diff --git a/sys/fs/nfsclient/nfs_clstate.c.freeown b/sys/fs/nfsclient/nfs_clstate.c
--- a/sys/fs/nfsclient/nfs_clstate.c.freeown
+++ b/sys/fs/nfsclient/nfs_clstate.c
@@ -164,7 +164,7 @@
 static void nfscl_freedeleg(struct nfscldeleghead *, struct nfscldeleg *,
     bool);
 static int nfscl_errmap(struct nfsrv_descript *, u_int32_t);
-static void nfscl_cleanup_common(struct nfsclclient *, u_int8_t *);
+static bool nfscl_cleanup_common(struct nfsclclient *, u_int8_t *);
 static int nfscl_recalldeleg(struct nfsclclient *, struct nfsmount *,
     struct nfscldeleg *, vnode_t, struct ucred *, NFSPROC_T *, int,
     vnode_t *);
@@ -1648,8 +1648,21 @@
 static void
 nfscl_freeopenowner(struct nfsclowner *owp, int local)
 {
+	int owned;
 
+	/*
+	 * Make sure the NFSCLSTATE mutex is held, to avoid races with
+	 * calls in nfscl_renewthread() that do not hold a reference
+	 * count on the nfsclclient and just the mutex.
+	 * The mutex will not be held for calls done with the exclusive
+	 * nfsclclient lock held.
+	 */
+	owned = mtx_owned(NFSCLSTATEMUTEXPTR);
+	if (owned == 0)
+		NFSLOCKCLSTATE();
 	LIST_REMOVE(owp, nfsow_list);
+	if (owned == 0)
+		NFSUNLOCKCLSTATE();
 	free(owp, M_NFSCLOWNER);
 	if (local)
 		nfsstatsv1.cllocalopenowners--;
@@ -1664,8 +1677,21 @@
 nfscl_freelockowner(struct nfscllockowner *lp, int local)
 {
 	struct nfscllock *lop, *nlop;
+	int owned;
 
+	/*
+	 * Make sure the NFSCLSTATE mutex is held, to avoid races with
+	 * calls in nfscl_renewthread() that do not hold a reference
+	 * count on the nfsclclient and just the mutex.
+	 * The mutex will not be held for calls done with the exclusive
+	 * nfsclclient lock held.
+	 */
+	owned = mtx_owned(NFSCLSTATEMUTEXPTR);
+	if (owned == 0)
+		NFSLOCKCLSTATE();
 	LIST_REMOVE(lp, nfsl_list);
+	if (owned == 0)
+		NFSUNLOCKCLSTATE();
 	LIST_FOREACH_SAFE(lop, &lp->nfsl_lock, nfslo_list, nlop) {
 		nfscl_freelock(lop, local);
 	}
@@ -1851,13 +1877,15 @@
  * This function must be called after the process represented by "own" has
  * exited. Must be called with CLSTATE lock held.
  */
-static void
+static bool
 nfscl_cleanup_common(struct nfsclclient *clp, u_int8_t *own)
 {
 	struct nfsclowner *owp, *nowp;
 	struct nfscllockowner *lp, *nlp;
 	struct nfscldeleg *dp;
+	bool didfree;
 
+	didfree = false;
 	/* First, get rid of local locks on delegations. */
 	TAILQ_FOREACH(dp, &clp->nfsc_deleg, nfsdl_list) {
 		LIST_FOREACH_SAFE(lp, &dp->nfsdl_lock, nfsl_list, nlp) {
@@ -1865,6 +1893,7 @@
 			if ((lp->nfsl_rwlock.nfslock_lock & NFSV4LOCK_WANTED))
 			    panic("nfscllckw");
 			nfscl_freelockowner(lp, 1);
+			didfree = true;
 		    }
 		}
 	}
@@ -1879,13 +1908,15 @@
 			 * here. For that case, let the renew thread clear
 			 * out the OpenOwner later.
 			 */
-			if (LIST_EMPTY(&owp->nfsow_open))
+			if (LIST_EMPTY(&owp->nfsow_open)) {
 				nfscl_freeopenowner(owp, 0);
-			else
+				didfree = true;
+			} else
 				owp->nfsow_defunct = 1;
 		}
 		owp = nowp;
 	}
+	return (didfree);
 }
 
 /*
@@ -1894,10 +1925,11 @@
 static void
 nfscl_cleanupkext(struct nfsclclient *clp, struct nfscllockownerfhhead *lhp)
 {
-	struct nfsclowner *owp, *nowp;
+	struct nfsclowner *owp;
 	struct nfsclopen *op;
 	struct nfscllockowner *lp, *nlp;
 	struct nfscldeleg *dp;
+	uint8_t own[NFSV4CL_LOCKNAMELEN];
 
 	/*
 	 * All the pidhash locks must be acquired, since they are sx locks
@@ -1907,15 +1939,19 @@
 	 */
 	pidhash_slockall();
 	NFSLOCKCLSTATE();
-	LIST_FOREACH_SAFE(owp, &clp->nfsc_owner, nfsow_list, nowp) {
+tryagain:
+	LIST_FOREACH(owp, &clp->nfsc_owner, nfsow_list) {
 		LIST_FOREACH(op, &owp->nfsow_open, nfso_list) {
 			LIST_FOREACH_SAFE(lp, &op->nfso_lock, nfsl_list, nlp) {
 				if (LIST_EMPTY(&lp->nfsl_lock))
 					nfscl_emptylockowner(lp, lhp);
 			}
 		}
-		if (nfscl_procdoesntexist(owp->nfsow_owner))
-			nfscl_cleanup_common(clp, owp->nfsow_owner);
+		if (nfscl_procdoesntexist(owp->nfsow_owner)) {
+			memcpy(own, owp->nfsow_owner, NFSV4CL_LOCKNAMELEN);
+			if (nfscl_cleanup_common(clp, own))
+				goto tryagain;
+		}
 	}
 
 	/*
@@ -1926,9 +1962,14 @@
 	 * nfscl_cleanup_common().
 	 */
 	TAILQ_FOREACH(dp, &clp->nfsc_deleg, nfsdl_list) {
-		LIST_FOREACH_SAFE(lp, &dp->nfsdl_lock, nfsl_list, nlp) {
-			if (nfscl_procdoesntexist(lp->nfsl_owner))
-				nfscl_cleanup_common(clp, lp->nfsl_owner);
+tryagain2:
+		LIST_FOREACH(lp, &dp->nfsdl_lock, nfsl_list) {
+			if (nfscl_procdoesntexist(lp->nfsl_owner)) {
+				memcpy(own, lp->nfsl_owner,
+				    NFSV4CL_LOCKNAMELEN);
+				if (nfscl_cleanup_common(clp, own))
+					goto tryagain2;
+			}
 		}
 	}
 	NFSUNLOCKCLSTATE();