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

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

[FUJITA Tomonori]

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.

Signed-off-by: FUJITA Tomonori <fujita.tomonori@lab.ntt.co.jp>
---
 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);
+
+	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;
 
-- 
1.5.5.GIT

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

[Andrew Morton]

On Wed, 11 Jun 2008 11:14:45 +0900 FUJITA Tomonori <fujita.tomonori@lab.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;

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

[FUJITA Tomonori]

On Tue, 10 Jun 2008 22:52:36 -0700
Andrew Morton <akpm@linux-foundation.org> wrote:

> On Wed, 11 Jun 2008 11:14:45 +0900 FUJITA Tomonori <fujita.tomonori@lab.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?

If !defined __HAVE_THREAD_FUNCTIONS, we use the following macro in
sched.h:

#define task_stack_page(task)	((task)->stack)

So it works.