On Fri, Jul 19, 2019 at 9:27 AM Christian Brauner <christ...@brauner.io> wrote: > > 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. >
Yes, I think you are right. AFAIU in this code path p->exit_state should always be equal to EXIT_TRACE because of the earlier cmpxchg() call and the if condition before do_notify_parent(). That's of course unless there is a chance that p->exit_state gets changed by some other thread after cmpxchg() call and before do_notify_parent()... I'm not that familiar with this code to say for sure that it's impossible. If that can't happen I think we can remove this one but the change in exit_notify() should definitely stay. Thanks, Suren. > Christian > > -- > To unsubscribe from this group and stop receiving emails from it, send an > email to kernel-team+unsubscr...@android.com. >
