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

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Message-ID: <20240220-einwurf-depesche-d8682be0370c@brauner>
Date: Tue, 20 Feb 2024 09:34:49 +0100
From: Christian Brauner <brauner@...nel.org>
To: Oleg Nesterov <oleg@...hat.com>
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 Fri, Feb 16, 2024 at 07:12:14PM +0100, Oleg Nesterov wrote:
> On 02/16, Christian Brauner wrote:
> >
> > > SI_USER means that the target can trust the values of si_pid/si_uid
> > > in siginfo.
> >
> > Bah, what an annoying nonsense. I see that this can be used to emulate
> > stuff like SI_TIMER and SI_ASYNCIO. But I very much doubt the value of
> > e.g., emulating SI_DETHREAD. Maybe I'm missing something very obvious.
> 
> I don't understand...

My question was what the purpose of being able to to set si_code to
e.g., SI_DETHREAD is and then to send a signal to yourself? Because it
looks like that's what rt_{tg}sigqueueinfo() and pidfd_send_signal()
allows the caller to do. I'm just trying to understand use-cases for
this.