From: Oleg Nesterov <oleg@redhat.com>
To: Tycho Andersen <tycho@tycho.pizza>
Cc: Christian Brauner <brauner@kernel.org>,
linux-kernel@vger.kernel.org, linux-api@vger.kernel.org,
Tycho Andersen <tandersen@netflix.com>,
"Eric W. Biederman" <ebiederm@xmission.com>
Subject: Re: [PATCH v3 1/3] pidfd: allow pidfd_open() on non-thread-group leaders
Date: Sat, 27 Jan 2024 17:31:39 +0100 [thread overview]
Message-ID: <20240127163117.GB13787@redhat.com> (raw)
In-Reply-To: <ZbUngjQMg+YUBAME@tycho.pizza>
On 01/27, Tycho Andersen wrote:
>
> It seems like (and the current pidfd_test enforces for some cases)
Which pidfd_test ?
> we
> want exactly one notification for a task dying.
This can't be right. EVERY user of poll_wait() or wait_event/etc
must handle/tolerate the false wakeups.
> I don't understand
> how we guarantee this now, with all of these calls.
I don't understand why do we need or even want to guarantee this.
The extra wakeup must be always fine correctness-wise. Sure, it
would be nice to avoid the unnecessary wakeups, and perhaps we
can change wake_up_all() to pass a key to, say, only wake_up the
PIDFD_THREAD waiters from exit_notify(). But certainly this is
outside the scope of PIDFD_THREAD change we discuss.
The changes in do_notify_parent() (I have already sent the patch) and
in exit_notify() (proposed in my previous email) just ensure that,
with the minimal changes, we avoid 2 do_notify_pidfd's from the same
exit_notify() path.
> > exit_notify() is called after exit_files(). pidfd_getfd() returns
> > ESRCH if the exiting thread completes release_task(), otherwise it
> > returns EBADF because ->files == NULL. This too doesn't really
> > depend on PIDFD_THREAD.
>
> Yup, understood. It just seems like an inconsistency we might want to
> fix.
Not sure this worth "fixing"...
Oleg.
next prev parent reply other threads:[~2024-01-27 16:33 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 [this message]
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
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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