Merge branch 'multipath'

* multipath:
  NFS add callback_ops to nfs4_proc_bind_conn_to_session_callback
  pnfs/NFSv4.1: Add multipath capabilities to pNFS flexfiles servers over NFSv3
  SUNRPC: Allow addition of new transports to a struct rpc_clnt
  NFSv4.1: nfs4_proc_bind_conn_to_session must iterate over all connections
  SUNRPC: Make NFS swap work with multipath
  SUNRPC: Add a helper to apply a function to all the rpc_clnt's transports
  SUNRPC: Allow caller to specify the transport to use
  SUNRPC: Use the multipath iterator to assign a transport to each task
  SUNRPC: Make rpc_clnt store the multipath iterators
  SUNRPC: Add a structure to track multiple transports
  SUNRPC: Make freeing of struct xprt rcu-safe
  SUNRPC: Uninline xprt_get(); It isn't performance critical.
  SUNRPC: Reorder rpc_task to put waitqueue related info in same cachelines
  SUNRPC: Remove unused function rpc_task_reset_client

fs/nfs/nfs4proc.c

@@ -6782,13 +6782,26 @@ nfs41_same_server_scope(struct nfs41_server_scope *a,
 	return false;
 }
 
+static void
+nfs4_bind_one_conn_to_session_done(struct rpc_task *task, void *calldata)
+{
+}
+
+static const struct rpc_call_ops nfs4_bind_one_conn_to_session_ops = {
+	.rpc_call_done =  &nfs4_bind_one_conn_to_session_done,
+};
+
 /*
- * nfs4_proc_bind_conn_to_session()
+ * nfs4_proc_bind_one_conn_to_session()
  *
  * The 4.1 client currently uses the same TCP connection for the
  * fore and backchannel.
  */
-int nfs4_proc_bind_conn_to_session(struct nfs_client *clp, struct rpc_cred *cred)
+static
+int nfs4_proc_bind_one_conn_to_session(struct rpc_clnt *clnt,
+		struct rpc_xprt *xprt,
+		struct nfs_client *clp,
+		struct rpc_cred *cred)
 {
 	int status;
 	struct nfs41_bind_conn_to_session_args args = {
@@ -6803,6 +6816,14 @@ int nfs4_proc_bind_conn_to_session(struct nfs_client *clp, struct rpc_cred *cred
 		.rpc_resp = &res,
 		.rpc_cred = cred,
 	};
+	struct rpc_task_setup task_setup_data = {
+		.rpc_client = clnt,
+		.rpc_xprt = xprt,
+		.callback_ops = &nfs4_bind_one_conn_to_session_ops,
+		.rpc_message = &msg,
+		.flags = RPC_TASK_TIMEOUT,
+	};
+	struct rpc_task *task;
 
 	dprintk("--> %s\n", __func__);
 
@@ -6810,7 +6831,16 @@ int nfs4_proc_bind_conn_to_session(struct nfs_client *clp, struct rpc_cred *cred
 	if (!(clp->cl_session->flags & SESSION4_BACK_CHAN))
 		args.dir = NFS4_CDFC4_FORE;
 
-	status = rpc_call_sync(clp->cl_rpcclient, &msg, RPC_TASK_TIMEOUT);
+	/* Do not set the backchannel flag unless this is clnt->cl_xprt */
+	if (xprt != rcu_access_pointer(clnt->cl_xprt))
+		args.dir = NFS4_CDFC4_FORE;
+
+	task = rpc_run_task(&task_setup_data);
+	if (!IS_ERR(task)) {
+		status = task->tk_status;
+		rpc_put_task(task);
+	} else
+		status = PTR_ERR(task);
 	trace_nfs4_bind_conn_to_session(clp, status);
 	if (status == 0) {
 		if (memcmp(res.sessionid.data,
@@ -6837,6 +6867,31 @@ out:
 	return status;
 }
 
+struct rpc_bind_conn_calldata {
+	struct nfs_client *clp;
+	struct rpc_cred *cred;
+};
+
+static int
+nfs4_proc_bind_conn_to_session_callback(struct rpc_clnt *clnt,
+		struct rpc_xprt *xprt,
+		void *calldata)
+{
+	struct rpc_bind_conn_calldata *p = calldata;
+
+	return nfs4_proc_bind_one_conn_to_session(clnt, xprt, p->clp, p->cred);
+}
+
+int nfs4_proc_bind_conn_to_session(struct nfs_client *clp, struct rpc_cred *cred)
+{
+	struct rpc_bind_conn_calldata data = {
+		.clp = clp,
+		.cred = cred,
+	};
+	return rpc_clnt_iterate_for_each_xprt(clp->cl_rpcclient,
+			nfs4_proc_bind_conn_to_session_callback, &data);
+}
+
 /*
  * Minimum set of SP4_MACH_CRED operations from RFC 5661 in the enforce map
  * and operations we'd like to see to enable certain features in the allow map

fs/nfs/pnfs_nfs.c

@@ -606,12 +606,22 @@ static int _nfs4_pnfs_v3_ds_connect(struct nfs_server *mds_srv,
 		dprintk("%s: DS %s: trying address %s\n",
 			__func__, ds->ds_remotestr, da->da_remotestr);
 
-		clp = get_v3_ds_connect(mds_srv->nfs_client,
+		if (!IS_ERR(clp)) {
+			struct xprt_create xprt_args = {
+				.ident = XPRT_TRANSPORT_TCP,
+				.net = clp->cl_net,
+				.dstaddr = (struct sockaddr *)&da->da_addr,
+				.addrlen = da->da_addrlen,
+				.servername = clp->cl_hostname,
+			};
+			/* Add this address as an alias */
+			rpc_clnt_add_xprt(clp->cl_rpcclient, &xprt_args,
+					rpc_clnt_test_and_add_xprt, NULL);
+		} else
+			clp = get_v3_ds_connect(mds_srv->nfs_client,
 					(struct sockaddr *)&da->da_addr,
 					da->da_addrlen, IPPROTO_TCP,
 					timeo, retrans, au_flavor);
-		if (!IS_ERR(clp))
-			break;
 	}
 
 	if (IS_ERR(clp)) {

include/linux/sunrpc/clnt.h

@@ -25,6 +25,7 @@
 #include <asm/signal.h>
 #include <linux/path.h>
 #include <net/ipv6.h>
+#include <linux/sunrpc/xprtmultipath.h>
 
 struct rpc_inode;
 
@@ -67,6 +68,7 @@ struct rpc_clnt {
 #if IS_ENABLED(CONFIG_SUNRPC_DEBUG)
 	struct dentry		*cl_debugfs;	/* debugfs directory */
 #endif
+	struct rpc_xprt_iter	cl_xpi;
 };
 
 /*
@@ -139,7 +141,6 @@ struct rpc_clnt *rpc_create_xprt(struct rpc_create_args *args,
 					struct rpc_xprt *xprt);
 struct rpc_clnt	*rpc_bind_new_program(struct rpc_clnt *,
 				const struct rpc_program *, u32);
-void rpc_task_reset_client(struct rpc_task *task, struct rpc_clnt *clnt);
 struct rpc_clnt *rpc_clone_client(struct rpc_clnt *);
 struct rpc_clnt *rpc_clone_client_set_auth(struct rpc_clnt *,
 				rpc_authflavor_t);
@@ -181,6 +182,21 @@ size_t		rpc_peeraddr(struct rpc_clnt *, struct sockaddr *, size_t);
 const char	*rpc_peeraddr2str(struct rpc_clnt *, enum rpc_display_format_t);
 int		rpc_localaddr(struct rpc_clnt *, struct sockaddr *, size_t);
 
