[PATCH] exit-fix-2.5.34-C0, BK-curr

This fixes one more exit-time resource accounting issue - and it's also
a speedup and a thread-tree (to-be thread-aware pstree) visual
improvement.

In the current code we reparent detached threads to the init thread.
This worked but was not very nice in ps output: threads showed up as
being related to init.  There was also a resource-accounting issue, upon
exit they update their parent's (ie.  init's) rusage fields -
effectively losing these statistics.  Eg.  'time' under-reports CPU
usage if the threaded app is Ctrl-C-ed prematurely.

The solution is to reparent threads to the group leader - this is now
very easy since we have p->group_leader cached and it's also valid all
the time.  It's also somewhat faster for applications that use
CLONE_THREAD but do not use the CLONE_DETACHED feature.

kernel/exit.c

@@ -447,11 +447,7 @@ static inline void forget_original_parent(struct task_struct * father)
 	struct task_struct *p, *reaper = father;
 	struct list_head *_p;
 
-	if (father->exit_signal != -1)
-		reaper = prev_thread(reaper);
-	else
-		reaper = child_reaper;
-
+	reaper = father->group_leader;
 	if (reaper == father)
 		reaper = child_reaper;