Index: sys/kern/kern_sig.c
===================================================================
RCS file: /cvsroot/src/sys/kern/kern_sig.c,v
retrieving revision 1.369
diff -u -r1.369 kern_sig.c
--- sys/kern/kern_sig.c	12 Oct 2019 19:57:09 -0000	1.369
+++ sys/kern/kern_sig.c	12 Oct 2019 20:40:45 -0000
@@ -126,6 +126,7 @@
 static int	sigput(sigpend_t *, struct proc *, ksiginfo_t *);
 static int	sigunwait(struct proc *, const ksiginfo_t *);
 static void	sigswitch(int, int, bool);
+static void	sigswitch_unlock_and_switch_away(struct proc *, struct lwp *);
 
 static void	sigacts_poolpage_free(struct pool *, void *);
 static void	*sigacts_poolpage_alloc(struct pool *, int);
@@ -932,10 +933,11 @@
 	 * The process is already stopping.
 	 */
 	if ((p->p_sflag & PS_STOPPING) != 0) {
-		sigswitch(0, p->p_xsig, true);
+		mutex_exit(proc_lock);
+		sigswitch_unlock_and_switch_away(p, l);
 		mutex_enter(proc_lock);
 		mutex_enter(p->p_lock);
-		goto repeat; /* XXX */
+		goto repeat;
 	}
 
 	mask = &l->l_sigmask;
@@ -1642,10 +1644,11 @@
 	 * The process is already stopping.
 	 */
 	if ((p->p_sflag & PS_STOPPING) != 0) {
-		sigswitch(0, p->p_xsig, true);
+		mutex_exit(proc_lock);
+		sigswitch_unlock_and_switch_away(p, l);
 		mutex_enter(proc_lock);
 		mutex_enter(p->p_lock);
-		goto repeat; /* XXX */
+		goto repeat;
 	}
 
 	KSI_INIT_TRAP(&ksi);
@@ -1692,7 +1695,6 @@
 {
 	struct lwp *l = curlwp;
 	struct proc *p = l->l_proc;
-	int biglocks;
 
 	KASSERT(mutex_owned(p->p_lock));
 	KASSERT(l->l_stat == LSONPROC);
@@ -1752,10 +1754,23 @@
 		mutex_exit(proc_lock);
 	}
 
-	/*
-	 * Unlock and switch away.
-	 */
+	sigswitch_unlock_and_switch_away(p, l);
+}
+
+/*
+ * Unlock and switch away.
+ */
+static void
+sigswitch_unlock_and_switch_away(struct proc *p, struct lwp *l)
+{	
+	int biglocks;
+
+	KASSERT(mutex_owned(p->p_lock));
 	KASSERT(!mutex_owned(proc_lock));
+
+	KASSERT(l->l_stat == LSONPROC);
+	KASSERT(p->p_nrlwps > 0);
+
 	KERNEL_UNLOCK_ALL(l, &biglocks);
 	if (p->p_stat == SSTOP || (p->p_sflag & PS_STOPPING) != 0) {
 		p->p_nrlwps--;
@@ -1845,7 +1860,7 @@
 		 * we awaken, check for a signal from the debugger.
 		 */
 		if (p->p_stat == SSTOP || (p->p_sflag & PS_STOPPING) != 0) {
-			sigswitch(PS_NOCLDSTOP, 0, false);
+			sigswitch_unlock_and_switch_away(p, l);
 			mutex_enter(p->p_lock);
 			signo = sigchecktrace();
 		} else if (p->p_stat == SACTIVE)
@@ -2527,9 +2542,9 @@
 	 * The process is already stopping.
 	 */
 	if ((p->p_sflag & PS_STOPPING) != 0) {
-		sigswitch(0, p->p_xsig, false);
+		sigswitch_unlock_and_switch_away(p, l);
 		mutex_enter(p->p_lock);
-		goto repeat; /* XXX */
+		goto repeat;
 	}
 
 	/* Needed for ktrace */