From: Daniel Colascione <dancol@google.com>
To: Linus Torvalds <torvalds@linux-foundation.org>
Cc: Christian Brauner <christian@brauner.io>,
Joel Fernandes <joel@joelfernandes.org>,
Jann Horn <jannh@google.com>, Oleg Nesterov <oleg@redhat.com>,
Florian Weimer <fweimer@redhat.com>,
kernel list <linux-kernel@vger.kernel.org>,
Andy Lutomirski <luto@amacapital.net>,
Steven Rostedt <rostedt@goodmis.org>,
Suren Baghdasaryan <surenb@google.com>,
Alexey Dobriyan <adobriyan@gmail.com>,
Al Viro <viro@zeniv.linux.org.uk>,
Andrei Vagin <avagin@gmail.com>,
Andrew Morton <akpm@linux-foundation.org>,
Arnd Bergmann <arnd@arndb.de>,
"Eric W. Biederman" <ebiederm@xmission.com>,
Kees Cook <keescook@chromium.org>,
linux-fsdevel <linux-fsdevel@vger.kernel.org>,
"open list:KERNEL SELFTEST FRAMEWORK"
<linux-kselftest@vger.kernel.org>, Michal Hocko <mhocko@suse.com>,
Nadav Amit <namit@vmware.com>, Serge Hallyn <serge@hallyn.com>,
Shuah Khan <shuah@kernel.org>,
Stephen Rothwell <sfr@canb.auug.org.au>,
Taehee Yoo <ap420073@gmail.com>, Tejun Heo <tj@kernel.org>,
Thomas Gleixner <tglx@linutronix.de>,
kernel-team <kernel-team@android.com>,
Tycho Andersen <tycho@tycho.ws>
Subject: Re: [PATCH RFC 1/2] Add polling support to pidfd
Date: Fri, 19 Apr 2019 16:36:24 -0700 [thread overview]
Message-ID: <CAKOZuesaWK1Y7c85jNv71LNx7sKoGgn_eLzQVPnoi6e4eUx4aQ@mail.gmail.com> (raw)
In-Reply-To: <CAHk-=wh8DmfsOFY4OrqRjLYCYi+2Ej7uLbidmiPg+BhBOGZVcA@mail.gmail.com>
On Fri, Apr 19, 2019 at 4:33 PM Linus Torvalds
<torvalds@linux-foundation.org> wrote:
>
> On Fri, Apr 19, 2019 at 4:20 PM Christian Brauner <christian@brauner.io> wrote:
> >
> > On Sat, Apr 20, 2019 at 1:11 AM Linus Torvalds
> > <torvalds@linux-foundation.org> wrote:
> > >
> > > It's also worth noting that POLLERR/POLLHUP/POLLNVAL cannot be masked
> > > for "poll()". Even if you only ask for POLLIN/POLLOUT, you will always
> > > get POLLERR/POLLHUP notification. That is again historical behavior,
> > > and it's kind of a "you can't poll a hung up fd". But it once again
> > > means that you should consider POLLHUP to be something *exceptional*
> > > and final, where no further or other state changes can happen or are
> > > relevant.
> >
> > Which kind of makes sense for process exit. So the historical behavior
> > here is in our favor and having POLLIN | POLLHUP rather fitting.
> > It just seems right that POLLHUP indicates "there can be
> > no more state transitions".
>
> Note that that is *not* true of process exit.
>
> The final state transition isn't "exit", it is actually "process has
> been reaped". That's the point where data no longer exists.
FWIW, I think the exit status should be available via pidfd even after
process reaping. A non-parent holder of a pidfd has no ability to
control when the parent reaps the child, or even if reaping is
necessary at all --- the parent could make SIGCHLD SIG_IGN. Someone
trying to read exit status via a pidfd shouldn't fail to get that exit
status just because he lost the race with a concurrent waitpid().
WARNING: multiple messages have this Message-ID (diff)
From: dancol at google.com (Daniel Colascione)
Subject: [PATCH RFC 1/2] Add polling support to pidfd
Date: Fri, 19 Apr 2019 16:36:24 -0700 [thread overview]
Message-ID: <CAKOZuesaWK1Y7c85jNv71LNx7sKoGgn_eLzQVPnoi6e4eUx4aQ@mail.gmail.com> (raw)
In-Reply-To: <CAHk-=wh8DmfsOFY4OrqRjLYCYi+2Ej7uLbidmiPg+BhBOGZVcA@mail.gmail.com>
On Fri, Apr 19, 2019 at 4:33 PM Linus Torvalds
<torvalds at linux-foundation.org> wrote:
>
> On Fri, Apr 19, 2019 at 4:20 PM Christian Brauner <christian at brauner.io> wrote:
> >
> > On Sat, Apr 20, 2019 at 1:11 AM Linus Torvalds
> > <torvalds at linux-foundation.org> wrote:
> > >
> > > It's also worth noting that POLLERR/POLLHUP/POLLNVAL cannot be masked
> > > for "poll()". Even if you only ask for POLLIN/POLLOUT, you will always
> > > get POLLERR/POLLHUP notification. That is again historical behavior,
> > > and it's kind of a "you can't poll a hung up fd". But it once again
> > > means that you should consider POLLHUP to be something *exceptional*
> > > and final, where no further or other state changes can happen or are
> > > relevant.
