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    SubjectRe: [PATCH] KVM/Eventfd: Avoid crash when assign and deassign same eventfd in parallel.
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    On 18.12.2017 09:50, 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);
    >

    Was worried about the poll() call. But if that works, it would be very nice.

    > return 0;
    >
    > fail:
    > + /* irq_srcu is *not* held here. */
    > if (irqfd->resampler)
    > irqfd_resampler_shutdown(irqfd);
    >
    >
    > Thanks,
    >
    > Paolo
    >


    --

    Thanks,

    David / dhildenb

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