[PATCH 1/4] reparent_thread: don't call kill_orphaned_pgrp() if task_detached()

[Oleg Nesterov <oleg@redhat.com>]

If task_detached(p) == T, then either

	a) p is not the main thread, we will find the group leader
	   on the ->children list.
or
	b) p is the group leader but its ->exit_state = EXIT_DEAD.
	   This can only happen when the last sub-thread has died,
	   but in that case that thread has already called
	   kill_orphaned_pgrp() from exit_notify().

In both cases kill_orphaned_pgrp() looks bogus.

Move the task_detached() check up and simplify the code, this is also
right from the "common sense" pov: we should do nothing with the detached
childs, except move them to the new parent's ->children list.

Signed-off-by: Oleg Nesterov <oleg@redhat.com>

--- 6.29-rc3/kernel/exit.c~5_SIMPLIFY_REPARENT_THREAD	2009-01-29 04:09:40.000000000 +0100
+++ 6.29-rc3/kernel/exit.c	2009-01-29 06:21:51.000000000 +0100
@@ -812,6 +812,8 @@ static void reparent_thread(struct task_
 
 	list_move_tail(&p->sibling, &p->real_parent->children);
 
+	if (task_detached(p))
+		return;
 	/* If this is a threaded reparent there is no need to
 	 * notify anyone anything has happened.
 	 */
@@ -819,15 +821,13 @@ static void reparent_thread(struct task_
 		return;
 
 	/* We don't want people slaying init.  */
-	if (!task_detached(p))
-		p->exit_signal = SIGCHLD;
+	p->exit_signal = SIGCHLD;
 
 	/* If we'd notified the old parent about this child's death,
 	 * also notify the new parent.
 	 */
 	if (!ptrace_reparented(p) &&
-	    p->exit_state == EXIT_ZOMBIE &&
-	    !task_detached(p) && thread_group_empty(p))
+	    p->exit_state == EXIT_ZOMBIE && thread_group_empty(p))
 		do_notify_parent(p, p->exit_signal);
 
 	kill_orphaned_pgrp(p, father);