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

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Message-ID: <20240131184829.GE2609@redhat.com>
Date: Wed, 31 Jan 2024 19:48:29 +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()

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.