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    SubjectRe: i915 X lockup
    On Sat, 2009-02-28 at 00:47 -0800, Andrew Morton wrote:

    > The kernel deadlocked on struct_mutex, did it not? That's a kernel bug
    > regardless of what userspace you're running.

    No, it didn't deadlock on struct_mutex, it deadlocked because the
    hardware got wedged, and we still don't know how to unwedge the hardware
    and get it working again other than turning it off and back on again.

    > Do we know why this happened?

    Yes, the hardware will happily lock up when user space maps the PCI BAR
    covering the device registers and the application pokes various internal
    device registers directly.

    That's the fundamental contract KMS requires -- if the kernel is going
    to manage the device, then user space isn't supposed to manipulate it
    directly anymore.

    I suspect most any other device in the machine could be made to do 'bad
    things' if userspace went and poked it directly.

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