Index: sys/kern/kern_thread.c
===================================================================
--- sys/kern/kern_thread.c
+++ sys/kern/kern_thread.c
@@ -936,6 +936,14 @@
 		}
 
 		/*
+		 * Catch-all for other return codes for the case where
+		 * the process is in a suspending state, but we were
+		 * required to not suspend right now.
+		 */
+		if (return_instead)
+			return (ERESTART);
+
+		/*
 		 * If the process is waiting for us to exit,
 		 * this thread should just suicide.
 		 * Assumes that P_SINGLE_EXIT implies P_STOPPED_SINGLE.
Index: sys/kern/sys_process.c
===================================================================
--- sys/kern/sys_process.c
+++ sys/kern/sys_process.c
@@ -744,12 +744,23 @@
 	 */
 	switch (req) {
 	case PT_TRACE_ME:
-		/* Always legal. */
+		/*
+		 * Always legal, when there is a parent process which
+		 * could trace us.  Otherwise, reject.
+		 */
+		if ((p->p_flag & P_TRACED) != 0) {
+			error = EBUSY;
+			goto fail;
+		}
+		if (p->p_pptr == initproc) {
+			error = EPERM;
+			goto fail;
+		}
 		break;
 
 	case PT_ATTACH:
 		/* Self */
-		if (p->p_pid == td->td_proc->p_pid) {
+		if (p == td->td_proc) {
 			error = EINVAL;
 			goto fail;
 		}