--- sys/fs/nfs/nfs_commonsubs.c.slot	2022-05-20 16:07:41.772273000 -0700
+++ sys/fs/nfs/nfs_commonsubs.c	2022-05-21 05:19:50.789925000 -0700
@@ -81,6 +81,7 @@ NFSNAMEIDMUTEX;
 NFSSOCKMUTEX;
 extern int nfsrv_lughashsize;
 extern struct mtx nfsrv_dslock_mtx;
+extern struct mtx nfs_clstate_mutex;
 extern volatile int nfsrv_devidcnt;
 extern int nfscl_debuglevel;
 extern struct nfsdevicehead nfsrv_devidhead;
@@ -4823,31 +4824,73 @@ nfsv4_sequencelookup(struct nfsmount *nmp, struct nfsc
 {
 	int i, maxslot, slotpos;
 	uint64_t bitval;
+	bool fnd_okslot;
 
 	/* Find an unused slot. */
 	slotpos = -1;
 	maxslot = -1;
 	mtx_lock(&sep->nfsess_mtx);
+if (sep->nfsess_badslots != 0) printf("badslots=0x%lx\n", sep->nfsess_badslots);
 	do {
-		if (nmp != NULL && sep->nfsess_defunct != 0) {
-			/* Just return the bad session. */
-			bcopy(sep->nfsess_sessionid, sessionid,
-			    NFSX_V4SESSIONID);
-			mtx_unlock(&sep->nfsess_mtx);
-			return (NFSERR_BADSESSION);
+		fnd_okslot = true;
+		if (nmp != NULL) {
+			KASSERT(TAILQ_FIRST(&nmp->nm_sess) != NULL,
+			    ("nfsv4_sequencelookup: no mds sess"));
+			if (sep->nfsess_defunct != 0) {
+				/* Just return the bad session. */
+				bcopy(sep->nfsess_sessionid, sessionid,
+				    NFSX_V4SESSIONID);
+				mtx_unlock(&sep->nfsess_mtx);
+				return (NFSERR_BADSESSION);
+			}
+
+			/* Only check for bad slots on the MDS session. */
+			if (NFSMNT_MDSSESSION(nmp) == sep)
+				fnd_okslot = false;
 		}
 		bitval = 1;
 		for (i = 0; i < sep->nfsess_foreslots; i++) {
-			if ((bitval & sep->nfsess_slots) == 0) {
-				slotpos = i;
-				sep->nfsess_slots |= bitval;
-				sep->nfsess_slotseq[i]++;
-				*slotseqp = sep->nfsess_slotseq[i];
-				break;
+			if ((bitval & sep->nfsess_badslots) == 0) {
+				fnd_okslot = true;
+				if ((bitval & sep->nfsess_slots) == 0) {
+					slotpos = i;
+					sep->nfsess_slots |= bitval;
+					sep->nfsess_slotseq[i]++;
+					*slotseqp = sep->nfsess_slotseq[i];
+					break;
+				}
 			}
 			bitval <<= 1;
 		}
 		if (slotpos == -1) {
+			if (!fnd_okslot) {
+				/*
+				 * All slots are broken, so mark the session
+				 * defunct.
+				 */
+				bcopy(sep->nfsess_sessionid, sessionid,
+				    NFSX_V4SESSIONID);
+				sep->nfsess_defunct = 1;
+printf("all badslots\n");
+				mtx_unlock(&sep->nfsess_mtx);
+				NFSCL_DEBUG(1, "Marked defunct\n");
+
+				/*
+				 * If this is the current session,
+				 * initiate recovery.
+				 */
+				NFSLOCKCLSTATE();
+				NFSLOCKMNT(nmp);
+				if (nmp->nm_clp != NULL &&
+				    NFSMNT_MDSSESSION(nmp) == sep) {
+					nmp->nm_clp->nfsc_flags |=
+					    NFSCLFLAGS_RECOVER;
+					wakeup(nmp->nm_clp);
+				}
+				NFSUNLOCKCLSTATE();
+				NFSUNLOCKMNT(nmp);
+				return (NFSERR_BADSESSION);
+			}
 			/*
 			 * If a forced dismount is in progress, just return.
 			 * This RPC attempt will fail when it calls
--- sys/fs/nfs/nfs_commonkrpc.c.slot	2022-05-20 16:15:42.665994000 -0700
+++ sys/fs/nfs/nfs_commonkrpc.c	2022-05-21 17:06:45.283183000 -0700
@@ -606,6 +606,7 @@ newnfs_request(struct nfsrv_descript *nd, struct nfsmo
 	uint8_t sessionid[NFSX_V4SESSIONID];
 	bool nextconn_set;
 	struct timespec trylater_delay, ts, waituntil;
+	struct nfsclds *dsp;
 
