diff --git a/sys/fs/nwfs/nwfs_vfsops.c b/sys/fs/nwfs/nwfs_vfsops.c
index b37a856aaee6..2fb075296174 100644
--- a/sys/fs/nwfs/nwfs_vfsops.c
+++ b/sys/fs/nwfs/nwfs_vfsops.c
@@ -471,30 +471,41 @@ nwfs_sync(mp, waitfor, cred, p)
 	struct ucred *cred;
 	struct proc *p;
 {
-	struct vnode *vp;
+	struct vnode *vp, *nvp;
 	int error, allerror = 0;
 	/*
 	 * Force stale buffer cache information to be flushed.
 	 */
+	mtx_lock(&mntvnode_mtx);
 loop:
 	for (vp = LIST_FIRST(&mp->mnt_vnodelist);
 	     vp != NULL;
-	     vp = LIST_NEXT(vp, v_mntvnodes)) {
+	     vp = nvp) {
 		/*
 		 * If the vnode that we are about to sync is no longer
 		 * associated with this mount point, start over.
 		 */
 		if (vp->v_mount != mp)
 			goto loop;
+		nvp = LIST_NEXT(vp, v_mntvnodes);
+		mtx_unlock(&mntvnode_mtx);
+		mtx_lock(&vp->v_interlock);
 		if (VOP_ISLOCKED(vp, NULL) || TAILQ_EMPTY(&vp->v_dirtyblkhd) ||
-		    waitfor == MNT_LAZY)
+		    waitfor == MNT_LAZY) {
+			mtx_unlock(&vp->v_interlock);
+			mtx_lock(&mntvnode_mtx);
 			continue;
-		if (vget(vp, LK_EXCLUSIVE, p))
+		}
+		if (vget(vp, LK_EXCLUSIVE | LK_INTERLOCK, p)) {
+			mtx_lock(&mntvnode_mtx);
 			goto loop;
+		}
 		error = VOP_FSYNC(vp, cred, waitfor, p);
 		if (error)
 			allerror = error;
 		vput(vp);
+		mtx_lock(&mntvnode_mtx);
 	}
+	mtx_unlock(&mntvnode_mtx);
 	return (allerror);
 }
diff --git a/sys/fs/unionfs/union_vfsops.c b/sys/fs/unionfs/union_vfsops.c
index 1a5cb7090e95..aa4986c276e1 100644
--- a/sys/fs/unionfs/union_vfsops.c
+++ b/sys/fs/unionfs/union_vfsops.c
@@ -45,6 +45,8 @@
 #include <sys/param.h>
 #include <sys/systm.h>
 #include <sys/kernel.h>
+#include <sys/lock.h>
+#include <sys/mutex.h>
 #include <sys/proc.h>
 #include <sys/vnode.h>
 #include <sys/mount.h>
@@ -330,9 +332,11 @@ union_unmount(mp, mntflags, p)
 		int n;
 
 		/* count #vnodes held on mount list */
+		mtx_lock(&mntvnode_mtx);
 		n = 0;
 		LIST_FOREACH(vp, &mp->mnt_vnodelist, v_mntvnodes)
 			n++;
+		mtx_unlock(&mntvnode_mtx);
 
 		/* if this is unchanged then stop */
 		if (n == freeing)