+int 		rpc_clnt_iterate_for_each_xprt(struct rpc_clnt *clnt,
+			int (*fn)(struct rpc_clnt *, struct rpc_xprt *, void *),
+			void *data);
+
+int 		rpc_clnt_test_and_add_xprt(struct rpc_clnt *clnt,
+			struct rpc_xprt_switch *xps,
+			struct rpc_xprt *xprt,
+			void *dummy);
+int		rpc_clnt_add_xprt(struct rpc_clnt *, struct xprt_create *,
+			int (*setup)(struct rpc_clnt *,
+				struct rpc_xprt_switch *,
+				struct rpc_xprt *,
+				void *),
+			void *data);
+
 const char *rpc_proc_name(const struct rpc_task *task);
 #endif /* __KERNEL__ */
 #endif /* _LINUX_SUNRPC_CLNT_H */

include/linux/sunrpc/sched.h

@@ -42,40 +42,43 @@ struct rpc_wait {
  */
 struct rpc_task {
 	atomic_t		tk_count;	/* Reference count */
+	int			tk_status;	/* result of last operation */
 	struct list_head	tk_task;	/* global list of tasks */
-	struct rpc_clnt *	tk_client;	/* RPC client */
-	struct rpc_rqst *	tk_rqstp;	/* RPC request */
-
-	/*
-	 * RPC call state
-	 */
-	struct rpc_message	tk_msg;		/* RPC call info */
 
 	/*
 	 * callback	to be executed after waking up
 	 * action	next procedure for async tasks
-	 * tk_ops	caller callbacks
 	 */
 	void			(*tk_callback)(struct rpc_task *);
 	void			(*tk_action)(struct rpc_task *);
-	const struct rpc_call_ops *tk_ops;
-	void *			tk_calldata;
 
 	unsigned long		tk_timeout;	/* timeout for rpc_sleep() */
 	unsigned long		tk_runstate;	/* Task run status */
-	struct workqueue_struct	*tk_workqueue;	/* Normally rpciod, but could
-						 * be any workqueue
-						 */
+
 	struct rpc_wait_queue 	*tk_waitqueue;	/* RPC wait queue we're on */
 	union {
 		struct work_struct	tk_work;	/* Async task work queue */
 		struct rpc_wait		tk_wait;	/* RPC wait */
 	} u;
 
+	/*
+	 * RPC call state
+	 */
+	struct rpc_message	tk_msg;		/* RPC call info */
+	void *			tk_calldata;	/* Caller private data */
+	const struct rpc_call_ops *tk_ops;	/* Caller callbacks */
+
+	struct rpc_clnt *	tk_client;	/* RPC client */
+	struct rpc_xprt *	tk_xprt;	/* Transport */
+
+	struct rpc_rqst *	tk_rqstp;	/* RPC request */
+
+	struct workqueue_struct	*tk_workqueue;	/* Normally rpciod, but could
+						 * be any workqueue
+						 */
 	ktime_t			tk_start;	/* RPC task init timestamp */
 
 	pid_t			tk_owner;	/* Process id for batching tasks */
-	int			tk_status;	/* result of last operation */
 	unsigned short		tk_flags;	/* misc flags */
 	unsigned short		tk_timeouts;	/* maj timeouts */
 
@@ -100,6 +103,7 @@ struct rpc_call_ops {
 struct rpc_task_setup {
 	struct rpc_task *task;
 	struct rpc_clnt *rpc_client;
+	struct rpc_xprt *rpc_xprt;
 	const struct rpc_message *rpc_message;
 	const struct rpc_call_ops *callback_ops;
 	void *callback_data;

include/linux/sunrpc/xprt.h

@@ -13,6 +13,7 @@
 #include <linux/socket.h>
 #include <linux/in.h>
 #include <linux/ktime.h>
+#include <linux/kref.h>
 #include <linux/sunrpc/sched.h>
 #include <linux/sunrpc/xdr.h>
 #include <linux/sunrpc/msg_prot.h>
@@ -166,7 +167,7 @@ enum xprt_transports {
 };
 
 struct rpc_xprt {
-	atomic_t		count;		/* Reference count */
+	struct kref		kref;		/* Reference count */
 	struct rpc_xprt_ops *	ops;		/* transport methods */
 
 	const struct rpc_timeout *timeout;	/* timeout parms */
@@ -196,6 +197,11 @@ struct rpc_xprt {
 						   transport */
 	unsigned int		bind_index;	/* bind function index */
 
+	/*
+	 * Multipath
+	 */
+	struct list_head	xprt_switch;
+
 	/*
 	 * Connection of transports
 	 */
@@ -256,6 +262,7 @@ struct rpc_xprt {
 	struct dentry		*debugfs;		/* debugfs directory */
 	atomic_t		inject_disconnect;
 #endif
+	struct rcu_head		rcu;
 };
 
 #if defined(CONFIG_SUNRPC_BACKCHANNEL)
@@ -318,24 +325,13 @@ int			xprt_adjust_timeout(struct rpc_rqst *req);
 void			xprt_release_xprt(struct rpc_xprt *xprt, struct rpc_task *task);
 void			xprt_release_xprt_cong(struct rpc_xprt *xprt, struct rpc_task *task);
 void			xprt_release(struct rpc_task *task);
+struct rpc_xprt *	xprt_get(struct rpc_xprt *xprt);
 void			xprt_put(struct rpc_xprt *xprt);
 struct rpc_xprt *	xprt_alloc(struct net *net, size_t size,
 				unsigned int num_prealloc,
 				unsigned int max_req);
 void			xprt_free(struct rpc_xprt *);
 
-/**
- * xprt_get - return a reference to an RPC transport.
- * @xprt: pointer to the transport
- *
- */
-static inline struct rpc_xprt *xprt_get(struct rpc_xprt *xprt)
-{
-	if (atomic_inc_not_zero(&xprt->count))
-		return xprt;
-	return NULL;
-}
-
 static inline __be32 *xprt_skip_transport_header(struct rpc_xprt *xprt, __be32 *p)
 {
 	return p + xprt->tsh_size;

include/linux/sunrpc/xprtmultipath.h

@@ -0,0 +1,69 @@
+/*
+ * RPC client multipathing definitions
+ *
+ * Copyright (c) 2015, 2016, Primary Data, Inc. All rights reserved.
+ *
+ * Trond Myklebust <trond.myklebust@primarydata.com>
+ */
+#ifndef _NET_SUNRPC_XPRTMULTIPATH_H
+#define _NET_SUNRPC_XPRTMULTIPATH_H
+
+struct rpc_xprt_iter_ops;
+struct rpc_xprt_switch {
+	spinlock_t		xps_lock;
+	struct kref		xps_kref;
+
+	unsigned int		xps_nxprts;
+	struct list_head	xps_xprt_list;
+
+	struct net *		xps_net;
+
+	const struct rpc_xprt_iter_ops *xps_iter_ops;
+
+	struct rcu_head		xps_rcu;
+};
+
+struct rpc_xprt_iter {
+	struct rpc_xprt_switch __rcu *xpi_xpswitch;
+	struct rpc_xprt *	xpi_cursor;
+
+	const struct rpc_xprt_iter_ops *xpi_ops;
+};
+
+
+struct rpc_xprt_iter_ops {
+	void (*xpi_rewind)(struct rpc_xprt_iter *);
+	struct rpc_xprt *(*xpi_xprt)(struct rpc_xprt_iter *);
+	struct rpc_xprt *(*xpi_next)(struct rpc_xprt_iter *);
+};
+
+extern struct rpc_xprt_switch *xprt_switch_alloc(struct rpc_xprt *xprt,
+		gfp_t gfp_flags);
+
+extern struct rpc_xprt_switch *xprt_switch_get(struct rpc_xprt_switch *xps);
+extern void xprt_switch_put(struct rpc_xprt_switch *xps);
+
+extern void rpc_xprt_switch_set_roundrobin(struct rpc_xprt_switch *xps);
+
+extern void rpc_xprt_switch_add_xprt(struct rpc_xprt_switch *xps,
+		struct rpc_xprt *xprt);
+extern void rpc_xprt_switch_remove_xprt(struct rpc_xprt_switch *xps,
+		struct rpc_xprt *xprt);
+
+extern void xprt_iter_init(struct rpc_xprt_iter *xpi,
+		struct rpc_xprt_switch *xps);
+
+extern void xprt_iter_init_listall(struct rpc_xprt_iter *xpi,
+		struct rpc_xprt_switch *xps);
+
+extern void xprt_iter_destroy(struct rpc_xprt_iter *xpi);
+
+extern struct rpc_xprt_switch *xprt_iter_xchg_switch(
+		struct rpc_xprt_iter *xpi,
+		struct rpc_xprt_switch *newswitch);
+
+extern struct rpc_xprt *xprt_iter_xprt(struct rpc_xprt_iter *xpi);
+extern struct rpc_xprt *xprt_iter_get_xprt(struct rpc_xprt_iter *xpi);
+extern struct rpc_xprt *xprt_iter_get_next(struct rpc_xprt_iter *xpi);
+
+#endif

