> 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)
>
