[PATCH 4/4] exit: avoid sig->count in __exit_signal() to detect the group-dead case

[Oleg Nesterov <oleg@redhat.com>]

Change __exit_signal() to check thread_group_leader() instead of
atomic_dec_and_test(&sig->count). This must be equivalent, the
group leader must be released only after all other threads have
exited and passed __exit_signal().

>From now sig->count is not actually used, except in fs/proc for
get_nr_threads/etc.

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


--- 34-rc1/kernel/exit.c~4_EXIT_SIGNAL	2010-03-17 19:37:18.000000000 +0100
+++ 34-rc1/kernel/exit.c	2010-03-17 20:05:38.000000000 +0100
@@ -89,11 +89,12 @@ static void __exit_signal(struct task_st
 					rcu_read_lock_held() ||
 					lockdep_is_held(&tasklist_lock));
 	spin_lock(&sighand->siglock);
+	atomic_dec(&sig->count);
 
 	posix_cpu_timers_exit(tsk);
-	if (atomic_dec_and_test(&sig->count))
+	if (thread_group_leader(tsk)) {
 		posix_cpu_timers_exit_group(tsk);
-	else {
+	} else {
 		/*
 		 * If there is any task waiting for the group exit
 		 * then notify it: