- /* Wait for all children (clone and not) if __WALL is set;
- * otherwise, wait for clone children *only* if __WCLONE is
- * set; otherwise, wait for non-clone children *only*. (Note:
- * A "clone" child here is one that reports to its parent
- * using a signal other than SIGCHLD.) */
- if (((p->exit_signal != SIGCHLD) ^ !!(wo->wo_flags & __WCLONE))
- && !(wo->wo_flags & __WALL))
+
+ /*
+ * Wait for all children (clone and not) if __WALL is set or
+ * if it is traced by us.
+ */
+ if (ptrace || (wo->wo_flags & __WALL))
+ return 1;
+
+ /*
+ * Otherwise, wait for clone children *only* if __WCLONE is set;
+ * otherwise, wait for non-clone children *only*.
+ *
+ * Note: a "clone" child here is one that reports to its parent
+ * using a signal other than SIGCHLD, or a non-leader thread which
+ * we can only see if it is traced by us.
+ */
+ if ((p->exit_signal != SIGCHLD) ^ !!(wo->wo_flags & __WCLONE))