Commit 43f0df54 authored by Oleg Nesterov's avatar Oleg Nesterov Committed by Christian Brauner
Browse files

pidfd_poll: report POLLHUP when pid_task() == NULL 



Add another wake_up_all(wait_pidfd) into __change_pid() and change
pidfd_poll() to include EPOLLHUP if task == NULL.

This allows to wait until the target process/thread is reaped.

TODO: change do_notify_pidfd() to use the keyed wakeups.

Signed-off-by: default avatarOleg Nesterov <oleg@redhat.com>
Link: https://lore.kernel.org/r/20240202131226.GA26018@redhat.com


Signed-off-by: default avatarChristian Brauner <brauner@kernel.org>
parent 64bef697

kernel/fork.c

+7 −15
Original line number Diff line number Diff line
@@ -2071,20 +2071,6 @@ 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.

 */
@@ -2092,6 +2078,7 @@ static __poll_t pidfd_poll(struct file *file, struct poll_table_struct *pts) 
{

	struct pid *pid = file->private_data;

	bool thread = file->f_flags & PIDFD_THREAD;

	struct task_struct *task;

	__poll_t poll_flags = 0;



	poll_wait(file, &pid->wait_pidfd, pts);
@@ -2099,8 +2086,13 @@ 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.

	 */

	if (pidfd_task_exited(pid, thread))

	rcu_read_lock();

	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;

	rcu_read_unlock();



	return poll_flags;

}

kernel/pid.c

+5 −0
Original line number Diff line number Diff line
@@ -349,6 +349,11 @@ 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;