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    SubjectRe: [PATCH v5 2/4] kvm: KVM_EOIFD, an eventfd for EOIs
    On Tue, Jul 17, 2012 at 07:59:16AM -0600, Alex Williamson wrote:
    > On Tue, 2012-07-17 at 13:21 +0300, Michael S. Tsirkin wrote:
    > > On Mon, Jul 16, 2012 at 02:33:55PM -0600, Alex Williamson wrote:
    > > > + if (args->flags & KVM_EOIFD_FLAG_LEVEL_IRQFD) {
    > > > + struct _irqfd *irqfd = _irqfd_fdget_lock(kvm, args->irqfd);
    > > > + if (IS_ERR(irqfd)) {
    > > > + ret = PTR_ERR(irqfd);
    > > > + goto fail;
    > > > + }
    > > > +
    > > > + gsi = irqfd->gsi;
    > > > + level_irqfd = eventfd_ctx_get(irqfd->eventfd);
    > > > + source = _irq_source_get(irqfd->source);
    > > > + _irqfd_put_unlock(irqfd);
    > > > + if (!source) {
    > > > + ret = -EINVAL;
    > > > + goto fail;
    > > > + }
    > > > + } else {
    > > > + ret = -EINVAL;
    > > > + goto fail;
    > > > + }
    > > > +
    > > > + INIT_LIST_HEAD(&eoifd->list);
    > > > + eoifd->kvm = kvm;
    > > > + eoifd->eventfd = eventfd;
    > > > + eoifd->source = source;
    > > > + eoifd->level_irqfd = level_irqfd;
    > > > + eoifd->notifier.gsi = gsi;
    > > > + eoifd->notifier.irq_acked = eoifd_event;
    > >
    > > OK so this means eoifd keeps a reference to the irqfd.
    > > And since this is the case, can't we drop the reference counting
    > > around source ids now? Everything is referenced through irqfd.
    >
    > Holding a reference and using it as a reference count are not the same
    > thing. What if another module holds a reference to this eventfd? How
    > do we do anything on release?

    We don't as there is no release, and using kref on source id does not
    help: it just never gets invoked.

    --
    MST



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