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

Gleb Natapov
2009-07-13T13:06:00Z

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.

> > }
> >
> > @@ -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
> >
> > --
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--
Gleb.