From c3fa8b9d02661087ccb4852d7c3c619e7b66aa81 Mon Sep 17 00:00:00 2001
From: David du Colombier <0intro@gmail.com>
Date: Sun, 24 Jan 1999 00:00:00 +0000
Subject: [PATCH] Plan 9 from Bell Labs 1999-01-24

---
 port/qlock.c | 6 ++++++
 1 file changed, 6 insertions(+)

diff --git a/port/qlock.c b/port/qlock.c
index 0a06b46c9826bf72566d17094d163eb8999cb7f2..8b8da34722383e09cff7d97aba724e0d4a946cb6 100644
--- a/port/qlock.c
+++ b/port/qlock.c
@@ -28,6 +28,8 @@ rwstats.qlock++;
 rwstats.qlockq++;
 	p = q->tail;
 	mp = up;
+	if(mp == nil)
+		panic("qlock");
 	if(p == 0)
 		q->head = mp;
 	else
@@ -90,6 +92,8 @@ rwstats.rlock++;
 rwstats.rlockq++;
 	p = q->tail;
 	mp = up;
+	if(mp == nil)
+		panic("rlock");
 	if(p == 0)
 		q->head = mp;
 	else
@@ -142,6 +146,8 @@ rwstats.wlock++;
 rwstats.wlockq++;
 	p = q->tail;
 	mp = up;
+	if(mp == nil)
+		panic("wlock");
 	if(p == nil)
 		q->head = mp;
 	else