Index: head/sys/kern/sys_process.c
===================================================================
--- head/sys/kern/sys_process.c
+++ head/sys/kern/sys_process.c
@@ -688,6 +688,7 @@
 proc_set_traced(struct proc *p, bool stop)
 {
 
+	sx_assert(&proctree_lock, SX_XLOCKED);
 	PROC_LOCK_ASSERT(p, MA_OWNED);
 	p->p_flag |= P_TRACED;
 	if (stop)
Index: head/sys/sys/proc.h
===================================================================
--- head/sys/sys/proc.h
+++ head/sys/sys/proc.h
@@ -633,7 +633,7 @@
 	u_int		p_stype;	/* (c) Stop event type. */
 	char		p_step;		/* (c) Process is stopped. */
 	u_char		p_pfsflags;	/* (c) Procfs flags. */
-	u_int		p_ptevents;	/* (c) ptrace() event mask. */
+	u_int		p_ptevents;	/* (c + e) ptrace() event mask. */
 	struct nlminfo	*p_nlminfo;	/* (?) Only used by/for lockd. */
 	struct kaioinfo	*p_aioinfo;	/* (y) ASYNC I/O info. */
 	struct thread	*p_singlethread;/* (c + j) If single threading this is it */