[PATCH] missing helper - task_stack_page()

Patchset annotates arch/* uses of ->thread_info.  Ones that really are about
access of thread_info of given process are simply switched to
task_thread_info(task); ones that deal with access to objects on stack are
switched to new helper - task_stack_page().  A _lot_ of the latter are
actually open-coded instances of "find where pt_regs are"; those are
consolidated into task_pt_regs(task) (many architectures actually have such
helper already).

Note that these annotations are not mandatory - any code not converted to
these helpers still works.  However, they clean up a lot of places and have
actually caught a number of bugs, so converting out of tree ports would be a
good idea...

As an example of breakage caught by that stuff, see i386 pt_regs mess - we
used to have it open-coded in a bunch of places and when back in April Stas
had fixed a bug in copy_thread(), the rest had been left out of sync.  That
required two followup patches (the latest - just before 2.6.15) _and_ still
had left /proc/*/stat eip field broken.  Try ps -eo eip on i386 and watch the
junk...

This patch:

new helper - task_stack_page(task).  Returns pointer to the memory object
containing task stack; usually thread_info of task sits in the beginning
of that object.

Signed-off-by: Al Viro <viro@zeniv.linux.org.uk>
Signed-off-by: Andrew Morton <akpm@osdl.org>
Signed-off-by: Linus Torvalds <torvalds@osdl.org>

include/asm-m68k/thread_info.h

@@ -37,6 +37,7 @@ struct thread_info {
 #define init_stack		(init_thread_union.stack)
 
 #define task_thread_info(tsk)	(&(tsk)->thread.info)
+#define task_stack_page(tsk)	((void *)(tsk)->thread_info)
 #define current_thread_info()	task_thread_info(current)
 
 #define __HAVE_THREAD_FUNCTIONS

include/linux/sched.h

@@ -1240,6 +1240,7 @@ static inline void task_unlock(struct task_struct *p)
 #ifndef __HAVE_THREAD_FUNCTIONS
 
 #define task_thread_info(task) (task)->thread_info
+#define task_stack_page(task) ((void*)((task)->thread_info))
 
 static inline void setup_thread_stack(struct task_struct *p, struct task_struct *org)
 {