From: Andy Lutomirski <luto@amacapital.net>
To: Christian Brauner <brauner@kernel.org>
Cc: Oleg Nesterov <oleg@redhat.com>,
Tycho Andersen <tycho@tycho.pizza>,
linux-kernel@vger.kernel.org, linux-api@vger.kernel.org,
Tycho Andersen <tandersen@netflix.com>,
"Eric W. Biederman" <ebiederm@xmission.com>
Subject: Re: [RFC PATCH] pidfd: implement PIDFD_THREAD flag for pidfd_open()
Date: Thu, 1 Feb 2024 11:33:32 -0800 [thread overview]
Message-ID: <CALCETrUm3YWJCXeDufHKHj9-QU9A1sxZW2HW5a7OHEdTtB1UqQ@mail.gmail.com> (raw)
In-Reply-To: <20240201-flugzeit-modeschau-dab703fc8b6d@brauner>
On Thu, Feb 1, 2024 at 5:39 AM Christian Brauner <brauner@kernel.org> wrote:
>
> On Thu, Feb 01, 2024 at 02:30:46PM +0100, Christian Brauner wrote:
> > On Wed, Jan 31, 2024 at 11:50:23AM -0800, Andy Lutomirski wrote:
> > > On Wed, Jan 31, 2024 at 11:46 AM Christian Brauner <brauner@kernel.org> wrote:
> > > >
> > > > On Wed, Jan 31, 2024 at 11:24:48AM -0800, Andy Lutomirski wrote:
> > > > > > On 01/31, Oleg Nesterov wrote:
> > > > > > >
> > > > > > > On 01/31, Andy Lutomirski wrote:
> > > > > > > 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/
> > > > >
> > > > > I missed that. Whoops.
> > > > >
> > > > > On Wed, Jan 31, 2024 at 11:15 AM Oleg Nesterov <oleg@redhat.com> wrote:
> > > > > >
> > > > > > 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.
> > > > > >
> > > > >
> > > > > Hmm.
> > > > >
> > > > > When one works with regular (non-fd) pids / pgids etc, one specifies
> > > > > the signal domain at the time that one sends the signal. I don't know
> > > > > what pidfds should do. It seems a bit inefficient for anything that
> > > > > wants a pidfd and might send a signal in a different mode in the
> > > > > future to have to hold on to multiple pidfds, so it probably should be
> > > > > a pidfd_send_signal flag.
> > > > >
> > > > > Which leaves the question of what the default should be. Should
> > > > > pidfd_send_signal with flags = 0 on a PIDFD_THREAD signal the process
> > > > > or the thread? I guess there are two reasonable solutions:
> > > > >
> > > > > 1. flags = 0 always means process. And maybe there's a special flag
> > > > > to send a signal that matches the pidfd type, or maybe not.
> > > > >
> > > > > 2. flags = 0 does what the pidfd seems to imply, and a new
> > > > > PIDFD_SIGNAL_PID flag overrides it to signal the whole PID even if the
> > > > > pidfd is PIDFD_THREAD.
> > > > >
> > > > > Do any of you have actual use cases in mind where one choice is
> > > > > clearly better than the other choice?
> > > >
> > > > So conceptually I think having the type of pidfd dictate the default
> > > > scope of the signal is the most elegant approach. And then very likely
> > > > we should just have:
> > > >
> > > > PIDFD_SIGNAL_THREAD
> > > > PIDFD_SIGNAL_THREAD_GROUP
> > > > PIDFD_SIGNAL_PROCESS_GROUP
> > > >
> > > > I think for userspace it doesn't really matter as long as we clearly
> > > > document what's going on.
> > > >
> > >
> > > This seems reasonable unless we're likely to end up with a pidfd mode
> > > that doesn't actually make sense in a send_signal context. But I'm
> > > not immediately seeing any reason that that would happen.
> >
> > Yeah, I think that's very unlikely and we could reject it obased on api
> > design considerations.
>
> Ah, forgot to ask. Did you intend to send a patch for this?
I can try to get to it tomorrow. Currently trying to madly line up a
whole bunch of stuff in time for a maintenance window.
next prev parent reply other threads:[~2024-02-01 19:33 UTC|newest]
Thread overview: 44+ messages / expand[flat|nested] mbox.gz Atom feed top
2024-01-23 15:34 [PATCH v3 0/3] pidfds for non thread group leaders Tycho Andersen
2024-01-23 15:34 ` [PATCH v3 1/3] pidfd: allow pidfd_open() on non-thread-group leaders Tycho Andersen
2024-01-23 19:56 ` Oleg Nesterov
2024-01-23 21:10 ` Tycho Andersen
2024-01-23 22:22 ` Oleg Nesterov
2024-01-24 1:25 ` Oleg Nesterov
2024-01-25 14:08 ` Oleg Nesterov
2024-01-25 17:17 ` Christian Brauner
2024-01-25 17:51 ` Oleg Nesterov
2024-01-25 18:03 ` Tycho Andersen
2024-01-25 18:25 ` Oleg Nesterov
2024-01-25 18:30 ` Oleg Nesterov
2024-01-25 18:36 ` Tycho Andersen
2024-01-26 9:49 ` Christian Brauner
2024-01-26 9:42 ` Christian Brauner
2024-01-26 14:33 ` Oleg Nesterov
2024-01-26 9:47 ` Christian Brauner
2024-01-26 14:33 ` Oleg Nesterov
2024-01-27 14:26 ` Christian Brauner
2024-01-26 21:50 ` Tycho Andersen
2024-01-27 10:54 ` Oleg Nesterov
2024-01-27 14:33 ` Christian Brauner
2024-01-27 15:55 ` Tycho Andersen
2024-01-27 16:31 ` Oleg Nesterov
2024-01-27 17:20 ` Tycho Andersen
2024-01-27 19:31 ` Oleg Nesterov
2024-01-27 20:44 ` Tycho Andersen
2024-01-27 21:10 ` Oleg Nesterov
2024-01-29 11:23 ` [RFC PATCH] pidfd: implement PIDFD_THREAD flag for pidfd_open() Oleg Nesterov
2024-01-29 13:41 ` Christian Brauner
2024-01-29 14:31 ` Tycho Andersen
2024-01-29 15:14 ` Christian Brauner
2024-01-30 11:21 ` Oleg Nesterov
2024-01-31 18:11 ` Andy Lutomirski
2024-01-31 18:48 ` Oleg Nesterov
2024-01-31 19:14 ` Oleg Nesterov
2024-01-31 19:24 ` Andy Lutomirski
2024-01-31 19:46 ` Christian Brauner
2024-01-31 19:50 ` Andy Lutomirski
2024-02-01 13:30 ` Christian Brauner
2024-02-01 13:39 ` Christian Brauner
2024-02-01 19:33 ` Andy Lutomirski [this message]
2024-01-23 15:34 ` [PATCH v3 2/3] selftests/pidfd: add non-thread-group leader tests Tycho Andersen
2024-01-23 15:34 ` [PATCH v3 3/3] clone: allow CLONE_THREAD | CLONE_PIDFD together Tycho Andersen
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