From d3ec16ca12e27d8a5772dcade0fb19da5ab5bc0b Mon Sep 17 00:00:00 2001
From: Terence Tritton <ttritton@google.com>
Date: Wed, 14 Aug 2024 19:18:16 +0000
Subject: [PATCH] Revert "pidfd_poll: report POLLHUP when pid_task() == NULL"

This reverts commit 43f0df54c96fa5abcab9df8649c1e52119bf0238.

Change-Id: Id5c8932073dd90b073d8c8e1b7f06a9da5b5bc02
Signed-off-by: Terence Tritton <ttritton@google.com>
Bug: 352286227
---
 fs/pidfs.c   | 26 +++++++++++++++++++-------
 kernel/pid.c |  5 -----
 2 files changed, 19 insertions(+), 12 deletions(-)

diff --git a/fs/pidfs.c b/fs/pidfs.c
index 7ffdc88dfb52..af68bc8b4c0b 100644
--- a/fs/pidfs.c
+++ b/fs/pidfs.c
@@ -89,6 +89,23 @@ static void pidfd_show_fdinfo(struct seq_file *m, struct file *f)
 }
 #endif
 
+
+static bool pidfd_task_exited(struct pid *pid, bool thread)
+{
+       struct task_struct *task;
+       bool exited;
+
+       rcu_read_lock();
+       task = pid_task(pid, PIDTYPE_PID);
+       exited = !task ||
+               (READ_ONCE(task->exit_state) && (thread || thread_group_empty(task)));
+       rcu_read_unlock();
+
+       return exited;
+}
+
+
+
 /*
  * Poll support for process exit notification.
  */
@@ -96,7 +113,6 @@ static __poll_t pidfd_poll(struct file *file, struct poll_table_struct *pts)
 {
 	struct pid *pid = pidfd_pid(file);
 	bool thread = file->f_flags & PIDFD_THREAD;
-	struct task_struct *task;
 	__poll_t poll_flags = 0;
 
 	poll_wait(file, &pid->wait_pidfd, pts);
@@ -104,12 +120,8 @@ static __poll_t pidfd_poll(struct file *file, struct poll_table_struct *pts)
 	 * Depending on PIDFD_THREAD, inform pollers when the thread
 	 * or the whole thread-group exits.
 	 */
-	guard(rcu)();
-	task = pid_task(pid, PIDTYPE_PID);
-	if (!task)
-		poll_flags = EPOLLIN | EPOLLRDNORM | EPOLLHUP;
-	else if (task->exit_state && (thread || thread_group_empty(task)))
-		poll_flags = EPOLLIN | EPOLLRDNORM;
+        if(pidfd_task_exited(pid, thread))
+            poll_flags = EPOLLIN | EPOLLRDNORM;
 
 	return poll_flags;
 }
diff --git a/kernel/pid.c b/kernel/pid.c
index f3c8b40ba253..ed82446d7077 100644
--- a/kernel/pid.c
+++ b/kernel/pid.c
@@ -355,11 +355,6 @@ static void __change_pid(struct task_struct *task, enum pid_type type,
 	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;