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

["Michael S. Tsirkin" <mst@redhat.com>]

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);
>  }
>  
> @@ -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();
>  }

This is done under kvm->lock still, which means the lock might be held
potentially for a very long time. Can synchronize_rcu be moved out of
this lock?

>  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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