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    SubjectRe: [patch 0/6] lightweight robust futexes: -V3 - Why in userspace?
    I just jump into a thread somewhere to ask my question :-)

    Why does the list have to be in userspace?

    As I see it there can only be a problem when some thread has done
    FUTEX_WAIT and is blocked. If no task is blocked (or on it's way to
    being blocked) there is no problem.

    The solution I could imagine was the FUTEX_WAIT operation adds the
    waiting task to a list of waiters attached to the mutex owner's task_t
    (which is known by it's pid in the userspace flag) just before calling
    schedule(). This list needs to be protected by a spinlock, ofcourse.
    When a task dies it can wake up the waiters on it's list without relying
    on the userspace.

    What race conditions have I missed?

    Esben




    On Thu, 16 Feb 2006, Daniel Walker wrote:

    > On Thu, 2006-02-16 at 18:24 +0100, Ingo Molnar wrote:
    > > * Daniel Walker <dwalker@mvista.com> wrote:
    > >
    > > > Another thing I noticed was that futex_offset on the surface looks
    > > > like a malicious users dream variable .. [...]
    > >
    > > i have no idea what you mean by that - could you explain whatever threat
    > > you have in mind, in more detail?
    >
    > As I said, "on the surface" you could manipulate the futex_offset to
    > access memory unrelated to the futex structure . That's all I'm
    > referring too ..
    >
    > Daniel
    >
    > -
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