> >
> > Which kind of makes sense for process exit. So the historical behavior
> > here is in our favor and having POLLIN | POLLHUP rather fitting.
> > It just seems right that POLLHUP indicates "there can be
> > no more state transitions".
>
> Note that that is *not* true of process exit.
>
> The final state transition isn't "exit", it is actually "process has
> been reaped". That's the point where data no longer exists.
FWIW, I think the exit status should be available via pidfd even after
process reaping. A non-parent holder of a pidfd has no ability to
control when the parent reaps the child, or even if reaping is
necessary at all --- the parent could make SIGCHLD SIG_IGN. Someone
trying to read exit status via a pidfd shouldn't fail to get that exit
status just because he lost the race with a concurrent waitpid().
WARNING: multiple messages have this Message-ID (diff)
From: dancol@google.com (Daniel Colascione)
Subject: [PATCH RFC 1/2] Add polling support to pidfd
Date: Fri, 19 Apr 2019 16:36:24 -0700 [thread overview]
Message-ID: <CAKOZuesaWK1Y7c85jNv71LNx7sKoGgn_eLzQVPnoi6e4eUx4aQ@mail.gmail.com> (raw)
Message-ID: <20190419233624.kfBKhKwD2lzVMAZvfA3d2ufbtxqPo9jwfsnPoG-HBbs@z> (raw)
In-Reply-To: <CAHk-=wh8DmfsOFY4OrqRjLYCYi+2Ej7uLbidmiPg+BhBOGZVcA@mail.gmail.com>
On Fri, Apr 19, 2019 at 4:33 PM Linus Torvalds
<torvalds@linux-foundation.org> wrote:
>
> On Fri, Apr 19, 2019@4:20 PM Christian Brauner <christian@brauner.io> wrote:
> >
> > On Sat, Apr 20, 2019 at 1:11 AM Linus Torvalds
> > <torvalds@linux-foundation.org> wrote:
> > >
> > > It's also worth noting that POLLERR/POLLHUP/POLLNVAL cannot be masked
> > > for "poll()". Even if you only ask for POLLIN/POLLOUT, you will always
> > > get POLLERR/POLLHUP notification. That is again historical behavior,
> > > and it's kind of a "you can't poll a hung up fd". But it once again
> > > means that you should consider POLLHUP to be something *exceptional*
> > > and final, where no further or other state changes can happen or are
> > > relevant.
> >
> > Which kind of makes sense for process exit. So the historical behavior
> > here is in our favor and having POLLIN | POLLHUP rather fitting.
> > It just seems right that POLLHUP indicates "there can be
> > no more state transitions".
>
> Note that that is *not* true of process exit.
>
> The final state transition isn't "exit", it is actually "process has
> been reaped". That's the point where data no longer exists.
FWIW, I think the exit status should be available via pidfd even after
process reaping. A non-parent holder of a pidfd has no ability to
control when the parent reaps the child, or even if reaping is
necessary at all --- the parent could make SIGCHLD SIG_IGN. Someone
trying to read exit status via a pidfd shouldn't fail to get that exit
status just because he lost the race with a concurrent waitpid().
