From: Oleg Nesterov <oleg@tv-sign.ru>

A zombie must have a valid ->signal, we are going to release it and
__exit_signal() starts with BUG_ON(!sig).

Signed-off-by: Oleg Nesterov <oleg@tv-sign.ru>
Cc: Roland McGrath <roland@redhat.com>
Signed-off-by: Andrew Morton <akpm@linux-foundation.org>
---

 kernel/exit.c |    2 +-
 1 files changed, 1 insertion(+), 1 deletion(-)

diff -puN kernel/exit.c~wait_task_zombie-remove-unneeded-child-signal-check kernel/exit.c
--- a/kernel/exit.c~wait_task_zombie-remove-unneeded-child-signal-check
+++ a/kernel/exit.c
@@ -1209,7 +1209,7 @@ static int wait_task_zombie(struct task_
 		return 0;
 	}
 
-	if (likely(p->real_parent == p->parent) && likely(p->signal)) {
+	if (likely(p->real_parent == p->parent)) {
 		struct signal_struct *psig;
 		struct signal_struct *sig;
 
_