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

[Gregory Haskins <gregory.haskins@gmail.com>]

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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.
>   

Agreed.
>   
>>  }
>>  
>> @@ -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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>>     
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