linux-kernel - [PATCH v2 1/2] exit: move wake_up_all() pidfd waiters into __unhash

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Message-Id: <20250411-work-pidfs-enoent-v2-1-60b2d3bb545f@kernel.org>
Date: Fri, 11 Apr 2025 15:22:44 +0200
From: Christian Brauner <brauner@...nel.org>
To: Oleg Nesterov <oleg@...hat.com>
Cc: linux-fsdevel@...r.kernel.org, Jeff Layton <jlayton@...nel.org>, 
 Lennart Poettering <lennart@...ttering.net>, 
 Daan De Meyer <daan.j.demeyer@...il.com>, Mike Yuan <me@...dnzj.com>, 
 linux-kernel@...r.kernel.org, Peter Ziljstra <peterz@...radead.org>, 
 Christian Brauner <brauner@...nel.org>
Subject: [PATCH v2 1/2] exit: move wake_up_all() pidfd waiters into
 __unhash_process()

Move the pidfd notification out of __change_pid() and into
__unhash_process(). The only valid call to __change_pid() with a NULL
argument and PIDTYPE_PID is from __unhash_process(). This is a lot more
obvious than calling it from __change_pid().

Signed-off-by: Christian Brauner <brauner@...nel.org>
---
 kernel/exit.c | 5 +++++
 kernel/pid.c  | 5 -----
 2 files changed, 5 insertions(+), 5 deletions(-)

diff --git a/kernel/exit.c b/kernel/exit.c
index 1b51dc099f1e..abcd93ce4e18 100644
--- a/kernel/exit.c
+++ b/kernel/exit.c
@@ -133,8 +133,13 @@ struct release_task_post {
 static void __unhash_process(struct release_task_post *post, struct task_struct *p,
 			     bool group_dead)
 {
+	struct pid *pid = task_pid(p);
+
 	nr_threads--;
+
 	detach_pid(post->pids, p, PIDTYPE_PID);
+	wake_up_all(&pid->wait_pidfd);
+
 	if (group_dead) {
 		detach_pid(post->pids, p, PIDTYPE_TGID);
 		detach_pid(post->pids, p, PIDTYPE_PGID);
diff --git a/kernel/pid.c b/kernel/pid.c
index 4ac2ce46817f..26f1e136f017 100644
--- a/kernel/pid.c
+++ b/kernel/pid.c
@@ -359,11 +359,6 @@ static void __change_pid(struct pid **pids, struct task_struct *task,
 	hlist_del_rcu(&task->pid_links[type]);
 	*pid_ptr = new;
 
-	if (type == PIDTYPE_PID) {
-		WARN_ON_ONCE(pid_has_task(pid, PIDTYPE_PID));
-		wake_up_all(&pid->wait_pidfd);
-	}
-
 	for (tmp = PIDTYPE_MAX; --tmp >= 0; )
 		if (pid_has_task(pid, tmp))
 			return;

-- 
2.47.2