linux-kernel - Re: [RFC PATCH] pidfd: implement PIDFD_THREAD flag for pidfd

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Date: Wed, 31 Jan 2024 20:14:06 +0100
From: Oleg Nesterov <oleg@...hat.com>
To: Andy Lutomirski <luto@...capital.net>
Cc: Tycho Andersen <tycho@...ho.pizza>,
	Christian Brauner <brauner@...nel.org>,
	linux-kernel@...r.kernel.org, linux-api@...r.kernel.org,
	Tycho Andersen <tandersen@...flix.com>,
	"Eric W. Biederman" <ebiederm@...ssion.com>
Subject: Re: [RFC PATCH] pidfd: implement PIDFD_THREAD flag for pidfd_open()

Forgot to mention...

And I agree that pidfd_send_signal(flags => PGID/SID) can make
some sense too.

But this a) doesn't depend on PIDFD_THREAD, and b) needs another
patch/discussion.

But again, I am not sure I understood you correctly.

On 01/31, Oleg Nesterov wrote:
>
> On 01/31, Andy Lutomirski wrote:
> >
> > Right now, pidfd_send_signal() sends signals to processes, like so:
> >
> >  * The syscall currently only signals via PIDTYPE_PID which covers
> >  * kill(<positive-pid>, <signal>. It does not signal threads or process
> >  * groups.
> >
> > This patch adds PIDFD_THREAD which, potentially confusingly, doesn't
> > change this (AFAICS).
>
> Yes,
>
> > So at least that should be documented loudly
> > and clearly, IMO.
>
> Please note
>
> 	/* TODO: respect PIDFD_THREAD */
>
> this patch adds into pidfd_send_signal().
>
> See also this part of discussion
>
> 	> > +	/* 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 know. I am fine either way, but I think this needs a separate
> 	patch and another discussion in any case. Anyway should be trivial,
> 	pidfd_send_signal() has the "flags" argument.
>
> with Christian in https://lore.kernel.org/all/20240130112126.GA26108@redhat.com/
>
> Or did I misunderstand you?
>
> Oleg.