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[PATCH 2/2] task_stack.h: Clean-up stack_not_used() implementation

Linus Walleij posted 2 patches 1 month ago
[PATCH 2/2] task_stack.h: Clean-up stack_not_used() implementation
Posted by Linus Walleij 1 month ago 
From: Pasha Tatashin <pasha.tatashin@soleen.com>

Inside the small stack_not_used() function there are several ifdefs for
stack growing-up vs. regular versions. Instead just implement this
function two times, one for growing-up and another regular.

Add comments like /* !CONFIG_DEBUG_STACK_USAGE */ to clarify what the
ifdefs are doing.

[linus.walleij@linaro.org: Rebased, function moved elsewhere in the kernel]
Signed-off-by: Pasha Tatashin <pasha.tatashin@soleen.com>
Link: https://lore.kernel.org/20240311164638.2015063-13-pasha.tatashin@soleen.com
Signed-off-by: Linus Walleij <linus.walleij@linaro.org>
---
 kernel/exit.c | 23 ++++++++++++++---------
 1 file changed, 14 insertions(+), 9 deletions(-)

diff --git a/kernel/exit.c b/kernel/exit.c
index 343eb97543d568baeb23142edcc9050a8b8be8bf..9f74e8f1c431b6aa6e391ff71aadf9895a3857ae 100644
--- a/kernel/exit.c
+++ b/kernel/exit.c
@@ -780,24 +780,29 @@ static void exit_notify(struct task_struct *tsk, int group_dead)
 }
 
 #ifdef CONFIG_DEBUG_STACK_USAGE
+#ifdef CONFIG_STACK_GROWSUP
 unsigned long stack_not_used(struct task_struct *p)
 {
 	unsigned long *n = end_of_stack(p);
 
 	do {	/* Skip over canary */
-# ifdef CONFIG_STACK_GROWSUP
 		n--;
-# else
-		n++;
-# endif
 	} while (!*n);
 
-# ifdef CONFIG_STACK_GROWSUP
 	return (unsigned long)end_of_stack(p) - (unsigned long)n;
-# else
+}
+#else /* !CONFIG_STACK_GROWSUP */
+unsigned long stack_not_used(struct task_struct *p)
+{
+	unsigned long *n = end_of_stack(p);
+
+	do {	/* Skip over canary */
+		n++;
+	} while (!*n);
+
 	return (unsigned long)n - (unsigned long)end_of_stack(p);
-# endif
 }
+#endif /* CONFIG_STACK_GROWSUP */
 
 /* Count the maximum pages reached in kernel stacks */
 static inline void kstack_histogram(unsigned long used_stack)
@@ -856,9 +861,9 @@ static void check_stack_usage(void)
 	}
 	spin_unlock(&low_water_lock);
 }
-#else
+#else /* !CONFIG_DEBUG_STACK_USAGE */
 static inline void check_stack_usage(void) {}
-#endif
+#endif /* CONFIG_DEBUG_STACK_USAGE */
 
 static void synchronize_group_exit(struct task_struct *tsk, long code)
 {

-- 
2.50.1
Re: [PATCH 2/2] task_stack.h: Clean-up stack_not_used() implementation
Posted by Lorenzo Stoakes 1 month ago 
On Fri, Aug 29, 2025 at 01:44:41PM +0200, Linus Walleij wrote:
> From: Pasha Tatashin <pasha.tatashin@soleen.com>
>
> Inside the small stack_not_used() function there are several ifdefs for
> stack growing-up vs. regular versions. Instead just implement this
> function two times, one for growing-up and another regular.
>
> Add comments like /* !CONFIG_DEBUG_STACK_USAGE */ to clarify what the
> ifdefs are doing.
>
> [linus.walleij@linaro.org: Rebased, function moved elsewhere in the kernel]
> Signed-off-by: Pasha Tatashin <pasha.tatashin@soleen.com>
> Link: https://lore.kernel.org/20240311164638.2015063-13-pasha.tatashin@soleen.com
> Signed-off-by: Linus Walleij <linus.walleij@linaro.org>

LGTM, lovely change! :)

