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    SubjectRe: [KVM-RFC PATCH 1/2] eventfd: add an explicit srcu based notifier interface
    On Tue, Jun 16, 2009 at 10:40:55AM -0400, Gregory Haskins wrote:
    > > This is ugly, isn't it? With CONFIG_PREEMPT=no preemptible() is always false.
    > >
    > > Further, to do useful things it might not be enough that you can sleep:
    > > with iofd you also want to access current task with e.g. copy from user.
    > >
    >
    > Something else to consider: For iosignalfd, we can assume we will
    > always be called from vcpu process context so we might not really need
    > official affirmation from the system. For irqfd, we cannot predict who
    > may be injecting the interrupt (for instance, it might be a
    > PCI-passthrough hard-irq context). I am not sure if this knowledge
    > actually helps to simplify the problem space, but I thought I should
    > mention it.
    >
    > -Greg
    >
    >

    The way this is addressed with eventfd_signal_task proposal is:
    - user calls eventfd_signal_task
    we look at current->mm and figure out whether this is the right
    context or we need a context switch
    - everyone else calls eventfd_signal
    we know that we need a context switch




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