 	/* Initially 1msec. */
 	trylater_delay.tv_sec = 0;
@@ -951,6 +952,7 @@ tryagain:
 			 */
 			mtx_lock(&sep->nfsess_mtx);
 			sep->nfsess_slotseq[nd->nd_slotid] += 10;
+			sep->nfsess_badslots |= (1 << nd->nd_slotid);
 			mtx_unlock(&sep->nfsess_mtx);
 			/* And free the slot. */
 			nfsv4_freeslot(sep, nd->nd_slotid, false);
@@ -1093,16 +1095,28 @@ tryagain:
 				NFSCL_DEBUG(1, "Got badsession\n");
 				NFSLOCKCLSTATE();
 				NFSLOCKMNT(nmp);
-				sep = NFSMNT_MDSSESSION(nmp);
-				if (bcmp(sep->nfsess_sessionid, nd->nd_sequence,
-				    NFSX_V4SESSIONID) == 0) {
-					/* Initiate recovery. */
-					sep->nfsess_defunct = 1;
-					NFSCL_DEBUG(1, "Marked defunct\n");
-					if (nmp->nm_clp != NULL) {
-						nmp->nm_clp->nfsc_flags |=
-						    NFSCLFLAGS_RECOVER;
-						wakeup(nmp->nm_clp);
+				TAILQ_FOREACH(dsp, &nmp->nm_sess,
+				    nfsclds_list) {
+					sep = &dsp->nfsclds_sess;
+					if ((dsp->nfsclds_flags &
+					    NFSCLDS_DSSESS) == 0 &&
+					    bcmp(sep->nfsess_sessionid,
+					    nd->nd_sequence,
+					    NFSX_V4SESSIONID) == 0) {
+						/* Initiate recovery. */
+						sep->nfsess_defunct = 1;
+						NFSCL_DEBUG(1,
+						    "Marked defunct\n");
+printf("newnfs_req: sess defunct\n");
+						if (nmp->nm_clp != NULL &&
+						    NFSMNT_MDSSESSION(nmp) ==
+						    sep) {
+printf("newnfs_req: init recvr\n");
+						    nmp->nm_clp->nfsc_flags |=
+							NFSCLFLAGS_RECOVER;
+						    wakeup(nmp->nm_clp);
+						}
+						break;
 					}
 				}
 				NFSUNLOCKCLSTATE();
--- sys/fs/nfs/nfsclstate.h.slot	2022-05-20 16:16:48.454756000 -0700
+++ sys/fs/nfs/nfsclstate.h	2022-05-21 17:03:13.519408000 -0700
@@ -67,6 +67,7 @@ struct nfsclsession {
 	SVCXPRT		*nfsess_xprt;		/* For backchannel callback */
 	uint32_t	nfsess_slotseq[64];	/* Max for 64bit nm_slots */
 	uint64_t	nfsess_slots;
+	uint64_t	nfsess_badslots;	/* Slots that are broken */
 	uint32_t	nfsess_sequenceid;
 	uint32_t	nfsess_maxcache;	/* Max size for cached reply. */
 	uint32_t	nfsess_maxreq;		/* Max request size. */
@@ -103,6 +104,7 @@ struct nfsclds {
 #define	NFSCLDS_CLOSED		0x0008
 #define	NFSCLDS_SAMECONN	0x0010
 #define	NFSCLDS_MINORV2		0x0020
+#define	NFSCLDS_DSSESS		0x0040
 
 struct nfsclclient {
 	LIST_ENTRY(nfsclclient) nfsc_list;
--- sys/fs/nfsclient/nfs_clrpcops.c.slot	2022-05-20 16:18:41.641440000 -0700
+++ sys/fs/nfsclient/nfs_clrpcops.c	2022-05-21 17:02:31.326822000 -0700
@@ -6001,6 +6001,8 @@ nfsrpc_fillsa(struct nfsmount *nmp, struct sockaddr_in
 			    firsttry++ == 0);
 			if (error != 0)
 				newnfs_disconnect(NULL, nrp);
+			else
+				dsp->nfsclds_flags |= NFSCLDS_DSSESS;
 		} else {
 			dsp = malloc(sizeof(struct nfsclds), M_NFSCLDS,
 			    M_WAITOK | M_ZERO);
@@ -6107,6 +6109,7 @@ nfscl_initsessionslots(struct nfsclsession *sep)
 	for (i = 0; i < 64; i++)
 		sep->nfsess_slotseq[i] = 0;
 	sep->nfsess_slots = 0;
+	sep->nfsess_badslots = 0;
 }
 
 /*