Index: sys/kern/vfs_subr.c
===================================================================
RCS file: /mount/openbsd/cvs/src/sys/kern/vfs_subr.c,v
diff -u -p -u -p -r1.325 vfs_subr.c
--- sys/kern/vfs_subr.c	31 Oct 2024 10:06:51 -0000	1.325
+++ sys/kern/vfs_subr.c	20 Dec 2024 12:40:50 -0000
@@ -181,6 +181,7 @@ vfs_mount_alloc(struct vnode *vp, struct
 	struct mount *mp;
 
 	mp = malloc(sizeof(*mp), M_MOUNT, M_WAITOK|M_ZERO);
+	refcnt_init(&mp->mnt_refs);
 	rw_init_flags(&mp->mnt_lock, "vfslock", RWL_IS_VNODE);
 	(void)vfs_busy(mp, VB_READ|VB_NOWAIT);
 
@@ -196,14 +197,29 @@ vfs_mount_alloc(struct vnode *vp, struct
 	return (mp);
 }
 
+struct mount *
+vfs_mount_take(struct mount *mp)
+{
+	refcnt_take(&mp->mnt_refs);
+	return (mp);
+}
+
+static void
+vfs_mount_rele(struct mount *mp)
+{
+	if (refcnt_rele(&mp->mnt_refs))
+		free(mp, M_MOUNT, sizeof(*mp));
+}
+
 /*
  * Release a mount point.
  */
 void
 vfs_mount_free(struct mount *mp)
 {
+	SET(mp->mnt_flag, MNT_FREE);
 	atomic_dec_int(&mp->mnt_vfc->vfc_refcount);
-	free(mp, M_MOUNT, sizeof(*mp));
+	vfs_mount_rele(mp);
 }
 
 /*
@@ -216,27 +232,27 @@ vfs_mount_free(struct mount *mp)
 int
 vfs_busy(struct mount *mp, int flags)
 {
-	int rwflags = 0;
+	int rwflags = ISSET(flags, VB_WRITE) ? RW_WRITE : RW_READ;
+	int error = 0;
 
-	if (flags & VB_WRITE)
-		rwflags |= RW_WRITE;
-	else
-		rwflags |= RW_READ;
-
-	if (flags & VB_WAIT)
-		rwflags |= RW_SLEEPFAIL;
-	else
+	if (!ISSET(flags, VB_WAIT))
 		rwflags |= RW_NOSLEEP;
 
 #ifdef WITNESS
-	if (flags & VB_DUPOK)
+	if (ISSET(flags, VB_DUPOK)
 		rwflags |= RW_DUPOK;
 #endif
 
-	if (rw_enter(&mp->mnt_lock, rwflags))
-		return (EBUSY);
+	vfs_mount_take(mp);
+	if (rw_enter(&mp->mnt_lock, rwflags) != 0)
+		error = EBUSY;
+	else if (ISSET(mp->mnt_flag, MNT_FREE)) {
+		rw_exit(&mp->mnt_lock);
+		error = EBUSY;
+	}
+	vfs_mount_rele(mp);
 
-	return (0);
+	return (error);
 }
 
 /*
Index: sys/sys/mount.h
===================================================================
RCS file: /mount/openbsd/cvs/src/sys/sys/mount.h,v
diff -u -p -u -p -r1.152 mount.h
--- sys/sys/mount.h	5 Nov 2024 17:28:32 -0000	1.152
+++ sys/sys/mount.h	20 Dec 2024 12:40:50 -0000
@@ -340,6 +340,7 @@ struct mount {
 	struct vnode    *mnt_syncer;            /* syncer vnode */
 	TAILQ_HEAD(, vnode) mnt_vnodelist;	/* list of vnodes this mount */
 	struct rwlock   mnt_lock;               /* mount structure lock */
+	struct refcnt	mnt_refs;
 	int		mnt_flag;		/* flags */
 	struct statfs	mnt_stat;		/* cache of filesystem stats */
 	void		*mnt_data;		/* private data */
@@ -388,8 +389,8 @@ struct mount {
     "\20\001RDONLY\002SYNCHRONOUS\003NOEXEC\004NOSUID\005NODEV\006NOPERM" \
     "\007ASYNC\010EXRDONLY\011EXPORTED\012DEFEXPORTED\013EXPORTANON" \
     "\014WXALLOWED\015LOCAL\016QUOTA\017ROOTFS\020NOATIME\021UPDATE" \
-    "\022DELEXPORT\023RELOAD\024FORCE\025STALLED\026SWAPPABLE\032WANTRDWR" \
-    "\033SOFTDEP\034DOOMED"
+    "\022DELEXPORT\023RELOAD\024FORCE\025STALLED\026SWAPPABLE\031FREE" \
+    "\032WANTRDWR\033SOFTDEP\034DOOMED"
 
 /*
  * filesystem control flags.
@@ -400,6 +401,7 @@ struct mount {
 #define	MNT_FORCE	0x00080000	/* force unmount or readonly change */
 #define	MNT_STALLED	0x00100000	/* filesystem stalled */ 
 #define	MNT_SWAPPABLE	0x00200000	/* filesystem can be used for swap */
+#define MNT_FREE	0x01000000	/* filesystem is unmounted */
 #define MNT_WANTRDWR	0x02000000	/* want upgrade to read/write */
 #define MNT_SOFTDEP     0x04000000      /* soft dependencies being done - now ignored */
 #define MNT_DOOMED	0x08000000	/* device behind filesystem is gone */