linux-kernel - Re: [PATCH] pidfd: change do_notify_pidfd() to use __wake_up(poll_to

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Date: Mon, 5 Feb 2024 15:22:29 +0100
From: Oleg Nesterov <oleg@...hat.com>
To: Christian Brauner <brauner@...nel.org>
Cc: Andy Lutomirski <luto@...capital.net>,
	"Eric W. Biederman" <ebiederm@...ssion.com>,
	Tycho Andersen <tycho@...ho.pizza>, linux-kernel@...r.kernel.org
Subject: Re: [PATCH] pidfd: change do_notify_pidfd() to use
 __wake_up(poll_to_key(EPOLLIN))

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@...hat.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
> 
>