--- fs/nfs/nfs_var.h.orig	2017-05-26 17:26:36.190031000 -0400
+++ fs/nfs/nfs_var.h	2017-05-26 17:27:05.894831000 -0400
@@ -401,7 +401,7 @@ int nfsrpc_closerpc(struct nfsrv_descrip
 int nfsrpc_openconfirm(vnode_t, u_int8_t *, int, struct nfsclopen *,
     struct ucred *, NFSPROC_T *);
 int nfsrpc_setclient(struct nfsmount *, struct nfsclclient *, int,
-    struct ucred *, NFSPROC_T *);
+    struct ucred *, NFSPROC_T *, int *);
 int nfsrpc_getattr(vnode_t, struct ucred *, NFSPROC_T *,
     struct nfsvattr *, void *);
 int nfsrpc_getattrnovp(struct nfsmount *, u_int8_t *, int, int,
--- fs/nfsclient/nfs_clstate.c.orig	2017-05-26 17:26:51.520438000 -0400
+++ fs/nfsclient/nfs_clstate.c	2017-05-26 17:27:05.915325000 -0400
@@ -903,7 +903,7 @@ nfscl_getcl(struct mount *mp, struct ucr
 			clidinusedelay = 120;
 		trystalecnt = 3;
 		do {
-			error = nfsrpc_setclient(nmp, clp, 0, cred, p);
+			error = nfsrpc_setclient(nmp, clp, 0, cred, p, NULL);
 			if (error == NFSERR_STALECLIENTID ||
 			    error == NFSERR_STALEDONTRECOVER ||
 			    error == NFSERR_BADSESSION ||
@@ -1933,7 +1933,7 @@ nfscl_umount(struct nfsmount *nmp, NFSPR
 			(void)nfsrpc_destroysession(nmp, clp, cred, p);
 			(void)nfsrpc_destroyclient(nmp, clp, cred, p);
 		} else
-			(void)nfsrpc_setclient(nmp, clp, 0, cred, p);
+			(void)nfsrpc_setclient(nmp, clp, 0, cred, p, NULL);
 		nfscl_cleanclient(clp);
 		nmp->nm_clp = NULL;
 		NFSFREECRED(cred);
@@ -1963,7 +1963,7 @@ nfscl_recover(struct nfsclclient *clp, s
 	struct nfsreq *rep;
 	u_int64_t len;
 	u_int32_t delegtype = NFSV4OPEN_DELEGATEWRITE, mode;
-	int i, igotlock = 0, error, trycnt, firstlock;
+	int i, igotlock = 0, error, trycnt, firstlock, retok;
 	struct nfscllayout *lyp, *nlyp;
 
 	/*
@@ -1993,8 +1993,10 @@ nfscl_recover(struct nfsclclient *clp, s
 		LIST_INIT(&clp->nfsc_layouthash[i]);
 
 	trycnt = 5;
+	retok = 0;
+	tcred = NULL;
 	do {
-		error = nfsrpc_setclient(nmp, clp, 1, cred, p);
+		error = nfsrpc_setclient(nmp, clp, 1, cred, p, &retok);
 	} while ((error == NFSERR_STALECLIENTID ||
 	     error == NFSERR_BADSESSION ||
 	     error == NFSERR_STALEDONTRECOVER) && --trycnt > 0);
@@ -2026,6 +2028,10 @@ nfscl_recover(struct nfsclclient *clp, s
 	}
 	NFSUNLOCKREQ();
 
+	/* If nfsrpc_setclient() sets retok != 0, no more recovery is needed. */
+	if (retok != 0)
+		goto out;
+
 	/*
 	 * Now, mark all delegations "need reclaim".
 	 */
@@ -2259,12 +2265,14 @@ nfscl_recover(struct nfsclclient *clp, s
 	if (NFSHASNFSV4N(nmp))
 		(void)nfsrpc_reclaimcomplete(nmp, cred, p);
 
+out:
 	NFSLOCKCLSTATE();
 	clp->nfsc_flags &= ~NFSCLFLAGS_RECVRINPROG;
 	wakeup(&clp->nfsc_flags);
 	nfsv4_unlock(&clp->nfsc_lock, 0);
 	NFSUNLOCKCLSTATE();
-	NFSFREECRED(tcred);
+	if (tcred != NULL)
+		NFSFREECRED(tcred);
 }
 
 /*
@@ -2313,7 +2321,7 @@ nfscl_hasexpired(struct nfsclclient *clp
 	cred = newnfs_getcred();
 	trycnt = 5;
 	do {
-		error = nfsrpc_setclient(nmp, clp, 0, cred, p);
+		error = nfsrpc_setclient(nmp, clp, 0, cred, p, NULL);
 	} while ((error == NFSERR_STALECLIENTID ||
 	     error == NFSERR_BADSESSION ||
 	     error == NFSERR_STALEDONTRECOVER) && --trycnt > 0);
--- fs/nfsclient/nfs_clrpcops.c.orig	2017-05-26 17:26:51.522899000 -0400
+++ fs/nfsclient/nfs_clrpcops.c	2017-05-26 17:27:05.930762000 -0400
@@ -818,7 +818,7 @@ nfsmout:
  */
 APPLESTATIC int
 nfsrpc_setclient(struct nfsmount *nmp, struct nfsclclient *clp, int reclaim,
-    struct ucred *cred, NFSPROC_T *p)
+    struct ucred *cred, NFSPROC_T *p, int *retokp)
 {
 	u_int32_t *tl;
 	struct nfsrv_descript nfsd;
@@ -830,26 +830,72 @@ nfsrpc_setclient(struct nfsmount *nmp, s
 	nfsquad_t confirm;
 	u_int32_t lease;
 	static u_int32_t rev = 0;
-	struct nfsclds *dsp;
+	struct nfsclds *dsp, *odsp;
 	struct in6_addr a6;
 	struct nfsclsession *tsep;
 
