[src/trunk]: src/sys/rump/librump/rumpkern rump: don't touch p_nlwps without ...

[ozaki-r <ozaki-r%NetBSD.org@localhost>]

details:   https://anonhg.NetBSD.org/src/rev/e6c910e4279c
branches:  trunk
changeset: 372236:e6c910e4279c
user:      ozaki-r <ozaki-r%NetBSD.org@localhost>
date:      Wed Nov 02 09:01:42 2022 +0000

description:
rump: don't touch p_nlwps without holding p_lock

There was a race condition on p_nlwps.  Heavy thread switching could
cause a kernel panic like:
  panic: kernel diagnostic assertion "LIST_EMPTY(&p->p_lwps)" failed:
  file "(hidden)/src/lib/librump/../../sys/rump/librump/rumpkern/lwproc.c", line 177

diffstat:

 sys/rump/librump/rumpkern/lwproc.c |  20 ++++++++++----------
 1 files changed, 10 insertions(+), 10 deletions(-)

diffs (48 lines):

diff -r a7caf16cd4b5 -r e6c910e4279c sys/rump/librump/rumpkern/lwproc.c
--- a/sys/rump/librump/rumpkern/lwproc.c        Wed Nov 02 08:37:32 2022 +0000
+++ b/sys/rump/librump/rumpkern/lwproc.c        Wed Nov 02 09:01:42 2022 +0000
@@ -1,4 +1,4 @@
-/*      $NetBSD: lwproc.c,v 1.51 2020/05/30 19:16:53 ad Exp $  */
+/*      $NetBSD: lwproc.c,v 1.52 2022/11/02 09:01:42 ozaki-r Exp $     */
 
 /*
  * Copyright (c) 2010, 2011 Antti Kantee.  All Rights Reserved.
@@ -28,7 +28,7 @@
 #define RUMP__CURLWP_PRIVATE
 
 #include <sys/cdefs.h>
-__KERNEL_RCSID(0, "$NetBSD: lwproc.c,v 1.51 2020/05/30 19:16:53 ad Exp $");
+__KERNEL_RCSID(0, "$NetBSD: lwproc.c,v 1.52 2022/11/02 09:01:42 ozaki-r Exp $");
 
 #include <sys/param.h>
 #include <sys/atomic.h>
@@ -348,6 +348,14 @@
 {
        struct lwp *l = kmem_zalloc(sizeof(*l), KM_SLEEP);
 
+       l->l_refcnt = 1;
+       l->l_proc = p;
+       l->l_stat = LSIDL;
+       l->l_mutex = &unruntime_lock;
+
+       proc_alloc_lwpid(p, l);
+
+       mutex_enter(p->p_lock);
        /*
         * Account the new lwp to the owner of the process.
         * For some reason, NetBSD doesn't count the first lwp
@@ -357,14 +365,6 @@
                chglwpcnt(kauth_cred_getuid(p->p_cred), 1);
        }
 
-       l->l_refcnt = 1;
-       l->l_proc = p;
-       l->l_stat = LSIDL;
-       l->l_mutex = &unruntime_lock;
-
-       proc_alloc_lwpid(p, l);
-
-       mutex_enter(p->p_lock);
        KASSERT((p->p_sflag & PS_RUMP_LWPEXIT) == 0);
        LIST_INSERT_HEAD(&p->p_lwps, l, l_sibling);