From: Joel Fernandes <joel@joelfernandes.org>
To: Christian Brauner <christian@brauner.io>
Cc: 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>,
Daniel Colascione <dancol@google.com>,
Suren Baghdasaryan <surenb@google.com>,
Linus Torvalds <torvalds@linux-foundation.org>,
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>,
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 15:02:47 -0400 [thread overview]
Message-ID: <20190419190247.GB251571@google.com> (raw)
In-Reply-To: <CEB62F51-E8BF-4EFB-B438-8AF76633FF00@brauner.io>
On Thu, Apr 18, 2019 at 07:26:44PM +0200, Christian Brauner wrote:
> On April 18, 2019 7:23:38 PM GMT+02:00, Jann Horn <jannh@google.com> wrote:
> >On Wed, Apr 17, 2019 at 3:09 PM Oleg Nesterov <oleg@redhat.com> wrote:
> >> On 04/16, Joel Fernandes wrote:
> >> > On Tue, Apr 16, 2019 at 02:04:31PM +0200, Oleg Nesterov wrote:
> >> > >
> >> > > Could you explain when it should return POLLIN? When the whole
> >process exits?
> >> >
> >> > It returns POLLIN when the task is dead or doesn't exist anymore,
> >or when it
> >> > is in a zombie state and there's no other thread in the thread
> >group.
> >>
> >> IOW, when the whole thread group exits, so it can't be used to
> >monitor sub-threads.
> >>
> >> just in case... speaking of this patch it doesn't modify
> >proc_tid_base_operations,
> >> so you can't poll("/proc/sub-thread-tid") anyway, but iiuc you are
> >going to use
> >> the anonymous file returned by CLONE_PIDFD ?
> >
> >I don't think procfs works that way. /proc/sub-thread-tid has
> >proc_tgid_base_operations despite not being a thread group leader.
> >(Yes, that's kinda weird.) AFAICS the WARN_ON_ONCE() in this code can
> >be hit trivially, and then the code will misbehave.
> >
> >@Joel: I think you'll have to either rewrite this to explicitly bail
> >out if you're dealing with a thread group leader, or make the code
> >work for threads, too.
>
> The latter case probably being preferred if this API is supposed to be
> useable for thread management in userspace.
At the moment, we are not planning to use this for sub-thread management. I
am reworking this patch to only work on clone(2) pidfds which makes the above
discussion about /proc a bit unnecessary I think. Per the latest CLONE_PIDFD
patches, CLONE_THREAD with pidfd is not supported.
Also we wanted to make the polling of pidfd quite close to the wait(2) family
semantics which, as I understand correctly, is not something that works for
sub-threads. In the future, we could bail in poll(2) or return an error, if
clone(2) starts supporting thread pidfds, but at the moment I will like to
keep the WARN_ON just in case. Please let me know if I missed something.
thanks!
- Joel
WARNING: multiple messages have this Message-ID (diff)
From: joel at joelfernandes.org (Joel Fernandes)
Subject: [PATCH RFC 1/2] Add polling support to pidfd
Date: Fri, 19 Apr 2019 15:02:47 -0400 [thread overview]
Message-ID: <20190419190247.GB251571@google.com> (raw)
In-Reply-To: <CEB62F51-E8BF-4EFB-B438-8AF76633FF00@brauner.io>
On Thu, Apr 18, 2019 at 07:26:44PM +0200, Christian Brauner wrote:
> On April 18, 2019 7:23:38 PM GMT+02:00, Jann Horn <jannh at google.com> wrote:
> >On Wed, Apr 17, 2019 at 3:09 PM Oleg Nesterov <oleg at redhat.com> wrote:
> >> On 04/16, Joel Fernandes wrote:
> >> > On Tue, Apr 16, 2019 at 02:04:31PM +0200, Oleg Nesterov wrote:
> >> > >
> >> > > Could you explain when it should return POLLIN? When the whole
> >process exits?
> >> >
> >> > It returns POLLIN when the task is dead or doesn't exist anymore,
> >or when it
> >> > is in a zombie state and there's no other thread in the thread
> >group.
> >>
> >> IOW, when the whole thread group exits, so it can't be used to
> >monitor sub-threads.
