On Tue, Aug 25, 2015 at 12:05:27PM +0200, Peter Zijlstra wrote:
> On Tue, Aug 25, 2015 at 03:59:54PM +0800, Wanpeng Li wrote:
> > +++ b/kernel/cpuset.c
> > @@ -2376,8 +2376,12 @@ void cpuset_cpus_allowed(struct task_struct *tsk,
> > struct cpumask *pmask)
> >
> > void cpuset_cpus_allowed_fallback(struct task_struct *tsk)
> > {
> > + unsigned long flags;
> > +
> > rcu_read_lock();
> > + raw_spin_lock_irqsave(&tsk->pi_lock, flags);
> > do_set_cpus_allowed(tsk, task_cs(tsk)->effective_cpus);
> > + raw_spin_lock_irqsave(&tsk->pi_lock, flags);
> > rcu_read_unlock();
>
> Aside from the double lock thing that was already pointed out, I think
> this is wrong, because the select_task_rq() call can already have
> pi_lock held.
>
> Taking it again would result in a deadlock.
>
> Consider for instance:
>
> try_to_wake_up()
> raw_spin_lock_irqsave(->pi_lock)
> select_task_rq()
> select_ballback_rq()
> cpuset_cpus_allowed_fallback()
> raw_spin_lock_irqsave(->pi_lock)
>
>
> The problem is with the migration path and should be fixed there.
Another problem, migration_call() will have rq->lock held, so you're
proposing to acquire pi_lock while holding rq->lock, this is an
inversion from the regular nesting order.
--
To unsubscribe from this list: send the line "unsubscribe linux-kernel" in
the body of a message to [email protected]
More majordomo info at http://vger.kernel.org/majordomo-info.html
Please read the FAQ at http://www.tux.org/lkml/
