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    SubjectRe: [PATCH 3/6] futex: add double_unlock_hb()

    * Peter Zijlstra <peterz@infradead.org> wrote:

    > On Thu, 2009-03-12 at 00:55 -0700, Darren Hart wrote:
    > > The futex code uses double_lock_hb() which locks the hb->lock's in pointer
    > > value order. There is no parallel unlock routine, and the code unlocks them
    > > in name order, ignoring pointer value. This opens up a window for an ABBA
    > > deadlock. This patch adds double_unlock_hb() to remove the window as well
    > > as refactor the duplicated code segments.
    >
    > While I don't mind the patch per-se, I'm hard pressed to see
    > any deadlock potential in the unordered unlock.
    >
    > All sites (at least those in the patch) always release both
    > locks without taking another in between, therefore one would
    > think there's no deadlock possible.

    yeah.

    The patch is still nice (as you mention), it factors out the
    unlock sequence. I'll change the commit message accordingy.

    Ingo


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