From ffac73eb328c5cb90ad0e4a0aa5a9235fa15c7a0 Mon Sep 17 00:00:00 2001
From: joerg <joerg@NetBSD.org>
Date: Sun, 10 Nov 2019 23:39:03 +0000
Subject: [PATCH] Ensure that the second LWP of a new process uses a free LWP
 ID. Document overflow behavior.

---
 sys/kern/kern_lwp.c | 9 +++++++--
 1 file changed, 7 insertions(+), 2 deletions(-)

diff --git a/sys/kern/kern_lwp.c b/sys/kern/kern_lwp.c
index 5c9a256721a8..38df0a5eaec0 100644
--- a/sys/kern/kern_lwp.c
+++ b/sys/kern/kern_lwp.c
@@ -1,4 +1,4 @@
-/*	$NetBSD: kern_lwp.c,v 1.206 2019/11/07 19:45:18 joerg Exp $	*/
+/*	$NetBSD: kern_lwp.c,v 1.207 2019/11/10 23:39:03 joerg Exp $	*/
 
 /*-
  * Copyright (c) 2001, 2006, 2007, 2008, 2009 The NetBSD Foundation, Inc.
@@ -211,7 +211,7 @@
  */
 
 #include <sys/cdefs.h>
-__KERNEL_RCSID(0, "$NetBSD: kern_lwp.c,v 1.206 2019/11/07 19:45:18 joerg Exp $");
+__KERNEL_RCSID(0, "$NetBSD: kern_lwp.c,v 1.207 2019/11/10 23:39:03 joerg Exp $");
 
 #include "opt_ddb.h"
 #include "opt_lockdebug.h"
@@ -904,6 +904,11 @@ lwp_create(lwp_t *l1, proc_t *p2, vaddr_t uaddr, int flags,
 		l2->l_pflag |= LP_PIDLID;
 	} else if (p2->p_nlwps == 0) {
 		lid = l1->l_lid;
+		/*
+		 * Update next LWP ID, too. If this overflows to LID_SCAN,
+		 * the slow path of scanning will be used for the next LWP.
+		 */
+		p2->p_nlwpid = lid + 1;
 	} else {
 		lid = 0;
 	}