[Devel] Re: [PATCH 14/15] Destroy pid namespace on init's death

[Dave Hansen]

On Tue, 2007-07-31 at 23:16 -0700, sukadev at us.ibm.com wrote:
> Oleg Nesterov [oleg at tv-sign.ru] wrote:
> | On 07/30, sukadev at us.ibm.com wrote:
> | >
> | > --- lx26-23-rc1-mm1.orig/kernel/exit.c	2007-07-26 20:08:16.000000000 -0700
> | > +++ lx26-23-rc1-mm1/kernel/exit.c	2007-07-30 23:10:30.000000000 -0700
> | > @@ -915,6 +915,7 @@ fastcall NORET_TYPE void do_exit(long co
> | >  {
> | >  	struct task_struct *tsk = current;
> | >  	int group_dead;
> | > +	struct pid_namespace *pid_ns = tsk->nsproxy->pid_ns;
> | >  
> | >  	profile_task_exit(tsk);
> | >  
> | > @@ -925,9 +926,10 @@ fastcall NORET_TYPE void do_exit(long co
> | >  	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;
> | > +		if (pid_ns != &init_pid_ns) {
> | > +			zap_pid_ns_processes(pid_ns);
> | > +			pid_ns->child_reaper = init_pid_ns.child_reaper;
> | > +		}
> | >  		else
> | >  			panic("Attempted to kill init!");
> | >  	}
> | 
> | Just to remind you, this is not right when init is multi-threaded,
> | we should do this only when the last thread exits.
> 
> Sorry, I needed to clarify somethings about the multi-threaded init. I
> got the impresssion that you were sending a patch for the existing bug,
> and meant to review/clarify in the context of the patch.
> 
> Anyways, re: requirements for multi-threaded init:
> 
> 	Our current definition of is_container_init() and task_child_reaper()
> 	refer only to the main-thread of the container-init (since they check
> 	for pid_t == 1)

Remember, the "pid" is actually a tgid:
        
        asmlinkage long sys_getpid(void)
        {
                return current->tgid;
        }

So, there are multiple tasks with a "pid" == 1 with a multithreaded
init. 

> 	If the main-thread is exiting and is the last thread in the group,
> 	we want terminate other processes in the pid ns (simple case).
> 
> 	If the main thread is exiting, but is not the last thread in the
> 	group, should we let it exit and let the next thread in the group
> 	the reaper of the pid ns ?

Well, what happens with a multithreaded init today?
	
-- Dave