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    SubjectRe: [KVM PATCH v10] kvm: add support for irqfd
    Michael S. Tsirkin wrote:
    > On Wed, May 20, 2009 at 10:30:49AM -0400, Gregory Haskins wrote:
    >
    >> +static int
    >> +kvm_assign_irqfd(struct kvm *kvm, int fd, int gsi)
    >> +{
    >> + struct _irqfd *irqfd;
    >> + struct file *file = NULL;
    >> + int ret;
    >> +
    >> + irqfd = kzalloc(sizeof(*irqfd), GFP_KERNEL);
    >> + if (!irqfd)
    >> + return -ENOMEM;
    >> +
    >> + irqfd->kvm = kvm;
    >> + irqfd->gsi = gsi;
    >> + INIT_LIST_HEAD(&irqfd->list);
    >> + INIT_WORK(&irqfd->work, irqfd_inject);
    >> +
    >> + /*
    >> + * Embed the file* lifetime in the irqfd.
    >> + */
    >> + file = fget(fd);
    >> + if (IS_ERR(file)) {
    >> + ret = PTR_ERR(file);
    >> + goto fail;
    >> + }
    >>
    >
    > So we get a reference to a file, and unless the user is nice to us, it
    > will only be dropped when kvm char device file is closed?
    > I think this will deadlock if the fd in question is the open kvm char device.
    >
    >
    >
    Hmm...I hadn't considered this possibility, though I am not sure if it
    would cause a deadlock in the pattern you suggest. It seems more like
    it would result in, at worst, an extra reference to itself (and thus a
    leak) rather than a deadlock...

    I digress. In either case, perhaps I should s/fget/eventfd_fget to at
    least limit the type of fd to eventfd. I was trying to be "slick" by
    not needing the eventfd_fget() exported, but I am going to need to
    export it later anyway for iosignalfd, so its probably a moot point.

    Thanks Michael,
    -Greg

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