Reviewed-by: Lorenzo Stoakes <lorenzo.stoakes@oracle.com>

> ---
>  kernel/exit.c | 23 ++++++++++++++---------
>  1 file changed, 14 insertions(+), 9 deletions(-)
>
> diff --git a/kernel/exit.c b/kernel/exit.c
> index 343eb97543d568baeb23142edcc9050a8b8be8bf..9f74e8f1c431b6aa6e391ff71aadf9895a3857ae 100644
> --- a/kernel/exit.c
> +++ b/kernel/exit.c
> @@ -780,24 +780,29 @@ static void exit_notify(struct task_struct *tsk, int group_dead)
>  }
>
>  #ifdef CONFIG_DEBUG_STACK_USAGE
> +#ifdef CONFIG_STACK_GROWSUP
>  unsigned long stack_not_used(struct task_struct *p)
>  {
>  	unsigned long *n = end_of_stack(p);
>
>  	do {	/* Skip over canary */
> -# ifdef CONFIG_STACK_GROWSUP
>  		n--;
> -# else
> -		n++;
> -# endif
>  	} while (!*n);
>
> -# ifdef CONFIG_STACK_GROWSUP
>  	return (unsigned long)end_of_stack(p) - (unsigned long)n;
> -# else
> +}
> +#else /* !CONFIG_STACK_GROWSUP */
> +unsigned long stack_not_used(struct task_struct *p)
> +{
> +	unsigned long *n = end_of_stack(p);
> +
> +	do {	/* Skip over canary */
> +		n++;
> +	} while (!*n);
> +
>  	return (unsigned long)n - (unsigned long)end_of_stack(p);
> -# endif
>  }
> +#endif /* CONFIG_STACK_GROWSUP */
>
>  /* Count the maximum pages reached in kernel stacks */
>  static inline void kstack_histogram(unsigned long used_stack)
> @@ -856,9 +861,9 @@ static void check_stack_usage(void)
>  	}
>  	spin_unlock(&low_water_lock);
>  }
> -#else
> +#else /* !CONFIG_DEBUG_STACK_USAGE */
>  static inline void check_stack_usage(void) {}
> -#endif
> +#endif /* CONFIG_DEBUG_STACK_USAGE */
>
>  static void synchronize_group_exit(struct task_struct *tsk, long code)
>  {
>
> --
> 2.50.1
>
Re: [PATCH 2/2] task_stack.h: Clean-up stack_not_used() implementation
Posted by Liam R. Howlett 1 month ago 
* Linus Walleij <linus.walleij@linaro.org> [250829 07:44]:
> From: Pasha Tatashin <pasha.tatashin@soleen.com>
> 
> Inside the small stack_not_used() function there are several ifdefs for
> stack growing-up vs. regular versions. Instead just implement this
> function two times, one for growing-up and another regular.
> 
> Add comments like /* !CONFIG_DEBUG_STACK_USAGE */ to clarify what the
> ifdefs are doing.
> 
> [linus.walleij@linaro.org: Rebased, function moved elsewhere in the kernel]
> Signed-off-by: Pasha Tatashin <pasha.tatashin@soleen.com>
> Link: https://lore.kernel.org/20240311164638.2015063-13-pasha.tatashin@soleen.com
> Signed-off-by: Linus Walleij <linus.walleij@linaro.org>

Thanks for this.

Reviewed-by: Liam R. Howlett <Liam.Howlett@oracle.com>

> ---
>  kernel/exit.c | 23 ++++++++++++++---------
>  1 file changed, 14 insertions(+), 9 deletions(-)
> 
> diff --git a/kernel/exit.c b/kernel/exit.c
> index 343eb97543d568baeb23142edcc9050a8b8be8bf..9f74e8f1c431b6aa6e391ff71aadf9895a3857ae 100644
> --- a/kernel/exit.c
> +++ b/kernel/exit.c
> @@ -780,24 +780,29 @@ static void exit_notify(struct task_struct *tsk, int group_dead)
>  }
>  
>  #ifdef CONFIG_DEBUG_STACK_USAGE
> +#ifdef CONFIG_STACK_GROWSUP
>  unsigned long stack_not_used(struct task_struct *p)
>  {
>  	unsigned long *n = end_of_stack(p);
>  
>  	do {	/* Skip over canary */
> -# ifdef CONFIG_STACK_GROWSUP
>  		n--;
> -# else
> -		n++;
> -# endif
>  	} while (!*n);
>  
> -# ifdef CONFIG_STACK_GROWSUP
>  	return (unsigned long)end_of_stack(p) - (unsigned long)n;
> -# else
> +}
> +#else /* !CONFIG_STACK_GROWSUP */
> +unsigned long stack_not_used(struct task_struct *p)
> +{
> +	unsigned long *n = end_of_stack(p);
> +
> +	do {	/* Skip over canary */
> +		n++;
> +	} while (!*n);
> +
>  	return (unsigned long)n - (unsigned long)end_of_stack(p);
> -# endif
>  }
> +#endif /* CONFIG_STACK_GROWSUP */
>  
>  /* Count the maximum pages reached in kernel stacks */
>  static inline void kstack_histogram(unsigned long used_stack)
> @@ -856,9 +861,9 @@ static void check_stack_usage(void)
>  	}
>  	spin_unlock(&low_water_lock);
>  }
> -#else
> +#else /* !CONFIG_DEBUG_STACK_USAGE */
>  static inline void check_stack_usage(void) {}
> -#endif
> +#endif /* CONFIG_DEBUG_STACK_USAGE */
>  
>  static void synchronize_group_exit(struct task_struct *tsk, long code)
>  {
> 
> -- 
> 2.50.1
>

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