Re: [PATCH 1/3] pidfd_poll: report POLLHUP when pid_task() == NULL

[Oleg Nesterov <oleg@redhat.com>]

On 02/02, Christian Brauner wrote:
>
> > I think we need a simpler patch. I was going to send it as 4/4, but I'd
> > like to think more, _perhaps_ we can also discriminate the PIDFD_THREAD
> > and non-PIDFD_THREAD waiters. I'll try to make the patch(es) tomorrow or
>
> Right, I didn't go that far.
>
> > at least provided more info.
> >
> > 3 notes for now:
> >
> > 	1. we can't use wake_up_poll(), it passes nr_exclusive => 1
>
> Bah. So we need the same stuff we did for io_uring and use
> __wake_up() directly. Or we add wake_up_all_poll() and convert the other
> three callsites:

...

> +#define wake_up_all_poll(x, m)                                                 \
> +       __wake_up(x, TASK_NORMAL, 0, poll_to_key(m))

Agreed, but I think this + s/wake_up/wake_up_all_poll/ conversions
need a separate patch.


> -void do_notify_pidfd(struct task_struct *task)
> +void pidfd_wake_up_poll(struct task_struct *task, bool dead)
>  {
> -	struct pid *pid;
> -
>  	WARN_ON(task->exit_state == 0);
> -	pid = task_pid(task);
> -	wake_up_all(&pid->wait_pidfd);
> +	WARN_ON(mask == 0);
> +	wake_up_all_poll(&task_pid(task)->wait_pidfd,
> +			 EPOLLIN | EPOLLRDNORM | dead ? EPOLLHUP : 0);

No...

This is still overcomplicated and is not right.

Christian, I'll write another email tomorrow.

Oleg.