On Fri, 2020-04-03 at 15:42 -0400, Chuck Lever wrote:
> Commit 3832591e6fa5 ("SUNRPC: Handle connection issues correctly on
> the back channel") intended to make backchannel RPCs fail
> immediately when there is no forward channel connection. What's
> currently happening is, when the forward channel conneciton goes
> away, backchannel operations are causing hard loops because
> call_transmit_status's SOFTCONN logic ignores ENOTCONN.
Won't RPC_TASK_NOCONNECT do the right thing? It should cause the
request to exit with an ENOTCONN error when it hits call_connect().
>
> To avoid changing the behavior of call_transmit_status in the
> forward direction, make backchannel RPCs return with a different
> error than ENOTCONN when they fail.
>
> Signed-off-by: Chuck Lever <chuck.lever@xxxxxxxxxx>
> ---
> net/sunrpc/xprtrdma/svc_rdma_backchannel.c | 15 ++++++++++-----
> net/sunrpc/xprtsock.c | 6 ++++--
> 2 files changed, 14 insertions(+), 7 deletions(-)
>
> I'm playing with this fix. It seems to be required in order to get
> Kerberos mounts to work under load with NFSv4.1 and later on RDMA.
>
> If there are no objections, I can carry this for v5.7-rc ...
>
>
> diff --git a/net/sunrpc/xprtrdma/svc_rdma_backchannel.c
> b/net/sunrpc/xprtrdma/svc_rdma_backchannel.c
> index d510a3a15d4b..b8a72d7fbcc2 100644
> --- a/net/sunrpc/xprtrdma/svc_rdma_backchannel.c
> +++ b/net/sunrpc/xprtrdma/svc_rdma_backchannel.c
> @@ -207,11 +207,16 @@ rpcrdma_bc_send_request(struct svcxprt_rdma
> *rdma, struct rpc_rqst *rqst)
>
> drop_connection:
> dprintk("svcrdma: failed to send bc call\n");
> - return -ENOTCONN;
> + return -EHOSTUNREACH;
> }
>
> -/* Send an RPC call on the passive end of a transport
> - * connection.
> +/**
> + * xprt_rdma_bc_send_request - send an RPC backchannel Call
> + * @rqst: RPC Call in rq_snd_buf
> + *
> + * Returns:
> + * %0 if the RPC message has been sent
> + * %-EHOSTUNREACH if the Call could not be sent
> */
> static int
> xprt_rdma_bc_send_request(struct rpc_rqst *rqst)
> @@ -225,11 +230,11 @@ xprt_rdma_bc_send_request(struct rpc_rqst
> *rqst)
>
> mutex_lock(&sxprt->xpt_mutex);
>
> - ret = -ENOTCONN;
> + ret = -EHOSTUNREACH;
> rdma = container_of(sxprt, struct svcxprt_rdma, sc_xprt);
> if (!test_bit(XPT_DEAD, &sxprt->xpt_flags)) {
> ret = rpcrdma_bc_send_request(rdma, rqst);
> - if (ret == -ENOTCONN)
> + if (ret < 0)
> svc_close_xprt(sxprt);
> }
>
> diff --git a/net/sunrpc/xprtsock.c b/net/sunrpc/xprtsock.c
> index 17cb902e5153..92a358fd2ff0 100644
> --- a/net/sunrpc/xprtsock.c
> +++ b/net/sunrpc/xprtsock.c
> @@ -2543,7 +2543,9 @@ static int bc_sendto(struct rpc_rqst *req)
> req->rq_xtime = ktime_get();
> err = xprt_sock_sendmsg(transport->sock, &msg, xdr, 0, marker,
> &sent);
> xdr_free_bvec(xdr);
> - if (err < 0 || sent != (xdr->len + sizeof(marker)))
> + if (err < 0)
> + return -EHOSTUNREACH;
> + if (sent != (xdr->len + sizeof(marker)))
> return -EAGAIN;
> return sent;
> }
> @@ -2567,7 +2569,7 @@ static int bc_send_request(struct rpc_rqst
> *req)
> */
> mutex_lock(&xprt->xpt_mutex);
> if (test_bit(XPT_DEAD, &xprt->xpt_flags))
> - len = -ENOTCONN;
> + len = -EHOSTUNREACH;
> else
> len = bc_sendto(req);
> mutex_unlock(&xprt->xpt_mutex);
>
--
Trond Myklebust
Linux NFS client maintainer, Hammerspace
trond.myklebust@xxxxxxxxxxxxxxx
