diff mbox series

[v2,2/2] sunrpc: don't immediately retransmit on seqno miss

Message ID 20250319-rfc2203-seqnum-cache-v2-2-2c98b859f2dd@janestreet.com (mailing list archive)
State New
Delegated to: Netdev Maintainers
Headers show
Series fix gss seqno handling to be more rfc-compliant | expand

Checks

Context Check Description
netdev/series_format warning Target tree name not specified in the subject
netdev/tree_selection success Guessed tree name to be net-next
netdev/ynl success Generated files up to date; no warnings/errors; no diff in generated;
netdev/fixes_present success Fixes tag not required for -next series
netdev/header_inline success No static functions without inline keyword in header files
netdev/build_32bit success Errors and warnings before: 0 this patch: 0
netdev/build_tools success No tools touched, skip
netdev/cc_maintainers success CCed 14 of 14 maintainers
netdev/build_clang success Errors and warnings before: 0 this patch: 0
netdev/verify_signedoff success Signed-off-by tag matches author and committer
netdev/deprecated_api success None detected
netdev/check_selftest success No net selftest shell script
netdev/verify_fixes success No Fixes tag
netdev/build_allmodconfig_warn success Errors and warnings before: 1 this patch: 1
netdev/checkpatch success total: 0 errors, 0 warnings, 0 checks, 15 lines checked
netdev/build_clang_rust success No Rust files in patch. Skipping build
netdev/kdoc success Errors and warnings before: 22 this patch: 22
netdev/source_inline success Was 0 now: 0
netdev/contest fail net-next-2025-03-19--18-00 (tests: 896)

Commit Message

Nikhil Jha March 19, 2025, 5:02 p.m. UTC 
From: Nikhil Jha <njha@janestreet.com>

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>
---
 net/sunrpc/clnt.c | 9 +++++++--
 1 file changed, 7 insertions(+), 2 deletions(-)
diff mbox series

Patch

diff --git a/net/sunrpc/clnt.c b/net/sunrpc/clnt.c
index 2fe88ea79a70c134e58abfb03fca230883eddf1f..98c0880ec18a8b80371e20f65e7a57a8d9244f7f 100644
--- a/net/sunrpc/clnt.c
+++ b/net/sunrpc/clnt.c
@@ -2760,8 +2760,13 @@  rpc_decode_header(struct rpc_task *task, struct xdr_stream *xdr)
 	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;
 	}