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Subject[PATCH 2/3] signals: de_thread: simplify the ->child_reaper switching
Now that we rely on SIGNAL_UNKILLABLE flag, de_thread() doesn't need the nasty
hack to kill the old ->child_reaper during the mt-exec.

This also means we can avoid taking tasklist_lock around zap_other_threads().

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

--- 25/fs/exec.c~2_EXEC_KILL_HACK 2008-03-03 17:01:36.000000000 +0300
+++ 25/fs/exec.c 2008-03-16 15:20:25.000000000 +0300
@@ -757,9 +757,7 @@ static int de_thread(struct task_struct

/*
* Kill all other threads in the thread group.
- * We must hold tasklist_lock to call zap_other_threads.
*/
- read_lock(&tasklist_lock);
spin_lock_irq(lock);
if (signal_group_exit(sig)) {
/*
@@ -767,21 +765,10 @@ static int de_thread(struct task_struct
* return so that the signal is processed.
*/
spin_unlock_irq(lock);
- read_unlock(&tasklist_lock);
return -EAGAIN;
}
-
- /*
- * child_reaper ignores SIGKILL, change it now.
- * Reparenting needs write_lock on tasklist_lock,
- * so it is safe to do it under read_lock.
- */
- if (unlikely(tsk->group_leader == task_child_reaper(tsk)))
- task_active_pid_ns(tsk)->child_reaper = tsk;
-
sig->group_exit_task = tsk;
zap_other_threads(tsk);
- read_unlock(&tasklist_lock);

/* Account for the thread group leader hanging around: */
count = thread_group_leader(tsk) ? 1 : 2;
@@ -812,6 +799,8 @@ static int de_thread(struct task_struct
schedule();
}

+ if (unlikely(task_child_reaper(tsk) == leader))
+ task_active_pid_ns(tsk)->child_reaper = tsk;
/*
* The only record we have of the real-time age of a
* process, regardless of execs it's done, is start_time.


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