[src/trunk]: src/sys/kern Enhance locking of ptrace_update_lwp

[kamil <kamil%NetBSD.org@localhost>]

details:   https://anonhg.NetBSD.org/src/rev/4da91e2ac7bd
branches:  trunk
changeset: 457774:4da91e2ac7bd
user:      kamil <kamil%NetBSD.org@localhost>
date:      Thu Jul 18 20:10:46 2019 +0000

description:
Enhance locking of ptrace_update_lwp

Replace lwp_delref() + mutex_enter() with: mutex_enter() + lwp_delref2().
This avoids extra taking and exiting from a mutex.

Add missing mutex_exit() for LW_SYSTEM.

Do not switch lwp for PT_SET_SIGINFO. This operation is not needed and
avoids panic for >2 LWPs as p_lock is attempted to be entered again in a
critical section.

diffstat:

 sys/kern/sys_ptrace_common.c |  12 +++++-------
 1 files changed, 5 insertions(+), 7 deletions(-)

diffs (48 lines):

diff -r bd8a9c8a636c -r 4da91e2ac7bd sys/kern/sys_ptrace_common.c
--- a/sys/kern/sys_ptrace_common.c      Thu Jul 18 18:21:45 2019 +0000
+++ b/sys/kern/sys_ptrace_common.c      Thu Jul 18 20:10:46 2019 +0000
@@ -1,4 +1,4 @@
-/*     $NetBSD: sys_ptrace_common.c,v 1.57 2019/06/29 11:37:17 maxv Exp $      */
+/*     $NetBSD: sys_ptrace_common.c,v 1.58 2019/07/18 20:10:46 kamil Exp $     */
 
 /*-
  * Copyright (c) 2008, 2009 The NetBSD Foundation, Inc.
@@ -118,7 +118,7 @@
  */
 
 #include <sys/cdefs.h>
-__KERNEL_RCSID(0, "$NetBSD: sys_ptrace_common.c,v 1.57 2019/06/29 11:37:17 maxv Exp $");
+__KERNEL_RCSID(0, "$NetBSD: sys_ptrace_common.c,v 1.58 2019/07/18 20:10:46 kamil Exp $");
 
 #ifdef _KERNEL_OPT
 #include "opt_ptrace.h"
@@ -552,9 +552,9 @@
        if (lid == 0 || lid == (*lt)->l_lid || t->p_nlwps == 1)
                return 0;
 
-       lwp_delref(*lt);
+       mutex_enter(t->p_lock);
+       lwp_delref2(*lt);
 
-       mutex_enter(t->p_lock);
        *lt = lwp_find(t, lid);
        if (*lt == NULL) {
                mutex_exit(t->p_lock);
@@ -562,6 +562,7 @@
        }
 
        if ((*lt)->l_flag & LW_SYSTEM) {
+               mutex_exit(t->p_lock);
                *lt = NULL;
                return EINVAL;
        }
@@ -601,9 +602,6 @@
        if (psi.psi_siginfo.si_signo < 0 || psi.psi_siginfo.si_signo >= NSIG)
                return EINVAL;
 
-       if ((error = ptrace_update_lwp(t, lt, psi.psi_lwpid)) != 0)
-               return error;
-
        t->p_sigctx.ps_faked = true;
        t->p_sigctx.ps_info = psi.psi_siginfo._info;
        t->p_sigctx.ps_lwp = psi.psi_lwpid;