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    SubjectRe: [KVM PATCH v5 0/4] irqfd fixes and enhancements
    On 06/25/2009 04:59 PM, Gregory Haskins wrote:
    > Gregory Haskins wrote:
    >
    >> (Applies to kvm.git/master:4631e094)
    >>
    >> The following is the latest attempt to fix the races in irqfd/eventfd, as
    >> well as restore DEASSIGN support. For more details, please read the patch
    >> headers.
    >>
    >> This series has been tested against the kvm-eventfd unit test, and
    >> appears to be functioning properly. You can download this test here:
    >>
    >> ftp://ftp.novell.com/dev/ghaskins/kvm-eventfd.tar.bz2
    >>
    >> I've included version 4 of Davide's eventfd patch (ported to kvm.git) so
    >> that its a complete reviewable series. Note, however, that there may be
    >> later versions of his patch to consider for merging, so we should
    >> coordinate with him.
    >>
    >>
    >
    > So I know we talked yesterday in the review session about whether it was
    > actually worth all this complexity to deal with the POLLHUP or if we
    > should just revert to the prior "two syscall" model and be done with
    > it. Rusty reflected these same sentiments this morning in response to
    > Davide's patch in a different thread.
    >
    > I am a bit torn myself, tbh. I do feel as though I have a good handle
    > on the issue and that it is indeed now fixed (at least, if this series
    > is applied and the slow-work issue is fixed, still pending upstream
    > ACK). I have a lot invested in going the POLLHUP direction having spent
    > so much time thinking about the problem and working on the patches, so I
    > a bit of a biased opinion, I know.
    >
    > The reason why I am pushing this series out now is at least partly so we
    > can tie up these loose ends. We have both solutions in front of us and
    > can make a decision either way. At least the solution is formally
    > documented in the internet archives forever this way ;)
    >
    > I took the review comments to heart that the shutdown code was
    > substantially larger and more complex than the actual fast-path code. I
    > went though last night and simplified and clarified it. I think the
    > latest result is leaner and clearer, so please give it another review
    > (particularly for races) before dismissing it.
    >

    Yes, it's much nicer. I can't say I'm certain it's race free but it's a
    lot more digestible

    > Ultimately, I think the concept of a release notification for eventfd is
    > a good thing for all eventfd users, so I don't think this thing should
    > go away per se even if irqfd decides to not use it.
    >

    I agree that we want POLLHUP support, it's better than holding on to the
    eventfd. But I think we can make it even cleaner by merging it with
    deassign. Basically, when we get POLLHUP, we launch a slow_work (or
    something) that does a regular deassign. That slow_work can grab a ref
    to the vm, so we don't race with the VM disappearing.

    But given that the current slow_work does almost nothing, I'm not sure
    it's worth it.

    --
    error compiling committee.c: too many arguments to function



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