linux-kernel - Re: [PATCH -mm] add a helper function to test if an object is on the stack

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Message-Id: <20080610225236.5d698871.akpm@linux-foundation.org>
Date:	Tue, 10 Jun 2008 22:52:36 -0700
From:	Andrew Morton <akpm@...ux-foundation.org>
To:	FUJITA Tomonori <fujita.tomonori@....ntt.co.jp>
Cc:	linux-kernel@...r.kernel.org, tglx@...utronix.de
Subject: Re: [PATCH -mm] add a helper function to test if an object is on
 the stack

On Wed, 11 Jun 2008 11:14:45 +0900 FUJITA Tomonori <fujita.tomonori@....ntt.co.jp> wrote:

> lib/debugobjects.c has a function to test if an object is on the
> stack. The block layer and ide needs it (they need to avoid DMA
> from/to stack buffers). This patch moves the function to
> include/linux/sched.h so that everyone can use it.
> 
> lib/debugobjects.c uses current->stack but this patch uses a
> task_stack_page() accessor, which is a preferable way to access to
> stack.
> 

Seems reasonable.

> ---
>  include/linux/sched.h |    7 +++++++
>  lib/debugobjects.c    |    4 +---
>  2 files changed, 8 insertions(+), 3 deletions(-)
> 
> diff --git a/include/linux/sched.h b/include/linux/sched.h
> index 4efb39b..799bbdd 100644
> --- a/include/linux/sched.h
> +++ b/include/linux/sched.h
> @@ -1978,6 +1978,13 @@ static inline unsigned long *end_of_stack(struct task_struct *p)
>  
>  #endif
>  
> +static inline int object_is_on_stack(void *obj)
> +{
> +	void *stack = task_stack_page(current);

Are we sure that this will work if !defined __HAVE_THREAD_FUNCTIONS?

> +	return (obj >= stack) && (obj < (stack + THREAD_SIZE));
> +}
> +
>  extern void thread_info_cache_init(void);
>  
>  #ifdef CONFIG_DEBUG_STACK_USAGE
> diff --git a/lib/debugobjects.c b/lib/debugobjects.c
> index a76a5e1..2afddde 100644
> --- a/lib/debugobjects.c
> +++ b/lib/debugobjects.c
> @@ -231,15 +231,13 @@ debug_object_fixup(int (*fixup)(void *addr, enum debug_obj_state state),
>  
>  static void debug_object_is_on_stack(void *addr, int onstack)
>  {
> -	void *stack = current->stack;
>  	int is_on_stack;
>  	static int limit;
>  
>  	if (limit > 4)
>  		return;
>  
> -	is_on_stack = (addr >= stack && addr < (stack + THREAD_SIZE));
> -
> +	is_on_stack = object_is_on_stack(addr);
>  	if (is_on_stack == onstack)
>  		return;

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