net/sunrpc/Makefile

@@ -12,7 +12,8 @@ sunrpc-y := clnt.o xprt.o socklib.o xprtsock.o sched.o \
 	    svc.o svcsock.o svcauth.o svcauth_unix.o \
 	    addr.o rpcb_clnt.o timer.o xdr.o \
 	    sunrpc_syms.o cache.o rpc_pipe.o \
-	    svc_xprt.o
+	    svc_xprt.o \
+	    xprtmultipath.o
 sunrpc-$(CONFIG_SUNRPC_DEBUG) += debugfs.o
 sunrpc-$(CONFIG_SUNRPC_BACKCHANNEL) += backchannel_rqst.o
 sunrpc-$(CONFIG_PROC_FS) += stats.o

net/sunrpc/auth_gss/auth_gss.c

@@ -1181,12 +1181,12 @@ static struct rpc_auth *
 gss_create(struct rpc_auth_create_args *args, struct rpc_clnt *clnt)
 {
 	struct gss_auth *gss_auth;
-	struct rpc_xprt *xprt = rcu_access_pointer(clnt->cl_xprt);
+	struct rpc_xprt_switch *xps = rcu_access_pointer(clnt->cl_xpi.xpi_xpswitch);
 
 	while (clnt != clnt->cl_parent) {
 		struct rpc_clnt *parent = clnt->cl_parent;
 		/* Find the original parent for this transport */
-		if (rcu_access_pointer(parent->cl_xprt) != xprt)
+		if (rcu_access_pointer(parent->cl_xpi.xpi_xpswitch) != xps)
 			break;
 		clnt = parent;
 	}

net/sunrpc/clnt.c

@@ -354,6 +354,7 @@ static void rpc_free_clid(struct rpc_clnt *clnt)
 }
 
 static struct rpc_clnt * rpc_new_client(const struct rpc_create_args *args,
+		struct rpc_xprt_switch *xps,
 		struct rpc_xprt *xprt,
 		struct rpc_clnt *parent)
 {
@@ -411,6 +412,8 @@ static struct rpc_clnt * rpc_new_client(const struct rpc_create_args *args,
 	}
 
 	rpc_clnt_set_transport(clnt, xprt, timeout);
+	xprt_iter_init(&clnt->cl_xpi, xps);
+	xprt_switch_put(xps);
 
 	clnt->cl_rtt = &clnt->cl_rtt_default;
 	rpc_init_rtt(&clnt->cl_rtt_default, clnt->cl_timeout->to_initval);
@@ -438,6 +441,7 @@ out_no_clid:
 out_err:
 	rpciod_down();
 out_no_rpciod:
+	xprt_switch_put(xps);
 	xprt_put(xprt);
 	return ERR_PTR(err);
 }
@@ -446,8 +450,13 @@ struct rpc_clnt *rpc_create_xprt(struct rpc_create_args *args,
 					struct rpc_xprt *xprt)
 {
 	struct rpc_clnt *clnt = NULL;
+	struct rpc_xprt_switch *xps;
 
-	clnt = rpc_new_client(args, xprt, NULL);
+	xps = xprt_switch_alloc(xprt, GFP_KERNEL);
+	if (xps == NULL)
+		return ERR_PTR(-ENOMEM);
+
+	clnt = rpc_new_client(args, xps, xprt, NULL);
 	if (IS_ERR(clnt))
 		return clnt;
 
@@ -564,6 +573,7 @@ EXPORT_SYMBOL_GPL(rpc_create);
 static struct rpc_clnt *__rpc_clone_client(struct rpc_create_args *args,
 					   struct rpc_clnt *clnt)
 {
+	struct rpc_xprt_switch *xps;
 	struct rpc_xprt *xprt;
 	struct rpc_clnt *new;
 	int err;
@@ -571,13 +581,17 @@ static struct rpc_clnt *__rpc_clone_client(struct rpc_create_args *args,
 	err = -ENOMEM;
 	rcu_read_lock();
 	xprt = xprt_get(rcu_dereference(clnt->cl_xprt));
+	xps = xprt_switch_get(rcu_dereference(clnt->cl_xpi.xpi_xpswitch));
 	rcu_read_unlock();
-	if (xprt == NULL)
+	if (xprt == NULL || xps == NULL) {
+		xprt_put(xprt);
+		xprt_switch_put(xps);
 		goto out_err;
+	}
 	args->servername = xprt->servername;
 	args->nodename = clnt->cl_nodename;
 
-	new = rpc_new_client(args, xprt, clnt);
+	new = rpc_new_client(args, xps, xprt, clnt);
 	if (IS_ERR(new)) {
 		err = PTR_ERR(new);
 		goto out_err;
@@ -657,6 +671,7 @@ int rpc_switch_client_transport(struct rpc_clnt *clnt,
 {
 	const struct rpc_timeout *old_timeo;
 	rpc_authflavor_t pseudoflavor;
+	struct rpc_xprt_switch *xps, *oldxps;
 	struct rpc_xprt *xprt, *old;
 	struct rpc_clnt *parent;
 	int err;
@@ -668,10 +683,17 @@ int rpc_switch_client_transport(struct rpc_clnt *clnt,
 		return PTR_ERR(xprt);
 	}
 
+	xps = xprt_switch_alloc(xprt, GFP_KERNEL);
+	if (xps == NULL) {
+		xprt_put(xprt);
+		return -ENOMEM;
+	}
+
 	pseudoflavor = clnt->cl_auth->au_flavor;
 
 	old_timeo = clnt->cl_timeout;
 	old = rpc_clnt_set_transport(clnt, xprt, timeout);
+	oldxps = xprt_iter_xchg_switch(&clnt->cl_xpi, xps);
 
 	rpc_unregister_client(clnt);
 	__rpc_clnt_remove_pipedir(clnt);
@@ -697,20 +719,74 @@ int rpc_switch_client_transport(struct rpc_clnt *clnt,
 	synchronize_rcu();
 	if (parent != clnt)
 		rpc_release_client(parent);
+	xprt_switch_put(oldxps);
 	xprt_put(old);
 	dprintk("RPC:       replaced xprt for clnt %p\n", clnt);
 	return 0;
 
 out_revert:
+	xps = xprt_iter_xchg_switch(&clnt->cl_xpi, oldxps);
 	rpc_clnt_set_transport(clnt, old, old_timeo);
 	clnt->cl_parent = parent;
 	rpc_client_register(clnt, pseudoflavor, NULL);
+	xprt_switch_put(xps);
 	xprt_put(xprt);
 	dprintk("RPC:       failed to switch xprt for clnt %p\n", clnt);
 	return err;
 }
 EXPORT_SYMBOL_GPL(rpc_switch_client_transport);
 
