Re: [RFC PATCH] pidfd: implement PIDFD_THREAD flag for pidfd_open()

On Mon, Jan 29, 2024 at 07:31:35AM -0700, Tycho Andersen wrote:

On Mon, Jan 29, 2024 at 02:41:11PM +0100, Christian Brauner wrote:

quoted

On Mon, Jan 29, 2024 at 12:23:15PM +0100, Oleg Nesterov wrote:

quoted

--- a/kernel/signal.c
+++ b/kernel/signal.c

@@ -2051,7 +2051,8 @@ bool do_notify_parent(struct task_struct *tsk, int sig)
 	WARN_ON_ONCE(!tsk->ptrace &&
 	       (tsk->group_leader != tsk || !thread_group_empty(tsk)));
 	/*
-	 * tsk is a group leader and has no threads, wake up the pidfd waiters.
+	 * tsk is a group leader and has no threads, wake up the !PIDFD_THREAD
+	 * waiters.
 	 */
 	if (thread_group_empty(tsk))
 		do_notify_pidfd(tsk);

@@ -3926,6 +3927,7 @@ SYSCALL_DEFINE4(pidfd_send_signal, int, pidfd, int, sig,
 		prepare_kill_siginfo(sig, &kinfo);
 	}
 
+	/* TODO: respect PIDFD_THREAD */

So I've been thinking about this at the end of last week. Do we need to
give userspace a way to send a thread-group wide signal even when a
PIDFD_THREAD pidfd is passed? Or should we just not worry about this
right now and wait until someone needs this?

I don't need it currently, but it would have been handy for some of
the tests I wrote.

Should I fix those up and send them too on top of Oleg's v2?

Sure, I don't mind.