rather than wake_up_all(). This way do_notify_pidfd() won't wakeup the
POLLHUP-only waiters which wait for pid_task() == NULL.

TODO:
    - as Christian pointed out, this asks for the new wake_up_all_poll()
      helper, it can already have other users.

    - we can probably discriminate the PIDFD_THREAD and non-PIDFD_THREAD
      waiters, but this needs more work.

Signed-off-by: Oleg Nesterov <oleg@redhat.com>
---
 kernel/signal.c | 7 ++++---
 1 file changed, 4 insertions(+), 3 deletions(-)

diff --git a/kernel/signal.c b/kernel/signal.c
index 9b40109f0c56..c3fac06937e2 100644
--- a/kernel/signal.c
+++ b/kernel/signal.c
@@ -2021,11 +2021,12 @@ int send_sigqueue(struct sigqueue *q, struct pid *pid, enum pid_type type)
 
 void do_notify_pidfd(struct task_struct *task)
 {
-	struct pid *pid;
+	struct pid *pid = task_pid(task);
 
 	WARN_ON(task->exit_state == 0);
-	pid = task_pid(task);
-	wake_up_all(&pid->wait_pidfd);
+
+	__wake_up(&pid->wait_pidfd, TASK_NORMAL, 0,
+			poll_to_key(EPOLLIN | EPOLLRDNORM));
 }
 
 /*
-- 
2.25.1.362.g51ebf55

Argh, sorry for noise Christian, I have sent the same patch twice.

Please ignore this email, the next email from me with the same
subject adds the reference to our discussion into the changelog.

On 02/05, Oleg Nesterov wrote:
>
> rather than wake_up_all(). This way do_notify_pidfd() won't wakeup the
> POLLHUP-only waiters which wait for pid_task() == NULL.
> 
> TODO:
>     - as Christian pointed out, this asks for the new wake_up_all_poll()
>       helper, it can already have other users.
> 
>     - we can probably discriminate the PIDFD_THREAD and non-PIDFD_THREAD
>       waiters, but this needs more work.
> 
> Signed-off-by: Oleg Nesterov <oleg@redhat.com>
> ---
>  kernel/signal.c | 7 ++++---
>  1 file changed, 4 insertions(+), 3 deletions(-)
> 
> diff --git a/kernel/signal.c b/kernel/signal.c
> index 9b40109f0c56..c3fac06937e2 100644
> --- a/kernel/signal.c
> +++ b/kernel/signal.c
> @@ -2021,11 +2021,12 @@ int send_sigqueue(struct sigqueue *q, struct pid *pid, enum pid_type type)
>  
>  void do_notify_pidfd(struct task_struct *task)
>  {
> -	struct pid *pid;
> +	struct pid *pid = task_pid(task);
>  
>  	WARN_ON(task->exit_state == 0);
> -	pid = task_pid(task);
> -	wake_up_all(&pid->wait_pidfd);
> +
> +	__wake_up(&pid->wait_pidfd, TASK_NORMAL, 0,
> +			poll_to_key(EPOLLIN | EPOLLRDNORM));
>  }
>  
>  /*
> -- 
> 2.25.1.362.g51ebf55
> 
>