               qp->comp.rnr_retry--;
>
>                                 qp->req.need_retry = 1;
>                                 pr_debug("qp#%d set rnr nak timer\n",
> --
> 2.27.0
>
>