[PATCH 0/2] hung_task: improve rcu_lock_break() logic

Oleg Nesterov
2015-03-17T19:26:52Z

On 03/17, Oleg Nesterov wrote:
>
> On 03/17, Aaron Tomlin wrote:
> >
> > --- a/kernel/hung_task.c
> > +++ b/kernel/hung_task.c
> > @@ -169,7 +169,7 @@ static void check_hung_uninterruptible_tasks(unsigned long timeout)
> > return;
> >
> > rcu_read_lock();
> > - do_each_thread(g, t) {
> > + for_each_process_thread(g, t) {
> > if (!max_count--)
> > goto unlock;
> > if (!--batch_count) {
> > @@ -180,7 +180,7 @@ static void check_hung_uninterruptible_tasks(unsigned long timeout)
> > /* use "==" to skip the TASK_KILLABLE tasks waiting on NFS */
> > if (t->state == TASK_UNINTERRUPTIBLE)
> > check_hung_task(t, timeout);
> > - } while_each_thread(g, t);
> > + }
>
>
> Acked-by: Oleg Nesterov <oleg@redhat.com>
>
>
>
> Perhaps it also makes sense to improve this rcu_lock_break a bit...
> For example, if 't' is dead but 'g' is alive we can continue the
> "for_each_process" part of this double loop. And if 't' is still
> alive then we can find the new leader and continue...
>
> But I agree, lets start from this fix, then we will see.

Something like this. on top of Aaron's change.

But actually I am not sure this really makes a lot of sense. But if
yes, we can do more. We can save g->start_time before rcu_lock_break(),
and then "both dead" case can use for_each_process() to (try to) find
the first process whis has a ge start_time.

Oleg.