+static
+int rpc_clnt_xprt_iter_init(struct rpc_clnt *clnt, struct rpc_xprt_iter *xpi)
+{
+	struct rpc_xprt_switch *xps;
+
+	rcu_read_lock();
+	xps = xprt_switch_get(rcu_dereference(clnt->cl_xpi.xpi_xpswitch));
+	rcu_read_unlock();
+	if (xps == NULL)
+		return -EAGAIN;
+	xprt_iter_init_listall(xpi, xps);
+	xprt_switch_put(xps);
+	return 0;
+}
+
+/**
+ * rpc_clnt_iterate_for_each_xprt - Apply a function to all transports
+ * @clnt: pointer to client
+ * @fn: function to apply
+ * @data: void pointer to function data
+ *
+ * Iterates through the list of RPC transports currently attached to the
+ * client and applies the function fn(clnt, xprt, data).
+ *
+ * On error, the iteration stops, and the function returns the error value.
+ */
+int rpc_clnt_iterate_for_each_xprt(struct rpc_clnt *clnt,
+		int (*fn)(struct rpc_clnt *, struct rpc_xprt *, void *),
+		void *data)
+{
+	struct rpc_xprt_iter xpi;
+	int ret;
+
+	ret = rpc_clnt_xprt_iter_init(clnt, &xpi);
+	if (ret)
+		return ret;
+	for (;;) {
+		struct rpc_xprt *xprt = xprt_iter_get_next(&xpi);
+
+		if (!xprt)
+			break;
+		ret = fn(clnt, xprt, data);
+		xprt_put(xprt);
+		if (ret < 0)
+			break;
+	}
+	xprt_iter_destroy(&xpi);
+	return ret;
+}
+EXPORT_SYMBOL_GPL(rpc_clnt_iterate_for_each_xprt);
+
 /*
  * Kill all tasks for the given client.
  * XXX: kill their descendants as well?
@@ -783,6 +859,7 @@ rpc_free_client(struct rpc_clnt *clnt)
 	rpc_free_iostats(clnt->cl_metrics);
 	clnt->cl_metrics = NULL;
 	xprt_put(rcu_dereference_raw(clnt->cl_xprt));
+	xprt_iter_destroy(&clnt->cl_xpi);
 	rpciod_down();
 	rpc_free_clid(clnt);
 	kfree(clnt);
@@ -868,6 +945,7 @@ EXPORT_SYMBOL_GPL(rpc_bind_new_program);
 void rpc_task_release_client(struct rpc_task *task)
 {
 	struct rpc_clnt *clnt = task->tk_client;
+	struct rpc_xprt *xprt = task->tk_xprt;
 
 	if (clnt != NULL) {
 		/* Remove from client task list */
@@ -878,13 +956,22 @@ void rpc_task_release_client(struct rpc_task *task)
 
 		rpc_release_client(clnt);
 	}
+
+	if (xprt != NULL) {
+		task->tk_xprt = NULL;
+
+		xprt_put(xprt);
+	}
 }
 
 static
 void rpc_task_set_client(struct rpc_task *task, struct rpc_clnt *clnt)
 {
+
 	if (clnt != NULL) {
 		rpc_task_release_client(task);
+		if (task->tk_xprt == NULL)
+			task->tk_xprt = xprt_iter_get_next(&clnt->cl_xpi);
 		task->tk_client = clnt;
 		atomic_inc(&clnt->cl_count);
 		if (clnt->cl_softrtry)
@@ -900,14 +987,6 @@ void rpc_task_set_client(struct rpc_task *task, struct rpc_clnt *clnt)
 	}
 }
 
-void rpc_task_reset_client(struct rpc_task *task, struct rpc_clnt *clnt)
-{
-	rpc_task_release_client(task);
-	rpc_task_set_client(task, clnt);
-}
-EXPORT_SYMBOL_GPL(rpc_task_reset_client);
-
-
 static void
 rpc_task_set_rpc_message(struct rpc_task *task, const struct rpc_message *msg)
 {
@@ -2104,11 +2183,9 @@ call_timeout(struct rpc_task *task)
 	}
 	if (RPC_IS_SOFT(task)) {
 		if (clnt->cl_chatty) {
-			rcu_read_lock();
 			printk(KERN_NOTICE "%s: server %s not responding, timed out\n",
 				clnt->cl_program->name,
-				rcu_dereference(clnt->cl_xprt)->servername);
-			rcu_read_unlock();
+				task->tk_xprt->servername);
 		}
 		if (task->tk_flags & RPC_TASK_TIMEOUT)
 			rpc_exit(task, -ETIMEDOUT);
@@ -2120,11 +2197,9 @@ call_timeout(struct rpc_task *task)
 	if (!(task->tk_flags & RPC_CALL_MAJORSEEN)) {
 		task->tk_flags |= RPC_CALL_MAJORSEEN;
 		if (clnt->cl_chatty) {
-			rcu_read_lock();
 			printk(KERN_NOTICE "%s: server %s not responding, still trying\n",
 			clnt->cl_program->name,
-			rcu_dereference(clnt->cl_xprt)->servername);
-			rcu_read_unlock();
+			task->tk_xprt->servername);
 		}
 	}
 	rpc_force_rebind(clnt);
@@ -2154,11 +2229,9 @@ call_decode(struct rpc_task *task)
 
 	if (task->tk_flags & RPC_CALL_MAJORSEEN) {
 		if (clnt->cl_chatty) {
-			rcu_read_lock();
 			printk(KERN_NOTICE "%s: server %s OK\n",
 				clnt->cl_program->name,
-				rcu_dereference(clnt->cl_xprt)->servername);
-			rcu_read_unlock();
+				task->tk_xprt->servername);
 		}
 		task->tk_flags &= ~RPC_CALL_MAJORSEEN;
 	}
@@ -2312,11 +2385,9 @@ rpc_verify_header(struct rpc_task *task)
 			task->tk_action = call_bind;
 			goto out_retry;
 		case RPC_AUTH_TOOWEAK:
-			rcu_read_lock();
 			printk(KERN_NOTICE "RPC: server %s requires stronger "
 			       "authentication.\n",
-			       rcu_dereference(clnt->cl_xprt)->servername);
-			rcu_read_unlock();
+			       task->tk_xprt->servername);
 			break;
 		default:
 			dprintk("RPC: %5u %s: unknown auth error: %x\n",
@@ -2341,27 +2412,27 @@ rpc_verify_header(struct rpc_task *task)
 	case RPC_SUCCESS:
 		return p;
 	case RPC_PROG_UNAVAIL:
-		dprintk_rcu("RPC: %5u %s: program %u is unsupported "
+		dprintk("RPC: %5u %s: program %u is unsupported "
 				"by server %s\n", task->tk_pid, __func__,
 				(unsigned int)clnt->cl_prog,
-				rcu_dereference(clnt->cl_xprt)->servername);
+				task->tk_xprt->servername);
 		error = -EPFNOSUPPORT;
 		goto out_err;
 	case RPC_PROG_MISMATCH:
-		dprintk_rcu("RPC: %5u %s: program %u, version %u unsupported "
+		dprintk("RPC: %5u %s: program %u, version %u unsupported "
 				"by server %s\n", task->tk_pid, __func__,
 				(unsigned int)clnt->cl_prog,
 				(unsigned int)clnt->cl_vers,
-				rcu_dereference(clnt->cl_xprt)->servername);
+				task->tk_xprt->servername);
 		error = -EPROTONOSUPPORT;
 		goto out_err;
 	case RPC_PROC_UNAVAIL:
-		dprintk_rcu("RPC: %5u %s: proc %s unsupported by program %u, "
+		dprintk("RPC: %5u %s: proc %s unsupported by program %u, "
 				"version %u on server %s\n",
 				task->tk_pid, __func__,
 				rpc_proc_name(task),
 				clnt->cl_prog, clnt->cl_vers,
-				rcu_dereference(clnt->cl_xprt)->servername);
+				task->tk_xprt->servername);
 		error = -EOPNOTSUPP;
 		goto out_err;
 	case RPC_GARBAGE_ARGS:
@@ -2421,7 +2492,10 @@ static int rpc_ping(struct rpc_clnt *clnt)
 	return err;
 }
 
-struct rpc_task *rpc_call_null(struct rpc_clnt *clnt, struct rpc_cred *cred, int flags)
+static
+struct rpc_task *rpc_call_null_helper(struct rpc_clnt *clnt,
+		struct rpc_xprt *xprt, struct rpc_cred *cred, int flags,
+		const struct rpc_call_ops *ops, void *data)
 {
 	struct rpc_message msg = {
 		.rpc_proc = &rpcproc_null,
@@ -2429,14 +2503,140 @@ struct rpc_task *rpc_call_null(struct rpc_clnt *clnt, struct rpc_cred *cred, int
 	};
 	struct rpc_task_setup task_setup_data = {
 		.rpc_client = clnt,
+		.rpc_xprt = xprt,
 		.rpc_message = &msg,
-		.callback_ops = &rpc_default_ops,
+		.callback_ops = (ops != NULL) ? ops : &rpc_default_ops,
+		.callback_data = data,
 		.flags = flags,
 	};
+
 	return rpc_run_task(&task_setup_data);
 }
+
+struct rpc_task *rpc_call_null(struct rpc_clnt *clnt, struct rpc_cred *cred, int flags)
+{
+	return rpc_call_null_helper(clnt, NULL, cred, flags, NULL, NULL);
+}
 EXPORT_SYMBOL_GPL(rpc_call_null);
 
