[PATCH 3/20] Move checking for init's death in do_exit()

[xemul-GEFAQzZX7r8dnm+yROfE0A@public.gmane.org]

From: Oleg Nesterov <oleg-6lXkIZvqkOAvJsYlp49lxw@public.gmane.org>

If some system uses multi-threaded init the kernel panics when the main
thread exits. Perhaps this is just a "quality of implementation" question.
sys_exit() from the main thread should be OK, why /sbin/init should be
special? That said, I personally do not think that multi-threaded init is
terribly useful.

So I think the patch below makes sense for now. Note that it removes
the games with pid_ns->child_reaper: this doesn't work currently, and
this has to be modified when we actually support pid namespaces anyway.

Signed-off-by: Oleg Nesterov <oleg-6lXkIZvqkOAvJsYlp49lxw@public.gmane.org>
Acked-by: Pavel Emelyanov <xemul-GEFAQzZX7r8dnm+yROfE0A@public.gmane.org>

---

 exit.c |   17 +++++++++--------
 1 files changed, 9 insertions(+), 8 deletions(-)

--- ./kernel/exit.c.ve3	2007-08-06 12:14:53.000000000 +0400
+++ ./kernel/exit.c	2007-08-06 12:15:19.000000000 +0400
@@ -895,6 +895,14 @@ static void check_stack_usage(void)
 static inline void check_stack_usage(void) {}
 #endif
 
+static inline void exit_child_reaper(struct task_struct *tsk)
+{
+	if (likely(tsk->group_leader != task_child_reaper(tsk)))
+		return;
+
+	panic("Attempted to kill init!");
+}
+
 fastcall NORET_TYPE void do_exit(long code)
 {
 	struct task_struct *tsk = current;
@@ -908,14 +916,6 @@ fastcall NORET_TYPE void do_exit(long co
 		panic("Aiee, killing interrupt handler!");
 	if (unlikely(!tsk->pid))
 		panic("Attempted to kill the idle task!");
-	if (unlikely(tsk == task_child_reaper(tsk))) {
-		if (task_active_pid_ns(tsk) != &init_pid_ns)
-			task_active_pid_ns(tsk)->child_reaper =
-					init_pid_ns.child_reaper;
-		else
-			panic("Attempted to kill init!");
-	}
-
 
 	if (unlikely(current->ptrace & PT_TRACE_EXIT)) {
 		current->ptrace_message = code;
@@ -965,6 +965,7 @@ fastcall NORET_TYPE void do_exit(long co
 	}
 	group_dead = atomic_dec_and_test(&tsk->signal->live);
 	if (group_dead) {
+		exit_child_reaper(tsk);
 		hrtimer_cancel(&tsk->signal->real_timer);
 		exit_itimers(tsk->signal);
 	}