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    SubjectRe: [BUG] completely bonkers use of set_need_resched + VM_FAULT_NOPAGE
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    On Thu, Sep 12, 2013 at 9:58 PM, Thomas Gleixner <tglx@linutronix.de> wrote:
    >
    >> On Thu, Sep 12, 2013 at 6:22 PM, Peter Zijlstra <peterz@infradead.org> wrote:
    >> > If 'sane' userspace is never supposed to do this, then only insane
    >> > userspace is going to hurt from this and that's a GOOD (tm) thing,
    >> > right? ;-)
    >>
    >> Afaik sane userspace doesn't hit the _deadlock_ (or lifelock if we
    >> have the set_need_resched in there). drm/i915 is a bit different since
    >> we have just one lock, and so the same design would actually deadlock
    >> even for sane userspace. But hitting contention there and yielding is
    >> somewhat expected. Obviously shouldn't happen too often since it'll
    >> hurt performance, with either blocking or the yield spinning loop.
    >
    > So this is actually a non priviledged DoS interface, right?

    I think for ttm drivers it's just execbuf being exploitable. But on
    drm/i915 we've
    had the same issue with the pwrite/pread ioctls, so a simple
    glBufferData(glMap) kind of recursion from gl clients blew the kernel
    to pieces ...
    -Daniel
    --
    Daniel Vetter
    Software Engineer, Intel Corporation
    +41 (0) 79 365 57 48 - http://blog.ffwll.ch


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