next prev parent reply other threads:[~2019-04-19 23:36 UTC|newest]
Thread overview: 198+ messages / expand[flat|nested] mbox.gz Atom feed top
2019-04-11 17:50 [PATCH RFC 1/2] Add polling support to pidfd Joel Fernandes (Google)
2019-04-11 17:50 ` Joel Fernandes (Google)
2019-04-11 17:50 ` joel
2019-04-11 17:50 ` [PATCH RFC 2/2] Add selftests for pidfd polling Joel Fernandes (Google)
2019-04-11 17:50 ` Joel Fernandes (Google)
2019-04-11 17:50 ` joel
2019-04-12 14:51 ` Tycho Andersen
2019-04-12 14:51 ` Tycho Andersen
2019-04-12 14:51 ` tycho
2019-04-11 20:00 ` [PATCH RFC 1/2] Add polling support to pidfd Joel Fernandes
2019-04-11 20:00 ` Joel Fernandes
2019-04-11 20:00 ` joel
2019-04-11 20:02 ` Christian Brauner
2019-04-11 20:02 ` Christian Brauner
2019-04-11 20:02 ` christian
2019-04-11 20:20 ` Joel Fernandes
2019-04-11 20:20 ` Joel Fernandes
2019-04-11 20:20 ` joel
2019-04-12 21:32 ` Andy Lutomirski
2019-04-12 21:32 ` Andy Lutomirski
2019-04-12 21:32 ` luto
2019-04-13 0:09 ` Joel Fernandes
2019-04-13 0:09 ` Joel Fernandes
2019-04-13 0:09 ` joel
[not found] ` <CAKOZuetX4jMPDtDqAvGgSNo4BHf9BOnu79ufEiULfM5X5nDyyQ@mail.gmail.com>
2019-04-13 0:56 ` Daniel Colascione
2019-04-13 0:56 ` Daniel Colascione
2019-04-13 0:56 ` dancol
2019-04-14 18:19 ` Linus Torvalds
2019-04-14 18:19 ` Linus Torvalds
2019-04-14 18:19 ` torvalds
2019-04-16 12:04 ` Oleg Nesterov
2019-04-16 12:04 ` Oleg Nesterov
2019-04-16 12:04 ` oleg
2019-04-16 12:43 ` Oleg Nesterov
2019-04-16 12:43 ` Oleg Nesterov
2019-04-16 12:43 ` oleg
2019-04-16 19:20 ` Joel Fernandes
2019-04-16 19:20 ` Joel Fernandes
2019-04-16 19:20 ` joel
2019-04-16 19:32 ` Joel Fernandes
2019-04-16 19:32 ` Joel Fernandes
2019-04-16 19:32 ` joel
2019-04-17 13:09 ` Oleg Nesterov
2019-04-17 13:09 ` Oleg Nesterov
2019-04-17 13:09 ` oleg
2019-04-18 17:23 ` Jann Horn
2019-04-18 17:23 ` Jann Horn
2019-04-18 17:23 ` jannh
2019-04-18 17:26 ` Christian Brauner
2019-04-18 17:26 ` Christian Brauner
2019-04-18 17:26 ` christian
2019-04-18 17:53 ` Daniel Colascione
2019-04-18 17:53 ` Daniel Colascione
2019-04-18 17:53 ` dancol
2019-04-19 19:02 ` Joel Fernandes
2019-04-19 19:02 ` Joel Fernandes
2019-04-19 19:02 ` joel
2019-04-19 19:18 ` Christian Brauner
2019-04-19 19:18 ` Christian Brauner
2019-04-19 19:18 ` christian
2019-04-19 19:22 ` Christian Brauner
2019-04-19 19:22 ` Christian Brauner
2019-04-19 19:22 ` christian
2019-04-19 19:42 ` Christian Brauner
2019-04-19 19:42 ` Christian Brauner
2019-04-19 19:42 ` christian
2019-04-19 19:49 ` Joel Fernandes
2019-04-19 19:49 ` Joel Fernandes
2019-04-19 19:49 ` joel
2019-04-19 20:01 ` Christian Brauner
2019-04-19 20:01 ` Christian Brauner
2019-04-19 20:01 ` christian
2019-04-19 21:13 ` Joel Fernandes
2019-04-19 21:13 ` Joel Fernandes
2019-04-19 21:13 ` joel
2019-04-19 20:34 ` Daniel Colascione
2019-04-19 20:34 ` Daniel Colascione
2019-04-19 20:34 ` dancol
2019-04-19 20:57 ` Christian Brauner
2019-04-19 20:57 ` Christian Brauner
2019-04-19 20:57 ` christian
2019-04-19 21:20 ` Joel Fernandes
2019-04-19 21:20 ` Joel Fernandes
2019-04-19 21:20 ` joel
2019-04-19 21:24 ` Daniel Colascione
2019-04-19 21:24 ` Daniel Colascione
2019-04-19 21:24 ` dancol
2019-04-19 21:45 ` Joel Fernandes
2019-04-19 21:45 ` Joel Fernandes
2019-04-19 21:45 ` joel
2019-04-19 22:08 ` Daniel Colascione
2019-04-19 22:08 ` Daniel Colascione
2019-04-19 22:08 ` dancol
2019-04-19 22:17 ` Christian Brauner
2019-04-19 22:17 ` Christian Brauner
2019-04-19 22:17 ` christian
2019-04-19 22:37 ` Daniel Colascione
2019-04-19 22:37 ` Daniel Colascione
