linux-kernel - Re: [PATCH v2 2/2] pidfd: change pidfd_send_signal() to respect PIDFD

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Message-ID: <20240210165133.GD27557@redhat.com>
Date: Sat, 10 Feb 2024 17:51:33 +0100
From: Oleg Nesterov <oleg@...hat.com>
To: Christian Brauner <brauner@...nel.org>
Cc: Andy Lutomirski <luto@...capital.net>,
	"Eric W. Biederman" <ebiederm@...ssion.com>,
	Tycho Andersen <tycho@...ho.pizza>, linux-api@...r.kernel.org,
	linux-kernel@...r.kernel.org
Subject: Re: [PATCH v2 2/2] pidfd: change pidfd_send_signal() to respect
 PIDFD_THREAD

On 02/10, Christian Brauner wrote:
>
> On Sat, Feb 10, 2024 at 02:15:18PM +0100, Oleg Nesterov wrote:
> > On 02/10, Christian Brauner wrote:
> > >
> > > The question is what is more useful for userspace when they do:
> > > pidfd_send_signal(1234, PIDFD_SEND_PROCESS_GROUP)?
> > >
> > > (1) They either mean to signal a process group that is headed by 1234.
> >
> > Yes, this is what I had in mind, see also another email from me.
> > Simple, clear, and matches kill(-1234).
>
> I went for a walk and kept thinking about this and I agree with you.
> It will require that 1234 will be a process group leader but I think
> that this is ok to require that.

Yes... but I am starting to understand why you mentioned the new
open PIDFD_PROCESS_GROUP flag... perhaps we can do something like
this later, but this needs more thinking.

> +	if (type == PIDFD_SIGNAL_PROCESS_GROUP)
> +		ret = kill_pgrp_info(sig, &kinfo, pid);

I guess you meant

	if (type == PIDTYPE_PGID)

other than that,

Reviewed-by: Oleg Nesterov <oleg@...hat.com>