wait_task_zombie: remove ->exit_state/exit_signal checks for WNOWAIT

The first "p->exit_state != EXIT_ZOMBIE" check doesn't make too much sense.
The exit_state was EXIT_ZOMBIE when the function was called, and another
thread can change it to EXIT_DEAD right after the check.

The second condition is not possible, detached non-traced threads were already
filtered out by eligible_child(), we didn't drop tasklist since then.
Signed-off-by: Oleg Nesterov <oleg@tv-sign.ru>
Cc: Roland McGrath <roland@redhat.com>
Signed-off-by: Andrew Morton <akpm@linux-foundation.org>
Signed-off-by: Linus Torvalds <torvalds@linux-foundation.org>

kernel/exit.c

@@ -1196,10 +1196,6 @@ static int wait_task_zombie(struct task_struct *p, int noreap,
 		int exit_code = p->exit_code;
 		int why, status;
 
-		if (unlikely(p->exit_state != EXIT_ZOMBIE))
-			return 0;
-		if (unlikely(p->exit_signal == -1 && p->ptrace == 0))
-			return 0;
 		get_task_struct(p);
 		read_unlock(&tasklist_lock);
 		if ((exit_code & 0x7f) == 0) {