Re: [PATCH 4/4] Convert irq notifiers lists to RCU locking.

Michael S. Tsirkin
2009-07-13T13:30:22Z

On Mon, Jul 13, 2009 at 04:05:58PM +0300, Gleb Natapov wrote:
> On Mon, Jul 13, 2009 at 03:56:40PM +0300, Michael S. Tsirkin wrote:
> > On Sun, Jul 12, 2009 at 03:03:53PM +0300, Gleb Natapov wrote:
> > > Use RCU locking for mask/ack notifiers lists.
> > >
> > > Signed-off-by: Gleb Natapov <gleb@redhat.com>
> > > ---
> > > virt/kvm/irq_comm.c | 20 +++++++++++---------
> > > 1 files changed, 11 insertions(+), 9 deletions(-)
> > >
> > > diff --git a/virt/kvm/irq_comm.c b/virt/kvm/irq_comm.c
> > > index 5dde1ef..ba3a115 100644
> > > --- a/virt/kvm/irq_comm.c
> > > +++ b/virt/kvm/irq_comm.c
> > > @@ -179,18 +179,18 @@ void kvm_notify_acked_irq(struct kvm *kvm, unsigned irqchip, unsigned pin)
> > > break;
> > > }
> > > }
> > > - rcu_read_unlock();
> > >
> > > - hlist_for_each_entry(kian, n, &kvm->irq_ack_notifier_list, link)
> > > + hlist_for_each_entry_rcu(kian, n, &kvm->irq_ack_notifier_list, link)
> > > if (kian->gsi == gsi)
> > > kian->irq_acked(kian);
> > > + rcu_read_unlock();
> > > }
> > >
> > > void kvm_register_irq_ack_notifier(struct kvm *kvm,
> > > struct kvm_irq_ack_notifier *kian)
> > > {
> > > mutex_lock(&kvm->irq_lock);
> > > - hlist_add_head(&kian->link, &kvm->irq_ack_notifier_list);
> > > + hlist_add_head_rcu(&kian->link, &kvm->irq_ack_notifier_list);
> > > mutex_unlock(&kvm->irq_lock);
> >
> > I think we need synchronize_rcu here as well. If the user adds a
> > notifier, he expects to get notified of irqs immediately
> > after the function returns, not after the next rcu grace period.
> >
> If ack notifier registration races with acknowledgment of the interrupt
> it adds notifier for a user already does something terribly wrong.

Hmm, good point.

> > > }
> > >
> > > @@ -198,8 +198,9 @@ void kvm_unregister_irq_ack_notifier(struct kvm *kvm,
> > > struct kvm_irq_ack_notifier *kian)
> > > {
> > > mutex_lock(&kvm->irq_lock);
> > > - hlist_del_init(&kian->link);
> > > + hlist_del_init_rcu(&kian->link);
> > > mutex_unlock(&kvm->irq_lock);
> > > + synchronize_rcu();
> > > }
> > >
> > > int kvm_request_irq_source_id(struct kvm *kvm)
> > > @@ -246,7 +247,7 @@ void kvm_register_irq_mask_notifier(struct kvm *kvm, int irq,
> > > {
> > > mutex_lock(&kvm->irq_lock);
> > > kimn->irq = irq;
> > > - hlist_add_head(&kimn->link, &kvm->mask_notifier_list);
> > > + hlist_add_head_rcu(&kimn->link, &kvm->mask_notifier_list);
> > > mutex_unlock(&kvm->irq_lock);
> > > }
> > >
> > > @@ -254,8 +255,9 @@ void kvm_unregister_irq_mask_notifier(struct kvm *kvm, int irq,
> > > struct kvm_irq_mask_notifier *kimn)
> > > {
> > > mutex_lock(&kvm->irq_lock);
> > > - hlist_del(&kimn->link);
> > > + hlist_del_rcu(&kimn->link);
> > > mutex_unlock(&kvm->irq_lock);
> > > + synchronize_rcu();
> > > }
> > >
> > > void kvm_fire_mask_notifiers(struct kvm *kvm, int irq, bool mask)
> > > @@ -263,11 +265,11 @@ void kvm_fire_mask_notifiers(struct kvm *kvm, int irq, bool mask)
> > > struct kvm_irq_mask_notifier *kimn;
> > > struct hlist_node *n;
> > >
> > > - WARN_ON(!mutex_is_locked(&kvm->irq_lock));
> > > -
> > > - hlist_for_each_entry(kimn, n, &kvm->mask_notifier_list, link)
> > > + rcu_read_lock();
> > > + hlist_for_each_entry_rcu(kimn, n, &kvm->mask_notifier_list, link)
> > > if (kimn->irq == irq)
> > > kimn->func(kimn, mask);
> > > + rcu_read_unlock();
> > > }
> > >
> > > void kvm_free_irq_routing(struct kvm *kvm)
> > > --
> > > 1.6.2.1
> > >
> > > --
> > > To unsubscribe from this list: send the line "unsubscribe kvm" in
> > > the body of a message to majordomo@vger.kernel.org
> > > More majordomo info at http://vger.kernel.org/majordomo-info.html
>
> --
> Gleb.
> --
> To unsubscribe from this list: send the line "unsubscribe kvm" in
> the body of a message to majordomo@vger.kernel.org
> More majordomo info at http://vger.kernel.org/majordomo-info.html