linux-kernel - Re: [PATCH v9 2/2] kvm: On Ack, De-assert & Notify KVM

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Date:	Tue, 21 Aug 2012 19:48:14 -0600
From:	Alex Williamson <alex.williamson@...hat.com>
To:	"Michael S. Tsirkin" <mst@...hat.com>
Cc:	avi@...hat.com, gleb@...hat.com, kvm@...r.kernel.org,
	linux-kernel@...r.kernel.org
Subject: Re: [PATCH v9 2/2] kvm: On Ack, De-assert & Notify KVM_IRQFD
 extension

On Wed, 2012-08-22 at 03:14 +0300, Michael S. Tsirkin wrote:
> On Tue, Aug 21, 2012 at 03:11:41PM -0600, Alex Williamson wrote:
> > On Tue, 2012-08-21 at 23:37 +0300, Michael S. Tsirkin wrote:
> > > On Tue, Aug 21, 2012 at 01:29:14PM -0600, Alex Williamson wrote:
> > > > +	}
> > > > +
> > > >  	irq_rt = rcu_dereference_protected(kvm->irq_routing,
> > > >  					   lockdep_is_held(&kvm->irqfds.lock));
> > > >  	irqfd_update(kvm, irqfd, irq_rt);
> > > > @@ -267,6 +426,26 @@ kvm_irqfd_assign(struct kvm *kvm, struct kvm_irqfd *args)
> > > >  
> > > >  	spin_unlock_irq(&kvm->irqfds.lock);
> > > >  
> > > > +	if (oadn) {
> > > > +		synchronize_rcu();
> > > 
> > > Seems unexpected on assign.
> > > What does this synchronize_rcu do?
> > 
> > Because we force the notify below and we need the irqfd we just added to
> > the list to be visible on the list for that.
> 
> I do not see it yet - maybe add a comment?

It's entirely possible I'm wrong too.  This was an after thought and now
that I look at it again, the below irqfd_oadn_notify obviously starts
after the list_add, so there shouldn't be any need to wait.  Thanks,

Alex

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