On Thu, Nov 08, 2018 at 07:31:09AM -0800, Paul E. McKenney wrote: > On Thu, Nov 08, 2018 at 10:21:51AM +0100, Peter Zijlstra wrote: > > On Wed, Nov 07, 2018 at 03:00:02PM -0800, Paul E. McKenney wrote: > > > Hello! > > > > > > The header comment for for_each_domain() talks about a call to > > > synchronize_sched() within detach_destroy_domains(), but I am not > > > seeing any such call. Because synchronize_sched() is now folded into > > > synchronize_rcu(), I have a patch that edits the comment, but it looks > > > like a larger change is needed. > > > > > > Or am I blind today? > > > > I think you're quite right and that comment is a wee bit stale. > > > > The sched domain tree is indeed protected by regular RCU (not RCU-sched > > as the comment seems to imply) and this is per destroy_sched_domains() > > using call_rcu(). > > > > And most (I didn't look at all) uses for the sched-domain tree do indeed > > employ rcu_read_lock(). > > Ah, thank you for the info! Would this patch do the trick?
> diff --git a/kernel/sched/sched.h b/kernel/sched/sched.h > index 618577fc9aa8..00b91d16af9f 100644 > --- a/kernel/sched/sched.h > +++ b/kernel/sched/sched.h > @@ -1237,7 +1237,7 @@ extern void sched_ttwu_pending(void); > > /* > * The domain tree (rq->sd) is protected by RCU's quiescent state transition. > - * See detach_destroy_domains: synchronize_sched for details. > + * See destroy_sched_domains: call_rcu for details. > * > * The domain tree of any CPU may only be accessed from within > * preempt-disabled sections. > diff --git a/kernel/sched/topology.c b/kernel/sched/topology.c > index 8d7f15ba5916..04d458faf2c1 100644 > --- a/kernel/sched/topology.c > +++ b/kernel/sched/topology.c > @@ -248,7 +248,7 @@ void rq_attach_root(struct rq *rq, struct root_domain *rd) > raw_spin_unlock_irqrestore(&rq->lock, flags); > > if (old_rd) > - call_rcu_sched(&old_rd->rcu, free_rootdomain); > + call_rcu(&old_rd->rcu, free_rootdomain); > } > > void sched_get_rd(struct root_domain *rd) > @@ -261,7 +261,7 @@ void sched_put_rd(struct root_domain *rd) > if (!atomic_dec_and_test(&rd->refcount)) > return; > > - call_rcu_sched(&rd->rcu, free_rootdomain); > + call_rcu(&rd->rcu, free_rootdomain); > } > > static int init_rootdomain(struct root_domain *rd) > Argh, that is the rootdomain, not the regular sched-domain tree. Now I'll have to go audit that stuff again. ISTR there being slightly different rules for rootdomain, and with a reason. Can we hold onto this until after LPC?
