sunrpc: don't immediately retransmit on seqno miss

RFC2203 requires that retransmitted messages use a new gss sequence
number, but the same XID. This means that if the server is just slow
(e.x. overloaded), the client might receive a response using an older
seqno than the one it has recorded.

Currently, Linux's client immediately retransmits in this case. However,
this leads to a lot of wasted retransmits until the server eventually
responds faster than the client can resend.

Client -> SEQ 1 -> Server
Client -> SEQ 2 -> Server
Client <- SEQ 1 <- Server (misses, expecting seqno = 2)
Client -> SEQ 3 -> Server (immediate retransmission on miss)
Client <- SEQ 2 <- Server (misses, expecting seqno = 3)
Client -> SEQ 4 -> Server (immediate retransmission on miss)
... and so on ...

This commit makes it so that we ignore messages with bad checksums
due to seqnum mismatch, and rely on the usual timeout behavior for
retransmission instead of doing so immediately.

Signed-off-by: Nikhil Jha <njha@janestreet.com>
Acked-by: Chuck Lever <chuck.lever@oracle.com>
Signed-off-by: Anna Schumaker <anna.schumaker@oracle.com>

diff --git a/net/sunrpc/clnt.c b/net/sunrpc/clnt.c
index 6f75862d97820c9828b9281b37fd55dd0a9ecb90..21426c3049d35094b81c0915fc755b0f4e00804c 100644 (file)
--- a/net/sunrpc/clnt.c
+++ b/net/sunrpc/clnt.c
@@ -2771,8 +2771,13 @@ out_verifier:
        case -EPROTONOSUPPORT:
                goto out_err;
        case -EACCES:
-               /* Re-encode with a fresh cred */
-               fallthrough;
+               /* possible RPCSEC_GSS out-of-sequence event (RFC2203),
+                * reset recv state and keep waiting, don't retransmit
+                */
+               task->tk_rqstp->rq_reply_bytes_recvd = 0;
+               task->tk_status = xprt_request_enqueue_receive(task);
+               task->tk_action = call_transmit_status;
+               return -EBADMSG;
        default:
                goto out_garbage;
        }