[src/trunk]: src/sys/kern Enhance reliability of ptrace(2) in a debuggee with...

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

details:   https://anonhg.NetBSD.org/src/rev/1e1c52307e0a
branches:  trunk
changeset: 842239:1e1c52307e0a
user:      kamil <kamil%NetBSD.org@localhost>
date:      Fri Jun 21 04:02:57 2019 +0000

description:
Enhance reliability of ptrace(2) in a debuggee with multiple LWPs

Stop competing between threads which one emits event signal quicker and
overwriting the signal from another thread.

This fixes missed in action signals.

NetBSD truss can now report reliably all TRAP_SCE/SCX/etc events without
reports of missed ones.

This was one of the reasons why debuggee with multiple threads misbehaved
under a debugger.

diffstat:

 sys/kern/kern_sig.c |  36 ++++++++++++++++++++++++++++++++++--
 1 files changed, 34 insertions(+), 2 deletions(-)

diffs (92 lines):

diff -r bc5fb630ef9f -r 1e1c52307e0a sys/kern/kern_sig.c
--- a/sys/kern/kern_sig.c       Fri Jun 21 02:14:59 2019 +0000
+++ b/sys/kern/kern_sig.c       Fri Jun 21 04:02:57 2019 +0000
@@ -1,4 +1,4 @@
-/*     $NetBSD: kern_sig.c,v 1.362 2019/06/21 01:03:51 kamil Exp $     */
+/*     $NetBSD: kern_sig.c,v 1.363 2019/06/21 04:02:57 kamil Exp $     */
 
 /*-
  * Copyright (c) 2006, 2007, 2008 The NetBSD Foundation, Inc.
@@ -70,7 +70,7 @@
  */
 
 #include <sys/cdefs.h>
-__KERNEL_RCSID(0, "$NetBSD: kern_sig.c,v 1.362 2019/06/21 01:03:51 kamil Exp $");
+__KERNEL_RCSID(0, "$NetBSD: kern_sig.c,v 1.363 2019/06/21 04:02:57 kamil Exp $");
 
 #include "opt_ptrace.h"
 #include "opt_dtrace.h"
@@ -913,6 +913,7 @@
        mutex_enter(proc_lock);
        mutex_enter(p->p_lock);
 
+repeat:
        /*
         * If we are exiting, demise now.
         *
@@ -926,6 +927,16 @@
                /* NOTREACHED */
        }
 
+       /*
+        * The process is already stopping.
+        */
+       if ((p->p_sflag & PS_STOPPING) != 0) {
+               sigswitch(0, p->p_xsig, false);
+               mutex_enter(proc_lock);
+               mutex_enter(p->p_lock);
+               goto repeat; /* XXX */
+       }
+
        mask = &l->l_sigmask;
        ps = p->p_sigacts;
        action = SIGACTION_PS(ps, signo).sa_handler;
@@ -1580,6 +1591,7 @@
        KASSERT((code == TRAP_CHLD) || (code == TRAP_LWP) ||
                (code == TRAP_EXEC));
 
+repeat:
        /*
         * If we are exiting, demise now.
         *
@@ -1603,6 +1615,16 @@
                return;
        }
 
+       /*
+        * The process is already stopping.
+        */
+       if ((p->p_sflag & PS_STOPPING) != 0) {
+               sigswitch(0, p->p_xsig, false);
+               mutex_enter(proc_lock);
+               mutex_enter(p->p_lock);
+               goto repeat; /* XXX */
+       }
+
        KSI_INIT_TRAP(&ksi);
        ksi.ksi_lid = l->l_lid;
        ksi.ksi_info._signo = signo;
@@ -2434,6 +2456,7 @@
 
        mutex_enter(p->p_lock);
 
+repeat:
        /*
         * If we are exiting, demise now.
         *
@@ -2455,6 +2478,15 @@
                return;
        }
 
+       /*
+        * The process is already stopping.
+        */
+       if ((p->p_sflag & PS_STOPPING) != 0) {
+               sigswitch(0, p->p_xsig, true);
+               mutex_enter(p->p_lock);
+               goto repeat; /* XXX */
+       }
+
        /* Needed for ktrace */
        ps = p->p_sigacts;
        action = SIGACTION_PS(ps, signo).sa_handler;