NFS: disconnect before retrying NFSv4 requests over TCP

RFC3530 section 3.1.1 states an NFSv4 client MUST NOT send a request
twice on the same connection unless it is the NULL procedure.  Section
3.1.1 suggests that the client should disconnect and reconnect if it
wants to retry a request.

Implement this by adding an rpc_clnt flag that an ULP can use to
specify that the underlying transport should be disconnected on a
major timeout.  The NFSv4 client asserts this new flag, and requests
no retries after a minor retransmit timeout.

Note that disconnecting on a retransmit is in general not safe to do
if the RPC client does not reuse the TCP port number when reconnecting.

See http://bugzilla.linux-nfs.org/show_bug.cgi?id=6

Signed-off-by: Chuck Lever <chuck.lever@oracle.com>
Signed-off-by: Trond Myklebust <Trond.Myklebust@netapp.com>

fs/nfs/client.c

@@ -394,7 +394,8 @@ static void nfs_init_timeout_values(struct rpc_timeout *to, int proto,
 static int nfs_create_rpc_client(struct nfs_client *clp, int proto,
 						unsigned int timeo,
 						unsigned int retrans,
-						rpc_authflavor_t flavor)
+						rpc_authflavor_t flavor,
+						int flags)
 {
 	struct rpc_timeout	timeparms;
 	struct rpc_clnt		*clnt = NULL;
@@ -407,6 +408,7 @@ static int nfs_create_rpc_client(struct nfs_client *clp, int proto,
 		.program	= &nfs_program,
 		.version	= clp->rpc_ops->version,
 		.authflavor	= flavor,
+		.flags		= flags,
 	};
 
 	if (!IS_ERR(clp->cl_rpcclient))
@@ -548,7 +550,7 @@ static int nfs_init_client(struct nfs_client *clp, const struct nfs_mount_data *
 	 * - RFC 2623, sec 2.3.2
 	 */
 	error = nfs_create_rpc_client(clp, proto, data->timeo, data->retrans,
-			RPC_AUTH_UNIX);
+					RPC_AUTH_UNIX, 0);
 	if (error < 0)
 		goto error;
 	nfs_mark_client_ready(clp, NFS_CS_READY);
@@ -868,7 +870,8 @@ static int nfs4_init_client(struct nfs_client *clp,
 	/* Check NFS protocol revision and initialize RPC op vector */
 	clp->rpc_ops = &nfs_v4_clientops;
 
-	error = nfs_create_rpc_client(clp, proto, timeo, retrans, authflavour);
+	error = nfs_create_rpc_client(clp, proto, timeo, retrans, authflavour,
+					RPC_CLNT_CREATE_DISCRTRY);
 	if (error < 0)
 		goto error;
 	memcpy(clp->cl_ipaddr, ip_addr, sizeof(clp->cl_ipaddr));

include/linux/sunrpc/clnt.h

@@ -40,6 +40,7 @@ struct rpc_clnt {
 
 	unsigned int		cl_softrtry : 1,/* soft timeouts */
 				cl_intr     : 1,/* interruptible */
+				cl_discrtry : 1,/* disconnect before retry */
 				cl_autobind : 1,/* use getport() */
 				cl_oneshot  : 1,/* dispose after use */
 				cl_dead     : 1;/* abandoned */
@@ -111,6 +112,7 @@ struct rpc_create_args {
 #define RPC_CLNT_CREATE_ONESHOT		(1UL << 3)
 #define RPC_CLNT_CREATE_NONPRIVPORT	(1UL << 4)
 #define RPC_CLNT_CREATE_NOPING		(1UL << 5)
+#define RPC_CLNT_CREATE_DISCRTRY	(1UL << 6)
 
 struct rpc_clnt *rpc_create(struct rpc_create_args *args);
 struct rpc_clnt	*rpc_bind_new_program(struct rpc_clnt *,

net/sunrpc/clnt.c

@@ -249,6 +249,8 @@ struct rpc_clnt *rpc_create(struct rpc_create_args *args)
 		clnt->cl_autobind = 1;
 	if (args->flags & RPC_CLNT_CREATE_ONESHOT)
 		clnt->cl_oneshot = 1;
+	if (args->flags & RPC_CLNT_CREATE_DISCRTRY)
+		clnt->cl_discrtry = 1;
 
 	return clnt;
 }

net/sunrpc/xprt.c

@@ -735,6 +735,16 @@ void xprt_transmit(struct rpc_task *task)
 			xprt_reset_majortimeo(req);
 			/* Turn off autodisconnect */
 			del_singleshot_timer_sync(&xprt->timer);
+		} else {
+			/* If all request bytes have been sent,
+			 * then we must be retransmitting this one */
+			if (!req->rq_bytes_sent) {
+				if (task->tk_client->cl_discrtry) {
+					xprt_disconnect(xprt);
+					task->tk_status = -ENOTCONN;
+					return;
+				}
+			}
 		}
 	} else if (!req->rq_bytes_sent)
 		return;