Re: [RFC] fs, proc: Introduce /proc/<pid>/task/<tid>/children entry v6

[Cyrill Gorcunov <gorcunov@gmail.com>]

On Mon, Jan 16, 2012 at 05:11:14PM +0100, Oleg Nesterov wrote:
> On 01/16, Cyrill Gorcunov wrote:
> >
> > +get_children_pid(struct proc_pid_children_iter *iter, struct pid *pid_prev, loff_t pos)
> > +{
> > +	struct task_struct *start, *task;
> > +	struct pid *pid = NULL;
> > +
> > +	read_lock(&tasklist_lock);
> > +
> > +	start = pid_task(iter->pid_start, PIDTYPE_PID);
> > +	if (!start)
> > +		goto out;
> > +
> > +	/*
> > +	 * Lets try to continue searching first, this gives
> > +	 * us significant speedup on children-rich processes.
> > +	 */
> > +	if (pid_prev) {
> > +		task = pid_task(pid_prev, PIDTYPE_PID);
> > +		if (task && task->real_parent == start &&
> > +		    !(list_empty(&task->sibling))) {
> 
> Damn. No, this is wrong.
> 
> Damn! Yes, it was we who told you to check list_empty(sibling) ;)
> 
> But this is not enough. exit_ptrace() can do list_move() without
> changing ->real_parent.
> 
> I'll try to think. At first glance we can rely on EXIT_DEAD, but
> I'd like to avoid this, I think EXIT_DEAD should die.
> 

Ouch! Thanks for catching this Oleg. I'll try to come with something
to show as well.

	Cyrill