On Fri, Feb 02, 2024 at 08:05:29PM +0100, Oleg Nesterov wrote:

On 02/02, Christian Brauner wrote:

quoted

quoted

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.

quoted

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:

...

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+#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.

Yeah, I know. This is just a scribbled draft.

quoted

-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.

I'm all ears.

Christian, I'll write another email tomorrow.

Sure, there's no rush. I had not intended that this patch be used. I
have another large series I need to take care of so I can't spend a lot
of time on writing this anyway. I just hadn't used the keyed apis before
and got curious. So don't get the impression that I intend to write
this. I fully expected you to do it.