On Fri, Jul 19, 2019 at 06:14:05PM +0200, Oleg Nesterov wrote:
> it seems that I missed something else...
>
> On 07/17, Joel Fernandes (Google) wrote:
> >
> > @@ -1156,10 +1157,11 @@ static int wait_task_zombie(struct wait_opts *wo,
> > struct task_struct *p)
> > ptrace_unlink(p);
> >
> > /* If parent wants a zombie, don't release it now */
> > - state = EXIT_ZOMBIE;
> > + p->exit_state = EXIT_ZOMBIE;
> > if (do_notify_parent(p, p->exit_signal))
> > - state = EXIT_DEAD;
> > - p->exit_state = state;
> > + p->exit_state = EXIT_DEAD;
> > +
> > + state = p->exit_state;
> > write_unlock_irq(&tasklist_lock);
>
> why do you think we also need to change wait_task_zombie() ?
>
> pidfd_poll() only needs the exit_state != 0 check, we know that it
> is not zero at this point. Why do we need to change exit_state before
> do_notify_parent() ?
Oh, because of?:
/*
* Move the task's state to DEAD/TRACE, only one thread can do this.
*/
state = (ptrace_reparented(p) && thread_group_leader(p)) ?
EXIT_TRACE : EXIT_DEAD;
if (cmpxchg(&p->exit_state, EXIT_ZOMBIE, state) != EXIT_ZOMBIE)
return 0;
So exit_state will definitely be set in this scenario. Good point.
Christian
