[PATCH] Reinstate const in next_thread()

Before commit 47e65328a7b1cdfc4e3102e50d60faf94ebba7d3, next_thread() took
a const task_t.  Reinstate the const qualifier, getting the next thread
never changes the current thread.

Signed-off-by: Keith Owens <kaos@sgi.com>
Signed-off-by: Andrew Morton <akpm@osdl.org>
Signed-off-by: Linus Torvalds <torvalds@osdl.org>

include/linux/sched.h

@@ -1206,7 +1206,7 @@ extern void wait_task_inactive(task_t * p);
 /* de_thread depends on thread_group_leader not being a pid based check */
 #define thread_group_leader(p)	(p == p->group_leader)
 
-static inline task_t *next_thread(task_t *p)
+static inline task_t *next_thread(const task_t *p)
 {
 	return list_entry(rcu_dereference(p->thread_group.next),
 				task_t, thread_group);