From: Oleg Nesterov <oleg@redhat.com>
To: Joel Fernandes <joel@joelfernandes.org>
Cc: linux-kernel@vger.kernel.org, luto@amacapital.net,
rostedt@goodmis.org, dancol@google.com, christian@brauner.io,
jannh@google.com, surenb@google.com,
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@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@android.com, Tycho Andersen <tycho@tycho.ws>
Subject: Re: [PATCH RFC 1/2] Add polling support to pidfd
Date: Wed, 17 Apr 2019 15:09:41 +0200 [thread overview]
Message-ID: <20190417130940.GC32622@redhat.com> (raw)
In-Reply-To: <20190416192051.GA184889@google.com>
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 ?
> > Then all you need is
> >
> > !task || task->exit_state && thread_group_empty(task)
>
> Yes this works as well, all the tests pass with your suggestion so I'll
> change it to that. Although I will the be giving up returing EPOLLERR if the
> task_struct doesn't exit. We don't need that, but I thought it was cool to
> return it anyway.
OK, task == NULL means that it was already reaped by parent, pid_nr is free,
probably useful....
> > Please do not use EXIT_DEAD/EXIT_ZOMBIE. And ->wait_pidfd should probably
> > live in task->signal_struct.
>
> About wait_pidfd living in signal_struct, that wont work since the waitqueue
> has to survive for the duration of the poll system call.
That is why I said this will need the additional cleanup in free_signal_struct().
But I was wrong, somehow I forgot that free_poll_entry() needs wq_head->lock ;)
so this will need much more complications, lets forget it...
> Also the waitqueue living in struct pid solves the de_thread() issue I
> mentioned later in the following thread and in the commit message:
> https://lore.kernel.org/patchwork/comment/1257175/
Hmm...
2. By including the struct pid for the waitqueue means that during
de_exec, the thread doing de_thread() automatically gets the new
waitqueue/pid even though its task_struct is different.
this one?
this is not true, or I do not understand...
it gets the _same_ (old, not new) PIDTYPE_TGID pid even if it changes task_struct.
But probably this is what you actually meant, because this is what your patch wants
or I am totally confused.
And note that exec/de_thread doesn't change ->signal_struct, so I do not understand
you anyway. Nevermind.
Oleg.
WARNING: multiple messages have this Message-ID (diff)
From: oleg at redhat.com (Oleg Nesterov)
Subject: [PATCH RFC 1/2] Add polling support to pidfd
Date: Wed, 17 Apr 2019 15:09:41 +0200 [thread overview]
Message-ID: <20190417130940.GC32622@redhat.com> (raw)
In-Reply-To: <20190416192051.GA184889@google.com>
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 ?
> > Then all you need is
> >
> > !task || task->exit_state && thread_group_empty(task)
>
> Yes this works as well, all the tests pass with your suggestion so I'll
> change it to that. Although I will the be giving up returing EPOLLERR if the
> task_struct doesn't exit. We don't need that, but I thought it was cool to
> return it anyway.
OK, task == NULL means that it was already reaped by parent, pid_nr is free,
probably useful....
> > Please do not use EXIT_DEAD/EXIT_ZOMBIE. And ->wait_pidfd should probably
> > live in task->signal_struct.
>
> About wait_pidfd living in signal_struct, that wont work since the waitqueue
> has to survive for the duration of the poll system call.
That is why I said this will need the additional cleanup in free_signal_struct().
But I was wrong, somehow I forgot that free_poll_entry() needs wq_head->lock ;)
so this will need much more complications, lets forget it...
> Also the waitqueue living in struct pid solves the de_thread() issue I
> mentioned later in the following thread and in the commit message:
> https://lore.kernel.org/patchwork/comment/1257175/
Hmm...
2. By including the struct pid for the waitqueue means that during
de_exec, the thread doing de_thread() automatically gets the new
waitqueue/pid even though its task_struct is different.
this one?
this is not true, or I do not understand...
it gets the _same_ (old, not new) PIDTYPE_TGID pid even if it changes task_struct.
But probably this is what you actually meant, because this is what your patch wants
or I am totally confused.
And note that exec/de_thread doesn't change ->signal_struct, so I do not understand
you anyway. Nevermind.
Oleg.
WARNING: multiple messages have this Message-ID (diff)
From: oleg@redhat.com (Oleg Nesterov)
Subject: [PATCH RFC 1/2] Add polling support to pidfd
Date: Wed, 17 Apr 2019 15:09:41 +0200 [thread overview]
Message-ID: <20190417130940.GC32622@redhat.com> (raw)
Message-ID: <20190417130941.QyHap7BU_7Gpyg_7fxc_yAqPXmRNc0jtR76XUfoSfU4@z> (raw)
In-Reply-To: <20190416192051.GA184889@google.com>
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 ?
> > Then all you need is
> >
> > !task || task->exit_state && thread_group_empty(task)
>
> Yes this works as well, all the tests pass with your suggestion so I'll
> change it to that. Although I will the be giving up returing EPOLLERR if the
> task_struct doesn't exit. We don't need that, but I thought it was cool to
> return it anyway.
OK, task == NULL means that it was already reaped by parent, pid_nr is free,
probably useful....
> > Please do not use EXIT_DEAD/EXIT_ZOMBIE. And ->wait_pidfd should probably
> > live in task->signal_struct.
>
> About wait_pidfd living in signal_struct, that wont work since the waitqueue
> has to survive for the duration of the poll system call.
That is why I said this will need the additional cleanup in free_signal_struct().
But I was wrong, somehow I forgot that free_poll_entry() needs wq_head->lock ;)
so this will need much more complications, lets forget it...
> Also the waitqueue living in struct pid solves the de_thread() issue I
> mentioned later in the following thread and in the commit message:
> https://lore.kernel.org/patchwork/comment/1257175/
Hmm...
2. By including the struct pid for the waitqueue means that during
de_exec, the thread doing de_thread() automatically gets the new
waitqueue/pid even though its task_struct is different.
this one?
this is not true, or I do not understand...
it gets the _same_ (old, not new) PIDTYPE_TGID pid even if it changes task_struct.
But probably this is what you actually meant, because this is what your patch wants
or I am totally confused.
And note that exec/de_thread doesn't change ->signal_struct, so I do not understand
you anyway. Nevermind.
Oleg.
next prev parent reply other threads:[~2019-04-17 13:09 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 [this message]
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
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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