get_task_exe_file: check PF_KTHREAD locklessly

[PATCH] get_task_exe_file: check PF_KTHREAD locklessly

Posted by Mateusz Guzik 1 year, 2 months ago

Same thing as 8ac5dc66599c ("get_task_mm: check PF_KTHREAD lockless")

Signed-off-by: Mateusz Guzik <mjguzik@gmail.com>
---
 kernel/fork.c | 9 +++++----
 1 file changed, 5 insertions(+), 4 deletions(-)

diff --git a/kernel/fork.c b/kernel/fork.c
index 22f43721d031..759902828e13 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;
 }
-- 
2.43.0

Re: [PATCH] get_task_exe_file: check PF_KTHREAD locklessly

Posted by Andrew Morton 1 year, 2 months ago

On Tue, 19 Nov 2024 15:35:26 +0100 Mateusz Guzik <mjguzik@gmail.com> wrote:

> Same thing as 8ac5dc66599c ("get_task_mm: check PF_KTHREAD lockless")

We prefer that patches have fuller changelogs, please.

I copied the 8ac5dc66599c changelog text into this patch's changelog.



From: Mateusz Guzik <mjguzik@gmail.com>
Subject: get_task_exe_file: check PF_KTHREAD locklessly
Date: Tue, 19 Nov 2024 15:35:26 +0100

Same thing as 8ac5dc66599c ("get_task_mm: check PF_KTHREAD lockless")

Nowadays PF_KTHREAD is sticky and it was never protected by ->alloc_lock. 
Move the PF_KTHREAD check outside of task_lock() section to make this code
more understandable.

Link: https://lkml.kernel.org/r/20241119143526.704986-1-mjguzik@gmail.com
Signed-off-by: Mateusz Guzik <mjguzik@gmail.com>
Acked-by: Oleg Nesterov <oleg@redhat.com>
Signed-off-by: Andrew Morton <akpm@linux-foundation.org>
---

 kernel/fork.c |    9 +++++----
 1 file changed, 5 insertions(+), 4 deletions(-)

--- a/kernel/fork.c~get_task_exe_file-check-pf_kthread-locklessly
+++ a/kernel/fork.c
@@ -1496,12 +1496,13 @@ struct file *get_task_exe_file(struct ta
 	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;
 }
_

Re: [PATCH] get_task_exe_file: check PF_KTHREAD locklessly

Posted by Oleg Nesterov 1 year, 2 months ago

On 11/19, Mateusz Guzik wrote:
>
> --- 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;

Acked-by: Oleg Nesterov <oleg@redhat.com>