On Mon, Dec 18, 2017 at 09:50:04AM +0100, Paolo Bonzini wrote: > On 18/12/2017 09:30, David Hildenbrand wrote: > > The ugly thing in kvm_irqfd_assign() is that we access irqfd without > > holding a lock. I think that should rather be fixed than working around > > that issue. (e.g. lock() -> lookup again -> verify still in list -> > > unlock()) > > I wonder if it's even simpler: > > diff --git a/virt/kvm/eventfd.c b/virt/kvm/eventfd.c > index f2ac53ab8243..17ed298bd66f 100644 > --- a/virt/kvm/eventfd.c > +++ b/virt/kvm/eventfd.c > @@ -387,7 +387,6 @@ kvm_irqfd_assign(struct kvm *kvm, struct kvm_irqfd *args) > > idx = srcu_read_lock(&kvm->irq_srcu); > irqfd_update(kvm, irqfd); > - srcu_read_unlock(&kvm->irq_srcu, idx); > > list_add_tail(&irqfd->list, &kvm->irqfds.items); > > @@ -420,10 +419,12 @@ kvm_irqfd_assign(struct kvm *kvm, struct kvm_irqfd *args) > irqfd->consumer.token, ret); > } > #endif > + srcu_read_unlock(&kvm->irq_srcu, idx); > > return 0; > > fail: > + /* irq_srcu is *not* held here. */ > if (irqfd->resampler) > irqfd_resampler_shutdown(irqfd); Sorry if I miss anything important, but... should we extend the unlock of kvm->irqfds.lock instead of kvm->irq_srcu here? AFAIU kvm->irq_srcu is protecting accesses to kvm->irq_routing, while kvm->irqfds.lock is the one that really protects kvm->irqfds? Thanks, -- Peter Xu