> >>
> >> just in case... speaking of this patch it doesn't modify
> >proc_tid_base_operations,
> >> so you can't poll("/proc/sub-thread-tid") anyway, but iiuc you are
> >going to use
> >> the anonymous file returned by CLONE_PIDFD ?
> >
> >I don't think procfs works that way. /proc/sub-thread-tid has
> >proc_tgid_base_operations despite not being a thread group leader.
> >(Yes, that's kinda weird.) AFAICS the WARN_ON_ONCE() in this code can
> >be hit trivially, and then the code will misbehave.
> >
> >@Joel: I think you'll have to either rewrite this to explicitly bail
> >out if you're dealing with a thread group leader, or make the code
> >work for threads, too.
>
> The latter case probably being preferred if this API is supposed to be
> useable for thread management in userspace.
At the moment, we are not planning to use this for sub-thread management. I
am reworking this patch to only work on clone(2) pidfds which makes the above
discussion about /proc a bit unnecessary I think. Per the latest CLONE_PIDFD
patches, CLONE_THREAD with pidfd is not supported.
Also we wanted to make the polling of pidfd quite close to the wait(2) family
semantics which, as I understand correctly, is not something that works for
sub-threads. In the future, we could bail in poll(2) or return an error, if
clone(2) starts supporting thread pidfds, but at the moment I will like to
keep the WARN_ON just in case. Please let me know if I missed something.
thanks!
- Joel
WARNING: multiple messages have this Message-ID (diff)
From: joel@joelfernandes.org (Joel Fernandes)
Subject: [PATCH RFC 1/2] Add polling support to pidfd
Date: Fri, 19 Apr 2019 15:02:47 -0400 [thread overview]
Message-ID: <20190419190247.GB251571@google.com> (raw)
Message-ID: <20190419190247.RySsR6ccxqcJCK8AUcWzayAiJdi2z7qtGkA66D62SMc@z> (raw)
In-Reply-To: <CEB62F51-E8BF-4EFB-B438-8AF76633FF00@brauner.io>
On Thu, Apr 18, 2019@07:26:44PM +0200, Christian Brauner wrote:
> On April 18, 2019 7:23:38 PM GMT+02:00, Jann Horn <jannh@google.com> wrote:
> >On Wed, Apr 17, 2019@3:09 PM Oleg Nesterov <oleg@redhat.com> wrote:
> >> On 04/16, Joel Fernandes wrote:
> >> > On Tue, Apr 16, 2019@02:04:31PM +0200, Oleg Nesterov wrote:
> >> > >
> >> > > Could you explain when it should return POLLIN? When the whole
> >process exits?
> >> >
> >> > It returns POLLIN when the task is dead or doesn't exist anymore,
> >or when it
> >> > is in a zombie state and there's no other thread in the thread
> >group.
> >>
> >> IOW, when the whole thread group exits, so it can't be used to
> >monitor sub-threads.
> >>
> >> just in case... speaking of this patch it doesn't modify
> >proc_tid_base_operations,
> >> so you can't poll("/proc/sub-thread-tid") anyway, but iiuc you are
> >going to use
> >> the anonymous file returned by CLONE_PIDFD ?
> >
> >I don't think procfs works that way. /proc/sub-thread-tid has
> >proc_tgid_base_operations despite not being a thread group leader.
> >(Yes, that's kinda weird.) AFAICS the WARN_ON_ONCE() in this code can
> >be hit trivially, and then the code will misbehave.
> >
> >@Joel: I think you'll have to either rewrite this to explicitly bail
> >out if you're dealing with a thread group leader, or make the code
> >work for threads, too.
>
> The latter case probably being preferred if this API is supposed to be
> useable for thread management in userspace.
At the moment, we are not planning to use this for sub-thread management. I
am reworking this patch to only work on clone(2) pidfds which makes the above
discussion about /proc a bit unnecessary I think. Per the latest CLONE_PIDFD
patches, CLONE_THREAD with pidfd is not supported.
Also we wanted to make the polling of pidfd quite close to the wait(2) family
semantics which, as I understand correctly, is not something that works for
sub-threads. In the future, we could bail in poll(2) or return an error, if
clone(2) starts supporting thread pidfds, but at the moment I will like to
keep the WARN_ON just in case. Please let me know if I missed something.
thanks!
- Joel
next prev parent reply other threads:[~2019-04-19 19:02 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 [this message]
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
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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