Index: sys/kern/kern_sig.c
===================================================================
RCS file: /cvsroot/src/sys/kern/kern_sig.c,v
retrieving revision 1.367
diff -u -r1.367 kern_sig.c
--- sys/kern/kern_sig.c	8 Oct 2019 18:02:46 -0000	1.367
+++ sys/kern/kern_sig.c	12 Oct 2019 19:10:45 -0000
@@ -1746,6 +1746,7 @@
 	/*
 	 * Unlock and switch away.
 	 */
+	KDASSERT(mutex_ownable(proc_lock));
 	KERNEL_UNLOCK_ALL(l, &biglocks);
 	if (p->p_stat == SSTOP || (p->p_sflag & PS_STOPPING) != 0) {
 		p->p_nrlwps--;