[v1] kernel/fork: Optimize by avoiding unnecessary locking for kernel threads

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

Posted by Zhen Ni 1 day, 23 hours ago

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@easystack.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

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

Posted by Oleg Nesterov 1 day, 15 hours ago

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@easystack.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
>