linux-kernel - [PATCH AUTOSEL 5.4 07/79] exit: fix the usage of delay_group_leader->exit_code in do_notify_parent() and pidfs

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Message-Id: <20250505232151.2698893-7-sashal@kernel.org>
Date: Mon,  5 May 2025 19:20:39 -0400
From: Sasha Levin <sashal@...nel.org>
To: linux-kernel@...r.kernel.org,
	stable@...r.kernel.org
Cc: Oleg Nesterov <oleg@...hat.com>,
	Christian Brauner <brauner@...nel.org>,
	Sasha Levin <sashal@...nel.org>,
	akpm@...ux-foundation.org,
	mhocko@...e.com,
	mjguzik@...il.com,
	pasha.tatashin@...een.com,
	alexjlzheng@...cent.com
Subject: [PATCH AUTOSEL 5.4 07/79] exit: fix the usage of delay_group_leader->exit_code in do_notify_parent() and pidfs_exit()

From: Oleg Nesterov <oleg@...hat.com>

[ Upstream commit 9133607de37a4887c6f89ed937176a0a0c1ebb17 ]

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@...hat.com>
Link: https://lore.kernel.org/r/20250324171941.GA13114@redhat.com
Signed-off-by: Christian Brauner <brauner@...nel.org>
Signed-off-by: Sasha Levin <sashal@...nel.org>
---
 kernel/exit.c | 3 +++
 1 file changed, 3 insertions(+)

diff --git a/kernel/exit.c b/kernel/exit.c
index 56d3a099825fb..5015ecdda6d95 100644
--- a/kernel/exit.c
+++ b/kernel/exit.c
@@ -262,6 +262,9 @@ 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,
-- 
2.39.5