From 607880ce788bbfb8585271af117a52e9359324dd Mon Sep 17 00:00:00 2001
From: Russ Cox <rsc@swtch.com>
Date: Wed, 8 Oct 2008 14:59:32 -0700
Subject: [PATCH] devdraw/OSX: correct access to reply buffer (fixes rpc tag
 crash)

---
 src/cmd/devdraw/osx-srv.c | 4 ++++
 1 file changed, 4 insertions(+)

diff --git a/src/cmd/devdraw/osx-srv.c b/src/cmd/devdraw/osx-srv.c
index 9329bc2f..10baf0f3 100644
--- a/src/cmd/devdraw/osx-srv.c
+++ b/src/cmd/devdraw/osx-srv.c
@@ -289,6 +289,7 @@ runmsg(Wsysmsg *m)
 /*
  * Reply to m.
  */
+QLock replylock;
 void
 replymsg(Wsysmsg *m)
 {
@@ -303,6 +304,8 @@ replymsg(Wsysmsg *m)
 	if(trace) fprint(2, "-> %W\n", m);
 	/* copy to output buffer */
 	n = sizeW2M(m);
+
+	qlock(&replylock);
 	if(n > nmbuf){
 		free(mbuf);
 		mbuf = malloc(n);
@@ -313,6 +316,7 @@ replymsg(Wsysmsg *m)
 	convW2M(m, mbuf, n);
 	if(write(4, mbuf, n) != n)
 		sysfatal("write: %r");
+	qunlock(&replylock);
 }
 
 /*