Index: sys/kern/kern_sig.c
===================================================================
RCS file: /cvsroot/src/sys/kern/kern_sig.c,v
retrieving revision 1.366
diff -u -r1.366 kern_sig.c
--- sys/kern/kern_sig.c	3 Oct 2019 22:48:44 -0000	1.366
+++ sys/kern/kern_sig.c	8 Oct 2019 17:38:28 -0000
@@ -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;
Index: sys/kern/sys_ptrace_common.c
===================================================================
RCS file: /cvsroot/src/sys/kern/sys_ptrace_common.c,v
retrieving revision 1.65
diff -u -r1.65 sys_ptrace_common.c
--- sys/kern/sys_ptrace_common.c	8 Oct 2019 12:29:57 -0000	1.65
+++ sys/kern/sys_ptrace_common.c	8 Oct 2019 17:38:28 -0000
@@ -511,8 +511,13 @@
 
 		/*
 		 *	(3) it's not currently stopped.
+		 *
+		 *	As an exception PT_CONTINUE is allowed here and will
+		 *	behave like kill(2) for a running process.
+		 *       
 		 */
-		if (t->p_stat != SSTOP || !t->p_waited /* XXXSMP */) {
+		if (req != PT_CONTINUE &&
+		    (t->p_stat != SSTOP || !t->p_waited /* XXXSMP */)) {
 			DPRINTF(("stat %d flag %d\n", t->p_stat,
 			    !t->p_waited));
 			return EBUSY;
@@ -1326,6 +1331,8 @@
 				CLR(lt2->l_pflag, LP_SINGLESTEP);
 			}
 			CLR(lt->l_pflag, LP_SINGLESTEP);
+		} else if (req == PT_CONTINUE && t->p_stat != SSTOP) {
+			t->p_sigctx.ps_faked = 0;
 		}
 	sendsig:
 		error = ptrace_sendsig(t, lt, signo, resume_all);