[PATCH] exit: fix the usage of delay_group_leader->exit_code in do_notify_parent() and pidfs_exit()

[Oleg Nesterov <oleg@redhat.com>]

Consider a process with a group leader L and a sub-thread T.
L does sys_exit(1), then T does sys_exit_group(2).

In this case wait_task_zombie(L) will notice SIGNAL_GROUP_EXIT and use
L->signal->group_exit_code, this is correct.

But, before that, do_notify_parent(L) called by release_task(T) will use
L->exit_code != L->signal->group_exit_code, and this is not consistent.
We don't really care, I think that nobody relies on the info which comes
with SIGCHLD, if nothing else SIGCHLD < SIGRTMIN can be queued only once.

But pidfs_exit() is more problematic, I think pidfs_exit_info->exit_code
should report ->group_exit_code in this case, just like wait_task_zombie().

TODO: with this change we can hopefully cleanup (or may be even kill) the
similar SIGNAL_GROUP_EXIT checks, at least in wait_task_zombie().

Signed-off-by: Oleg Nesterov <oleg@redhat.com>
---
 kernel/exit.c | 3 +++
 1 file changed, 3 insertions(+)

diff --git a/kernel/exit.c b/kernel/exit.c
index d0ebccb9dec0..4a0604f5cedd 100644
--- a/kernel/exit.c
+++ b/kernel/exit.c
@@ -267,6 +267,9 @@ void release_task(struct task_struct *p)
 	leader = p->group_leader;
 	if (leader != p && thread_group_empty(leader)
 			&& leader->exit_state == EXIT_ZOMBIE) {
+		/* for pidfs_exit() and do_notify_parent() */
+		if (leader->signal->flags & SIGNAL_GROUP_EXIT)
+			leader->exit_code = leader->signal->group_exit_code;
 		/*
 		 * If we were the last child thread and the leader has
 		 * exited already, and the leader's parent ignores SIGCHLD,
-- 
2.25.1.362.g51ebf55