From: Christian Brauner <brauner@kernel.org>
To: Oleg Nesterov <oleg@redhat.com>
Cc: 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: [PATCH v3 1/3] pidfd: allow pidfd_open() on non-thread-group leaders
Date: Fri, 26 Jan 2024 10:47:58 +0100 [thread overview]
Message-ID: <20240126-kulinarisch-ausziehen-d2af51882d2f@brauner> (raw)
In-Reply-To: <20240125140830.GA5513@redhat.com>
> Please the the incomplete/untested patch below.
>
> - The change in exit_notify() is sub-optimal, we can do better
> to avoid 2 do_notify_pidfd() calls from exit_notify(). But
> so far this is only for discussion, lets keep it simple.
>
> - __pidfd_prepare() needs some minor cleanups regardless of
> this change, I'll send the patch...
>
> What do you think?
>
> And why is thread_group_exited() exported?
>
> Oleg.
>
> diff --git a/include/uapi/linux/pidfd.h b/include/uapi/linux/pidfd.h
> index 5406fbc13074..2e6461459877 100644
> --- a/include/uapi/linux/pidfd.h
> +++ b/include/uapi/linux/pidfd.h
> @@ -7,6 +7,7 @@
> #include <linux/fcntl.h>
>
> /* Flags for pidfd_open(). */
> -#define PIDFD_NONBLOCK O_NONBLOCK
> +#define PIDFD_NONBLOCK O_NONBLOCK
> +#define PIDFD_THREAD O_EXCL // or anything else not used by anon_inode's
I like it!
The only request I would have is to not alias O_EXCL and PIDFD_THREAD.
Because it doesn't map as clearly as NONBLOCK did.
>
> #endif /* _UAPI_LINUX_PIDFD_H */
> diff --git a/kernel/exit.c b/kernel/exit.c
> index dfb963d2f862..9f8526b7d717 100644
> --- a/kernel/exit.c
> +++ b/kernel/exit.c
> @@ -752,6 +752,10 @@ static void exit_notify(struct task_struct *tsk, int group_dead)
> autoreap = true;
> }
>
> + /* unnecessary if do_notify_parent() was already called,
> + we can do better */
> + do_notify_pidfd(tsk);
> +
> if (autoreap) {
> tsk->exit_state = EXIT_DEAD;
> list_add(&tsk->ptrace_entry, &dead);
> diff --git a/kernel/fork.c b/kernel/fork.c
> index c981fa6171c1..38f2c7423fb4 100644
> --- a/kernel/fork.c
> +++ b/kernel/fork.c
> @@ -101,6 +101,7 @@
> #include <linux/user_events.h>
> #include <linux/iommu.h>
> #include <linux/rseq.h>
> +#include <uapi/linux/pidfd.h>
>
> #include <asm/pgalloc.h>
> #include <linux/uaccess.h>
> @@ -2068,12 +2069,27 @@ static void pidfd_show_fdinfo(struct seq_file *m, struct file *f)
> }
> #endif
>
> +static bool xxx_exited(struct pid *pid, int excl)
> +{
> + struct task_struct *task;
> + bool exited;
> +
> + rcu_read_lock();
> + task = pid_task(pid, PIDTYPE_PID);
> + exited = !task ||
> + (READ_ONCE(task->exit_state) && (excl || thread_group_empty(task)));
> + rcu_read_unlock();
> +
> + return exited;
> +}
> +
> /*
> * Poll support for process exit notification.
> */
> static __poll_t pidfd_poll(struct file *file, struct poll_table_struct *pts)
> {
> struct pid *pid = file->private_data;
> + int excl = file->f_flags & PIDFD_THREAD;
> __poll_t poll_flags = 0;
>
> poll_wait(file, &pid->wait_pidfd, pts);
> @@ -2083,7 +2099,7 @@ static __poll_t pidfd_poll(struct file *file, struct poll_table_struct *pts)
> * If the thread group leader exits before all other threads in the
> * group, then poll(2) should block, similar to the wait(2) family.
> */
> - if (thread_group_exited(pid))
> + if (xxx_exited(pid, excl))
> poll_flags = EPOLLIN | EPOLLRDNORM;
>
> return poll_flags;
> @@ -2129,7 +2145,9 @@ static int __pidfd_prepare(struct pid *pid, unsigned int flags, struct file **re
> {
> int pidfd;
> struct file *pidfd_file;
> + unsigned excl = flags & PIDFD_THREAD;
>
> + flags &= ~PIDFD_THREAD;
> if (flags & ~(O_NONBLOCK | O_RDWR | O_CLOEXEC))
> return -EINVAL;
>
> @@ -2144,6 +2162,7 @@ static int __pidfd_prepare(struct pid *pid, unsigned int flags, struct file **re
> return PTR_ERR(pidfd_file);
> }
> get_pid(pid); /* held by pidfd_file now */
> + pidfd_file->f_flags |= excl;
> *ret = pidfd_file;
> return pidfd;
> }
> @@ -2176,7 +2195,9 @@ static int __pidfd_prepare(struct pid *pid, unsigned int flags, struct file **re
> */
> int pidfd_prepare(struct pid *pid, unsigned int flags, struct file **ret)
> {
> - if (!pid || !pid_has_task(pid, PIDTYPE_TGID))
> + unsigned excl = flags & PIDFD_THREAD;
> +
> + if (!pid || !pid_has_task(pid, excl ? PIDTYPE_PID : PIDTYPE_TGID))
> return -EINVAL;
>
> return __pidfd_prepare(pid, flags, ret);
> diff --git a/kernel/pid.c b/kernel/pid.c
> index b52b10865454..5257197f9493 100644
> --- a/kernel/pid.c
> +++ b/kernel/pid.c
> @@ -629,7 +629,7 @@ SYSCALL_DEFINE2(pidfd_open, pid_t, pid, unsigned int, flags)
> int fd;
> struct pid *p;
>
> - if (flags & ~PIDFD_NONBLOCK)
> + if (flags & ~(PIDFD_NONBLOCK | PIDFD_THREAD))
> return -EINVAL;
>
> if (pid <= 0)
>
next prev parent reply other threads:[~2024-01-26 9:48 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 [this message]
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
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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