--- /usr/src/sys/kern/kern_lock.c	2008-02-06 14:26:01.000000000 +0100
+++ sys/kern/kern_lock.c	2008-02-08 13:01:40.000000000 +0100
@@ -205,6 +205,15 @@
 	error = 0;
 	td = curthread;
 
+#ifdef INVARIANTS
+	if (lkp->lk_flags & LK_DESTROYED) {
+		if (flags & LK_INTERLOCK)
+			mtx_unlock(interlkp);
+		if (panicstr != NULL)
+			return (0);
+	    	panic("%s: %p lockmgr is destroyed", __func__, lkp);
+	}
+#endif
 	if ((flags & LK_INTERNAL) == 0)
 		mtx_lock(lkp->lk_interlock);
 	CTR6(KTR_LOCK,
@@ -562,6 +571,10 @@
 
 	CTR2(KTR_LOCK, "lockdestroy(): lkp == %p (lk_wmesg == \"%s\")",
 	    lkp, lkp->lk_wmesg);
+	KASSERT((lkp->lk_flags & (LK_HAVE_EXCL | LK_SHARE_NONZERO)) == 0,
+	    ("lockmgr still held"));
+	KASSERT(lkp->lk_exclusivecount == 0, ("lockmgr still recursed"));
+	lkp->lk_flags = LK_DESTROYED;
 	lock_destroy(&lkp->lk_object);
 }
 
@@ -574,6 +587,8 @@
 	struct thread *td;
 
 	td = curthread;
+	KASSERT(panicstr != NULL || (lkp->lk_flags & LK_DESTROYED) == 0,
+	    ("%s: %p lockmgr is destroyed", __func__, lkp));
 	KASSERT(panicstr != NULL || lkp->lk_exclusivecount,
 	    ("%s: %p lockmgr must be exclusively locked", __func__, lkp));
 	KASSERT(panicstr != NULL || lkp->lk_lockholder == td ||
@@ -608,6 +623,8 @@
 
 	KASSERT(td == NULL || td == curthread,
 	    ("%s: thread passed argument (%p) is not valid", __func__, td));
+	KASSERT((lkp->lk_flags & LK_DESTROYED) == 0,
+	    ("%s: %p lockmgr is destroyed", __func__, lkp));
 
 	if (!kdb_active) {
 		interlocked = 1;
@@ -635,6 +652,8 @@
 {
 	int count;
 
+	KASSERT((lkp->lk_flags & LK_DESTROYED) == 0,
+	    ("%s: %p lockmgr is destroyed", __func__, lkp));
 	mtx_lock(lkp->lk_interlock);
 	count = lkp->lk_waitcount;
 	mtx_unlock(lkp->lk_interlock);
--- /usr/src/sys/sys/lockmgr.h	2008-02-06 01:37:14.000000000 +0100
+++ sys/sys/lockmgr.h	2008-02-08 12:43:00.000000000 +0100
@@ -137,7 +137,8 @@
 #define	LK_HAVE_EXCL	0x00040000	/* exclusive lock obtained */
 #define	LK_WAITDRAIN	0x00080000	/* process waiting for lock to drain */
 #define	LK_DRAINING	0x00100000	/* lock is being drained */
-#define	LK_INTERNAL	0x00200000/* The internal lock is already held */
+#define	LK_INTERNAL	0x00200000	/* The internal lock is already held */
+#define	LK_DESTROYED	0x00400000	/* lock is destroyed */
 /*
  * Internal state flags corresponding to lk_sharecount, and lk_waitcount
  */