+struct rpc_cb_add_xprt_calldata {
+	struct rpc_xprt_switch *xps;
+	struct rpc_xprt *xprt;
+};
+
+static void rpc_cb_add_xprt_done(struct rpc_task *task, void *calldata)
+{
+	struct rpc_cb_add_xprt_calldata *data = calldata;
+
+	if (task->tk_status == 0)
+		rpc_xprt_switch_add_xprt(data->xps, data->xprt);
+}
+
+static void rpc_cb_add_xprt_release(void *calldata)
+{
+	struct rpc_cb_add_xprt_calldata *data = calldata;
+
+	xprt_put(data->xprt);
+	xprt_switch_put(data->xps);
+	kfree(data);
+}
+
+const static struct rpc_call_ops rpc_cb_add_xprt_call_ops = {
+	.rpc_call_done = rpc_cb_add_xprt_done,
+	.rpc_release = rpc_cb_add_xprt_release,
+};
+
+/**
+ * rpc_clnt_test_and_add_xprt - Test and add a new transport to a rpc_clnt
+ * @clnt: pointer to struct rpc_clnt
+ * @xps: pointer to struct rpc_xprt_switch,
+ * @xprt: pointer struct rpc_xprt
+ * @dummy: unused
+ */
+int rpc_clnt_test_and_add_xprt(struct rpc_clnt *clnt,
+		struct rpc_xprt_switch *xps, struct rpc_xprt *xprt,
+		void *dummy)
+{
+	struct rpc_cb_add_xprt_calldata *data;
+	struct rpc_cred *cred;
+	struct rpc_task *task;
+
+	data = kmalloc(sizeof(*data), GFP_NOFS);
+	if (!data)
+		return -ENOMEM;
+	data->xps = xprt_switch_get(xps);
+	data->xprt = xprt_get(xprt);
+
+	cred = authnull_ops.lookup_cred(NULL, NULL, 0);
+	task = rpc_call_null_helper(clnt, xprt, cred,
+			RPC_TASK_SOFT|RPC_TASK_SOFTCONN|RPC_TASK_ASYNC,
+			&rpc_cb_add_xprt_call_ops, data);
+	put_rpccred(cred);
+	if (IS_ERR(task))
+		return PTR_ERR(task);
+	rpc_put_task(task);
+	return 1;
+}
+EXPORT_SYMBOL_GPL(rpc_clnt_test_and_add_xprt);
+
+/**
+ * rpc_clnt_add_xprt - Add a new transport to a rpc_clnt
+ * @clnt: pointer to struct rpc_clnt
+ * @xprtargs: pointer to struct xprt_create
+ * @setup: callback to test and/or set up the connection
+ * @data: pointer to setup function data
+ *
+ * Creates a new transport using the parameters set in args and
+ * adds it to clnt.
+ * If ping is set, then test that connectivity succeeds before
+ * adding the new transport.
+ *
+ */
+int rpc_clnt_add_xprt(struct rpc_clnt *clnt,
+		struct xprt_create *xprtargs,
+		int (*setup)(struct rpc_clnt *,
+			struct rpc_xprt_switch *,
+			struct rpc_xprt *,
+			void *),
+		void *data)
+{
+	struct rpc_xprt_switch *xps;
+	struct rpc_xprt *xprt;
+	unsigned char resvport;
+	int ret = 0;
+
+	rcu_read_lock();
+	xps = xprt_switch_get(rcu_dereference(clnt->cl_xpi.xpi_xpswitch));
+	xprt = xprt_iter_xprt(&clnt->cl_xpi);
+	if (xps == NULL || xprt == NULL) {
+		rcu_read_unlock();
+		return -EAGAIN;
+	}
+	resvport = xprt->resvport;
+	rcu_read_unlock();
+
+	xprt = xprt_create_transport(xprtargs);
+	if (IS_ERR(xprt)) {
+		ret = PTR_ERR(xprt);
+		goto out_put_switch;
+	}
+	xprt->resvport = resvport;
+
+	rpc_xprt_switch_set_roundrobin(xps);
+	if (setup) {
+		ret = setup(clnt, xps, xprt, data);
+		if (ret != 0)
+			goto out_put_xprt;
+	}
+	rpc_xprt_switch_add_xprt(xps, xprt);
+out_put_xprt:
+	xprt_put(xprt);
+out_put_switch:
+	xprt_switch_put(xps);
+	return ret;
+}
+EXPORT_SYMBOL_GPL(rpc_clnt_add_xprt);
+
 #if IS_ENABLED(CONFIG_SUNRPC_DEBUG)
 static void rpc_show_header(void)
 {
@@ -2483,57 +2683,39 @@ void rpc_show_tasks(struct net *net)
 #endif
 
 #if IS_ENABLED(CONFIG_SUNRPC_SWAP)
+static int
+rpc_clnt_swap_activate_callback(struct rpc_clnt *clnt,
+		struct rpc_xprt *xprt,
+		void *dummy)
+{
+	return xprt_enable_swap(xprt);
+}
+
 int
 rpc_clnt_swap_activate(struct rpc_clnt *clnt)
 {
-	int ret = 0;
-	struct rpc_xprt	*xprt;
-
-	if (atomic_inc_return(&clnt->cl_swapper) == 1) {
-retry:
-		rcu_read_lock();
-		xprt = xprt_get(rcu_dereference(clnt->cl_xprt));
-		rcu_read_unlock();
-		if (!xprt) {
-			/*
-			 * If we didn't get a reference, then we likely are
-			 * racing with a migration event. Wait for a grace
-			 * period and try again.
-			 */
-			synchronize_rcu();
-			goto retry;
-		}
-
-		ret = xprt_enable_swap(xprt);
-		xprt_put(xprt);
-	}
-	return ret;
+	if (atomic_inc_return(&clnt->cl_swapper) == 1)
+		return rpc_clnt_iterate_for_each_xprt(clnt,
+				rpc_clnt_swap_activate_callback, NULL);
+	return 0;
 }
 EXPORT_SYMBOL_GPL(rpc_clnt_swap_activate);
 
+static int
+rpc_clnt_swap_deactivate_callback(struct rpc_clnt *clnt,
+		struct rpc_xprt *xprt,
+		void *dummy)
+{
+	xprt_disable_swap(xprt);
+	return 0;
+}
+
 void
 rpc_clnt_swap_deactivate(struct rpc_clnt *clnt)
 {
-	struct rpc_xprt	*xprt;
-
-	if (atomic_dec_if_positive(&clnt->cl_swapper) == 0) {
-retry:
-		rcu_read_lock();
-		xprt = xprt_get(rcu_dereference(clnt->cl_xprt));
-		rcu_read_unlock();
-		if (!xprt) {
-			/*
-			 * If we didn't get a reference, then we likely are
-			 * racing with a migration event. Wait for a grace
-			 * period and try again.
-			 */
-			synchronize_rcu();
-			goto retry;
-		}
-
-		xprt_disable_swap(xprt);
-		xprt_put(xprt);
-	}
+	if (atomic_dec_if_positive(&clnt->cl_swapper) == 0)
+		rpc_clnt_iterate_for_each_xprt(clnt,
+				rpc_clnt_swap_deactivate_callback, NULL);
 }
 EXPORT_SYMBOL_GPL(rpc_clnt_swap_deactivate);
 #endif /* CONFIG_SUNRPC_SWAP */

net/sunrpc/rpcb_clnt.c

@@ -648,10 +648,10 @@ static struct rpc_task *rpcb_call_async(struct rpc_clnt *rpcb_clnt, struct rpcbi
 static struct rpc_clnt *rpcb_find_transport_owner(struct rpc_clnt *clnt)
 {
 	struct rpc_clnt *parent = clnt->cl_parent;
-	struct rpc_xprt *xprt = rcu_dereference(clnt->cl_xprt);
+	struct rpc_xprt_switch *xps = rcu_access_pointer(clnt->cl_xpi.xpi_xpswitch);
 
 	while (parent != clnt) {
-		if (rcu_dereference(parent->cl_xprt) != xprt)
+		if (rcu_access_pointer(parent->cl_xpi.xpi_xpswitch) != xps)
 			break;
 		if (clnt->cl_autobind)
 			break;
@@ -683,11 +683,9 @@ void rpcb_getport_async(struct rpc_task *task)
 	int status;
 
 	rcu_read_lock();
-	do {
-		clnt = rpcb_find_transport_owner(task->tk_client);
-		xprt = xprt_get(rcu_dereference(clnt->cl_xprt));
-	} while (xprt == NULL);
+	clnt = rpcb_find_transport_owner(task->tk_client);
 	rcu_read_unlock();
+	xprt = xprt_get(task->tk_xprt);
 
 	dprintk("RPC: %5u %s(%s, %u, %u, %d)\n",
 		task->tk_pid, __func__,

net/sunrpc/sched.c

@@ -909,6 +909,8 @@ static void rpc_init_task(struct rpc_task *task, const struct rpc_task_setup *ta
 	/* Initialize workqueue for async tasks */
 	task->tk_workqueue = task_setup_data->workqueue;
 
