[PATCH 3/7] SUNRPC: Record last-request timestamp on svc_xprt

[Chuck Lever <cel@kernel.org>]

On a connection-oriented transport, the arrival of a later request
suggests the client received the prior reply. It is not proof: a
client with several requests outstanding sends the next one without
waiting for a reply.

Add xpt_last_recv to struct svc_xprt and update it in
svc_handle_xprt() after each successful xpo_recvfrom(). A revisited
deferred request leaves it alone, since that request arrived before
the deferral and is not fresh client activity. The DRC reads this
value as a best-effort signal that a completed reply has been
delivered.

Signed-off-by: Chuck Lever <cel@kernel.org>
---
 include/linux/sunrpc/svc_xprt.h | 1 +
 net/sunrpc/svc_xprt.c           | 7 +++++++
 2 files changed, 8 insertions(+)

diff --git a/include/linux/sunrpc/svc_xprt.h b/include/linux/sunrpc/svc_xprt.h
index 88d73da5f46f..53ed073640a6 100644
--- a/include/linux/sunrpc/svc_xprt.h
+++ b/include/linux/sunrpc/svc_xprt.h
@@ -78,6 +78,7 @@ struct svc_xprt {
 	struct net		*xpt_net;
 	netns_tracker		ns_tracker;
 	const struct cred	*xpt_cred;
+	unsigned long		xpt_last_recv;	/* jiffies of last request */
 	struct rpc_xprt		*xpt_bc_xprt;	/* NFSv4.1 backchannel */
 	struct rpc_xprt_switch	*xpt_bc_xps;	/* NFSv4.1 backchannel */
 };
diff --git a/net/sunrpc/svc_xprt.c b/net/sunrpc/svc_xprt.c
index ca10ef965443..1d4a40627244 100644
--- a/net/sunrpc/svc_xprt.c
+++ b/net/sunrpc/svc_xprt.c
@@ -914,6 +914,13 @@ static void svc_handle_xprt(struct svc_rqst *rqstp, struct svc_xprt *xprt)
 
 		clear_bit(XPT_OLD, &xprt->xpt_flags);
 
+		/*
+		 * A deferred request is a replay of one that arrived
+		 * earlier, not fresh client activity on this connection.
+		 */
+		if (!rqstp->rq_deferred)
+			WRITE_ONCE(xprt->xpt_last_recv, jiffies);
+
 		rqstp->rq_chandle.defer = svc_defer;
 
 		if (serv->sv_stats)

-- 
2.55.0