2019-04-19 22:37 ` dancol
2019-04-24 8:04 ` Enrico Weigelt, metux IT consult
2019-04-24 8:04 ` Enrico Weigelt, metux IT consult
2019-04-24 8:04 ` lkml
2019-04-19 21:59 ` Christian Brauner
2019-04-19 21:59 ` Christian Brauner
2019-04-19 21:59 ` christian
2019-04-20 11:51 ` Oleg Nesterov
2019-04-20 11:51 ` Oleg Nesterov
2019-04-20 11:51 ` oleg
2019-04-20 12:26 ` Oleg Nesterov
2019-04-20 12:26 ` Oleg Nesterov
2019-04-20 12:26 ` oleg
2019-04-20 12:35 ` Christian Brauner
2019-04-20 12:35 ` Christian Brauner
2019-04-20 12:35 ` christian
2019-04-19 23:11 ` Linus Torvalds
2019-04-19 23:11 ` Linus Torvalds
2019-04-19 23:11 ` torvalds
2019-04-19 23:20 ` Christian Brauner
2019-04-19 23:20 ` Christian Brauner
2019-04-19 23:20 ` christian
2019-04-19 23:32 ` Linus Torvalds
2019-04-19 23:32 ` Linus Torvalds
2019-04-19 23:32 ` torvalds
2019-04-19 23:36 ` Daniel Colascione [this message]
2019-04-19 23:36 ` Daniel Colascione
2019-04-19 23:36 ` dancol
2019-04-20 0:46 ` Joel Fernandes
2019-04-20 0:46 ` Joel Fernandes
2019-04-20 0:46 ` joel
2019-04-19 21:21 ` Daniel Colascione
2019-04-19 21:21 ` Daniel Colascione
2019-04-19 21:21 ` dancol
2019-04-19 21:48 ` Christian Brauner
2019-04-19 21:48 ` Christian Brauner
2019-04-19 21:48 ` christian
2019-04-19 22:02 ` Christian Brauner
2019-04-19 22:02 ` Christian Brauner
2019-04-19 22:02 ` christian
2019-04-19 22:46 ` Daniel Colascione
2019-04-19 22:46 ` Daniel Colascione
2019-04-19 22:46 ` dancol
2019-04-19 23:12 ` Christian Brauner
2019-04-19 23:12 ` Christian Brauner
2019-04-19 23:12 ` christian
2019-04-19 23:46 ` Daniel Colascione
2019-04-19 23:46 ` Daniel Colascione
2019-04-19 23:46 ` dancol
2019-04-20 0:17 ` Christian Brauner
2019-04-20 0:17 ` Christian Brauner
2019-04-20 0:17 ` christian
2019-04-24 9:05 ` Enrico Weigelt, metux IT consult
2019-04-24 9:05 ` Enrico Weigelt, metux IT consult
2019-04-24 9:05 ` lkml
2019-04-24 9:03 ` Enrico Weigelt, metux IT consult
2019-04-24 9:03 ` Enrico Weigelt, metux IT consult
2019-04-24 9:03 ` lkml
2019-04-19 22:35 ` Daniel Colascione
2019-04-19 22:35 ` Daniel Colascione
2019-04-19 22:35 ` dancol
2019-04-19 23:02 ` Christian Brauner
2019-04-19 23:02 ` Christian Brauner
2019-04-19 23:02 ` christian
2019-04-19 23:29 ` Daniel Colascione
2019-04-19 23:29 ` Daniel Colascione
2019-04-19 23:29 ` dancol
2019-04-20 0:02 ` Christian Brauner
2019-04-20 0:02 ` Christian Brauner
2019-04-20 0:02 ` christian
2019-04-24 9:17 ` Enrico Weigelt, metux IT consult
2019-04-24 9:17 ` Enrico Weigelt, metux IT consult
2019-04-24 9:17 ` lkml
2019-04-24 9:11 ` Enrico Weigelt, metux IT consult
2019-04-24 9:11 ` Enrico Weigelt, metux IT consult
2019-04-24 9:11 ` lkml
2019-04-24 8:56 ` Enrico Weigelt, metux IT consult
2019-04-24 8:56 ` Enrico Weigelt, metux IT consult
2019-04-24 8:56 ` lkml
2019-04-24 8:20 ` Enrico Weigelt, metux IT consult
2019-04-24 8:20 ` Enrico Weigelt, metux IT consult
2019-04-24 8:20 ` lkml
2019-04-19 15:43 ` Oleg Nesterov
2019-04-19 15:43 ` Oleg Nesterov
2019-04-19 15:43 ` oleg
2019-04-19 18:12 ` Joel Fernandes
2019-04-19 18:12 ` Joel Fernandes
2019-04-19 18:12 ` joel
2019-04-18 18:44 ` Jonathan Kowalski
2019-04-18 18:44 ` Jonathan Kowalski
2019-04-18 18:44 ` bl0pbl33p
2019-04-18 18:57 ` Daniel Colascione
2019-04-18 18:57 ` Daniel Colascione
2019-04-18 18:57 ` dancol
2019-04-18 19:14 ` Linus Torvalds
2019-04-18 19:14 ` Linus Torvalds
2019-04-18 19:14 ` torvalds
2019-04-19 19:05 ` Joel Fernandes
2019-04-19 19:05 ` Joel Fernandes
2019-04-19 19:05 ` joel
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