linux-kernel - Re: [PATCH] kernel/fork: Optimize by avoiding unnecessary locking for kernel threads

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Message-ID: <20241202173131.GB9551@redhat.com>
Date: Mon, 2 Dec 2024 18:31:32 +0100
From: Oleg Nesterov <oleg@...hat.com>
To: Zhen Ni <zhen.ni@...ystack.cn>
Cc: akpm@...ux-foundation.org, brauner@...nel.org, tglx@...utronix.de,
	frederic@...nel.org, richard.weiyang@...il.com,
	zhangpeng.00@...edance.com, linux-kernel@...r.kernel.org
Subject: Re: [PATCH] kernel/fork: Optimize by avoiding unnecessary locking
 for kernel threads

Already in -mm tree, please see
https://lore.kernel.org/all/20241119143526.704986-1-mjguzik@gmail.com/

Oleg.

On 12/02, Zhen Ni wrote:
>
> Improves the function by checking if the task is a kernel thread
> (PF_KTHREAD) before acquiring the task lock. Kernel threads do not
> have an associated executable file, so the function now returns NULL
> immediately in such cases. This change reduces unnecessary locking
> overhead and simplifies the code logic, while maintaining consistent
> behavior for regular tasks.
>
> Signed-off-by: Zhen Ni <zhen.ni@...ystack.cn>
> ---
>  kernel/fork.c | 9 +++++----
>  1 file changed, 5 insertions(+), 4 deletions(-)
>
> diff --git a/kernel/fork.c b/kernel/fork.c
> index e58d27c05788..9fadde6c7c98 100644
> --- a/kernel/fork.c
> +++ b/kernel/fork.c
> @@ -1500,12 +1500,13 @@ struct file *get_task_exe_file(struct task_struct *task)
>  	struct file *exe_file = NULL;
>  	struct mm_struct *mm;
>
> +	if (task->flags & PF_KTHREAD)
> +		return NULL;
> +
>  	task_lock(task);
>  	mm = task->mm;
> -	if (mm) {
> -		if (!(task->flags & PF_KTHREAD))
> -			exe_file = get_mm_exe_file(mm);
> -	}
> +	if (mm)
> +		exe_file = get_mm_exe_file(mm);
>  	task_unlock(task);
>  	return exe_file;
>  }
> --
> 2.20.1
>