+	task->tk_xprt = xprt_get(task_setup_data->rpc_xprt);
+
 	if (task->tk_ops->rpc_call_prepare != NULL)
 		task->tk_action = rpc_prepare_task;
 

net/sunrpc/xprt.c

@@ -48,6 +48,7 @@
 #include <linux/sunrpc/clnt.h>
 #include <linux/sunrpc/metrics.h>
 #include <linux/sunrpc/bc_xprt.h>
+#include <linux/rcupdate.h>
 
 #include <trace/events/sunrpc.h>
 
@@ -1166,7 +1167,7 @@ void xprt_free(struct rpc_xprt *xprt)
 {
 	put_net(xprt->xprt_net);
 	xprt_free_all_slots(xprt);
-	kfree(xprt);
+	kfree_rcu(xprt, rcu);
 }
 EXPORT_SYMBOL_GPL(xprt_free);
 
@@ -1180,7 +1181,7 @@ EXPORT_SYMBOL_GPL(xprt_free);
  */
 void xprt_reserve(struct rpc_task *task)
 {
-	struct rpc_xprt	*xprt;
+	struct rpc_xprt *xprt = task->tk_xprt;
 
 	task->tk_status = 0;
 	if (task->tk_rqstp != NULL)
@@ -1188,11 +1189,8 @@ void xprt_reserve(struct rpc_task *task)
 
 	task->tk_timeout = 0;
 	task->tk_status = -EAGAIN;
-	rcu_read_lock();
-	xprt = rcu_dereference(task->tk_client->cl_xprt);
 	if (!xprt_throttle_congested(xprt, task))
 		xprt->ops->alloc_slot(xprt, task);
-	rcu_read_unlock();
 }
 
 /**
@@ -1206,7 +1204,7 @@ void xprt_reserve(struct rpc_task *task)
  */
 void xprt_retry_reserve(struct rpc_task *task)
 {
-	struct rpc_xprt	*xprt;
+	struct rpc_xprt *xprt = task->tk_xprt;
 
 	task->tk_status = 0;
 	if (task->tk_rqstp != NULL)
@@ -1214,10 +1212,7 @@ void xprt_retry_reserve(struct rpc_task *task)
 
 	task->tk_timeout = 0;
 	task->tk_status = -EAGAIN;
-	rcu_read_lock();
-	xprt = rcu_dereference(task->tk_client->cl_xprt);
 	xprt->ops->alloc_slot(xprt, task);
-	rcu_read_unlock();
 }
 
 static inline __be32 xprt_alloc_xid(struct rpc_xprt *xprt)
@@ -1264,11 +1259,9 @@ void xprt_release(struct rpc_task *task)
 
 	if (req == NULL) {
 		if (task->tk_client) {
-			rcu_read_lock();
-			xprt = rcu_dereference(task->tk_client->cl_xprt);
+			xprt = task->tk_xprt;
 			if (xprt->snd_task == task)
 				xprt_release_write(xprt, task);
-			rcu_read_unlock();
 		}
 		return;
 	}
@@ -1307,7 +1300,7 @@ void xprt_release(struct rpc_task *task)
 
 static void xprt_init(struct rpc_xprt *xprt, struct net *net)
 {
-	atomic_set(&xprt->count, 1);
+	kref_init(&xprt->kref);
 
 	spin_lock_init(&xprt->transport_lock);
 	spin_lock_init(&xprt->reserve_lock);
@@ -1318,6 +1311,7 @@ static void xprt_init(struct rpc_xprt *xprt, struct net *net)
 	spin_lock_init(&xprt->bc_pa_lock);
 	INIT_LIST_HEAD(&xprt->bc_pa_list);
 #endif /* CONFIG_SUNRPC_BACKCHANNEL */
+	INIT_LIST_HEAD(&xprt->xprt_switch);
 
 	xprt->last_used = jiffies;
 	xprt->cwnd = RPC_INITCWND;
@@ -1415,6 +1409,24 @@ static void xprt_destroy(struct rpc_xprt *xprt)
 	xprt->ops->destroy(xprt);
 }
 
+static void xprt_destroy_kref(struct kref *kref)
+{
+	xprt_destroy(container_of(kref, struct rpc_xprt, kref));
+}
+
+/**
+ * xprt_get - return a reference to an RPC transport.
+ * @xprt: pointer to the transport
+ *
+ */
+struct rpc_xprt *xprt_get(struct rpc_xprt *xprt)
+{
+	if (xprt != NULL && kref_get_unless_zero(&xprt->kref))
+		return xprt;
+	return NULL;
+}
+EXPORT_SYMBOL_GPL(xprt_get);
+
 /**
  * xprt_put - release a reference to an RPC transport.
  * @xprt: pointer to the transport
@@ -1422,7 +1434,7 @@ static void xprt_destroy(struct rpc_xprt *xprt)
  */
 void xprt_put(struct rpc_xprt *xprt)
 {
-	if (atomic_dec_and_test(&xprt->count))
-		xprt_destroy(xprt);
+	if (xprt != NULL)
+		kref_put(&xprt->kref, xprt_destroy_kref);
 }
 EXPORT_SYMBOL_GPL(xprt_put);

