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

[sukadev at us.ibm.com]

Dave Hansen [haveblue at us.ibm.com] wrote:
| 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. 

Yes, and so am now wondering if is_container_init(), is_global_init()
and the "tsk == task_child_reaper(tsk)" checks be replaced with with
something that covers other threads in the reaper ?

| 
| > 	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