[src/netbsd-9]: src/sys/kern Pull up following revision(s) (requested by kami...

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

details:   https://anonhg.NetBSD.org/src/rev/4a32b9ae4096
branches:  netbsd-9
changeset: 458496:4a32b9ae4096
user:      martin <martin%NetBSD.org@localhost>
date:      Tue Oct 15 19:08:46 2019 +0000

description:
Pull up following revision(s) (requested by kamil in ticket #324):

        sys/kern/kern_sig.c: revision 1.367

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

This change is v.2 of the previously reverted commit for the same fix.

This version contains recovery path that stopps triggering event SIGTRAP
for a detached debugger.

diffstat:

 sys/kern/kern_sig.c |  59 ++++++++++++++++++++++++++++++++++++++++++++++++++--
 1 files changed, 56 insertions(+), 3 deletions(-)

diffs (126 lines):

diff -r 270777ce0cdb -r 4a32b9ae4096 sys/kern/kern_sig.c
--- a/sys/kern/kern_sig.c       Tue Oct 15 19:07:14 2019 +0000
+++ b/sys/kern/kern_sig.c       Tue Oct 15 19:08:46 2019 +0000
@@ -1,4 +1,4 @@
-/*     $NetBSD: kern_sig.c,v 1.364.2.2 2019/10/15 19:01:06 martin Exp $        */
+/*     $NetBSD: kern_sig.c,v 1.364.2.3 2019/10/15 19:08:46 martin 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 1.364.2.2 2019/10/15 19:01:06 martin Exp $");
+__KERNEL_RCSID(0, "$NetBSD: kern_sig.c,v 1.364.2.3 2019/10/15 19:08:46 martin 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;
@@ -1589,11 +1600,12 @@
        KASSERT((code == TRAP_CHLD) || (code == TRAP_LWP) ||
                (code == TRAP_EXEC));
 
+repeat:
        /*
         * If we are exiting, demise now.
         *
         * This avoids notifying tracer and deadlocking.
-       */
+        */
        if (__predict_false(ISSET(p->p_sflag, PS_WEXIT))) {
                mutex_exit(p->p_lock);
                mutex_exit(proc_lock);
@@ -1603,6 +1615,17 @@
        }
 
        /*
+        * If we are no longer traced, abandon this event signal.
+        *
+        * This avoids killing a process after detaching the debugger.
+        */
+       if (__predict_false(!ISSET(p->p_slflag, PSL_TRACED))) {
+               mutex_exit(p->p_lock);
+               mutex_exit(proc_lock);
+               return;
+       }
+
+       /*
         * If there's a pending SIGKILL process it immediately.
         */
        if (p->p_xsig == SIGKILL ||
@@ -1612,6 +1635,16 @@
                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_signo = signo;
@@ -2448,6 +2481,7 @@
 
        mutex_enter(p->p_lock);
 
+repeat:
        /*
         * If we are exiting, demise now.
         *
@@ -2469,6 +2503,25 @@
                return;
        }
 
+       /*
+        * If we are no longer traced, abandon this event signal.
+        *
+        * This avoids killing a process after detaching the debugger.
+        */
+       if (__predict_false(!ISSET(p->p_slflag, PSL_TRACED))) {
+               mutex_exit(p->p_lock);
+               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;