net/sunrpc/xprtmultipath.c

@@ -0,0 +1,475 @@
+/*
+ * Multipath support for RPC
+ *
+ * Copyright (c) 2015, 2016, Primary Data, Inc. All rights reserved.
+ *
+ * Trond Myklebust <trond.myklebust@primarydata.com>
+ *
+ */
+#include <linux/types.h>
+#include <linux/kref.h>
+#include <linux/list.h>
+#include <linux/rcupdate.h>
+#include <linux/rculist.h>
+#include <linux/slab.h>
+#include <asm/cmpxchg.h>
+#include <linux/spinlock.h>
+#include <linux/sunrpc/xprt.h>
+#include <linux/sunrpc/xprtmultipath.h>
+
+typedef struct rpc_xprt *(*xprt_switch_find_xprt_t)(struct list_head *head,
+		const struct rpc_xprt *cur);
+
+static const struct rpc_xprt_iter_ops rpc_xprt_iter_singular;
+static const struct rpc_xprt_iter_ops rpc_xprt_iter_roundrobin;
+static const struct rpc_xprt_iter_ops rpc_xprt_iter_listall;
+
+static void xprt_switch_add_xprt_locked(struct rpc_xprt_switch *xps,
+		struct rpc_xprt *xprt)
+{
+	if (unlikely(xprt_get(xprt) == NULL))
+		return;
+	list_add_tail_rcu(&xprt->xprt_switch, &xps->xps_xprt_list);
+	smp_wmb();
+	if (xps->xps_nxprts == 0)
+		xps->xps_net = xprt->xprt_net;
+	xps->xps_nxprts++;
+}
+
+/**
+ * rpc_xprt_switch_add_xprt - Add a new rpc_xprt to an rpc_xprt_switch
+ * @xps: pointer to struct rpc_xprt_switch
+ * @xprt: pointer to struct rpc_xprt
+ *
+ * Adds xprt to the end of the list of struct rpc_xprt in xps.
+ */
+void rpc_xprt_switch_add_xprt(struct rpc_xprt_switch *xps,
+		struct rpc_xprt *xprt)
+{
+	if (xprt == NULL)
+		return;
+	spin_lock(&xps->xps_lock);
+	if (xps->xps_net == xprt->xprt_net || xps->xps_net == NULL)
+		xprt_switch_add_xprt_locked(xps, xprt);
+	spin_unlock(&xps->xps_lock);
+}
+
+static void xprt_switch_remove_xprt_locked(struct rpc_xprt_switch *xps,
+		struct rpc_xprt *xprt)
+{
+	if (unlikely(xprt == NULL))
+		return;
+	xps->xps_nxprts--;
+	if (xps->xps_nxprts == 0)
+		xps->xps_net = NULL;
+	smp_wmb();
+	list_del_rcu(&xprt->xprt_switch);
+}
+
+/**
+ * rpc_xprt_switch_remove_xprt - Removes an rpc_xprt from a rpc_xprt_switch
+ * @xps: pointer to struct rpc_xprt_switch
+ * @xprt: pointer to struct rpc_xprt
+ *
+ * Removes xprt from the list of struct rpc_xprt in xps.
+ */
+void rpc_xprt_switch_remove_xprt(struct rpc_xprt_switch *xps,
+		struct rpc_xprt *xprt)
+{
+	spin_lock(&xps->xps_lock);
+	xprt_switch_remove_xprt_locked(xps, xprt);
+	spin_unlock(&xps->xps_lock);
+	xprt_put(xprt);
+}
+
+/**
+ * xprt_switch_alloc - Allocate a new struct rpc_xprt_switch
+ * @xprt: pointer to struct rpc_xprt
+ * @gfp_flags: allocation flags
+ *
+ * On success, returns an initialised struct rpc_xprt_switch, containing
+ * the entry xprt. Returns NULL on failure.
+ */
+struct rpc_xprt_switch *xprt_switch_alloc(struct rpc_xprt *xprt,
+		gfp_t gfp_flags)
+{
+	struct rpc_xprt_switch *xps;
+
+	xps = kmalloc(sizeof(*xps), gfp_flags);
+	if (xps != NULL) {
+		spin_lock_init(&xps->xps_lock);
+		kref_init(&xps->xps_kref);
+		xps->xps_nxprts = 0;
+		INIT_LIST_HEAD(&xps->xps_xprt_list);
+		xps->xps_iter_ops = &rpc_xprt_iter_singular;
+		xprt_switch_add_xprt_locked(xps, xprt);
+	}
+
+	return xps;
+}
+
+static void xprt_switch_free_entries(struct rpc_xprt_switch *xps)
+{
+	spin_lock(&xps->xps_lock);
+	while (!list_empty(&xps->xps_xprt_list)) {
+		struct rpc_xprt *xprt;
+
+		xprt = list_first_entry(&xps->xps_xprt_list,
+				struct rpc_xprt, xprt_switch);
+		xprt_switch_remove_xprt_locked(xps, xprt);
+		spin_unlock(&xps->xps_lock);
+		xprt_put(xprt);
+		spin_lock(&xps->xps_lock);
+	}
+	spin_unlock(&xps->xps_lock);
+}
+
+static void xprt_switch_free(struct kref *kref)
+{
+	struct rpc_xprt_switch *xps = container_of(kref,
+			struct rpc_xprt_switch, xps_kref);
+
+	xprt_switch_free_entries(xps);
+	kfree_rcu(xps, xps_rcu);
+}
+
+/**
+ * xprt_switch_get - Return a reference to a rpc_xprt_switch
+ * @xps: pointer to struct rpc_xprt_switch
+ *
+ * Returns a reference to xps unless the refcount is already zero.
+ */
+struct rpc_xprt_switch *xprt_switch_get(struct rpc_xprt_switch *xps)
+{
+	if (xps != NULL && kref_get_unless_zero(&xps->xps_kref))
+		return xps;
+	return NULL;
+}
+
+/**
+ * xprt_switch_put - Release a reference to a rpc_xprt_switch
+ * @xps: pointer to struct rpc_xprt_switch
+ *
+ * Release the reference to xps, and free it once the refcount is zero.
+ */
+void xprt_switch_put(struct rpc_xprt_switch *xps)
+{
+	if (xps != NULL)
+		kref_put(&xps->xps_kref, xprt_switch_free);
+}
+
+/**
+ * rpc_xprt_switch_set_roundrobin - Set a round-robin policy on rpc_xprt_switch
+ * @xps: pointer to struct rpc_xprt_switch
+ *
+ * Sets a round-robin default policy for iterators acting on xps.
+ */
+void rpc_xprt_switch_set_roundrobin(struct rpc_xprt_switch *xps)
+{
+	if (READ_ONCE(xps->xps_iter_ops) != &rpc_xprt_iter_roundrobin)
+		WRITE_ONCE(xps->xps_iter_ops, &rpc_xprt_iter_roundrobin);
+}
+
+static
+const struct rpc_xprt_iter_ops *xprt_iter_ops(const struct rpc_xprt_iter *xpi)
+{
+	if (xpi->xpi_ops != NULL)
+		return xpi->xpi_ops;
+	return rcu_dereference(xpi->xpi_xpswitch)->xps_iter_ops;
+}
+
+static
+void xprt_iter_no_rewind(struct rpc_xprt_iter *xpi)
+{
+}
+
+static
+void xprt_iter_default_rewind(struct rpc_xprt_iter *xpi)
+{
+	WRITE_ONCE(xpi->xpi_cursor, NULL);
+}
+
+static
+struct rpc_xprt *xprt_switch_find_first_entry(struct list_head *head)
+{
+	return list_first_or_null_rcu(head, struct rpc_xprt, xprt_switch);
+}
+
+static
+struct rpc_xprt *xprt_iter_first_entry(struct rpc_xprt_iter *xpi)
+{
+	struct rpc_xprt_switch *xps = rcu_dereference(xpi->xpi_xpswitch);
+
+	if (xps == NULL)
+		return NULL;
+	return xprt_switch_find_first_entry(&xps->xps_xprt_list);
+}
+
+static
+struct rpc_xprt *xprt_switch_find_current_entry(struct list_head *head,
+		const struct rpc_xprt *cur)
+{
+	struct rpc_xprt *pos;
+
+	list_for_each_entry_rcu(pos, head, xprt_switch) {
+		if (cur == pos)
+			return pos;
+	}
+	return NULL;
+}
+
+static
+struct rpc_xprt *xprt_iter_current_entry(struct rpc_xprt_iter *xpi)
+{
+	struct rpc_xprt_switch *xps = rcu_dereference(xpi->xpi_xpswitch);
+	struct list_head *head;
+
+	if (xps == NULL)
+		return NULL;
+	head = &xps->xps_xprt_list;
+	if (xpi->xpi_cursor == NULL || xps->xps_nxprts < 2)
+		return xprt_switch_find_first_entry(head);
+	return xprt_switch_find_current_entry(head, xpi->xpi_cursor);
+}
+
+static
+struct rpc_xprt *xprt_switch_find_next_entry(struct list_head *head,
+		const struct rpc_xprt *cur)
+{
+	struct rpc_xprt *pos, *prev = NULL;
+
+	list_for_each_entry_rcu(pos, head, xprt_switch) {
+		if (cur == prev)
+			return pos;
