Index: sys/kern/kern_umtx.c
===================================================================
--- sys/kern/kern_umtx.c	(revision 232618)
+++ sys/kern/kern_umtx.c	(working copy)
@@ -129,6 +129,7 @@
 	struct umtx_key		key;
 	LIST_ENTRY(umtxq_queue)	link;
 	int			length;
+	int 			max_length;
 };
 
 LIST_HEAD(umtxq_list, umtxq_queue);
@@ -189,6 +190,8 @@
 static SYSCTL_NODE(_debug, OID_AUTO, umtx, CTLFLAG_RW, 0, "umtx debug");
 SYSCTL_INT(_debug_umtx, OID_AUTO, umtx_pi_allocated, CTLFLAG_RD,
     &umtx_pi_allocated, 0, "Allocated umtx_pi");
+static long max_length;
+SYSCTL_LONG(_debug_umtx, OID_AUTO, max_length, CTLFLAG_RD, &max_length, 0, "max_length");
 
 static void umtxq_sysinit(void *);
 static void umtxq_hash(struct umtx_key *key);
@@ -384,6 +387,11 @@
 
 	TAILQ_INSERT_TAIL(&uh->head, uq, uq_link);
 	uh->length++;
+	if (uh->length > uh->max_length) {
+		uh->max_length = uh->length;
+		if (uh->max_length > max_length)
+			max_length = uh->max_length;	
+	}
 	uq->uq_flags |= UQF_UMTXQ;
 	uq->uq_cur_queue = uh;
 	return;