2013/4/13 Oleg Nesterov <oleg@redhat.com>
>
> exit_notify() does exit_task_namespaces() after
> forget_original_parent(). This was needed to ensure that ->nsproxy
> can't be cleared prematurely, an exiting child we are going to
> reparent can do do_notify_parent() and use the parent's (ours) pid_ns.
>
> However, after 32084504 "pidns: use task_active_pid_ns in
> do_notify_parent" ->nsproxy != NULL is no longer needed, we rely
> on task_active_pid_ns().
>
> Move exit_task_namespaces() from exit_notify() to do_exit(), after
> exit_fs() and before exit_task_work().
>
> This solves the problem reported by Andrey, free_ipc_ns()->shm_destroy()
> does fput() which needs task_work_add(). And this allows us do simplify
> exit_notify(), we can avoid unlock/lock(tasklist) and we can change
> ->exit_state instead of PF_EXITING in forget_original_parent().
>

It looks good for me. I have tested it a bit and don't find any problem.
Oleg, thank you.

Acked-by: Andrew Vagin <avagin@gmail.com>

> Reported-by: Andrey Vagin <avagin@openvz.org>
> Signed-off-by: Oleg Nesterov <oleg@redhat.com>
>
> --- x/kernel/exit.c
> +++ x/kernel/exit.c
> @@ -649,7 +649,6 @@ static void exit_notify(struct task_stru
>          *      jobs, send them a SIGHUP and then a SIGCONT.  (POSIX 3.2.2.2)
>          */
>         forget_original_parent(tsk);
> -       exit_task_namespaces(tsk);
>
>         write_lock_irq(&tasklist_lock);
>         if (group_dead)
> @@ -795,6 +794,7 @@ void do_exit(long code)
>         exit_shm(tsk);
>         exit_files(tsk);
>         exit_fs(tsk);
> +       exit_task_namespaces(tsk);
>         exit_task_work(tsk);
>         check_stack_usage();
>         exit_thread();
>