+		prev = pos;
+	}
+	return NULL;
+}
+
+static
+struct rpc_xprt *xprt_switch_set_next_cursor(struct list_head *head,
+		struct rpc_xprt **cursor,
+		xprt_switch_find_xprt_t find_next)
+{
+	struct rpc_xprt *cur, *pos, *old;
+
+	cur = READ_ONCE(*cursor);
+	for (;;) {
+		old = cur;
+		pos = find_next(head, old);
+		if (pos == NULL)
+			break;
+		cur = cmpxchg_relaxed(cursor, old, pos);
+		if (cur == old)
+			break;
+	}
+	return pos;
+}
+
+static
+struct rpc_xprt *xprt_iter_next_entry_multiple(struct rpc_xprt_iter *xpi,
+		xprt_switch_find_xprt_t find_next)
+{
+	struct rpc_xprt_switch *xps = rcu_dereference(xpi->xpi_xpswitch);
+	struct list_head *head;
+
+	if (xps == NULL)
+		return NULL;
+	head = &xps->xps_xprt_list;
+	if (xps->xps_nxprts < 2)
+		return xprt_switch_find_first_entry(head);
+	return xprt_switch_set_next_cursor(head, &xpi->xpi_cursor, find_next);
+}
+
+static
+struct rpc_xprt *xprt_switch_find_next_entry_roundrobin(struct list_head *head,
+		const struct rpc_xprt *cur)
+{
+	struct rpc_xprt *ret;
+
+	ret = xprt_switch_find_next_entry(head, cur);
+	if (ret != NULL)
+		return ret;
+	return xprt_switch_find_first_entry(head);
+}
+
+static
+struct rpc_xprt *xprt_iter_next_entry_roundrobin(struct rpc_xprt_iter *xpi)
+{
+	return xprt_iter_next_entry_multiple(xpi,
+			xprt_switch_find_next_entry_roundrobin);
+}
+
+static
+struct rpc_xprt *xprt_iter_next_entry_all(struct rpc_xprt_iter *xpi)
+{
+	return xprt_iter_next_entry_multiple(xpi, xprt_switch_find_next_entry);
+}
+
+/*
+ * xprt_iter_rewind - Resets the xprt iterator
+ * @xpi: pointer to rpc_xprt_iter
+ *
+ * Resets xpi to ensure that it points to the first entry in the list
+ * of transports.
+ */
+static
+void xprt_iter_rewind(struct rpc_xprt_iter *xpi)
+{
+	rcu_read_lock();
+	xprt_iter_ops(xpi)->xpi_rewind(xpi);
+	rcu_read_unlock();
+}
+
+static void __xprt_iter_init(struct rpc_xprt_iter *xpi,
+		struct rpc_xprt_switch *xps,
+		const struct rpc_xprt_iter_ops *ops)
+{
+	rcu_assign_pointer(xpi->xpi_xpswitch, xprt_switch_get(xps));
+	xpi->xpi_cursor = NULL;
+	xpi->xpi_ops = ops;
+}
+
+/**
+ * xprt_iter_init - Initialise an xprt iterator
+ * @xpi: pointer to rpc_xprt_iter
+ * @xps: pointer to rpc_xprt_switch
+ *
+ * Initialises the iterator to use the default iterator ops
+ * as set in xps. This function is mainly intended for internal
+ * use in the rpc_client.
+ */
+void xprt_iter_init(struct rpc_xprt_iter *xpi,
+		struct rpc_xprt_switch *xps)
+{
+	__xprt_iter_init(xpi, xps, NULL);
+}
+
+/**
+ * xprt_iter_init_listall - Initialise an xprt iterator
+ * @xpi: pointer to rpc_xprt_iter
+ * @xps: pointer to rpc_xprt_switch
+ *
+ * Initialises the iterator to iterate once through the entire list
+ * of entries in xps.
+ */
+void xprt_iter_init_listall(struct rpc_xprt_iter *xpi,
+		struct rpc_xprt_switch *xps)
+{
+	__xprt_iter_init(xpi, xps, &rpc_xprt_iter_listall);
+}
+
+/**
+ * xprt_iter_xchg_switch - Atomically swap out the rpc_xprt_switch
+ * @xpi: pointer to rpc_xprt_iter
+ * @xps: pointer to a new rpc_xprt_switch or NULL
+ *
+ * Swaps out the existing xpi->xpi_xpswitch with a new value.
+ */
+struct rpc_xprt_switch *xprt_iter_xchg_switch(struct rpc_xprt_iter *xpi,
+		struct rpc_xprt_switch *newswitch)
+{
+	struct rpc_xprt_switch __rcu *oldswitch;
+
+	/* Atomically swap out the old xpswitch */
+	oldswitch = xchg(&xpi->xpi_xpswitch, RCU_INITIALIZER(newswitch));
+	if (newswitch != NULL)
+		xprt_iter_rewind(xpi);
+	return rcu_dereference_protected(oldswitch, true);
+}
+
+/**
+ * xprt_iter_destroy - Destroys the xprt iterator
+ * @xpi pointer to rpc_xprt_iter
+ */
+void xprt_iter_destroy(struct rpc_xprt_iter *xpi)
+{
+	xprt_switch_put(xprt_iter_xchg_switch(xpi, NULL));
+}
+
+/**
+ * xprt_iter_xprt - Returns the rpc_xprt pointed to by the cursor
+ * @xpi: pointer to rpc_xprt_iter
+ *
+ * Returns a pointer to the struct rpc_xprt that is currently
+ * pointed to by the cursor.
+ * Caller must be holding rcu_read_lock().
+ */
+struct rpc_xprt *xprt_iter_xprt(struct rpc_xprt_iter *xpi)
+{
+	WARN_ON_ONCE(!rcu_read_lock_held());
+	return xprt_iter_ops(xpi)->xpi_xprt(xpi);
+}
+
+static
+struct rpc_xprt *xprt_iter_get_helper(struct rpc_xprt_iter *xpi,
+		struct rpc_xprt *(*fn)(struct rpc_xprt_iter *))
+{
+	struct rpc_xprt *ret;
+
+	do {
+		ret = fn(xpi);
+		if (ret == NULL)
+			break;
+		ret = xprt_get(ret);
+	} while (ret == NULL);
+	return ret;
+}
+
+/**
+ * xprt_iter_get_xprt - Returns the rpc_xprt pointed to by the cursor
+ * @xpi: pointer to rpc_xprt_iter
+ *
+ * Returns a reference to the struct rpc_xprt that is currently
+ * pointed to by the cursor.
+ */
+struct rpc_xprt *xprt_iter_get_xprt(struct rpc_xprt_iter *xpi)
+{
+	struct rpc_xprt *xprt;
+
+	rcu_read_lock();
+	xprt = xprt_iter_get_helper(xpi, xprt_iter_ops(xpi)->xpi_xprt);
+	rcu_read_unlock();
+	return xprt;
+}
+
+/**
+ * xprt_iter_get_next - Returns the next rpc_xprt following the cursor
+ * @xpi: pointer to rpc_xprt_iter
+ *
+ * Returns a reference to the struct rpc_xprt that immediately follows the
+ * entry pointed to by the cursor.
+ */
+struct rpc_xprt *xprt_iter_get_next(struct rpc_xprt_iter *xpi)
+{
+	struct rpc_xprt *xprt;
+
+	rcu_read_lock();
+	xprt = xprt_iter_get_helper(xpi, xprt_iter_ops(xpi)->xpi_next);
+	rcu_read_unlock();
+	return xprt;
+}
+
+/* Policy for always returning the first entry in the rpc_xprt_switch */
+static
+const struct rpc_xprt_iter_ops rpc_xprt_iter_singular = {
+	.xpi_rewind = xprt_iter_no_rewind,
+	.xpi_xprt = xprt_iter_first_entry,
+	.xpi_next = xprt_iter_first_entry,
+};
+
+/* Policy for round-robin iteration of entries in the rpc_xprt_switch */
+static
+const struct rpc_xprt_iter_ops rpc_xprt_iter_roundrobin = {
+	.xpi_rewind = xprt_iter_default_rewind,
+	.xpi_xprt = xprt_iter_current_entry,
+	.xpi_next = xprt_iter_next_entry_roundrobin,
+};
+
+/* Policy for once-through iteration of entries in the rpc_xprt_switch */
+static
+const struct rpc_xprt_iter_ops rpc_xprt_iter_listall = {
+	.xpi_rewind = xprt_iter_default_rewind,
+	.xpi_xprt = xprt_iter_current_entry,
+	.xpi_next = xprt_iter_next_entry_all,
+};

net/sunrpc/xprtsock.c

@@ -1844,9 +1844,7 @@ static int xs_bind(struct sock_xprt *transport, struct socket *sock)
  */
 static void xs_local_rpcbind(struct rpc_task *task)
 {
-	rcu_read_lock();
-	xprt_set_bound(rcu_dereference(task->tk_client->cl_xprt));
-	rcu_read_unlock();
+	xprt_set_bound(task->tk_xprt);
 }
 
 static void xs_local_set_port(struct rpc_xprt *xprt, unsigned short port)