[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@xxxxxxxxxxxxx>
---
 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

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