Re: [PATCH] pidns: Guarantee that the pidns init will be the last pidns process reaped. v2

[Oleg Nesterov <oleg@redhat.com>]

On 05/21, Eric W. Biederman wrote:
>
> Andrew can you replace your earlier version of this patch in your tree
> with this one,

Yes, please, the old one is

	pidns-guarantee-that-the-pidns-init-will-be-the-last-pidns-process-reaped.patch

> after Oleg takes a look at it.  I think this is about
> as simple and maintainable and obvious as we can make this bug fix.

I believe the patch is fine.

Thanks Eric.

> --- a/kernel/exit.c
> +++ b/kernel/exit.c
> @@ -64,15 +64,26 @@ static void exit_mm(struct task_struct * tsk);
>  static void __unhash_process(struct task_struct *p, bool group_dead)
>  {
>  	nr_threads--;
> -	detach_pid(p, PIDTYPE_PID);
>  	if (group_dead) {
> +		struct task_struct *parent;
> +
>  		detach_pid(p, PIDTYPE_PGID);
>  		detach_pid(p, PIDTYPE_SID);
>  
>  		list_del_rcu(&p->tasks);
>  		list_del_init(&p->sibling);
>  		__this_cpu_dec(process_counts);
> +
> +		/* If we are the last child process in a pid namespace
> +		 * to be reaped notify the child_reaper.
> +		 */
> +		parent = p->real_parent;
> +		if ((task_active_pid_ns(p)->child_reaper == parent) &&
> +		    list_empty(&parent->children) &&
> +		    (parent->flags & PF_EXITING))
> +			wake_up_process(parent);
>  	}
> +	detach_pid(p, PIDTYPE_PID);
>  	list_del_rcu(&p->thread_group);
>  }
>  
> diff --git a/kernel/pid_namespace.c b/kernel/pid_namespace.c
> index b98b0ed..ba1cbb8 100644
> --- a/kernel/pid_namespace.c
> +++ b/kernel/pid_namespace.c
> @@ -189,6 +189,17 @@ void zap_pid_ns_processes(struct pid_namespace *pid_ns)
>  		rc = sys_wait4(-1, NULL, __WALL, NULL);
>  	} while (rc != -ECHILD);
>  
> +	read_lock(&tasklist_lock);
> +	for (;;) {
> +		__set_current_state(TASK_UNINTERRUPTIBLE);
> +		if (list_empty(&current->children))
> +			break;
> +		read_unlock(&tasklist_lock);
> +		schedule();
> +		read_lock(&tasklist_lock);
> +	}
> +	read_unlock(&tasklist_lock);
> +
>  	if (pid_ns->reboot)
>  		current->signal->group_exit_code = pid_ns->reboot;
>  
> -- 
> 1.7.5.4
>