+	if (retokp != NULL)
+		*retokp = 0;
 	if (nfsboottime.tv_sec == 0)
 		NFSSETBOOTTIME(nfsboottime);
 	clp->nfsc_rev = rev++;
 	if (NFSHASNFSV4N(nmp)) {
-		/*
-		 * Either there was no previous session or the
-		 * previous session has failed, so...
-		 * do an ExchangeID followed by the CreateSession.
-		 */
-		error = nfsrpc_exchangeid(nmp, clp, &nmp->nm_sockreq,
-		    NFSV4EXCH_USEPNFSMDS | NFSV4EXCH_USENONPNFS, &dsp, cred, p);
-		NFSCL_DEBUG(1, "aft exch=%d\n", error);
-		if (error == 0)
+		error = NFSERR_BADSESSION;
+		dsp = NULL;
+		NFSLOCKMNT(nmp);
+		odsp = TAILQ_FIRST(&nmp->nm_sess);
+		NFSUNLOCKMNT(nmp);
+		if (odsp != NULL) {
+			/*
+			 * When a session already exists, first try a
+			 * CreateSession with the extant ClientID.
+			 */
+			dsp = malloc(sizeof(struct nfsclds) +
+			    odsp->nfsclds_servownlen + 1, M_NFSCLDS,
+			    M_WAITOK | M_ZERO);
+			dsp->nfsclds_expire = NFSD_MONOSEC + clp->nfsc_renew;
+			dsp->nfsclds_servownlen = odsp->nfsclds_servownlen;
+			dsp->nfsclds_sess.nfsess_clientid =
+			    odsp->nfsclds_sess.nfsess_clientid;
+			dsp->nfsclds_sess.nfsess_sequenceid =
+			    odsp->nfsclds_sess.nfsess_sequenceid;
+			dsp->nfsclds_flags = odsp->nfsclds_flags;
+			if (dsp->nfsclds_servownlen > 0)
+				bcopy(odsp->nfsclds_serverown,
+				    dsp->nfsclds_serverown,
+				    dsp->nfsclds_servownlen + 1);
+			mtx_init(&dsp->nfsclds_mtx, "nfsds", NULL, MTX_DEF);
+			mtx_init(&dsp->nfsclds_sess.nfsess_mtx, "nfssession",
+			    NULL, MTX_DEF);
+			nfscl_initsessionslots(&dsp->nfsclds_sess);
 			error = nfsrpc_createsession(nmp, &dsp->nfsclds_sess,
 			    &nmp->nm_sockreq,
 			    dsp->nfsclds_sess.nfsess_sequenceid, 1, cred, p);
+			NFSCL_DEBUG(1, "create session for extant "
+			    "ClientID=%d\n", error);
+			if (error != 0) {
+				nfscl_freenfsclds(dsp);
+				dsp = NULL;
+			} else if (retokp != NULL)
+				*retokp = 1;
+		}
+		if (error != 0) {
+			/*
+			 * Either there was no previous session or the
+			 * CreateSession attempt failed, so...
+			 * Do an ExchangeID followed by the CreateSession.
+			 */
+			error = nfsrpc_exchangeid(nmp, clp, &nmp->nm_sockreq,
+			    NFSV4EXCH_USEPNFSMDS | NFSV4EXCH_USENONPNFS, &dsp,
+			    cred, p);
+			NFSCL_DEBUG(1, "aft exch=%d\n", error);
+			if (error == 0)
+				error = nfsrpc_createsession(nmp,
+				    &dsp->nfsclds_sess, &nmp->nm_sockreq,
+				    dsp->nfsclds_sess.nfsess_sequenceid, 1,
+				    cred, p);
+			NFSCL_DEBUG(1, "aft createsess=%d\n", error);
+		}
 		if (error == 0) {
 			NFSLOCKMNT(nmp);
 			/*
@@ -860,8 +906,7 @@ nfsrpc_setclient(struct nfsmount *nmp, s
 			tsep = NULL;
 			if (TAILQ_FIRST(&nmp->nm_sess) != NULL)
 				tsep = NFSMNT_MDSSESSION(nmp);
-			TAILQ_INSERT_HEAD(&nmp->nm_sess, dsp,
-			    nfsclds_list);
+			TAILQ_INSERT_HEAD(&nmp->nm_sess, dsp, nfsclds_list);
 			/*
 			 * Wake up RPCs waiting for a slot on the
 			 * old session. These will then fail with
@@ -874,9 +919,8 @@ nfsrpc_setclient(struct nfsmount *nmp, s
 				wakeup(&tsep->nfsess_slots);
 			wakeup(&nmp->nm_sess);
 			NFSUNLOCKMNT(nmp);
-		} else
+		} else if (dsp != NULL)
 			nfscl_freenfsclds(dsp);
-		NFSCL_DEBUG(1, "aft createsess=%d\n", error);
 		if (error == 0 && reclaim == 0) {
 			error = nfsrpc_reclaimcomplete(nmp, cred, p);
 			NFSCL_DEBUG(1, "aft reclaimcomp=%d\n", error);