NFSv4: Cap the transport reconnection timer at 1/2 lease period

We don't want to miss a lease period renewal due to the TCP connection
failing to reconnect in a timely fashion. To ensure this doesn't happen,
cap the reconnection timer so that we retry the connection attempt
at least every 1/2 lease period.
Signed-off-by: Trond Myklebust <trond.myklebust@primarydata.com>

fs/nfs/nfs4renewd.c

@@ -151,6 +151,9 @@ void nfs4_set_lease_period(struct nfs_client *clp,
 	clp->cl_lease_time = lease;
 	clp->cl_last_renewal = lastrenewed;
 	spin_unlock(&clp->cl_lock);
+
+	/* Cap maximum reconnect timeout at 1/2 lease period */
+	rpc_cap_max_reconnect_timeout(clp->cl_rpcclient, lease >> 1);
 }
 
 /*

include/linux/sunrpc/clnt.h

@@ -195,6 +195,8 @@ int		rpc_clnt_add_xprt(struct rpc_clnt *, struct xprt_create *,
 				struct rpc_xprt *,
 				void *),
 			void *data);
+void		rpc_cap_max_reconnect_timeout(struct rpc_clnt *clnt,
+			unsigned long timeo);
 
 const char *rpc_proc_name(const struct rpc_task *task);
 #endif /* __KERNEL__ */

net/sunrpc/clnt.c

@@ -2676,6 +2676,27 @@ int rpc_clnt_add_xprt(struct rpc_clnt *clnt,
 }
 EXPORT_SYMBOL_GPL(rpc_clnt_add_xprt);
 
+static int
+rpc_xprt_cap_max_reconnect_timeout(struct rpc_clnt *clnt,
+		struct rpc_xprt *xprt,
+		void *data)
+{
+	unsigned long timeout = *((unsigned long *)data);
+
+	if (timeout < xprt->max_reconnect_timeout)
+		xprt->max_reconnect_timeout = timeout;
+	return 0;
+}
+
+void
+rpc_cap_max_reconnect_timeout(struct rpc_clnt *clnt, unsigned long timeo)
+{
+	rpc_clnt_iterate_for_each_xprt(clnt,
+			rpc_xprt_cap_max_reconnect_timeout,
+			&timeo);
+}
+EXPORT_SYMBOL_GPL(rpc_cap_max_reconnect_timeout);
+
 #if IS_ENABLED(CONFIG_SUNRPC_DEBUG)
 static void rpc_show_header(void)
 {