[PATCH 3/3] do __unhash_process() under ->siglock

[Oleg Nesterov <oleg@tv-sign.ru>]

This patch moves __unhash_process() call from realease_task()
to __exit_signal(), so __detach_pid() is called with ->siglock
held.

This means we don't need tasklist_lock to iterate over thread
group anymore:
 
	copy_process() was already changed to do attach_pid()
	under ->siglock.

	Eric's "pidhash-kill-switch_exec_pids.patch" from -mm
	changed de_thread() so it doesn't touch PIDTYPE_TGID.

NOTE: de_thread() still needs some attention. It still changes
task->pid lockless. Taking ->sighand.siglock here allows to do
more tasklist_lock removals.

Signed-off-by: Oleg Nesterov <oleg@tv-sign.ru>

--- 2.6.16-rc3/kernel/exit.c~3_FIN	2006-02-23 00:54:28.000000000 +0300
+++ 2.6.16-rc3/kernel/exit.c	2006-02-23 01:00:35.000000000 +0300
@@ -110,6 +110,8 @@ static void __exit_signal(struct task_st
 		sig = NULL; /* Marker for below. */
 	}
 
+	__unhash_process(tsk);
+
 	tsk->signal = NULL;
 	cleanup_sighand(tsk);
 	spin_unlock(&sighand->siglock);
@@ -138,8 +140,6 @@ repeat:
 	BUG_ON(!list_empty(&p->ptrace_list) || !list_empty(&p->ptrace_children));
 	__exit_signal(p);
 
-	__unhash_process(p);
-
 	/*
 	 * If we are the last non-leader member of the thread
 	 * group, and the leader is zombie, then notify the