linux-kernel - Re: [PATCH] release_task: kill the no longer needed get/put_pid(thread

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Message-ID: <CAGudoHFc0u2tpodDV9GXw6raUvnr3mDR8tN+Ec3ZXCR1v3q19g@mail.gmail.com>
Date: Fri, 11 Apr 2025 14:33:10 +0200
From: Mateusz Guzik <mjguzik@...il.com>
To: Oleg Nesterov <oleg@...hat.com>
Cc: Christian Brauner <brauner@...nel.org>, "Eric W. Biederman" <ebiederm@...ssion.com>, 
	"Liam R. Howlett" <Liam.Howlett@...cle.com>, linux-kernel@...r.kernel.org
Subject: Re: [PATCH] release_task: kill the no longer needed get/put_pid(thread_pid)

On Fri, Apr 11, 2025 at 2:19 PM Oleg Nesterov <oleg@...hat.com> wrote:
>
> After the commit 7903f907a2260 ("pid: perform free_pid() calls outside
> of tasklist_lock") __unhash_process() -> detach_pid() no longer calls
> free_pid(), proc_flush_pid() can just use p->thread_pid without the
> now pointless get_pid() + put_pid().
>
> Signed-off-by: Oleg Nesterov <oleg@...hat.com>
> ---
>  kernel/exit.c | 7 ++-----
>  1 file changed, 2 insertions(+), 5 deletions(-)
>
> diff --git a/kernel/exit.c b/kernel/exit.c
> index 1b51dc099f1e..96d639383f86 100644
> --- a/kernel/exit.c
> +++ b/kernel/exit.c
> @@ -239,7 +239,6 @@ void release_task(struct task_struct *p)
>  {
>         struct release_task_post post;
>         struct task_struct *leader;
> -       struct pid *thread_pid;
>         int zap_leader;
>  repeat:
>         memset(&post, 0, sizeof(post));
> @@ -253,8 +252,6 @@ void release_task(struct task_struct *p)
>         pidfs_exit(p);
>         cgroup_release(p);
>
> -       thread_pid = get_pid(p->thread_pid);
> -
>         write_lock_irq(&tasklist_lock);
>         ptrace_release_task(p);
>         __exit_signal(&post, p);
> @@ -282,8 +279,8 @@ void release_task(struct task_struct *p)
>         }
>
>         write_unlock_irq(&tasklist_lock);
> -       proc_flush_pid(thread_pid);
> -       put_pid(thread_pid);
> +       /* p->thread_pid can't go away until free_pids() below */
> +       proc_flush_pid(p->thread_pid);
>         add_device_randomness(&p->se.sum_exec_runtime,
>                               sizeof(p->se.sum_exec_runtime));
>         free_pids(post.pids);

I'm trying to remember why I did not just remove it.

Interestingly I see my v2 *did* do the same thing:
https://lore.kernel.org/all/20250128160743.3142544-1-mjguzik@gmail.com/

+ proc_flush_pid(p->thread_pid);

I guess it fell through the cracks during reworks, shit happens.

that said:
Reviewed-by: Mateusz Guzik <mjguzik@...il.com>

thanks

-- 
Mateusz Guzik <mjguzik gmail.com>