wait: completely ignore the EXIT_DEAD tasks

Now that EXIT_DEAD is the terminal state it doesn't make sense to call
eligible_child() or security_task_wait() if the task is really dead.

Signed-off-by: Oleg Nesterov <[email protected]>
Tested-by: Michal Schmidt <[email protected]>
Cc: Jan Kratochvil <[email protected]>
Cc: Al Viro <[email protected]>
Cc: Lennart Poettering <[email protected]>
Cc: Roland McGrath <[email protected]>
Cc: Tejun Heo <[email protected]>
Signed-off-by: Andrew Morton <[email protected]>
Signed-off-by: Linus Torvalds <[email protected]>

Author: oleg-nesterov

kernel/exit.c

@@ -1329,7 +1329,12 @@ static int wait_task_continued(struct wait_opts *wo, struct task_struct *p)
 static int wait_consider_task(struct wait_opts *wo, int ptrace,
 				struct task_struct *p)
 {
-	int ret = eligible_child(wo, p);
+	int ret;
+
+	if (unlikely(p->exit_state == EXIT_DEAD))
+		return 0;
+
+	ret = eligible_child(wo, p);
 	if (!ret)
 		return ret;
 
@@ -1347,10 +1352,6 @@ static int wait_consider_task(struct wait_opts *wo, int ptrace,
 		return 0;
 	}
 
-	/* dead body doesn't have much to contribute */
-	if (unlikely(p->exit_state == EXIT_DEAD))
-		return 0;
-
 	if (unlikely(p->exit_state == EXIT_TRACE)) {
 		/*
 		 * ptrace == 0 means we are the natural parent. In this case