On Wed, Feb 04, 2015 at 09:25:09PM +0100, Oleg Nesterov wrote: > > I'm not entire sure why we need two PF flags for this; once PF_EXITING > > is set userspace is _dead_ and it doesn't make sense to keep adding > > (futex) PI-state to the task. > > This is what I _seem_ to understand: exit_robust_list(). Although I am > not sure this all is by design... > > And this is the reason why I still can't finish the patch. Perhaps I am > totally confused, but I think there is yet another problem here. > > Please forget about PF_EXIT.*. attach_to_pi_owner() returns -ESRCH if > futex_find_get_task() and even this looks wrong.
You'll have to help me out a little here; where do we unhash the PIDs? >From what I can find we set PF_EXITING _before_ unhashing ourselves. In fact, from what I can tell we only unhash after calling both exit_robust_list and exit_pi_state_list. > Because handle_futex_death() > updates *uaddr lockless and does nothing if "pi". This means that the owner > of PI + robust mutex can go away (or just set PF_EXITPIDONE) and the caller > of futex_lock_pi() can miss unlock. > > Peter, could you confirm that this problem does exist, or I missed something? So as long as we unhash _last_ I can't see this happening, we'll always find the task, the robust list walk doesn't care about PI state. The exit_pi_state_list() will serialize against any concurrent attach that might be in progress -- and we nkow there won't be a new one since we've set PF_EXITING. And kill all the PI owners stuff. But please, if you suspect, share a little more detail on how you see this happening, this is not code I've looked at in detail before. -- To unsubscribe from this list: send the line "unsubscribe linux-kernel" in the body of a message to majord...@vger.kernel.org More majordomo info at http://vger.kernel.org/majordomo-info.html Please read the FAQ at http://www.tux.org/lkml/
